diff --git a/README.md b/README.md
index b86dbdc..a34dc85 100644
--- a/README.md
+++ b/README.md
@@ -12,19 +12,6 @@ The point is painfully simple:
   become "everything phones home for every request"
 - keep app-domain data separate so "shared auth" does not become "shared swamp"
 
-## Front Door
-
-- **Value:** one shared auth authority: provider OAuth (Discord, Patreon, GitHub, Twitch, YouTube, Spotify), linked identities, grants, entitlements and session issuance, with Ed25519-signed claims that app backends verify locally.
-- **Problem:** every GameCult app was rebuilding Discord/Patreon login glue. Heimdall centralizes identity authority and keeps app-domain data in the apps.
-- **Entry points:**
-  - `src/index.ts` and `src/app.ts`: the Fastify service. `src/signing.ts` and `src/claims.ts` issue JWTs and serve `/.well-known/jwks.json`; `src/oauth.ts` and `src/providers.ts` own provider flows.
-  - `src/verifier.ts`: the local verifier helper an app backend imports to validate Heimdall JWTs without phoning home.
-  - `src/odin-publication.ts` and `plugins/gamecult.heimdall.access`: the redacted Odin/Eve provider advertisement and the `gamecult.heimdall.access` plugin (`docs/eve-access-plugin.md`).
-  - `docs/architecture.md`, `docs/service-contract.md`, `docs/verse-service-contract.md`, `docs/app-profiles/`: the contracts.
-  - `pnpm install`, `pnpm dev`, `pnpm test` (see Dev Commands).
-- **Live:** a stateful first slice: signing and JWKS, OAuth state for six providers, in-memory and Postgres stores, a real Discord callback path for the Repixelizer flow, sealed provider tokens, the loopback CultNet operation boundary, Idunn health publication, and the deployed Ghostlight Eve host consuming the discovered boundary.
-- **Planned:** the two-account and eight-account Ghostlight human canaries, refresh and revocation flows, admin surfaces, and broader inspection projections beyond the redacted access boundary.
-
 ## Current Shape
 
 This repo now has a stateful first slice instead of a decorative skeleton.
diff --git a/docs/architecture.md b/docs/architecture.md
index 8ae5c19..f816a14 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -154,7 +154,11 @@ The important split:
 
 - Heimdall owns provider OAuth, identity linking, entitlement refresh, signed
   sessions, claims, grants, audit surfaces, and managed provider credential
-  custody
+  custody. It authenticates; it does not issue GameCult identity. Bifrost is
+  the identity provider, and the account id Heimdall mints is an authenticator
+  handle. Remaining scar: Heimdall still creates that account id on first
+  login (`store.createAccount`, `src/app.ts`), which the chat work does not
+  need moved
 - the host experiment owns its workload, queue, editor, render path, viewer
   profile model, creator model, or other product-specific machinery
 - the host experiment also owns which local entity a connection attaches to,
@@ -613,8 +617,9 @@ Only the browser-driven OAuth flow:
 
 | Path | Why it must be public |
 |---|---|
-| `/v1/oauth/{provider}/start` | the user's browser goes here |
-| `/v1/oauth/{provider}/callback` | the provider redirects here; one-shot and not retryable |
+| `/v1/oauth/{provider}/start` | the app's server calls it, with its app secret where the profile requires one |
+| `/v1/oauth/{provider}/launch` | the user's browser goes here first; it sets the binding cookie and redirects to the provider, once per state |
+| `/v1/oauth/{provider}/callback` | the provider redirects here; one-shot: it needs the binding cookie and consumes the state |
 | `/.well-known/jwks.json` | *nothing external consumes it today* — see below |
 
 Everything else is internal by the design already written down:
diff --git a/docs/service-contract.md b/docs/service-contract.md
index 1567ae5..13b1374 100644
--- a/docs/service-contract.md
+++ b/docs/service-contract.md
@@ -149,12 +149,29 @@ Response:
   "appSlug": "repixelizer",
   "mode": "sign_in",
   "callbackUrl": "https://heimdall.gamecult.org/v1/oauth/discord/callback",
-  "authorizationUrl": "https://discord.com/oauth2/authorize?...",
-  "stateToken": "<signed-jwt>",
+  "authorizationUrl": "https://heimdall.gamecult.org/v1/oauth/discord/launch?state=<signed-jwt>",
   "stateExpiresAt": "2026-04-26T12:10:00.000Z"
 }
 ```
 
+Send the user's browser to `authorizationUrl` unchanged. It is Heimdall's launch
+hop, not the provider's URL.
+
+### `GET /v1/oauth/{provider}/launch?state=<signed-jwt>`
+
+The first thing the user's browser does with a state. Heimdall verifies the
+state (signature, issuer, provider, `nbf`/`exp` with 30 s of skew), claims the
+state's single launch, sets the binding cookie
+`__Host-heimdall-oauth-<jti>` (`Path=/`, `Secure`, `HttpOnly`, `SameSite=Lax`,
+`Max-Age` until the state expires; the value is a Heimdall-signed binding for
+that state) and answers `302` to the provider's authorize URL, with
+`Cache-Control: no-store` and `Referrer-Policy: no-referrer`. A second launch of
+the same state is `400 state_already_launched` and sets no cookie. The state is
+refused with `400 invalid_state`, `state_provider_mismatch` or `state_expired`.
+
+The binding cookie needs an `https` public base URL (or `localhost`). A browser
+must finish the flow in the browser that launched it.
+
 Failure modes:
 
 - `503 provider_not_configured` when the provider client id is missing
@@ -168,7 +185,12 @@ Failure modes:
 - `401 app_auth_required` when the request body carries `entitlementPolicy` and
   the caller did not authenticate as that app via `x-heimdall-app-secret`
   (`resolveAppCaller`, `src/app-caller.ts`) -- this applies regardless of
-  `handoff.kind` or app slug; a caller with no policy to attach needs no secret
+  `handoff.kind` or app slug; a caller with no policy to attach needs no secret,
+  unless the app's profile sets `startRequiresAppCaller` (Bifrost only): then
+  every start for that app, with or without a policy, needs that app's secret.
+  Bifrost binds browser completion to a nonce that rides readable in the signed
+  state's `return_to`, so only Bifrost may mint a Bifrost state; apps whose
+  browser starts are public by design leave the flag unset
 
 Launch note:
 
@@ -189,7 +211,9 @@ Purpose:
 
 Current status:
 
-- validates signed `state`
+- validates signed `state` (signature, issuer, provider, expiry), requires the
+  binding cookie the launch hop set, and consumes the state: a second callback
+  is `400 state_already_used`, a missing or foreign cookie `400 state_not_bound`
 - returns provider errors cleanly
 - for Discord, exchanges the authorization code, resolves the provider
   identity, persists the local account/link/session/audit records, evaluates
diff --git a/docs/verse-service-contract.md b/docs/verse-service-contract.md
index fcfa4ac..f3c98e9 100644
--- a/docs/verse-service-contract.md
+++ b/docs/verse-service-contract.md
@@ -11,7 +11,8 @@ evidence only.
 
 ## Owner Map
 
-- Owner: Heimdall owns provider identity/linking, OAuth attempts, signed session and claim
+- Owner: Heimdall owns provider identity/linking (an authenticator handle, not
+  GameCult identity, which is Bifrost's), OAuth attempts, signed session and claim
   issuance, entitlement refresh, managed provider token custody, grants,
   auth-completion handoffs, refresh sessions, and audit events.
 - Inputs: provider OAuth callbacks, app profile requests, caller-supplied
diff --git a/package.json b/package.json
index 36394ef..4eb8e55 100644
--- a/package.json
+++ b/package.json
@@ -17,12 +17,13 @@
     "bundle": "esbuild src/index.ts --bundle --platform=node --format=esm --target=node24 --outfile=dist/heimdall --external:pg-native --banner:js=\"#!/usr/bin/env node\nimport{createRequire}from'node:module';const require=createRequire(import.meta.url);\""
   },
   "dependencies": {
+    "@fastify/cookie": "^11.1.3",
     "@fastify/cors": "^11.2.0",
     "@msgpack/msgpack": "^3.1.3",
     "@gamecult/cultcache-ts": "file:vendor/CultLib/packages/cultcache-ts",
     "cultmesh-ts": "file:vendor/CultLib/packages/cultmesh-ts",
     "cultnet-ts": "file:vendor/CultLib/packages/cultnet-ts",
-    "fastify": "^5.12.6",
+    "fastify": "^5.8.5",
     "pg": "^8.20.0",
     "zod": "^3.25.76"
   },
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 855ad01..eb1d1db 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -12,6 +12,9 @@ importers:
 
   .:
     dependencies:
+      '@fastify/cookie':
+        specifier: ^11.1.3
+        version: 11.1.3
       '@fastify/cors':
         specifier: ^11.2.0
         version: 11.2.0
@@ -28,8 +31,8 @@ importers:
         specifier: file:vendor/CultLib/packages/cultnet-ts
         version: file:vendor/CultLib/packages/cultnet-ts
       fastify:
-        specifier: ^5.12.6
-        version: 5.12.7
+        specifier: ^5.8.5
+        version: 5.8.5
       pg:
         specifier: ^8.20.0
         version: 8.20.0
@@ -229,6 +232,9 @@ packages:
   '@fastify/ajv-compiler@4.0.5':
     resolution: {integrity: sha512-KoWKW+MhvfTRWL4qrhUwAAZoaChluo0m0vbiJlGMt2GXvL4LVPQEjt8kSpHI3IBq5Rez8fg+XeH3cneztq+C7A==}
 
+  '@fastify/cookie@11.1.3':
+    resolution: {integrity: sha512-RBhlMNsmSG6C5KGiTkhSXBF75xIrUMSytDDBcpnVewhJ8XVYnJTu+SV6FYKXClIRsBuRjOfKbBSULvnPD3X/mg==}
+
   '@fastify/cors@11.2.0':
     resolution: {integrity: sha512-LbLHBuSAdGdSFZYTLVA3+Ch2t+sA6nq3Ejc6XLAKiQ6ViS2qFnvicpj0htsx03FyYeLs04HfRNBsz/a8SvbcUw==}
 
@@ -469,6 +475,10 @@ packages:
     resolution: {integrity: sha512-ei8Aos7ja0weRpFzJnEA9UHJ/7XQmqglbRwnf2ATjcB9Wq874VKH9kfjjirM6UhU2/E5fFYadylyhFldcqSidQ==}
     engines: {node: '>=18'}
 
+  cookie@2.0.1:
+    resolution: {integrity: sha512-yuToqVvRrj6pfDXREyQAAv8SkAEk/8GS3jQRTiUMm66TVtBYmqQeoEjL2Lmq8Rpo6271vH76InTChTitEAm65w==}
+    engines: {node: '>=22'}
+
   cultmesh-ts@file:vendor/CultLib/packages/cultmesh-ts:
     resolution: {directory: vendor/CultLib/packages/cultmesh-ts, type: directory}
     engines: {node: '>=18'}
@@ -532,23 +542,20 @@ packages:
   fast-json-stringify@6.3.0:
     resolution: {integrity: sha512-oRCntNDY/329HJPlmdNLIdogNtt6Vyjb1WuT01Soss3slIdyUp8kAcDU3saQTOquEK8KFVfwIIF7FebxUAu+yA==}
 
-  fast-json-stringify@7.1.3:
-    resolution: {integrity: sha512-5TDM1yOF/BDFOclKz2G6rs1RsIl5HXMCrg/npmdNIPNQCezshR5kIHjhwBNuMY67jhkTUAm9DguL8xkL/x0Wtw==}
-
   fast-querystring@1.1.2:
     resolution: {integrity: sha512-g6KuKWmFXc0fID8WWH0jit4g0AGBoJhCkJMb1RmbsSEUNvQ+ZC8D6CUZ+GtF8nMzSPXnhiePyyqqipzNNEnHjg==}
 
   fast-uri@3.1.0:
     resolution: {integrity: sha512-iPeeDKJSWf4IEOasVVrknXpaBV0IApz/gp7S2bb7Z4Lljbl2MGJRqInZiUrQwV16cpzw/D3S5j5Julj/gT52AA==}
 
-  fast-uri@4.2.3:
-    resolution: {integrity: sha512-I1PXwP5eAhlNlcdpjt9CgB59op2ZvZfxw+BkqGFVIUOgNpCVTcTqp3HhTX7brxj5vsip+nSY4nTvff+eIA76hg==}
-
   fastify-plugin@5.1.0:
     resolution: {integrity: sha512-FAIDA8eovSt5qcDgcBvDuX/v0Cjz0ohGhENZ/wpc3y+oZCY2afZ9Baqql3g/lC+OHRnciQol4ww7tuthOb9idw==}
 
-  fastify@5.12.7:
-    resolution: {integrity: sha512-v4pEPsTRPuqlDIYiQFB+BHjVN4SdHX9u0ABk0ZDUKbbdY1vsNryUd1j4Z+jQEZajvYIVk047Kimva9/AJ79GYw==}
+  fastify-plugin@6.0.1:
+    resolution: {integrity: sha512-4wW4RxSmvPXLrh5mgQEiu43qU3bw44N2ss4FTkTkQIbprUhE+/s43QX0j/ttcztdWK7PEkHqVthdc5GdEGDvjA==}
+
+  fastify@5.8.5:
+    resolution: {integrity: sha512-Yqptv59pQzPgQUSIm87hMqHJmdkb1+GPxdE6vW6FRyVE9G86mt7rOghitiU4JHRaTyDUk9pfeKmDeu70lAwM4Q==}
 
   fastq@1.20.1:
     resolution: {integrity: sha512-GGToxJ/w1x32s/D2EKND7kTil4n8OVk/9mycTc4VDza13lOvpUZTGX3mFSCtV9ksdGBVzvsyAVLM6mHFThxXxw==}
@@ -562,8 +569,8 @@ packages:
       picomatch:
         optional: true
 
-  find-my-way@9.10.0:
-    resolution: {integrity: sha512-eru+uCPQ2g+nLBkf84MHP/KyNNMar0BDy0j+i8Fb72GF9/YHBZ58q7FODUtfVV7XU9nfRUHXSmaM8NmZcIbZ4Q==}
+  find-my-way@9.5.0:
+    resolution: {integrity: sha512-VW2RfnmscZO5KgBY5XVyKREMW5nMZcxDy+buTOsL+zIPnBlbKm+00sgzoQzq1EVh4aALZLfKdwv6atBGcjvjrQ==}
     engines: {node: '>=20'}
 
   fsevents@2.3.3:
@@ -859,8 +866,8 @@ packages:
   process-warning@4.0.1:
     resolution: {integrity: sha512-3c2LzQ3rY9d0hc1emcsHhfT9Jwz0cChib/QN89oME2R451w5fy3f0afAhERFZAwrbDU43wk12d0ORBpDVME50Q==}
 
-  process-warning@5.1.1:
-    resolution: {integrity: sha512-oCkNVj4OKnKEcocVBcDfiIugN1/cE6rgfT3nCtzeqZPA8+rIxMaQ0xXzIkGP8Gj2qUaP1UR7uhJ1VD8lUCpzCg==}
+  process-warning@5.0.0:
+    resolution: {integrity: sha512-a39t9ApHNx2L4+HBnQKqxxHNs1r7KF+Intd8Q/g1bUh6q0WIp9voPXJ/x0j+ZL45KF1pJd9+q2jLIRMfvEshkA==}
 
   quick-format-unescaped@4.0.4:
     resolution: {integrity: sha512-tYC1Q1hgyRuHgloV/YXs2w15unPVh8qfu/qCTfhTYamaw7fyhumKa2yGpdSo87vY32rIclj+4fWYQXUMs9EHvg==}
@@ -1186,6 +1193,11 @@ snapshots:
       ajv-formats: 3.0.1(ajv@8.20.0)
       fast-uri: 3.1.0
 
+  '@fastify/cookie@11.1.3':
+    dependencies:
+      cookie: 2.0.1
+      fastify-plugin: 6.0.1
+
   '@fastify/cors@11.2.0':
     dependencies:
       fastify-plugin: 5.1.0
@@ -1393,6 +1405,8 @@ snapshots:
 
   cookie@1.1.1: {}
 
+  cookie@2.0.1: {}
+
   cultmesh-ts@file:vendor/CultLib/packages/cultmesh-ts:
     dependencies:
       '@gamecult/cultcache-ts': file:vendor/CultLib/packages/cultcache-ts
@@ -1481,26 +1495,17 @@ snapshots:
       json-schema-ref-resolver: 3.0.0
       rfdc: 1.4.1
 
-  fast-json-stringify@7.1.3:
-    dependencies:
-      '@fastify/merge-json-schemas': 0.2.1
-      ajv: 8.20.0
-      ajv-formats: 3.0.1(ajv@8.20.0)
-      fast-uri: 4.2.3
-      json-schema-ref-resolver: 3.0.0
-      rfdc: 1.4.1
-
   fast-querystring@1.1.2:
     dependencies:
       fast-decode-uri-component: 1.0.1
 
   fast-uri@3.1.0: {}
 
-  fast-uri@4.2.3: {}
-
   fastify-plugin@5.1.0: {}
 
-  fastify@5.12.7:
+  fastify-plugin@6.0.1: {}
+
+  fastify@5.8.5:
     dependencies:
       '@fastify/ajv-compiler': 4.0.5
       '@fastify/error': 4.2.0
@@ -1508,11 +1513,11 @@ snapshots:
       '@fastify/proxy-addr': 5.1.0
       abstract-logging: 2.0.1
       avvio: 9.2.0
-      fast-json-stringify: 7.1.3
-      find-my-way: 9.10.0
+      fast-json-stringify: 6.3.0
+      find-my-way: 9.5.0
       light-my-request: 6.6.0
       pino: 10.3.1
-      process-warning: 5.1.1
+      process-warning: 5.0.0
       rfdc: 1.4.1
       secure-json-parse: 4.1.0
       semver: 7.7.4
@@ -1526,7 +1531,7 @@ snapshots:
     optionalDependencies:
       picomatch: 4.0.4
 
-  find-my-way@9.10.0:
+  find-my-way@9.5.0:
     dependencies:
       fast-deep-equal: 3.1.3
       fast-querystring: 1.1.2
@@ -1750,7 +1755,7 @@ snapshots:
       on-exit-leak-free: 2.1.2
       pino-abstract-transport: 3.0.0
       pino-std-serializers: 7.1.0
-      process-warning: 5.1.1
+      process-warning: 5.0.0
       quick-format-unescaped: 4.0.4
       real-require: 0.2.0
       safe-stable-stringify: 2.5.0
@@ -1775,7 +1780,7 @@ snapshots:
 
   process-warning@4.0.1: {}
 
-  process-warning@5.1.1: {}
+  process-warning@5.0.0: {}
 
   quick-format-unescaped@4.0.4: {}
 
diff --git a/src/app-profiles.ts b/src/app-profiles.ts
index 3489a48..70a9b34 100644
--- a/src/app-profiles.ts
+++ b/src/app-profiles.ts
@@ -45,6 +45,17 @@ export interface AppProfile {
    * plane; absent for apps with no such requirement.
    */
   requiredEntitlementPolicyKind?: OAuthEntitlementPolicy["kind"];
+  /**
+   * The app binds browser completion to its own pending attempt, and the
+   * binding is the secrecy of the attempt nonce, which rides readable in the
+   * signed (not encrypted) state's return_to. If anyone could start a flow for
+   * this app, whoever learned a victim's nonce could mint a completion bound
+   * to it and sign the victim's browser in as themselves (login CSRF, finding
+   * known-nonce-login-csrf). So a start for this app is refused unless the
+   * caller is this app's authenticated caller: only the app can mint its own
+   * state. Absent for apps whose browser starts are public by design.
+   */
+  startRequiresAppCaller?: boolean;
 }
 
 /** The membership signal shared by every app that gates on GameCult membership. */
@@ -142,6 +153,7 @@ const bifrostProfile: AppProfile = {
   entitlementSources: ["discord", "patreon"],
   managedConnectionProviders: [],
   allowedReturnOrigins: ["https://bifrost.gamecult.org"],
+  startRequiresAppCaller: true,
   capabilities: [
     {
       key: "member_access",
diff --git a/src/app.ts b/src/app.ts
index 40ceb20..96f107b 100644
--- a/src/app.ts
+++ b/src/app.ts
@@ -1,6 +1,7 @@
 import { createHmac, randomUUID } from "node:crypto";
+import cookie from "@fastify/cookie";
 import cors from "@fastify/cors";
-import Fastify, { type FastifyError, type FastifyInstance } from "fastify";
+import Fastify, { type FastifyError, type FastifyInstance, type FastifyReply } from "fastify";
 import { type AppCaller, isAppCaller, resolveAppCaller } from "./app-caller.js";
 import { deliverBackendHandoff, type BackendHandoffPayload } from "./backend-handoff.js";
 import {
@@ -93,6 +94,7 @@ function buildOAuthStateToken(options: {
   connection: OAuthConnectionBinding | undefined;
   handoff: OAuthHandoff;
   entitlementPolicy: OAuthEntitlementPolicy | undefined;
+  requestedScopes: string[] | undefined;
   keys: ReturnType<typeof createRuntimeKeyMaterial>;
 }): { token: string; expiresAt: string } {
   const issuedAt = nowEpochSeconds();
@@ -113,6 +115,7 @@ function buildOAuthStateToken(options: {
     connection: options.connection ?? null,
     handoff: options.handoff,
     entitlement_policy: options.entitlementPolicy ?? null,
+    requested_scopes: options.requestedScopes ?? null,
   };
   const token = signJwt(payload as unknown as Record<string, unknown>, options.keys);
 
@@ -151,6 +154,11 @@ function parseOAuthStatePayload(payload: Record<string, unknown>): OAuthStatePay
         entitlementPolicy !== null &&
         (entitlementPolicy as Record<string, unknown>).kind === "patreon_membership_access" &&
         typeof (entitlementPolicy as Record<string, unknown>).requiredTierTitle === "string"));
+  const requestedScopes = payload.requested_scopes;
+  const requestedScopesAreValid =
+    requestedScopes === null ||
+    requestedScopes === undefined ||
+    (Array.isArray(requestedScopes) && requestedScopes.every((scope) => typeof scope === "string"));
   if (
     payload.typ !== "heimdall_oauth_state" ||
     typeof payload.provider !== "string" ||
@@ -168,7 +176,8 @@ function parseOAuthStatePayload(payload: Record<string, unknown>): OAuthStatePay
     typeof payload.nbf !== "number" ||
     typeof payload.exp !== "number" ||
     !handoffIsValid ||
-    !entitlementPolicyIsValid
+    !entitlementPolicyIsValid ||
+    !requestedScopesAreValid
   ) {
     return null;
   }
@@ -180,10 +189,99 @@ function parseOAuthStatePayload(payload: Record<string, unknown>): OAuthStatePay
   if (!normalizedPayload.entitlement_policy) {
     normalizedPayload.entitlement_policy = null;
   }
+  if (!normalizedPayload.requested_scopes) {
+    normalizedPayload.requested_scopes = null;
+  }
 
   return normalizedPayload;
 }
 
+type OAuthStateVerdict =
+  | { ok: true; payload: OAuthStatePayload }
+  | { ok: false; error: "invalid_state" | "state_provider_mismatch" | "state_expired" };
+
+/**
+ * The one place a signed OAuth state becomes trusted: signature, shape, issuer,
+ * audience and provider, and the time window with the same 30 s skew refresh
+ * tokens use. Every route that turns a state into navigation or a completion
+ * runs this first; the refusals are fixed codes and never echo the token.
+ */
+function verifyOAuthState(
+  config: HeimdallConfig,
+  keys: ReturnType<typeof createRuntimeKeyMaterial>,
+  token: string,
+  provider: Provider
+): OAuthStateVerdict {
+  const verification = verifyJwt(token, keys.publicKey);
+  if (!verification.valid) {
+    return { ok: false, error: "invalid_state" };
+  }
+
+  const payload = parseOAuthStatePayload(verification.payload);
+  if (!payload || payload.iss !== config.issuer) {
+    return { ok: false, error: "invalid_state" };
+  }
+  if (payload.aud !== payload.provider || payload.provider !== provider) {
+    return { ok: false, error: "state_provider_mismatch" };
+  }
+
+  const now = nowEpochSeconds();
+  if (payload.nbf > now + 30 || payload.exp <= now - 30) {
+    return { ok: false, error: "state_expired" };
+  }
+
+  return { ok: true, payload };
+}
+
+const oauthBindingType = "heimdall_oauth_binding";
+
+function oauthBindingCookieName(jti: string): string {
+  return `__Host-heimdall-oauth-${jti}`;
+}
+
+/** The signed claim that this browser launched this state: it is the cookie's value, and needs no store read to check. */
+function signOAuthBinding(
+  config: HeimdallConfig,
+  keys: ReturnType<typeof createRuntimeKeyMaterial>,
+  state: OAuthStatePayload
+): string {
+  return signJwt(
+    { typ: oauthBindingType, iss: config.issuer, jti: state.jti, iat: nowEpochSeconds(), exp: state.exp },
+    keys
+  );
+}
+
+function oauthBindingHolds(
+  config: HeimdallConfig,
+  keys: ReturnType<typeof createRuntimeKeyMaterial>,
+  token: string | undefined,
+  state: OAuthStatePayload
+): boolean {
+  if (!token) {
+    return false;
+  }
+  const verification = verifyJwt(token, keys.publicKey);
+  if (!verification.valid) {
+    return false;
+  }
+  const { typ, iss, jti, exp } = verification.payload;
+  return typ === oauthBindingType && iss === config.issuer && jti === state.jti && typeof exp === "number" && exp > nowEpochSeconds();
+}
+
+function setOAuthBindingCookie(reply: FastifyReply, state: OAuthStatePayload, value: string, maxAgeSeconds: number): void {
+  reply.setCookie(oauthBindingCookieName(state.jti), value, {
+    path: "/",
+    secure: true,
+    httpOnly: true,
+    sameSite: "lax",
+    maxAge: Math.max(0, maxAgeSeconds),
+  });
+}
+
+function oauthCallbackUrl(config: HeimdallConfig, provider: Provider): string {
+  return `${config.publicBaseUrl}/v1/oauth/${provider}/callback`;
+}
+
 function buildGrantFacts(grants: StoredCapabilityGrant[]): string[] {
   return grants.map((grant) => grantFact(grant.capability));
 }
@@ -554,7 +652,7 @@ export async function startOAuthFlow(
   if (options?.trustedBrowserAttemptId && handoff.kind === "browser_completion") {
     handoff = { kind: "browser_completion", attemptId: options.trustedBrowserAttemptId };
   }
-  if (entitlementPolicy && (!isAppCaller(caller) || caller.appSlug !== profile.slug)) {
+  if ((entitlementPolicy || profile.startRequiresAppCaller) && (!isAppCaller(caller) || caller.appSlug !== profile.slug)) {
     return { statusCode: 401, body: { error: "app_auth_required" } };
   }
 
@@ -566,7 +664,6 @@ export async function startOAuthFlow(
     };
   }
 
-  const callbackUrl = `${config.publicBaseUrl}/v1/oauth/${provider}/callback`;
   const state = buildOAuthStateToken({
     config,
     provider,
@@ -576,6 +673,7 @@ export async function startOAuthFlow(
     connection: input.connection,
     handoff,
     entitlementPolicy,
+    requestedScopes: input.requestedScopes,
     keys,
   });
 
@@ -585,16 +683,9 @@ export async function startOAuthFlow(
       provider,
       appSlug: profile.slug,
       mode: input.mode,
-      callbackUrl,
-      authorizationUrl: buildAuthorizationUrl({
-        provider,
-        clientId: providerConfig.clientId,
-        redirectUri: callbackUrl,
-        state: state.token,
-        requestedScopes: input.requestedScopes,
-      }),
+      callbackUrl: oauthCallbackUrl(config, provider),
+      authorizationUrl: `${config.publicBaseUrl}/v1/oauth/${provider}/launch?state=${encodeURIComponent(state.token)}`,
       handoff,
-      stateToken: state.token,
       stateExpiresAt: state.expiresAt,
     },
   };
@@ -738,6 +829,7 @@ export async function buildApp(options: BuildAppOptions = {}): Promise<FastifyIn
     origin: true,
     credentials: true,
   });
+  await app.register(cookie);
 
   app.get("/healthz", async () => ({
     ok: true,
@@ -872,6 +964,72 @@ export async function buildApp(options: BuildAppOptions = {}): Promise<FastifyIn
     }
   );
 
+  app.get<{
+    Params: { provider: Provider };
+    Querystring: { state: string };
+  }>(
+    "/v1/oauth/:provider/launch",
+    {
+      schema: {
+        params: {
+          type: "object",
+          required: ["provider"],
+          additionalProperties: false,
+          properties: {
+            provider: { type: "string", enum: [...providers] },
+          },
+        },
+        querystring: {
+          type: "object",
+          required: ["state"],
+          additionalProperties: false,
+          properties: {
+            state: { type: "string", minLength: 1 },
+          },
+        },
+      },
+    },
+    async (request, reply) => {
+      const verified = verifyOAuthState(config, keys, request.query.state, request.params.provider);
+      if (!verified.ok) {
+        reply.code(400);
+        return { error: verified.error };
+      }
+      const state = verified.payload;
+      const clientId = config.providers[state.provider].clientId;
+      if (!clientId) {
+        reply.code(503);
+        return { error: "provider_not_configured", provider: state.provider, expectedEnv: providerExpectedEnv(state.provider) };
+      }
+
+      const first = await store.claimOAuthStateUse({
+        jti: state.jti,
+        phase: "launch",
+        appSlug: state.app_slug,
+        usedAt: new Date().toISOString(),
+        expiresAt: new Date(state.exp * 1000).toISOString(),
+      });
+      if (!first) {
+        reply.code(400);
+        return { error: "state_already_launched" };
+      }
+
+      setOAuthBindingCookie(reply, state, signOAuthBinding(config, keys, state), state.exp - nowEpochSeconds());
+      reply.header("Cache-Control", "no-store");
+      reply.header("Referrer-Policy", "no-referrer");
+      return reply.redirect(
+        buildAuthorizationUrl({
+          provider: state.provider,
+          clientId,
+          redirectUri: oauthCallbackUrl(config, state.provider),
+          state: request.query.state,
+          requestedScopes: state.requested_scopes ?? undefined,
+        }),
+        302
+      );
+    }
+  );
+
   app.get<{
     Params: { provider: Provider };
     Querystring: { code?: string; state?: string; error?: string; error_description?: string };
@@ -905,16 +1063,29 @@ export async function buildApp(options: BuildAppOptions = {}): Promise<FastifyIn
         return { error: "missing_state" };
       }
 
-      const verification = verifyJwt(request.query.state, keys.publicKey);
-      if (!verification.valid) {
+      const verified = verifyOAuthState(config, keys, request.query.state, request.params.provider);
+      if (!verified.ok) {
         reply.code(400);
-        return { error: "invalid_state", detail: verification.error };
+        return { error: verified.error };
       }
-
-      const statePayload = parseOAuthStatePayload(verification.payload);
-      if (!statePayload || statePayload.provider !== request.params.provider) {
+      const statePayload = verified.payload;
+      // The cookie is checked before the claim: a stranger without it must not be
+      // able to burn the state that the browser that launched it still needs.
+      if (!oauthBindingHolds(config, keys, request.cookies[oauthBindingCookieName(statePayload.jti)], statePayload)) {
         reply.code(400);
-        return { error: "state_provider_mismatch" };
+        return { error: "state_not_bound" };
+      }
+      setOAuthBindingCookie(reply, statePayload, "", 0);
+      const firstCallback = await store.claimOAuthStateUse({
+        jti: statePayload.jti,
+        phase: "callback",
+        appSlug: statePayload.app_slug,
+        usedAt: new Date().toISOString(),
+        expiresAt: new Date(statePayload.exp * 1000).toISOString(),
+      });
+      if (!firstCallback) {
+        reply.code(400);
+        return { error: "state_already_used" };
       }
       const handoff = statePayload.handoff ?? { kind: "browser_completion" };
       const denyBrowserAttempt = async (denialCode: string): Promise<void> => {
diff --git a/src/contracts.ts b/src/contracts.ts
index d6cab2a..daa559a 100644
--- a/src/contracts.ts
+++ b/src/contracts.ts
@@ -94,6 +94,8 @@ export interface OAuthStatePayload {
   connection: OAuthConnectionBinding | null;
   handoff: OAuthHandoff | null;
   entitlement_policy: OAuthEntitlementPolicy | null;
+  /** The start's requestedScopes, carried so the launch hop can build the provider URL from the signed state alone. */
+  requested_scopes: string[] | null;
 }
 
 export interface LinkedIdentityInput {
diff --git a/src/index.ts b/src/index.ts
index 0bc13c3..4c89a70 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,3 +1,4 @@
+import path from "node:path";
 import { resolveWriteLease, WriteLeaseNotHeldError } from "./process-write-lease.js";
 import { buildApp } from "./app.js";
 import { loadConfig } from "./config.js";
@@ -6,16 +7,14 @@ import { publishHeimdallOdinState } from "./odin-publication.js";
 import { startHeimdallPrivateCommandPlane } from "./private-command-plane.js";
 import type { CultNetOperationServer } from "cultnet-ts";
 import { createHeimdallRuntimePulse, buildHeimdallHealthDetail, publishHeimdallVerseState } from "./verse-state.js";
-import { openPresenceAuthority } from "./runtime-presence.js";
+import {
+  buildPresenceStatement,
+  nextPublisherSequence,
+  readRuntimeBundleFacts,
+  type RuntimeBundleFacts,
+} from "./runtime-presence.js";
 
 const config = loadConfig();
-// Under Idunn the launch's presence keys, bundle facts and publisher sequence
-// open here, before anything listens. A launch-contract fault throws, uncaught,
-// and the process exits non-zero with no listener: Idunn fails Warming in
-// seconds rather than waiting on a candidate that can never sign.
-const presenceAuthority = config.idunnRuntimeBundlePath
-  ? await openPresenceAuthority(config)
-  : undefined;
 const app = await buildApp({ config });
 const versePulseIntervalMs = 60_000;
 const healthPulseIntervalMs = 10_000;
@@ -71,6 +70,13 @@ async function publishVerseState(): Promise<void> {
   await publishHeimdallOdinState(config, pulse);
 }
 
+/**
+ * Read once and keep: the bundle is Idunn's immutable record of this launch and
+ * cannot change while the process lives, so re-reading it every pulse would be
+ * work that can only ever return the same answer or fail.
+ */
+let runtimeBundleFacts: RuntimeBundleFacts | undefined;
+
 async function publishHealthState(): Promise<void> {
   const pulse = createHeimdallRuntimePulse(config);
 
@@ -88,17 +94,32 @@ async function publishHealthState(): Promise<void> {
     ? buildHeimdallHealthDetail(config, pulse)
     : `Heimdall candidate warming; ${lease.reason}`;
 
-  if (!presenceAuthority) {
+  if (!config.idunnRuntimeBundlePath) {
     // Outside Idunn there is no launch to attest and nothing that admits the
     // statement; publishing is simply not part of that world.
     return;
   }
-  const state = lease.mayWrite ? "active" : "warming";
-  const presence = presenceAuthority.sign(state, detail, Date.parse(pulse.updatedAt));
+  runtimeBundleFacts ??= await readRuntimeBundleFacts(config.idunnRuntimeBundlePath);
+
+  const observedAtUnixMillis = Date.parse(pulse.updatedAt);
+  const presence = await buildPresenceStatement({
+    bundle: runtimeBundleFacts,
+    state: lease.mayWrite ? "active" : "warming",
+    detail,
+    boundEndpoint: `http://${config.host}:${config.port}`,
+    // A warming candidate holds no lease and must not claim one; the contract
+    // refuses the pair, and Idunn needs the warming statement to promote it.
+    writeLeaseSha256: null,
+    observedAtUnixMillis,
+    publisherSequence: await nextPublisherSequence(
+      path.join(config.dataRoot, "runtime-presence-sequence"),
+    ),
+    providerHealthIdentityPath: config.providerHealthIdentityPath,
+  });
 
   await publishIdunnRudpHealth(config, {
     daemonId: config.daemonId,
-    state,
+    state: lease.mayWrite ? "active" : "warming",
     detail,
     observedAt: pulse.updatedAt,
     presence,
diff --git a/src/private-command-plane.ts b/src/private-command-plane.ts
index 6d3025b..8e9fb8d 100644
--- a/src/private-command-plane.ts
+++ b/src/private-command-plane.ts
@@ -305,7 +305,6 @@ async function beginAuth(
     throw new Error(String(startPayload.detail ?? startPayload.error ?? "OAuth start was denied."));
   }
   const authorizationUrl = String(startPayload.authorizationUrl ?? "");
-  const authorizationOrigin = new URL(authorizationUrl).origin;
   return {
     status: "accepted",
     payloadSchema: "heimdall.auth_begin_receipt.v1",
@@ -316,7 +315,7 @@ async function beginAuth(
       expiresAt: attempt.expiresAt,
       navigation: {
         url: authorizationUrl,
-        allowedOrigins: [authorizationOrigin, new URL(config.publicBaseUrl).origin],
+        allowedOrigins: [new URL(config.publicBaseUrl).origin],
       },
     },
   };
diff --git a/src/provider-health-identity.ts b/src/provider-health-identity.ts
index ca89f2c..847d39c 100644
--- a/src/provider-health-identity.ts
+++ b/src/provider-health-identity.ts
@@ -7,7 +7,7 @@ import {
   sign,
   type KeyObject,
 } from "node:crypto";
-import { closeSync, fstatSync, readSync } from "node:fs";
+import { readFileSync } from "node:fs";
 import { chmod, readFile } from "node:fs/promises";
 import { SingleFileMessagePackBackingStore, type CultCacheEnvelope } from "@gamecult/cultcache-ts";
 import { readPrivateStoreRecord } from "./idunn-store.js";
@@ -71,7 +71,7 @@ export async function openOrEnrollProviderHealthIdentity(path: string): Promise<
   if (existing.length !== 1) {
     throw new Error("Provider-health identity store must contain exactly one record.");
   }
-  return decodePrivateIdentity(existing[0]!.payload, await readMachineId(), "bin");
+  return decodePrivateIdentity(existing[0]!.payload, await readMachineId());
 }
 
 const PRESENCE_IDENTITY_FD_NAME = "gamecult-runtime-presence-identity";
@@ -124,50 +124,19 @@ export function passedDescriptor(
  */
 export async function openProviderHealthIdentity(
   path: string,
-  env: NodeJS.ProcessEnv = process.env,
-  machineId: () => Promise<string> = readMachineId
+  env: NodeJS.ProcessEnv = process.env
 ): Promise<PrivateIdentity> {
   const descriptor = passedDescriptor(PRESENCE_IDENTITY_FD_NAME, env);
   if (descriptor === undefined) {
-    if (env.GAMECULT_IDUNN_RUNTIME_BUNDLE) {
-      // Inside an Idunn generation a self-enrolled key is one Idunn does not
-      // trust, and its private store would land in a state root the next
-      // generation must share. The descriptor is the only identity there.
-      throw new Error(
-        `Idunn runtime bundle is set but the ${PRESENCE_IDENTITY_FD_NAME} descriptor was not passed; refusing to self-enroll`
-      );
-    }
     return openOrEnrollProviderHealthIdentity(path);
   }
 
   const payload = readPrivateStoreRecord(
-    readPassedDescriptor(descriptor),
+    readFileSync(descriptor),
     "Idunn runtime presence identity"
   );
 
-  // The descriptor's writer is the Rust owner, whose key fields are integer arrays.
-  return decodePrivateIdentity(payload, await machineId(), "int-array");
-}
-
-/**
- * Read a passed descriptor whole, from offset 0, and close it. A descriptor is
- * a one-shot input: reading it again starts at the offset the last read left,
- * which is the end, so the owner reads once at open and keeps what it decoded.
- */
-export function readPassedDescriptor(descriptor: number): Buffer {
-  try {
-    const size = fstatSync(descriptor).size;
-    const bytes = Buffer.alloc(size);
-    let read = 0;
-    while (read < size) {
-      const count = readSync(descriptor, bytes, read, size - read, read);
-      if (count === 0) break;
-      read += count;
-    }
-    return bytes.subarray(0, read);
-  } finally {
-    closeSync(descriptor);
-  }
+  return decodePrivateIdentity(payload, await readMachineId());
 }
 
 export function signProviderHealthPayload(identity: PrivateIdentity, payload: Uint8Array): Uint8Array {
@@ -199,58 +168,23 @@ export function providerHealthPublicIdentity(identity: PrivateIdentity): {
   return { identityId: identity.identityId, publicKeyHex: Buffer.from(identity.publicKey).toString("hex") };
 }
 
-/**
- * Which writer produced the record. The self-enrolling store this process
- * writes keeps key fields as MessagePack bin; the Rust owner (cultnet-rs
- * service_identity.rs) serialises a Vec<u8> without serde_bytes, so its key
- * fields are arrays of integers. Each source is read in its own shape and the
- * other is refused.
- */
-type KeyShape = "bin" | "int-array";
-
-function keyBytes(value: unknown, shape: KeyShape, field: string): Uint8Array {
-  const bytes =
-    shape === "bin"
-      ? value instanceof Uint8Array
-        ? value
-        : undefined
-      : Array.isArray(value) &&
-          value.every((byte) => typeof byte === "number" && Number.isInteger(byte) && byte >= 0 && byte <= 255)
-        ? Uint8Array.from(value as number[])
-        : undefined;
-  if (bytes === undefined || bytes.length !== 32) {
-    throw new Error(
-      `Provider-health identity key shape check failed: ${field} is not a 32-byte ${shape === "bin" ? "binary" : "integer-array"} key field.`
-    );
-  }
-  return bytes;
-}
-
-function decodePrivateIdentity(payload: Uint8Array, machineId: string, shape: KeyShape): PrivateIdentity {
+function decodePrivateIdentity(payload: Uint8Array, machineId: string): PrivateIdentity {
   const value = decode(payload);
   if (!Array.isArray(value) || value.length !== 10) {
-    throw new Error("Provider-health identity schema check failed: payload is not a 10-field record.");
+    throw new Error("Provider-health identity payload is malformed.");
   }
-  const [schema, identityId, publicKeyField, protectedSeedField, protector, binding, version] = value;
-  if (schema !== PRIVATE_SCHEMA) {
-    throw new Error("Provider-health identity schema check failed: unexpected schema id.");
-  }
-  if (typeof identityId !== "string") {
-    throw new Error("Provider-health identity id check failed: id is not a string.");
-  }
-  const publicKey = keyBytes(publicKeyField, shape, "public key");
-  const protectedSeed = keyBytes(protectedSeedField, shape, "protected seed");
-  if (protector !== "linux_file_mode_machine_id_binding") {
-    throw new Error("Provider-health identity protector check failed: unexpected protector.");
-  }
-  if (binding !== protectorBinding(machineId)) {
-    throw new Error("Provider-health identity binding check failed: not bound to this host's machine id.");
-  }
-  if (version !== "v1") {
-    throw new Error("Provider-health identity version check failed: unexpected version.");
-  }
-  if (identityId !== deriveIdentityId(publicKey)) {
-    throw new Error("Provider-health identity id check failed: id does not derive from the public key.");
+  const [schema, identityId, publicKey, protectedSeed, protector, binding, version] = value;
+  if (
+    schema !== PRIVATE_SCHEMA ||
+    typeof identityId !== "string" ||
+    !(publicKey instanceof Uint8Array) || publicKey.length !== 32 ||
+    !(protectedSeed instanceof Uint8Array) || protectedSeed.length !== 32 ||
+    protector !== "linux_file_mode_machine_id_binding" ||
+    binding !== protectorBinding(machineId) ||
+    version !== "v1" ||
+    identityId !== deriveIdentityId(publicKey)
+  ) {
+    throw new Error("Provider-health identity does not belong to this host or profile.");
   }
   const seed = xorSeed(protectedSeed, binding);
   const privateKey = privateKeyFromSeed(seed);
diff --git a/src/runtime-presence.ts b/src/runtime-presence.ts
index 3c1054b..8cf0615 100644
--- a/src/runtime-presence.ts
+++ b/src/runtime-presence.ts
@@ -19,6 +19,8 @@
 
 import path from "node:path";
 import { createHash, createPrivateKey, type KeyObject } from "node:crypto";
+import { readFileSync } from "node:fs";
+import { readFile, writeFile, rename } from "node:fs/promises";
 
 import { decode } from "@msgpack/msgpack";
 import {
@@ -32,14 +34,11 @@ import {
   type RuntimePresenceState,
 } from "cultnet-ts";
 
-import type { HeimdallConfig } from "./config.js";
 import { readIdunnStoreRecord } from "./idunn-store.js";
 import {
   openProviderHealthIdentity,
   passedDescriptor,
-  readPassedDescriptor,
   signWithIdentity,
-  type PrivateIdentity,
 } from "./provider-health-identity.js";
 
 const PKCS8_ED25519_SEED_PREFIX = Buffer.from("302e020100300506032b657004220420", "hex");
@@ -179,37 +178,70 @@ export async function readRuntimeBundleFacts(bundlePath: string): Promise<Runtim
 }
 
 /**
- * The publisher sequence a process stamps on its presence statements.
+ * Open the activation signing key Idunn passed as a descriptor.
  *
- * Odin compares `publisher_sequence` only against stored presence of the same
- * activation, and Idunn mints a fresh activation for every start, continuity
- * restarts included. So the sequence need only strictly increase within this
- * process; nothing has to survive a restart, and nothing is written to the
- * state root. Muninn derives its sequence the same way: the observation clock,
- * never below the previous value plus one.
+ * The credential is exactly 32 bytes: the raw Ed25519 seed. It is passed as a
+ * parent-only descriptor and not as a path, so only the process Idunn launched
+ * can produce this half of the proof.
  */
-export class PublisherSequence {
-  private last = 0;
-
-  next(observedAtUnixMillis: number): number {
-    if (!Number.isSafeInteger(observedAtUnixMillis)) {
-      throw new Error("observedAtUnixMillis is not a safe integer");
-    }
-    this.last = Math.max(observedAtUnixMillis, this.last + 1);
-    return this.last;
+export function openActivationSigner(env: NodeJS.ProcessEnv = process.env): KeyObject | undefined {
+  const descriptor = passedDescriptor(IDUNN_RUNTIME_ACTIVATION_CREDENTIAL_NAME, env);
+  if (descriptor === undefined) {
+    return undefined;
   }
+  const seed = readFileSync(descriptor);
+  if (seed.length !== 32) {
+    throw new Error("Idunn runtime activation credential is not a 32-byte seed");
+  }
+  return createPrivateKey({
+    key: Buffer.concat([PKCS8_ED25519_SEED_PREFIX, seed]),
+    format: "der",
+    type: "pkcs8",
+  });
+}
+
+/**
+ * The publisher sequence must strictly increase for the life of a signer
+ * identity, because Idunn treats a repeat or a regression as a replay and
+ * refuses the observation.
+ *
+ * An in-process counter is therefore not enough: a restart would reset it and
+ * every statement afterwards would be refused until the count climbed past the
+ * old high-water mark. It lives beside the target's state instead, and is
+ * advanced before use.
+ */
+export async function nextPublisherSequence(sequencePath: string): Promise<number> {
+  let current = 0;
+  try {
+    const raw = (await readFile(sequencePath, "utf8")).trim();
+    const parsed = Number(raw);
+    if (Number.isSafeInteger(parsed) && parsed > 0) {
+      current = parsed;
+    }
+  } catch (error) {
+    if ((error as NodeJS.ErrnoException).code !== "ENOENT") {
+      throw error;
+    }
+  }
+  const next = current + 1;
+  // Written through a temporary file: a torn write here would look like a
+  // regression and cost the target every future observation.
+  const temporary = `${sequencePath}.next`;
+  await writeFile(temporary, `${next}\n`, { mode: 0o600 });
+  await rename(temporary, sequencePath);
+  return next;
 }
 
 export interface PresenceStatementInputs {
   bundle: RuntimeBundleFacts;
-  identity: PrivateIdentity;
-  activationKey: KeyObject;
   state: RuntimePresenceState;
   detail: string;
   boundEndpoint: string | null;
   writeLeaseSha256: string | null;
   observedAtUnixMillis: number;
   publisherSequence: number;
+  providerHealthIdentityPath: string;
+  env?: NodeJS.ProcessEnv;
 }
 
 export interface PresenceStatement {
@@ -218,14 +250,24 @@ export interface PresenceStatement {
 }
 
 /**
- * Build and dual-sign one presence statement from keys and facts already open.
+ * Build and dual-sign one presence statement.
  *
  * Returns the target alongside the bytes because the document key must equal
  * the signed target; Odin refuses the pair when they differ, and that is the
  * one part of the envelope the transport cannot infer.
  */
-export function buildPresenceStatement(inputs: PresenceStatementInputs): PresenceStatement {
-  const { identity } = inputs;
+export async function buildPresenceStatement(
+  inputs: PresenceStatementInputs,
+): Promise<PresenceStatement> {
+  const env = inputs.env ?? process.env;
+  const activationKey = openActivationSigner(env);
+  if (activationKey === undefined) {
+    throw new Error(
+      "Idunn passed no runtime activation credential, so this process cannot prove it is the " +
+        "incarnation Idunn started",
+    );
+  }
+  const identity = await openProviderHealthIdentity(inputs.providerHealthIdentityPath, env);
 
   const presence: RuntimePresenceHealth = {
     target: inputs.bundle.target,
@@ -253,7 +295,7 @@ export function buildPresenceStatement(inputs: PresenceStatementInputs): Presenc
   const proof = runtimePresenceProofPayload(presence);
   const signature = signWithIdentity(identity, runtimePresenceProviderSigningMessage(proof));
   const activationSignature = signWithIdentity(
-    { ...identity, privateKey: inputs.activationKey },
+    { ...identity, privateKey: activationKey },
     runtimePresenceActivationSigningMessage(proof),
   );
 
@@ -262,72 +304,3 @@ export function buildPresenceStatement(inputs: PresenceStatementInputs): Presenc
     payload: encodeRuntimePresenceHealth(presence, signature, activationSignature),
   };
 }
-
-export interface PresenceAuthority {
-  sign(
-    state: RuntimePresenceState,
-    detail: string,
-    observedAtUnixMillis: number,
-  ): PresenceStatement;
-}
-
-/**
- * Open everything this launch's presence statements stand on, once, before the
- * process listens: Idunn's bundle facts, the activation seed and the presence
- * identity (each descriptor is read whole and closed), and the one publisher
- * sequence. It owns them for the life of the process; a pulse supplies only its
- * state, detail and observation time.
- *
- * A launch-contract fault (a missing or malformed bundle, descriptor or
- * identity) throws here, so the process exits before it accepts a request and
- * Idunn fails Warming at once, instead of a listener that can never sign.
- */
-export async function openPresenceAuthority(
-  config: Pick<HeimdallConfig, "idunnRuntimeBundlePath" | "host" | "port" | "providerHealthIdentityPath">,
-  env: NodeJS.ProcessEnv = process.env,
-  machineId?: () => Promise<string>,
-): Promise<PresenceAuthority> {
-  if (!config.idunnRuntimeBundlePath) {
-    throw new Error("no Idunn runtime bundle path: presence has no launch to attest");
-  }
-  const bundle = await readRuntimeBundleFacts(config.idunnRuntimeBundlePath);
-
-  const activationDescriptor = passedDescriptor(IDUNN_RUNTIME_ACTIVATION_CREDENTIAL_NAME, env);
-  if (activationDescriptor === undefined) {
-    throw new Error(
-      "Idunn passed no runtime activation credential, so this process cannot prove it is the " +
-        "incarnation Idunn started",
-    );
-  }
-  const seed = readPassedDescriptor(activationDescriptor);
-  if (seed.length !== 32) {
-    throw new Error("Idunn runtime activation credential is not a 32-byte seed");
-  }
-  const activationKey = createPrivateKey({
-    key: Buffer.concat([PKCS8_ED25519_SEED_PREFIX, seed]),
-    format: "der",
-    type: "pkcs8",
-  });
-
-  const identity = await openProviderHealthIdentity(config.providerHealthIdentityPath, env, machineId);
-  const boundEndpoint = `http://${config.host}:${config.port}`;
-  const sequence = new PublisherSequence();
-
-  return {
-    sign: (state, detail, observedAtUnixMillis) =>
-      buildPresenceStatement({
-        bundle,
-        identity,
-        activationKey,
-        state,
-        detail,
-        boundEndpoint,
-        // A warming candidate holds no lease and must not claim one; the
-        // contract refuses the pair, and Idunn needs the warming statement to
-        // promote it.
-        writeLeaseSha256: null,
-        observedAtUnixMillis,
-        publisherSequence: sequence.next(observedAtUnixMillis),
-      }),
-  };
-}
diff --git a/src/store/in-memory.ts b/src/store/in-memory.ts
index 6a53dad..5fc91ba 100644
--- a/src/store/in-memory.ts
+++ b/src/store/in-memory.ts
@@ -3,6 +3,7 @@ import { type AppSlug, type LinkedIdentityInput, type Provider } from "../contra
 import {
   type CreateAccountInput,
   type CreateAuthAttemptInput,
+  type ClaimOAuthStateUseInput,
   type CreateAuthCompletionInput,
   type CreateAuditEventInput,
   type CreateCapabilityGrantInput,
@@ -48,6 +49,8 @@ export class InMemoryStore implements HeimdallStore {
   private readonly privateCommandReceipts = new Map<string, StoredPrivateCommandReceipt>();
   private readonly authCompletions = new Map<string, StoredAuthCompletion>();
   private readonly authCompletionsByAttempt = new Map<string, string>();
+  /** `${jti}:${phase}` -> the state's expiresAt. */
+  private readonly oauthStateUses = new Map<string, string>();
   private readonly entitlementSnapshots = new Map<string, CreateEntitlementSnapshotInput>();
   private readonly auditEvents = new Map<string, CreateAuditEventInput>();
 
@@ -424,6 +427,20 @@ export class InMemoryStore implements HeimdallStore {
     return this.consumeAuthCompletion(appSlug, code, at);
   }
 
+  async claimOAuthStateUse(input: ClaimOAuthStateUseInput): Promise<boolean> {
+    for (const [key, expiresAt] of this.oauthStateUses) {
+      if (expiresAt <= input.usedAt) {
+        this.oauthStateUses.delete(key);
+      }
+    }
+    const key = `${input.jti}:${input.phase}`;
+    if (this.oauthStateUses.has(key)) {
+      return false;
+    }
+    this.oauthStateUses.set(key, input.expiresAt);
+    return true;
+  }
+
   async upsertEntitlementSnapshot(input: CreateEntitlementSnapshotInput): Promise<void> {
     const key = `${input.accountId}:${input.provider}:${input.scope}`;
     this.entitlementSnapshots.set(key, clone(input));
diff --git a/src/store/postgres.ts b/src/store/postgres.ts
index 487f375..4ee0ea1 100644
--- a/src/store/postgres.ts
+++ b/src/store/postgres.ts
@@ -5,6 +5,7 @@ import { CREATE_SCHEMA_SQL, REQUIRED_COLUMNS, REQUIRED_KEYS, REQUIRED_TABLES } f
 import {
   type CreateAccountInput,
   type CreateAuthAttemptInput,
+  type ClaimOAuthStateUseInput,
   type CreateAuthCompletionInput,
   type CreateAuditEventInput,
   type CreateCapabilityGrantInput,
@@ -378,6 +379,7 @@ export const STORE_TABLE_PRIVILEGES: Readonly<Record<string, readonly ("SELECT"
   auth_attempts: ["SELECT", "INSERT", "UPDATE"],
   private_command_receipts: ["SELECT", "INSERT"],
   auth_completions: ["SELECT", "INSERT", "UPDATE"],
+  oauth_state_uses: ["INSERT"],
   capability_grants: ["SELECT", "INSERT"],
   entitlement_snapshots: ["SELECT", "INSERT", "UPDATE"],
   audit_events: ["INSERT"],
@@ -1061,6 +1063,19 @@ export class PostgresStore implements HeimdallStore {
     return result.rowCount ? mapAuthCompletionRow(expectRow(result.rows[0], "consumeAuthCompletionByAttempt")) : null;
   }
 
+  async claimOAuthStateUse(input: ClaimOAuthStateUseInput): Promise<boolean> {
+    // No conflict target and no RETURNING: both need SELECT, and the role has INSERT only.
+    const result = await this.pool.query(
+      `
+      INSERT INTO oauth_state_uses (jti, phase, app_slug, used_at, expires_at)
+      VALUES ($1, $2, $3, $4, $5)
+      ON CONFLICT DO NOTHING
+      `,
+      [input.jti, input.phase, input.appSlug, input.usedAt, input.expiresAt]
+    );
+    return result.rowCount === 1;
+  }
+
   async upsertEntitlementSnapshot(input: CreateEntitlementSnapshotInput): Promise<void> {
     await this.pool.query(
       `
diff --git a/src/store/schema.ts b/src/store/schema.ts
index 420f5e6..80dfa6e 100644
--- a/src/store/schema.ts
+++ b/src/store/schema.ts
@@ -119,6 +119,20 @@ CREATE UNIQUE INDEX IF NOT EXISTS auth_completions_attempt_unconsumed_unique_idx
   ON auth_completions(app_slug, attempt_id)
   WHERE attempt_id IS NOT NULL AND consumed_at IS NULL;
 
+-- One use per (state jti, phase): a signed OAuth state launches once and
+-- completes once. The first INSERT for a pair wins; ON CONFLICT DO NOTHING
+-- reports every later claim as no row. The store deletes nothing, so rows stay
+-- like consumed auth_completions; after expires_at a state is refused before
+-- any claim, so a row is never consulted again.
+CREATE TABLE IF NOT EXISTS oauth_state_uses (
+  jti TEXT NOT NULL,
+  phase TEXT NOT NULL,
+  app_slug TEXT NOT NULL,
+  used_at TIMESTAMPTZ NOT NULL,
+  expires_at TIMESTAMPTZ NOT NULL,
+  PRIMARY KEY (jti, phase)
+);
+
 CREATE TABLE IF NOT EXISTS capability_grants (
   id TEXT PRIMARY KEY,
   account_id TEXT NOT NULL REFERENCES accounts(id) ON DELETE CASCADE,
diff --git a/src/store/types.ts b/src/store/types.ts
index 5307e1f..d6a2f93 100644
--- a/src/store/types.ts
+++ b/src/store/types.ts
@@ -165,6 +165,14 @@ export interface StoredAuthCompletion {
   payloadJson: Record<string, unknown>;
 }
 
+export interface ClaimOAuthStateUseInput {
+  jti: string;
+  phase: "launch" | "callback";
+  appSlug: AppSlug;
+  usedAt: string;
+  expiresAt: string;
+}
+
 export interface CreateAuthCompletionInput {
   /**
    * Correlation handle only (see StoredAuthCompletion.attemptId). The store
@@ -272,5 +280,15 @@ export interface HeimdallStore {
    */
   consumeAuthCompletionByAttempt(appSlug: AppSlug, attemptId: string, at: string): Promise<StoredAuthCompletion | null>;
   upsertEntitlementSnapshot(input: CreateEntitlementSnapshotInput): Promise<void>;
+  /**
+   * Claim one use of a signed OAuth state: true only for the first claim of
+   * (jti, phase), false for every later one. Without it a state is a bearer
+   * token any number of browsers can complete, so an attacker who learns a
+   * victim's state completes it as themselves and hands the victim a code
+   * for the attacker's account. `expiresAt` is the state's own expiry; the
+   * state is refused at that time before any claim, so the record is dead
+   * after it and a store may drop it.
+   */
+  claimOAuthStateUse(input: ClaimOAuthStateUseInput): Promise<boolean>;
   createAuditEvent(input: CreateAuditEventInput): Promise<void>;
 }
diff --git a/tests/access-plugin.test.ts b/tests/access-plugin.test.ts
index 4789bf8..6afcdb8 100644
--- a/tests/access-plugin.test.ts
+++ b/tests/access-plugin.test.ts
@@ -8,6 +8,7 @@ import { entitlementFacts } from "../src/facts.js";
 import { startHeimdallPrivateCommandPlane } from "../src/private-command-plane.js";
 import { openPrivateEnvelope, sealPrivateEnvelope, type HeimdallPrivateEnvelope } from "../src/private-command-security.js";
 import { type OAuthProviderRuntime } from "../src/oauth.js";
+import { launchState } from "./oauth-flow.js";
 
 const secret = "ghostlight-private-command-secret";
 const resources: Array<{ close(): Promise<unknown> }> = [];
@@ -107,9 +108,12 @@ describe("Heimdall Eve access plugin", () => {
     const begin = openPrivateEnvelope(beginWire, secret);
     expect(begin.schema).toBe("heimdall.auth_begin_receipt.v1");
     const handle = String(begin.handle);
-    const navigation = begin.navigation as { url: string };
+    const navigation = begin.navigation as { url: string; allowedOrigins: string[] };
     const state = new URL(navigation.url).searchParams.get("state");
     expect(state).toBeTruthy();
+    // The browser goes to Heimdall's launch hop first, and only Heimdall's origin is allowed.
+    expect(navigation.url.startsWith("https://heimdall.gamecult.org/v1/oauth/discord/launch?state=")).toBe(true);
+    expect(navigation.allowedOrigins).toEqual(["https://heimdall.gamecult.org"]);
 
     const pendingEnvelope = sealPrivateEnvelope({
       appSlug: "ghostlight",
@@ -124,9 +128,11 @@ describe("Heimdall Eve access plugin", () => {
     const pending = openPrivateEnvelope(decodeEnvelope(pendingResponse.payload), secret);
     expect(pending).toMatchObject({ status: "pending", handle });
 
+    const { cookie } = await launchState(app, state ?? "");
     const callback = await app.inject({
       method: "GET",
       url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(state ?? "")}`,
+      headers: { cookie },
     });
     expect(callback.statusCode, callback.body).toBe(201);
     // The completion code is always minted by the store now, never the
diff --git a/tests/app.test.ts b/tests/app.test.ts
index 7f4d96d..1cfe062 100644
--- a/tests/app.test.ts
+++ b/tests/app.test.ts
@@ -4,7 +4,8 @@ import { join } from "node:path";
 import { inspect } from "node:util";
 import { afterEach, describe, expect, it } from "vitest";
 import { type FastifyInstance } from "fastify";
-import { buildApp, errorIdentity } from "../src/app.js";
+import { buildApp, errorIdentity, getHeimdallRuntimeContext, startOAuthFlow } from "../src/app.js";
+import { resolveAppCaller } from "../src/app-caller.js";
 import { builtInAppProfiles, callbackMint } from "../src/app-profiles.js";
 import { deliverBackendHandoff, type BackendHandoffPayload } from "../src/backend-handoff.js";
 import { type HeimdallConfig, loadConfig } from "../src/config.js";
@@ -12,96 +13,7 @@ import { entitlementFacts, identityFacts } from "../src/facts.js";
 import { createOAuthRuntimeRegistry, ProviderResponseError, type OAuthProviderRuntime } from "../src/oauth.js";
 import { createRuntimeKeyMaterial, signJwt, verifyJwt } from "../src/signing.js";
 import { InMemoryStore } from "../src/store/index.js";
-
-function createTestConfig(): HeimdallConfig {
-  return {
-    serviceName: "heimdall",
-    host: "127.0.0.1",
-    port: 4100,
-    workspaceRoot: "E:/Projects/Heimdall",
-    dataRoot: "E:/Projects/Heimdall/.heimdall-data",
-    cultCachePath: "E:/Projects/Heimdall/.heimdall-data/cultcache/heimdall.service.cc",
-    publicBaseUrl: "https://heimdall.gamecult.org",
-    issuer: "https://heimdall.gamecult.org",
-    daemonId: "yggdrasil-heimdall",
-    idunnRudpHealth: undefined,
-    idunnHealthContract: "heimdall.cultnet-rudp-provider-health",
-    providerHealthIdentityPath: "E:/Projects/Heimdall/.heimdall-data/provider-health-identity.cc",
-    sessionTtlSeconds: 3600,
-    refreshTtlSeconds: 60 * 60 * 24 * 30,
-    stateTtlSeconds: 600,
-    completionTtlSeconds: 300,
-    bootstrapSigningPrivateKeyOnMissing: false,
-    tokenEncryptionKeyBase64: Buffer.alloc(32, 7).toString("base64"),
-    appSharedSecrets: {
-      streampixels: "streampixels-secret",
-      repixelizer: "repixelizer-secret",
-      bifrost: "bifrost-secret",
-    },
-    appBackendCallbacks: {
-      bifrost: ["https://bifrost.gamecult.org/auth/heimdall/callback"],
-      repixelizer: ["https://repixelizer.gamecult.org/api/auth/heimdall/callback"],
-    },
-    storage: {
-      backend: "memory",
-      applySchemaOnStartup: true,
-    },
-    providers: {
-      discord: { clientId: "discord-client", clientSecret: "discord-secret" },
-      patreon: { clientId: "patreon-client", clientSecret: "patreon-secret" },
-      github: { clientId: "github-client", clientSecret: "github-secret" },
-      twitch: { clientId: "twitch-client", clientSecret: "twitch-secret" },
-      youtube: { clientId: "youtube-client", clientSecret: "youtube-secret" },
-      spotify: { clientId: "spotify-client", clientSecret: "spotify-secret" },
-      joystick: { clientId: "joystick-client", clientSecret: "joystick-secret" },
-    },
-  };
-}
-
-function createMockDiscordRuntime(): OAuthProviderRuntime {
-  return {
-    async exchangeAuthorizationCode() {
-      return {
-        accessToken: "discord-access-token",
-        refreshToken: "discord-refresh-token",
-        tokenType: "Bearer",
-        scope: ["identify", "guilds.members.read"],
-        expiresAt: "2026-04-26T13:00:00.000Z",
-        raw: { source: "test" },
-      };
-    },
-    async resolveIdentity() {
-      return {
-        provider: "discord",
-        providerUserId: "discord-user-123",
-        username: "meta",
-        displayName: "Meta",
-        primaryEmail: "meta@gamecult.org",
-        profile: { id: "discord-user-123", username: "meta" },
-      };
-    },
-    async evaluateEntitlements({ callback }) {
-      return {
-        facts: [entitlementFacts.appAccess],
-        snapshots: [
-          {
-            accountId: callback.accountId,
-            provider: "discord",
-            scope: "repixelizer:discord_role_access:gamecult-guild",
-            evaluatedAt: "2026-04-26T12:00:00.000Z",
-            isAllowed: true,
-            reasonCode: "matched_role",
-            reasonDetail: "Matched Repixelizer access role.",
-            rawSummaryJson: {
-              guildId: "gamecult-guild",
-              matchedRoles: ["role-repixelizer"],
-            },
-          },
-        ],
-      };
-    },
-  };
-}
+import { createMockDiscordRuntime, createTestConfig, launchFlow, providerRedirect, stateOf, type LaunchedFlow } from "./oauth-flow.js";
 
 const apps: Awaited<ReturnType<typeof buildApp>>[] = [];
 const originalFetch = globalThis.fetch;
@@ -134,7 +46,7 @@ function getHeimdallContext(app: FastifyInstance) {
   }).heimdallContext;
 }
 
-async function startDiscordSignIn(app: FastifyInstance): Promise<string> {
+async function startDiscordSignIn(app: FastifyInstance): Promise<LaunchedFlow> {
   const response = await app.inject({
     method: "POST",
     url: "/v1/oauth/discord/start",
@@ -146,7 +58,7 @@ async function startDiscordSignIn(app: FastifyInstance): Promise<string> {
   });
 
   expect(response.statusCode).toBe(201);
-  return response.json().stateToken as string;
+  return launchFlow(app, response.json());
 }
 
 afterEach(async () => {
@@ -207,9 +119,9 @@ describe("Heimdall service", () => {
 
     expect(response.statusCode).toBe(201);
     const payload = response.json();
-    expect(payload.authorizationUrl).toContain("discord.com/oauth2/authorize");
+    expect((await providerRedirect(app, payload)).href).toContain("discord.com/oauth2/authorize");
 
-    const verified = verifyJwt(payload.stateToken as string, getPublicKey(app));
+    const verified = verifyJwt(stateOf(payload), getPublicKey(app));
     expect(verified.valid).toBe(true);
     if (verified.valid) {
       expect(verified.payload).toEqual(
@@ -249,6 +161,161 @@ describe("Heimdall service", () => {
     expect(response.json()).toEqual(expect.objectContaining({ error: "app_auth_required" }));
   });
 
+  describe("apps that bind browser completion to their own attempt", () => {
+    // Bifrost's browser binding is the secrecy of its attempt nonce, which
+    // travels readable in the signed state. Only Bifrost may mint a Bifrost
+    // state, so a known nonce cannot carry a stranger's completion
+    // (finding known-nonce-login-csrf).
+    const victimAttempt = "VICTIM-ATTEMPT-NONCE";
+    const bifrostReturn = `https://bifrost.gamecult.org/auth/heimdall/complete?attempt=${victimAttempt}`;
+    const bifrostStart = (handoff?: { kind: "browser_completion" }) => ({
+      appSlug: "bifrost" as const,
+      mode: "sign_in" as const,
+      returnTo: bifrostReturn,
+      ...(handoff ? { handoff } : {}),
+    });
+
+    it("refuses an unauthenticated Bifrost start for browser_completion and for an omitted handoff", async () => {
+      const app = await buildApp({ config: createTestConfig() });
+      apps.push(app);
+
+      for (const payload of [bifrostStart({ kind: "browser_completion" }), bifrostStart()]) {
+        const response = await app.inject({ method: "POST", url: "/v1/oauth/discord/start", payload });
+        expect(response.statusCode).toBe(401);
+        expect(response.json()).toEqual({ error: "app_auth_required" });
+      }
+    });
+
+    it("the attack fails: a stranger cannot obtain a Bifrost state carrying a chosen return_to nonce", async () => {
+      const app = await buildApp({ config: createTestConfig() });
+      apps.push(app);
+
+      const response = await app.inject({
+        method: "POST",
+        url: "/v1/oauth/discord/start",
+        payload: bifrostStart({ kind: "browser_completion" }),
+      });
+      expect(response.statusCode).toBe(401);
+      expect(response.body).not.toContain(victimAttempt);
+      expect(response.body).not.toContain("stateToken");
+      expect(response.body).not.toContain("authorizationUrl");
+    });
+
+    it("still starts for Bifrost's own app secret, with the requested return_to in the state", async () => {
+      const app = await buildApp({ config: createTestConfig() });
+      apps.push(app);
+
+      const response = await app.inject({
+        method: "POST",
+        url: "/v1/oauth/discord/start",
+        headers: { "x-heimdall-app-secret": "bifrost-secret" },
+        payload: bifrostStart({ kind: "browser_completion" }),
+      });
+      expect(response.statusCode).toBe(201);
+      const verified = verifyJwt(stateOf(response.json()), getPublicKey(app));
+      expect(verified.valid).toBe(true);
+      if (verified.valid) {
+        expect(verified.payload).toEqual(expect.objectContaining({ app_slug: "bifrost", return_to: bifrostReturn }));
+      }
+    });
+
+    it("refuses another app's credentials on a Bifrost start", async () => {
+      const app = await buildApp({ config: createTestConfig() });
+      apps.push(app);
+
+      for (const secret of ["streampixels-secret", "repixelizer-secret"]) {
+        const response = await app.inject({
+          method: "POST",
+          url: "/v1/oauth/discord/start",
+          headers: { "x-heimdall-app-secret": secret },
+          payload: bifrostStart({ kind: "browser_completion" }),
+        });
+        expect(response.statusCode, secret).toBe(401);
+        expect(response.json()).toEqual({ error: "app_auth_required" });
+      }
+    });
+
+    it("refuses another app's authenticated caller on a direct Bifrost start, with no policy attached", async () => {
+      // Over HTTP the caller is resolved against the body's slug, so a foreign
+      // secret never becomes a caller at all. The command plane and direct
+      // callers hand startOAuthFlow a caller of their own, so the slug match is
+      // decided here too.
+      const config = createTestConfig();
+      const app = await buildApp({ config });
+      apps.push(app);
+      const foreign = resolveAppCaller(config, "repixelizer", { "x-heimdall-app-secret": "repixelizer-secret" });
+      const own = resolveAppCaller(config, "bifrost", { "x-heimdall-app-secret": "bifrost-secret" });
+
+      const refused = await startOAuthFlow(getHeimdallRuntimeContext(app), "discord", foreign, bifrostStart({ kind: "browser_completion" }));
+      expect(refused.statusCode).toBe(401);
+      const allowed = await startOAuthFlow(getHeimdallRuntimeContext(app), "discord", own, bifrostStart({ kind: "browser_completion" }));
+      expect(allowed.statusCode).toBe(201);
+    });
+
+    it("gates every mode, provider and handoff kind Bifrost admits, not one spelling of them", async () => {
+      // Hand mutants narrowing the gate to browser_completion or to sign_in
+      // survived the single-case tests (finding gate-tests-narrow).
+      const app = await buildApp({ config: createTestConfig() });
+      apps.push(app);
+      const handoffs = [
+        undefined,
+        { kind: "browser_completion" },
+        {
+          kind: "backend_callback",
+          attemptId: "bifrost-attempt-1",
+          callbackUrl: "https://bifrost.gamecult.org/auth/heimdall/callback",
+        },
+      ];
+
+      let cases = 0;
+      for (const mode of ["sign_in", "link", "connect"] as const) {
+        for (const provider of ["discord", "patreon"] as const) {
+          for (const handoff of handoffs) {
+            const label = `${mode} ${provider} ${handoff?.kind ?? "omitted"}`;
+            const payload = { appSlug: "bifrost", mode, returnTo: bifrostReturn, ...(handoff ? { handoff } : {}) };
+            const refused = await app.inject({ method: "POST", url: `/v1/oauth/${provider}/start`, payload });
+            expect(refused.statusCode, label).toBe(401);
+            expect(refused.json(), label).toEqual({ error: "app_auth_required" });
+
+            const allowed = await app.inject({
+              method: "POST",
+              url: `/v1/oauth/${provider}/start`,
+              headers: { "x-heimdall-app-secret": "bifrost-secret" },
+              payload,
+            });
+            expect(allowed.statusCode, label).toBe(201);
+            expect(allowed.json().authorizationUrl, label).toContain(`/v1/oauth/${provider}/launch?state=`);
+            cases += 1;
+          }
+        }
+      }
+      expect(cases).toBe(18);
+    });
+
+    it("leaves public-by-design apps unchanged: unauthenticated browser_completion starts still succeed", async () => {
+      const app = await buildApp({ config: createTestConfig() });
+      apps.push(app);
+
+      for (const [appSlug, provider, returnTo] of [
+        ["repixelizer", "discord", "https://repixelizer.gamecult.org/app/"],
+        ["streampixels", "twitch", "https://streampixels.gamecult.org/app/"],
+      ] as const) {
+        const response = await app.inject({
+          method: "POST",
+          url: `/v1/oauth/${provider}/start`,
+          payload: { appSlug, mode: "sign_in", returnTo, handoff: { kind: "browser_completion" } },
+        });
+        expect(response.statusCode, appSlug).toBe(201);
+      }
+    });
+
+    it("flags only Bifrost's profile", () => {
+      expect(
+        Object.values(builtInAppProfiles).filter((profile) => profile.startRequiresAppCaller).map((profile) => profile.slug)
+      ).toEqual(["bifrost"]);
+    });
+  });
+
   it("accepts caller-owned entitlement policy for a browser completion handoff when the caller is trusted", async () => {
     // The other half of the same pin: a caller holding the secret may attach
     // policy even without a backend_callback handoff, because identity no
@@ -302,9 +369,9 @@ describe("Heimdall service", () => {
 
     expect(response.statusCode).toBe(201);
     const payload = response.json();
-    expect(payload.authorizationUrl).toContain("discord.com/oauth2/authorize");
+    expect((await providerRedirect(app, payload)).href).toContain("discord.com/oauth2/authorize");
 
-    const verified = verifyJwt(payload.stateToken as string, getPublicKey(app));
+    const verified = verifyJwt(stateOf(payload), getPublicKey(app));
     expect(verified.valid).toBe(true);
     if (verified.valid) {
       expect(verified.payload).toEqual(
@@ -348,11 +415,11 @@ describe("Heimdall service", () => {
 
     expect(response.statusCode).toBe(201);
     const payload = response.json();
-    const authorizationUrl = new URL(payload.authorizationUrl as string);
+    const authorizationUrl = await providerRedirect(app, payload);
     expect(`${authorizationUrl.origin}${authorizationUrl.pathname}`).toBe("https://www.patreon.com/oauth2/authorize");
     expect(authorizationUrl.searchParams.get("scope")).toBe("identity identity[email]");
 
-    const verified = verifyJwt(payload.stateToken as string, getPublicKey(app));
+    const verified = verifyJwt(stateOf(payload), getPublicKey(app));
     expect(verified.valid).toBe(true);
     if (verified.valid) {
       expect(verified.payload).toEqual(
@@ -396,9 +463,9 @@ describe("Heimdall service", () => {
 
     expect(response.statusCode).toBe(201);
     const payload = response.json();
-    expect(payload.authorizationUrl).toContain("discord.com/oauth2/authorize");
+    expect((await providerRedirect(app, payload)).href).toContain("discord.com/oauth2/authorize");
 
-    const verified = verifyJwt(payload.stateToken as string, getPublicKey(app));
+    const verified = verifyJwt(stateOf(payload), getPublicKey(app));
     expect(verified.valid).toBe(true);
     if (verified.valid) {
       expect(verified.payload).toEqual(
@@ -442,10 +509,10 @@ describe("Heimdall service", () => {
 
     expect(response.statusCode).toBe(201);
     const payload = response.json();
-    const authorizationUrl = new URL(payload.authorizationUrl as string);
+    const authorizationUrl = await providerRedirect(app, payload);
     expect(`${authorizationUrl.origin}${authorizationUrl.pathname}`).toBe("https://www.patreon.com/oauth2/authorize");
 
-    const verified = verifyJwt(payload.stateToken as string, getPublicKey(app));
+    const verified = verifyJwt(stateOf(payload), getPublicKey(app));
     expect(verified.valid).toBe(true);
     if (verified.valid) {
       expect(verified.payload).toEqual(
@@ -473,10 +540,11 @@ describe("Heimdall service", () => {
     });
     apps.push(app);
 
-    const stateToken = await startDiscordSignIn(app);
+    const flow = await startDiscordSignIn(app);
     const response = await app.inject({
       method: "GET",
-      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(stateToken)}`,
+      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(flow.state)}`,
+      headers: { cookie: flow.cookie },
     });
 
     expect(response.statusCode).toBe(201);
@@ -689,10 +757,11 @@ describe("Heimdall service", () => {
     });
     apps.push(app);
 
-    const stateToken = await startDiscordSignIn(app);
+    const flow = await startDiscordSignIn(app);
     const callbackResponse = await app.inject({
       method: "GET",
-      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(stateToken)}`,
+      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(flow.state)}`,
+      headers: { cookie: flow.cookie },
     });
     const completionCode = callbackResponse.json().completion.code as string;
 
@@ -731,10 +800,11 @@ describe("Heimdall service", () => {
     const auditEvents = () =>
       [...(store as unknown as { auditEvents: Map<string, { eventType: string; sessionId?: string; eventPayloadJson: unknown }> }).auditEvents.values()];
 
-    const stateToken = await startDiscordSignIn(app);
+    const flow = await startDiscordSignIn(app);
     const callback = await app.inject({
       method: "GET",
-      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(stateToken)}`,
+      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(flow.state)}`,
+      headers: { cookie: flow.cookie },
     });
     const { code, expiresAt } = callback.json().completion as { code: string; expiresAt: string };
     const created = auditEvents().filter((event) => event.eventType === "auth_completion_created");
@@ -815,10 +885,11 @@ describe("Heimdall service", () => {
     });
     apps.push(app);
 
-    const stateToken = await startDiscordSignIn(app);
+    const flow = await startDiscordSignIn(app);
     const callbackResponse = await app.inject({
       method: "GET",
-      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(stateToken)}`,
+      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(flow.state)}`,
+      headers: { cookie: flow.cookie },
     });
     expect(callbackResponse.statusCode).toBe(201);
     const refreshToken = callbackResponse.json().refreshToken as string;
@@ -862,11 +933,12 @@ describe("Heimdall service", () => {
     });
     apps.push(app);
 
-    const stateToken = await startDiscordSignIn(app);
+    const flow = await startDiscordSignIn(app);
     const response = await app.inject({
       method: "GET",
-      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(stateToken)}`,
+      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(flow.state)}`,
       headers: {
+        cookie: flow.cookie,
         accept: "text/html",
       },
     });
@@ -912,12 +984,13 @@ describe("Heimdall service", () => {
       },
     });
     expect(startResponse.statusCode).toBe(201);
-    const stateToken = startResponse.json().stateToken as string;
+    const flow = await launchFlow(app, startResponse.json());
 
     const response = await app.inject({
       method: "GET",
-      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(stateToken)}`,
+      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(flow.state)}`,
       headers: {
+        cookie: flow.cookie,
         accept: "text/html",
       },
     });
@@ -1123,11 +1196,12 @@ describe("Heimdall service", () => {
         returnTo: "https://streampixels.gamecult.org/auth/connect",
       },
     });
-    const stateToken = startResponse.json().stateToken as string;
+    const flow = await launchFlow(app, startResponse.json());
 
     const callbackResponse = await app.inject({
       method: "GET",
-      url: `/v1/oauth/twitch/callback?code=test-code&state=${encodeURIComponent(stateToken)}`,
+      url: `/v1/oauth/twitch/callback?code=test-code&state=${encodeURIComponent(flow.state)}`,
+      headers: { cookie: flow.cookie },
     });
     const accountId = callbackResponse.json().account.id as string;
 
@@ -1210,11 +1284,12 @@ describe("Heimdall service", () => {
         returnTo: "https://streampixels.gamecult.org/auth/connect",
       },
     });
-    const stateToken = startResponse.json().stateToken as string;
+    const flow = await launchFlow(app, startResponse.json());
 
     const callbackResponse = await app.inject({
       method: "GET",
-      url: `/v1/oauth/twitch/callback?code=test-code&state=${encodeURIComponent(stateToken)}`,
+      url: `/v1/oauth/twitch/callback?code=test-code&state=${encodeURIComponent(flow.state)}`,
+      headers: { cookie: flow.cookie },
     });
     const accountId = callbackResponse.json().account.id as string;
 
@@ -1276,10 +1351,11 @@ describe("Heimdall service", () => {
     });
     apps.push(app);
 
-    const stateToken = await startDiscordSignIn(app);
+    const flow = await startDiscordSignIn(app);
     const callbackResponse = await app.inject({
       method: "GET",
-      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(stateToken)}`,
+      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(flow.state)}`,
+      headers: { cookie: flow.cookie },
     });
     expect(callbackResponse.statusCode).toBe(201);
     const evaluationsAtSignIn = evaluations;
@@ -1377,7 +1453,7 @@ describe("Heimdall service", () => {
       expect(start.statusCode).toBe(400);
       expect(start.json().error).toBe(error);
       expect(start.json().authorizationUrl).toBeUndefined();
-      expect(start.json().stateToken).toBeUndefined();
+      expect(start.json()).not.toHaveProperty("stateToken");
     });
 
     it.each([
@@ -1393,14 +1469,15 @@ describe("Heimdall service", () => {
         apps.push(app);
         const keys = createRuntimeKeyMaterial({ ...config, bootstrapSigningPrivateKeyOnMissing: false });
         const calls = stubJoystick({ channel_id: "chan-forged", username: "deru" });
-        const stateToken = (await connect(app)).json().stateToken as string;
-        const verified = verifyJwt(stateToken, keys.publicKey);
+        const flow = await launchFlow(app, (await connect(app)).json());
+        const verified = verifyJwt(flow.state, keys.publicKey);
         expect(verified.valid).toBe(true);
         const forged = signJwt({ ...(verified as { payload: Record<string, unknown> }).payload, connection }, keys);
 
         const callback = await app.inject({
           method: "GET",
           url: `/v1/oauth/joystick/callback?code=c&state=${encodeURIComponent(forged)}`,
+          headers: { cookie: flow.cookie },
         });
         expect(callback.statusCode).toBeGreaterThanOrEqual(400);
         expect(calls).toEqual([]);
@@ -1432,9 +1509,11 @@ describe("Heimdall service", () => {
         handoff: { kind: "backend_callback", attemptId: "attempt-js-1", callbackUrl },
       });
       expect(start.statusCode).toBe(201);
+      const flow = await launchFlow(app, start.json());
       const callback = await app.inject({
         method: "GET",
-        url: `/v1/oauth/joystick/callback?code=c&state=${encodeURIComponent(start.json().stateToken as string)}`,
+        url: `/v1/oauth/joystick/callback?code=c&state=${encodeURIComponent(flow.state)}`,
+        headers: { cookie: flow.cookie },
       });
       expect(callback.statusCode).toBeLessThan(300);
 
@@ -1453,7 +1532,7 @@ describe("Heimdall service", () => {
       apps.push(app);
       const start = await connect(app);
       expect(start.statusCode).toBe(201);
-      const url = new URL(start.json().authorizationUrl as string);
+      const url = await providerRedirect(app, start.json());
       expect(`${url.origin}${url.pathname}`).toBe("https://joystick.tv/api/oauth/authorize");
       expect(url.searchParams.get("client_id")).toBe("joystick-client");
       expect(url.searchParams.get("scope")).toBe("identity:read stream:read chat:read followers:read subscribers:read");
@@ -1467,10 +1546,11 @@ describe("Heimdall service", () => {
         const app = await buildApp({ config: createTestConfig(), store });
         apps.push(app);
         stubJoystick({ channel_id: "deru-chan", username: "deru" });
-        const stateToken = (await connect(app)).json().stateToken as string;
+        const flow = await launchFlow(app, (await connect(app)).json());
         const connected = await app.inject({
           method: "GET",
-          url: `/v1/oauth/joystick/callback?code=a&state=${encodeURIComponent(stateToken)}`,
+          url: `/v1/oauth/joystick/callback?code=a&state=${encodeURIComponent(flow.state)}`,
+          headers: { cookie: flow.cookie },
         });
         const accountId = connected.json().account.id as string;
         const before = await store.findStoredLinkedIdentityForAccount(accountId, "joystick");
@@ -1518,14 +1598,15 @@ describe("Heimdall service", () => {
           apps.push(app);
           const keys = createRuntimeKeyMaterial({ ...config, bootstrapSigningPrivateKeyOnMissing: false });
           const calls = stubJoystick({ channel_id: "chan-forged", username: "deru" });
-          const stateToken = (await connect(app)).json().stateToken as string;
-          const verified = verifyJwt(stateToken, keys.publicKey);
+          const flow = await launchFlow(app, (await connect(app)).json());
+          const verified = verifyJwt(flow.state, keys.publicKey);
           expect(verified.valid).toBe(true);
           const forged = signJwt({ ...(verified as { payload: Record<string, unknown> }).payload, mode }, keys);
 
           const callback = await app.inject({
             method: "GET",
             url: `/v1/oauth/joystick/callback?code=c&state=${encodeURIComponent(forged)}`,
+            headers: { cookie: flow.cookie },
           });
           expect(callback.statusCode).toBeGreaterThanOrEqual(400);
           expect(callback.body).not.toContain("viewer_access");
@@ -1542,11 +1623,12 @@ describe("Heimdall service", () => {
       const app = await buildApp({ config: createTestConfig(), store });
       apps.push(app);
       const calls = stubJoystick({ channel_id: "chan-9", username: "deru", nickname: "Deru!", photo_url: "https://img/x.png" });
-      const stateToken = (await connect(app)).json().stateToken as string;
+      const flow = await launchFlow(app, (await connect(app)).json());
 
       const callback = await app.inject({
         method: "GET",
-        url: `/v1/oauth/joystick/callback?code=the-code&state=${encodeURIComponent(stateToken)}`,
+        url: `/v1/oauth/joystick/callback?code=the-code&state=${encodeURIComponent(flow.state)}`,
+        headers: { cookie: flow.cookie },
       });
       expect(callback.statusCode).toBeLessThan(300);
 
@@ -1575,10 +1657,11 @@ describe("Heimdall service", () => {
       const app = await buildApp({ config: createTestConfig(), store });
       apps.push(app);
       stubJoystick({ channel_id: "chan-9", username: "deru" });
-      const stateToken = (await connect(app)).json().stateToken as string;
+      const flow = await launchFlow(app, (await connect(app)).json());
       const callback = await app.inject({
         method: "GET",
-        url: `/v1/oauth/joystick/callback?code=c&state=${encodeURIComponent(stateToken)}`,
+        url: `/v1/oauth/joystick/callback?code=c&state=${encodeURIComponent(flow.state)}`,
+        headers: { cookie: flow.cookie },
       });
       const row = await store.findStoredLinkedIdentityForAccount(callback.json().account.id as string, "joystick");
       expect(row?.displayName).toBe("deru");
@@ -1589,10 +1672,11 @@ describe("Heimdall service", () => {
       const app = await buildApp({ config: createTestConfig(), store });
       apps.push(app);
       stubJoystick({ username: "deru" });
-      const stateToken = (await connect(app)).json().stateToken as string;
+      const flow = await launchFlow(app, (await connect(app)).json());
       const callback = await app.inject({
         method: "GET",
-        url: `/v1/oauth/joystick/callback?code=c&state=${encodeURIComponent(stateToken)}`,
+        url: `/v1/oauth/joystick/callback?code=c&state=${encodeURIComponent(flow.state)}`,
+        headers: { cookie: flow.cookie },
       });
       expect(callback.statusCode).toBeGreaterThanOrEqual(400);
       expect(await store.findStoredLinkedIdentity("joystick", "undefined")).toBeNull();
@@ -1787,11 +1871,11 @@ describe("error answers never echo an input", () => {
     const app = await buildApp({ config: createTestConfig(), oauthRuntimes: { discord: failingDiscordRuntime() } });
     apps.push(app);
 
-    const stateToken = await startDiscordSignIn(app);
+    const flow = await startDiscordSignIn(app);
     const response = await app.inject({
       method: "GET",
-      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(stateToken)}`,
-      headers: { accept: "text/html" },
+      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(flow.state)}`,
+      headers: { cookie: flow.cookie, accept: "text/html" },
     });
 
     expect(response.headers["content-type"]).toContain("text/html");
@@ -1823,9 +1907,11 @@ describe("error answers never echo an input", () => {
       },
     });
     expect(start.statusCode).toBe(201);
+    const flow = await launchFlow(app, start.json());
     const response = await app.inject({
       method: "GET",
-      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(start.json().stateToken as string)}`,
+      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(flow.state)}`,
+      headers: { cookie: flow.cookie },
     });
 
     expect(response.statusCode).toBe(502);
@@ -1843,16 +1929,16 @@ describe("the relayed provider error", () => {
   const injected = `<script>alert(1)</script>"\\\u0007é${"x".repeat(300)}`;
   const allowed = /^[\x20-\x21\x23-\x5b\x5d-\x7e]*$/;
 
-  function providerErrorUrl(stateToken: string): string {
-    const query = new URLSearchParams({ state: stateToken, error: `${"e".repeat(100)}\u0000`, error_description: injected });
-    return `/v1/oauth/discord/callback?${query.toString()}`;
+  function providerErrorRequest(flow: LaunchedFlow) {
+    const query = new URLSearchParams({ state: flow.state, error: `${"e".repeat(100)}\u0000`, error_description: injected });
+    return { method: "GET" as const, url: `/v1/oauth/discord/callback?${query.toString()}`, headers: { cookie: flow.cookie } };
   }
 
   it("is printable and bounded in the JSON answer", async () => {
     const app = await buildApp({ config: createTestConfig() });
     apps.push(app);
 
-    const response = await app.inject({ method: "GET", url: providerErrorUrl(await startDiscordSignIn(app)) });
+    const response = await app.inject(providerErrorRequest(await startDiscordSignIn(app)));
 
     expect(response.statusCode).toBe(400);
     const { providerError, providerErrorDescription } = response.json() as Record<string, string>;
@@ -1866,11 +1952,8 @@ describe("the relayed provider error", () => {
     const app = await buildApp({ config: createTestConfig() });
     apps.push(app);
 
-    const response = await app.inject({
-      method: "GET",
-      url: providerErrorUrl(await startDiscordSignIn(app)),
-      headers: { accept: "text/html" },
-    });
+    const request = providerErrorRequest(await startDiscordSignIn(app));
+    const response = await app.inject({ ...request, headers: { ...request.headers, accept: "text/html" } });
 
     expect(response.headers["content-type"]).toContain("text/html");
     expect(response.body.match(/<script/gi)).toHaveLength(1);
@@ -1902,7 +1985,7 @@ describe("the relayed provider error", () => {
     });
     expect(start.statusCode).toBe(201);
 
-    await app.inject({ method: "GET", url: providerErrorUrl(start.json().stateToken as string) });
+    await app.inject(providerErrorRequest(await launchFlow(app, start.json())));
 
     expect(deliveries).toHaveLength(1);
     const description = String(deliveries[0]!.errorDescription);
@@ -1928,10 +2011,11 @@ describe("the failed-callback audit event", () => {
     });
     apps.push(app);
 
-    const stateToken = await startDiscordSignIn(app);
+    const flow = await startDiscordSignIn(app);
     const response = await app.inject({
       method: "GET",
-      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(stateToken)}`,
+      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(flow.state)}`,
+      headers: { cookie: flow.cookie },
     });
     expect(response.statusCode).toBe(502);
 
@@ -1955,10 +2039,11 @@ describe("the failed-callback audit event for a provider's HTTP refusal", () =>
     const store = new InMemoryStore();
     const app = await buildApp({ config: createTestConfig(), store, oauthRuntimes: createOAuthRuntimeRegistry() });
     apps.push(app);
-    const stateToken = await startDiscordSignIn(app);
+    const flow = await startDiscordSignIn(app);
     const callback = await app.inject({
       method: "GET",
-      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(stateToken)}`,
+      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(flow.state)}`,
+      headers: { cookie: flow.cookie },
     });
     expect(callback.statusCode).toBe(502);
     const events = [...(store as unknown as { auditEvents: Map<string, { eventType: string; eventPayloadJson: unknown }> }).auditEvents.values()];
@@ -2012,8 +2097,12 @@ describe("the failed-callback audit event for a provider's HTTP refusal", () =>
       },
     });
     apps.push(app);
-    const stateToken = await startDiscordSignIn(app);
-    await app.inject({ method: "GET", url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(stateToken)}` });
+    const flow = await startDiscordSignIn(app);
+    await app.inject({
+      method: "GET",
+      url: `/v1/oauth/discord/callback?code=test-code&state=${encodeURIComponent(flow.state)}`,
+      headers: { cookie: flow.cookie },
+    });
 
     const events = [...(store as unknown as { auditEvents: Map<string, { eventType: string; eventPayloadJson: Record<string, unknown> }> }).auditEvents.values()];
     const failed = events.find((event) => event.eventType === "oauth_callback_failed");
diff --git a/tests/caller-identity-attack-soul-r21.test.ts b/tests/caller-identity-attack-soul-r21.test.ts
index de959a8..f7c0c0b 100644
--- a/tests/caller-identity-attack-soul-r21.test.ts
+++ b/tests/caller-identity-attack-soul-r21.test.ts
@@ -24,6 +24,7 @@ import { InMemoryStore } from "../src/store/index.js";
 import { PostgresStore } from "../src/store/postgres.js";
 import { CREATE_SCHEMA_SQL } from "../src/store/schema.js";
 import { type CreateAuthCompletionInput, type HeimdallStore } from "../src/store/types.js";
+import { launchState, stateOf } from "./oauth-flow.js";
 
 const ghostlightSecret = "ghostlight-private-command-secret";
 const resources: Array<{ close(): Promise<unknown> }> = [];
@@ -102,10 +103,11 @@ async function start(app: App, payload: unknown, headers: Record<string, string>
 }
 
 async function completeAs(app: App, stateToken: string, who: string) {
+  const { cookie } = await launchState(app, stateToken);
   return app.inject({
     method: "GET",
     url: `/v1/oauth/discord/callback?code=${who}&state=${encodeURIComponent(stateToken)}`,
-    headers: { accept: "application/json" },
+    headers: { accept: "application/json", cookie },
   });
 }
 
@@ -213,7 +215,7 @@ describe("R21.1: the attempt handle is unreachable from the public start route",
     });
     expect(response.statusCode, response.body).toBe(201);
     expect(response.json().handoff).toEqual({ kind: "browser_completion" });
-    const state = jwtPayload(response.json().stateToken as string);
+    const state = jwtPayload(stateOf(response.json()));
     expect(state.handoff).toEqual({ kind: "browser_completion" });
     expect(JSON.stringify(state)).not.toContain(attempt.handle);
   });
@@ -237,7 +239,7 @@ describe("R21.1: the attempt handle is unreachable from the public start route",
     expect(response.body).not.toContain(planted);
     if (response.statusCode === 201) {
       expect(response.json().handoff).toEqual({ kind: "browser_completion" });
-      expect(jwtPayload(response.json().stateToken as string).handoff).toEqual({ kind: "browser_completion" });
+      expect(jwtPayload(stateOf(response.json())).handoff).toEqual({ kind: "browser_completion" });
     } else {
       expect(response.statusCode, response.body).toBe(400);
     }
@@ -249,7 +251,7 @@ describe("R21.1: the attempt handle is unreachable from the public start route",
       const response = await start(app, { appSlug: "ghostlight", mode: "sign_in", returnTo: legitReturn, ...extra });
       expect(response.statusCode, response.body).toBe(201);
       expect(response.body).not.toContain(planted);
-      expect(jwtPayload(response.json().stateToken as string).handoff).toEqual({ kind: "browser_completion" });
+      expect(jwtPayload(stateOf(response.json())).handoff).toEqual({ kind: "browser_completion" });
     }
   });
 
@@ -306,7 +308,7 @@ describe("R21.1: the attempt handle is unreachable from the public start route",
       handoff: { kind: "browser_completion", attemptId: handle },
     });
     expect(attackerStart.statusCode).toBe(201);
-    const attackerCallback = await completeAs(app, attackerStart.json().stateToken as string, "attacker");
+    const attackerCallback = await completeAs(app, stateOf(attackerStart.json()), "attacker");
     expect(attackerCallback.statusCode, attackerCallback.body).toBe(201);
     expect((await store.findAuthAttempt("ghostlight", handle))?.status).toBe("pending");
 
@@ -340,7 +342,7 @@ describe("R21.1: the attempt handle is unreachable from the public start route",
     expect(response.statusCode, response.body).toBe(201);
     // Delivery to port 1 fails; whatever the callback returns, the attempt
     // must be untouched and no completion may be bound to it.
-    await completeAs(app, response.json().stateToken as string, "attacker");
+    await completeAs(app, stateOf(response.json()), "attacker");
     expect((await store.findAuthAttempt("ghostlight", attempt.handle))?.status).toBe("pending");
     expect(await store.consumeAuthCompletionByAttempt("ghostlight", attempt.handle, new Date().toISOString())).toBeNull();
   });
@@ -493,26 +495,27 @@ partialUniqueIndexContract("PostgresStore over pg-mem", async () => {
 });
 
 describe("duplicate-handle error surfacing through the callback route", () => {
-  it("state tokens are replayable, and a replay while the handle's completion is unconsumed echoes the store error in a 502", async () => {
+  it("a replayed state is refused as already used before any exchange, and leaves the real completion intact", async () => {
     const { app, store, begin } = await planeHarness();
     const receipt = await begin("begin-replay");
     const handle = String(receipt.handle);
     const state = new URL((receipt.navigation as { url: string }).url).searchParams.get("state") ?? "";
-    const first = await completeAs(app, state, "victim");
+    const { cookie } = await launchState(app, state);
+    const callbackWith = () =>
+      app.inject({
+        method: "GET",
+        url: `/v1/oauth/discord/callback?code=victim&state=${encodeURIComponent(state)}`,
+        headers: { accept: "application/json", cookie },
+      });
+    const first = await callbackWith();
     expect(first.statusCode).toBe(201);
-    const replay = await completeAs(app, state, "victim");
-    // Nothing consumed the state's jti, so the second exchange still runs and
-    // reaches createAuthCompletion, where the unique index refuses it. The
-    // route's catch (app.ts ~1290) now answers with a fixed detail rather than
-    // the store's own text, so a Postgres 23505 cannot hand the caller a
-    // constraint name. The full text stays in the audit event.
-    expect(replay.statusCode, replay.body).toBe(502);
-    expect(replay.json()).toMatchObject({
-      error: "oauth_callback_failed",
-      detail: "The provider callback could not be completed.",
-    });
-    expect(JSON.stringify(replay.json())).not.toContain("unconsumed completion");
-    // The failed replay must not have damaged the real completion.
+    // The state's jti was consumed by the first callback, so the second never
+    // reaches createAuthCompletion, whose unique index used to be the only
+    // thing refusing a replay (and whose Postgres 23505 text the route had to
+    // keep out of the answer).
+    const replay = await callbackWith();
+    expect(replay.statusCode, replay.body).toBe(400);
+    expect(replay.json()).toEqual({ error: "state_already_used" });
     expect((await store.findAuthAttempt("ghostlight", handle))?.status).toBe("completed");
     expect(await store.consumeAuthCompletionByAttempt("ghostlight", handle, new Date().toISOString())).toBeTruthy();
   });
diff --git a/tests/caller-identity-attack-soul.test.ts b/tests/caller-identity-attack-soul.test.ts
index 8f77801..4a714ad 100644
--- a/tests/caller-identity-attack-soul.test.ts
+++ b/tests/caller-identity-attack-soul.test.ts
@@ -11,6 +11,7 @@ import { type HeimdallConfig } from "../src/config.js";
 import { entitlementFacts } from "../src/facts.js";
 import { type OAuthProviderRuntime } from "../src/oauth.js";
 import { InMemoryStore } from "../src/store/index.js";
+import { launchState, stateOf } from "./oauth-flow.js";
 
 const resources: Array<{ close(): Promise<unknown> }> = [];
 
@@ -86,10 +87,11 @@ async function start(app: App, payload: Record<string, unknown>, headers: Record
 }
 
 async function completeAs(app: App, stateToken: string, who: string) {
+  const { cookie } = await launchState(app, stateToken);
   return app.inject({
     method: "GET",
     url: `/v1/oauth/discord/callback?code=${who}&state=${encodeURIComponent(stateToken)}`,
-    headers: { accept: "application/json" },
+    headers: { accept: "application/json", cookie },
   });
 }
 
@@ -110,7 +112,7 @@ describe("takeover chain: caller-chosen attemptId is never the redemption code",
     });
     expect(started.statusCode).toBe(201);
 
-    const callback = await completeAs(app, started.json().stateToken as string, "victim");
+    const callback = await completeAs(app, stateOf(started.json()), "victim");
     expect(callback.statusCode).toBe(201);
     const minted = callback.json().completion.code as string;
     expect(minted).not.toBe("attacker-fixed");
@@ -125,7 +127,7 @@ describe("takeover chain: caller-chosen attemptId is never the redemption code",
     const { app, store } = await harness();
     const started = await start(app, { appSlug: "repixelizer", mode: "sign_in", returnTo: "https://repixelizer.gamecult.org/app/" });
     expect(started.statusCode).toBe(201);
-    const callback = await completeAs(app, started.json().stateToken as string, "victim");
+    const callback = await completeAs(app, stateOf(started.json()), "victim");
     expect(callback.statusCode).toBe(201);
     const code = callback.json().completion.code as string;
     expect(code).toMatch(uuidV4);
@@ -159,7 +161,7 @@ describe("takeover chain: caller-chosen attemptId is never the redemption code",
   it("attemptId set to a real victim completion code does not let the attacker's flow touch the victim's completion", async () => {
     const { app } = await harness();
     const victimStart = await start(app, { appSlug: "repixelizer", mode: "sign_in", returnTo: "https://repixelizer.gamecult.org/app/" });
-    const victimCallback = await completeAs(app, victimStart.json().stateToken as string, "victim");
+    const victimCallback = await completeAs(app, stateOf(victimStart.json()), "victim");
     const victimCode = victimCallback.json().completion.code as string;
 
     const attackerStart = await start(app, {
@@ -168,7 +170,7 @@ describe("takeover chain: caller-chosen attemptId is never the redemption code",
       returnTo: "https://repixelizer.gamecult.org/app/",
       handoff: { kind: "browser_completion", attemptId: victimCode },
     });
-    const attackerCallback = await completeAs(app, attackerStart.json().stateToken as string, "attacker");
+    const attackerCallback = await completeAs(app, stateOf(attackerStart.json()), "attacker");
     expect(attackerCallback.statusCode).toBe(201);
     expect(attackerCallback.json().completion.code).not.toBe(victimCode);
 
@@ -204,7 +206,7 @@ describe("consumeAuthCompletion: single-use, scoped, expiring", () => {
   it("a code redeems exactly once under concurrent redemption, and never for another app", async () => {
     const { app } = await harness();
     const started = await start(app, { appSlug: "repixelizer", mode: "sign_in", returnTo: "https://repixelizer.gamecult.org/app/" });
-    const callback = await completeAs(app, started.json().stateToken as string, "victim");
+    const callback = await completeAs(app, stateOf(started.json()), "victim");
     const code = callback.json().completion.code as string;
 
     const crossApp = await redeem(app, "bifrost", code);
@@ -265,7 +267,7 @@ describe("attempt-handle binding: the public start route may attach a completion
       handoff: { kind: "browser_completion", attemptId: attempt.handle },
     });
     expect(attackerStart.statusCode).toBe(201);
-    await completeAs(app, attackerStart.json().stateToken as string, "attacker");
+    await completeAs(app, stateOf(attackerStart.json()), "attacker");
 
     const after = await store.findAuthAttempt("ghostlight", attempt.handle);
     expect(after?.status).toBe("pending");
diff --git a/tests/caller-identity-soul.test.ts b/tests/caller-identity-soul.test.ts
index b5562a7..fdb32ad 100644
--- a/tests/caller-identity-soul.test.ts
+++ b/tests/caller-identity-soul.test.ts
@@ -18,6 +18,7 @@ import { type OAuthProviderRuntime } from "../src/oauth.js";
 import { startHeimdallPrivateCommandPlane } from "../src/private-command-plane.js";
 import { sealPrivateEnvelope, type HeimdallPrivateEnvelope } from "../src/private-command-security.js";
 import { InMemoryStore } from "../src/store/index.js";
+import { launchFlow } from "./oauth-flow.js";
 
 const ghostlightSecret = "ghostlight-private-command-secret";
 const resources: Array<{ close(): Promise<unknown> }> = [];
@@ -104,10 +105,11 @@ describe("caller identity: unauthenticated mint paths", () => {
     });
     expect(start.statusCode).toBe(201);
 
+    const flow = await launchFlow(app, start.json());
     const callback = await app.inject({
       method: "GET",
-      url: `/v1/oauth/discord/callback?code=victim-code&state=${encodeURIComponent(start.json().stateToken as string)}`,
-      headers: { accept: "text/html" },
+      url: `/v1/oauth/discord/callback?code=victim-code&state=${encodeURIComponent(flow.state)}`,
+      headers: { accept: "text/html", cookie: flow.cookie },
     });
     expect(callback.statusCode).toBe(200);
 
diff --git a/tests/fastify-malformed-url.test.ts b/tests/fastify-malformed-url.test.ts
deleted file mode 100644
index f515c74..0000000
--- a/tests/fastify-malformed-url.test.ts
+++ /dev/null
@@ -1,47 +0,0 @@
-import Fastify, { type FastifyReply, type FastifyRequest } from "fastify";
-import { afterEach, describe, expect, it } from "vitest";
-
-// GHSA-p68q-wchp-6fh7 (fastify < 5.12.2): a malformed request target under one
-// plugin prefix, with a method that has no route in the main router, was
-// dispatched to the not-found handler of a sibling plugin, skipping that
-// handler's preHandler. This pins the framework fix; it is not about a Heimdall
-// route.
-describe("fastify malformed URL under sibling not-found handlers", () => {
-  const apps: Array<ReturnType<typeof Fastify>> = [];
-  afterEach(async () => {
-    await Promise.all(apps.splice(0).map((app) => app.close()));
-  });
-
-  async function build() {
-    const app = Fastify();
-    apps.push(app);
-    await app.register(async (pub) => {
-      pub.get("/ping", async () => "pong");
-    }, { prefix: "/public" });
-    await app.register(async (priv) => {
-      priv.setNotFoundHandler(
-        {
-          preHandler: async (request: FastifyRequest, reply: FastifyReply) => {
-            if (!request.headers.authorization) return reply.code(401).send({ error: "auth" });
-          },
-        },
-        (_request: FastifyRequest, reply: FastifyReply) => reply.code(404).send({ secret: "PRIVATE-TENANT-DATA" }),
-      );
-      priv.get("/x", async () => "x");
-    }, { prefix: "/private" });
-    return app;
-  }
-
-  it("fails closed with 400 and never reaches another prefix's not-found handler", async () => {
-    const app = await build();
-    const response = await app.inject({ method: "DELETE", url: "/public/%zz" });
-    expect(response.body).not.toContain("PRIVATE-TENANT-DATA");
-    expect(response.statusCode).toBe(400);
-  });
-
-  it("still runs the authenticated not-found preHandler for a well-formed URL", async () => {
-    const app = await build();
-    const response = await app.inject({ method: "DELETE", url: "/private/nothing" });
-    expect(response.statusCode).toBe(401);
-  });
-});
diff --git a/tests/fixtures/fake-idunn-rudp.ts b/tests/fixtures/fake-idunn-rudp.ts
deleted file mode 100644
index e084666..0000000
--- a/tests/fixtures/fake-idunn-rudp.ts
+++ /dev/null
@@ -1,64 +0,0 @@
-/**
- * A stand-in for Idunn's health endpoint: it accepts each RUDP connect, acks
- * the frame that follows and keeps every delivered frame. Heimdall opens a
- * fresh socket and session per publication, so sessions are kept per remote.
- */
-import dgram from "node:dgram";
-import {
-  CultNetRudpSession,
-  decodeRudpPacket,
-  encodeRudpPacket,
-  type CultNetTransportFrame,
-} from "cultnet-ts";
-
-export interface FakeIdunnRudp {
-  port: number;
-  frames: CultNetTransportFrame[];
-  /** Resolves with the nth delivered frame (0-based) once it has arrived. */
-  frame(index: number): Promise<CultNetTransportFrame>;
-  close(): void;
-}
-
-export async function startFakeIdunnRudp(): Promise<FakeIdunnRudp> {
-  const server = dgram.createSocket("udp4");
-  const sessions = new Map<string, CultNetRudpSession>();
-  const frames: CultNetTransportFrame[] = [];
-  const waiting: Array<{ index: number; resolve: (frame: CultNetTransportFrame) => void }> = [];
-
-  server.on("message", (wire, remote) => {
-    const packet = decodeRudpPacket(wire);
-    const key = `${remote.address}:${remote.port}`;
-    if (packet.packetType === "connect") {
-      const session = new CultNetRudpSession({
-        connectionId: 0x1d0d0001,
-        initialSequence: 1,
-        resendDelayMs: 100,
-      });
-      sessions.set(key, session);
-      server.send(encodeRudpPacket(session.acceptConnect(packet, Date.now())), remote.port, remote.address);
-      return;
-    }
-    const session = sessions.get(key);
-    if (!session) return;
-    const result = session.receive(packet, Date.now());
-    if (result.reply) server.send(encodeRudpPacket(result.reply), remote.port, remote.address);
-    for (const frame of result.delivered) {
-      frames.push(frame);
-      for (const waiter of waiting.filter((entry) => entry.index === frames.length - 1)) waiter.resolve(frame);
-    }
-    if (result.delivered.length > 0) {
-      server.send(encodeRudpPacket(session.createAck()), remote.port, remote.address);
-    }
-  });
-  await new Promise<void>((resolve) => server.bind(0, "127.0.0.1", resolve));
-
-  return {
-    port: server.address().port,
-    frames,
-    frame: (index) =>
-      frames[index]
-        ? Promise.resolve(frames[index]!)
-        : new Promise((resolve) => waiting.push({ index, resolve })),
-    close: () => server.close(),
-  };
-}
diff --git a/tests/fixtures/idunn-runtime/.gitattributes b/tests/fixtures/idunn-runtime/.gitattributes
deleted file mode 100644
index fa1385d..0000000
--- a/tests/fixtures/idunn-runtime/.gitattributes
+++ /dev/null
@@ -1 +0,0 @@
-* -text
diff --git a/tests/fixtures/idunn-runtime/README.md b/tests/fixtures/idunn-runtime/README.md
deleted file mode 100644
index 0f26117..0000000
--- a/tests/fixtures/idunn-runtime/README.md
+++ /dev/null
@@ -1,11 +0,0 @@
-# Idunn runtime fixtures
-
-Written by the Rust owner, not by Heimdall's tests. Copied byte for byte from CultLib
-`217a9480`, `packages/cultnet-ts/test/fixtures/idunn-runtime/web` (`expected.cc`,
-`activation.cc`, `activation-key.seed`, `provider-identity.credential`) and that directory's
-`machine-id`. CultLib regenerates them with `packages/cultnet-rs/examples/idunn_runtime_fixture.rs`
-(its own README has the Yggdrasil command); the provider identity is bound to `machine-id`, so a
-test that decodes it supplies that machine id instead of `/etc/machine-id`.
-
-Every key here is a test key. `provider-identity.credential` is the shape Idunn passes on the
-presence-identity descriptor: key fields are 32-integer arrays, which only the Rust owner writes.
diff --git a/tests/fixtures/idunn-runtime/activation-key.seed b/tests/fixtures/idunn-runtime/activation-key.seed
deleted file mode 100644
index 7b6d37f..0000000
--- a/tests/fixtures/idunn-runtime/activation-key.seed
+++ /dev/null
@@ -1 +0,0 @@
-��Od�f�l*o���F�v�n�hL��p�S
�p
\ No newline at end of file
diff --git a/tests/fixtures/idunn-runtime/activation.cc b/tests/fixtures/idunn-runtime/activation.cc
deleted file mode 100644
index 3931baf..0000000
Binary files a/tests/fixtures/idunn-runtime/activation.cc and /dev/null differ
diff --git a/tests/fixtures/idunn-runtime/expected.cc b/tests/fixtures/idunn-runtime/expected.cc
deleted file mode 100644
index dbf7153..0000000
Binary files a/tests/fixtures/idunn-runtime/expected.cc and /dev/null differ
diff --git a/tests/fixtures/idunn-runtime/machine-id b/tests/fixtures/idunn-runtime/machine-id
deleted file mode 100644
index a71716f..0000000
--- a/tests/fixtures/idunn-runtime/machine-id
+++ /dev/null
@@ -1 +0,0 @@
-c1c1c1c1c1c1c1c1c1c1c1c1c1c1c1c1
\ No newline at end of file
diff --git a/tests/fixtures/idunn-runtime/provider-identity.credential b/tests/fixtures/idunn-runtime/provider-identity.credential
deleted file mode 100644
index 2e61713..0000000
Binary files a/tests/fixtures/idunn-runtime/provider-identity.credential and /dev/null differ
diff --git a/tests/fixtures/presence-descriptors.ts b/tests/fixtures/presence-descriptors.ts
deleted file mode 100644
index 8e724f2..0000000
--- a/tests/fixtures/presence-descriptors.ts
+++ /dev/null
@@ -1,61 +0,0 @@
-/**
- * What Idunn hands a generation for runtime presence: the bundle directory, a
- * parent-only identity store and an activation seed, the last two passed as
- * descriptors named in LISTEN_FDNAMES. The bytes are the Rust owner's, copied
- * from CultLib (see idunn-runtime/README.md); every key in them is a test key.
- */
-import { closeSync, openSync } from "node:fs";
-import { chmod, copyFile, mkdir, readFile } from "node:fs/promises";
-import path from "node:path";
-
-import { IDUNN_RUNTIME_ACTIVATION_CREDENTIAL_NAME } from "cultnet-ts";
-
-export const idunnRuntimeFixtures = path.join(import.meta.dirname, "idunn-runtime");
-
-const FIXTURE_FILES = [
-  "expected.cc",
-  "activation.cc",
-  "activation-key.seed",
-  "provider-identity.credential",
-  "machine-id",
-] as const;
-
-/** The machine id the fixture identity is bound to, in place of /etc/machine-id. */
-export const fixtureMachineId = async (dir: string = idunnRuntimeFixtures): Promise<string> =>
-  (await readFile(path.join(dir, "machine-id"), "utf8")).trim();
-
-/** Copy the fixtures into `dir`, readable by any uid (the children run as others). */
-export async function writePresenceFixtures(dir: string): Promise<void> {
-  await mkdir(dir, { recursive: true });
-  await chmod(dir, 0o755);
-  for (const name of FIXTURE_FILES) {
-    const target = path.join(dir, name);
-    await copyFile(path.join(idunnRuntimeFixtures, name), target);
-    await chmod(target, 0o644);
-  }
-}
-
-/** Open both descriptors and name them the way systemd's LISTEN_FDNAMES does. */
-export function openPresenceDescriptors(dir: string): { env: NodeJS.ProcessEnv; close: () => void } {
-  const fds = [
-    [openSync(path.join(dir, "provider-identity.credential"), "r"), "gamecult-runtime-presence-identity"],
-    [openSync(path.join(dir, "activation-key.seed"), "r"), IDUNN_RUNTIME_ACTIVATION_CREDENTIAL_NAME],
-  ] as const;
-  const names: string[] = [];
-  for (const [fd, name] of fds) {
-    while (names.length < fd - 3) names.push(`pad-${names.length}`);
-    names[fd - 3] = name;
-  }
-  return {
-    env: { LISTEN_FDNAMES: names.join(":") },
-    // The authority closes each descriptor it reads; this releases only what it did not.
-    close: () =>
-      fds.forEach(([fd]) => {
-        try {
-          closeSync(fd);
-        } catch {
-          // already closed by the reader
-        }
-      }),
-  };
-}
diff --git a/tests/fixtures/state-root-generation-child.ts b/tests/fixtures/state-root-generation-child.ts
deleted file mode 100644
index 932d513..0000000
--- a/tests/fixtures/state-root-generation-child.ts
+++ /dev/null
@@ -1,57 +0,0 @@
-/**
- * One Idunn generation, as a process: it runs as the uid and gid its parent
- * gave it, under UMask=0007, and does what Heimdall does to a state root on a
- * pulse. The parent test spawns two of these under different uids that share
- * a group.
- *
- * argv: <role: first|next> <stateRoot> <fixtureDir>
- */
-import { readFile, writeFile } from "node:fs/promises";
-import path from "node:path";
-
-import { loadConfig } from "../../src/config.js";
-import { openPresenceAuthority } from "../../src/runtime-presence.js";
-import { fixtureMachineId, openPresenceDescriptors } from "./presence-descriptors.js";
-import { createHeimdallRuntimePulse, publishHeimdallVerseState } from "../../src/verse-state.js";
-
-const [role, stateRoot, fixtureDir] = process.argv.slice(2) as [string, string, string];
-process.umask(0o007);
-
-const config = loadConfig({
-  GC_ACCESS_BASE_URL: "https://heimdall.example.test",
-  GC_ACCESS_DATA_ROOT: stateRoot,
-});
-
-async function publishPresence(): Promise<void> {
-  const descriptors = openPresenceDescriptors(fixtureDir);
-  try {
-    const authority = await openPresenceAuthority(
-      {
-        idunnRuntimeBundlePath: fixtureDir,
-        host: config.host,
-        port: config.port,
-        providerHealthIdentityPath: path.join(stateRoot, "provider-health-identity.cc"),
-      },
-      descriptors.env,
-      () => fixtureMachineId(fixtureDir),
-    );
-    authority.sign("warming", "generation probe", Date.now());
-  } finally {
-    descriptors.close();
-  }
-}
-
-if (role === "next") {
-  // Generation N+1 reads what N left before it replaces it.
-  const previous = await readFile(config.cultCachePath);
-  if (previous.length === 0) throw new Error("previous generation's snapshot is empty");
-}
-
-await publishHeimdallVerseState(config, createHeimdallRuntimePulse(config));
-await publishPresence();
-
-if (role === "first") {
-  // The 0600 counter the 2026-09-07 generation left behind. Nothing reads it
-  // now; it stays as the stale fixture the next generation must live beside.
-  await writeFile(path.join(stateRoot, "runtime-presence-sequence"), "41\n", { mode: 0o600 });
-}
diff --git a/tests/idunn-boot.test.ts b/tests/idunn-boot.test.ts
deleted file mode 100644
index a645986..0000000
--- a/tests/idunn-boot.test.ts
+++ /dev/null
@@ -1,320 +0,0 @@
-import { execFile, spawn, type ChildProcess } from "node:child_process";
-import { createPublicKey, createPrivateKey, verify } from "node:crypto";
-import dgram from "node:dgram";
-import { chmod, copyFile, mkdir, mkdtemp, readFile, writeFile } from "node:fs/promises";
-import { closeSync, openSync } from "node:fs";
-import net from "node:net";
-import os from "node:os";
-import path from "node:path";
-import { promisify } from "node:util";
-
-import { decode, encode } from "@msgpack/msgpack";
-import {
-  RUNTIME_PRESENCE_SLOT,
-  parseCultNetMessage,
-  runtimePresenceActivationSigningMessage,
-  runtimePresenceProviderSigningMessage,
-} from "cultnet-ts";
-import { afterAll, beforeAll, describe, expect, it } from "vitest";
-
-import { startFakeIdunnRudp, type FakeIdunnRudp } from "./fixtures/fake-idunn-rudp.js";
-import { idunnRuntimeFixtures } from "./fixtures/presence-descriptors.js";
-
-const run = promisify(execFile);
-
-const GENERATION_UID = 61184;
-const STATE_GID = 4242;
-const ED25519_SPKI_PREFIX = Buffer.from("302a300506032b6570032100", "hex");
-const PKCS8_ED25519_SEED_PREFIX = Buffer.from("302e020100300506032b657004220420", "hex");
-
-// The launch needs root (to pick the uid and bind a machine-id) and a mount
-// namespace (so the fixture machine-id does not replace the host's). The
-// stopgap's node container has both; anywhere else the test steps aside.
-const canLaunch =
-  process.getuid?.() === 0 &&
-  (await run("unshare", ["--mount", "--", "true"]).then(
-    () => true,
-    () => false
-  ));
-
-/**
- * The artifact under test. By default the esbuild bundle `pnpm bundle` makes,
- * run by this process's node; a runbook proves a sealed release by naming its
- * bundle and node here instead.
- */
-const bundleOverride = process.env.HEIMDALL_BOOT_BUNDLE;
-const nodeOverride = process.env.HEIMDALL_BOOT_NODE;
-
-async function freePort(): Promise<number> {
-  return new Promise((resolve, reject) => {
-    const probe = net.createServer();
-    probe.once("error", reject);
-    probe.listen(0, "127.0.0.1", () => {
-      const { port } = probe.address() as net.AddressInfo;
-      probe.close(() => resolve(port));
-    });
-  });
-}
-
-interface Launch {
-  child: ChildProcess;
-  stderr: () => string;
-  exited: Promise<number | null>;
-  candidatePort: number;
-}
-
-describe.skipIf(!canLaunch)("the bundle booted as Idunn launches it", () => {
-  let base: string;
-  let bundle: string;
-  let node: string;
-  let idunn: FakeIdunnRudp;
-  let odin: dgram.Socket;
-  let odinPort: number;
-  const launched: ChildProcess[] = [];
-
-  beforeAll(async () => {
-    base = await mkdtemp(path.join(os.tmpdir(), "heimdall-boot-"));
-    await chmod(base, 0o755);
-    if (bundleOverride) {
-      bundle = bundleOverride;
-    } else {
-      await run("corepack", ["pnpm", "bundle"], { cwd: path.join(import.meta.dirname, "..") });
-      bundle = path.join(base, "heimdall.mjs");
-      await copyFile(path.join(import.meta.dirname, "..", "dist", "heimdall"), bundle);
-      await chmod(bundle, 0o644);
-    }
-    node = nodeOverride ?? process.execPath;
-    idunn = await startFakeIdunnRudp();
-    odin = dgram.createSocket("udp4");
-    await new Promise<void>((resolve) => odin.bind(0, "127.0.0.1", resolve));
-    odinPort = odin.address().port;
-  }, 120_000);
-
-  afterAll(() => {
-    for (const child of launched) child.kill("SIGKILL");
-    idunn?.close();
-    odin?.close();
-  });
-
-  /** Credential files as Idunn holds them: readable only by the parent. */
-  async function credentials(dir: string, identity: Buffer | undefined) {
-    await mkdir(dir, { recursive: true });
-    const seed = path.join(dir, "activation-key.seed");
-    await copyFile(path.join(idunnRuntimeFixtures, "activation-key.seed"), seed);
-    await chmod(seed, 0o400);
-    let identityFile: string | undefined;
-    if (identity) {
-      identityFile = path.join(dir, "provider-identity.credential");
-      await writeFile(identityFile, identity, { mode: 0o400 });
-    }
-    return { seed, identityFile };
-  }
-
-  /** Start the bundle as the generation unit does, with the fixture machine-id bound over the host's. */
-  async function launch(label: string, identity: Buffer | undefined): Promise<Launch> {
-    const dir = path.join(base, label);
-    await mkdir(dir, { recursive: true });
-    await chmod(dir, 0o755);
-
-    // Idunn's runtime bundle: the two records, read-only.
-    const bundleDir = path.join(dir, "bundle");
-    await mkdir(bundleDir);
-    for (const name of ["expected.cc", "activation.cc"]) {
-      await copyFile(path.join(idunnRuntimeFixtures, name), path.join(bundleDir, name));
-      await chmod(path.join(bundleDir, name), 0o444);
-    }
-    await chmod(bundleDir, 0o555);
-
-    const machineId = path.join(dir, "machine-id");
-    await copyFile(path.join(idunnRuntimeFixtures, "machine-id"), machineId);
-    await chmod(machineId, 0o444);
-
-    const stateRoot = path.join(dir, "state");
-    await mkdir(stateRoot);
-    await run("chown", [`0:${STATE_GID}`, stateRoot]);
-    await chmod(stateRoot, 0o2770);
-
-    const heimdall = path.join(dir, "heimdall.mjs");
-    await copyFile(bundle, heimdall);
-    await chmod(heimdall, 0o444);
-
-    const files = await credentials(path.join(dir, "credentials"), identity);
-    const candidatePort = await freePort();
-
-    const fds = [openSync(files.seed, "r")];
-    const names = ["gamecult-idunn-runtime-activation-key"];
-    if (files.identityFile) {
-      fds.push(openSync(files.identityFile, "r"));
-      names.push("gamecult-runtime-presence-identity");
-    }
-
-    const env = {
-      PATH: process.env.PATH ?? "",
-      LISTEN_FDS: String(fds.length),
-      LISTEN_FDNAMES: names.join(":"),
-      GAMECULT_IDUNN_CANDIDATE_BIND: `127.0.0.1:${candidatePort}`,
-      GAMECULT_IDUNN_RUNTIME_BUNDLE: bundleDir,
-      GAMECULT_IDUNN_PROCESS_WRITE_LEASE: path.join(dir, "process-write-lease.cc"),
-      GC_ACCESS_BASE_URL: "https://heimdall.test",
-      GC_ACCESS_ISSUER: "https://heimdall.test",
-      GC_ACCESS_STORAGE_BACKEND: "memory",
-      GC_ACCESS_IDUNN_RUDP_HEALTH: `127.0.0.1:${idunn.port}`,
-      GC_ACCESS_IDUNN_HEALTH_CONTRACT: "heimdall.cultnet-rudp-provider-health",
-      GC_ACCESS_ODIN_CULTMESH_URI: `rudp://127.0.0.1:${odinPort}`,
-      CULTMESH_URI_ODIN_RUDP: `rudp://127.0.0.1:${odinPort}`,
-      GC_ACCESS_SIGNING_PRIVATE_KEY_BOOTSTRAP: "1",
-      GC_ACCESS_SIGNING_PRIVATE_KEY_PATH: path.join(stateRoot, "signing.pem"),
-      GC_ACCESS_SIGNING_KEY_ID: "boot-test",
-    };
-
-    // uid, gid and umask as Idunn's DynamicUser unit gives them. The fixture
-    // machine-id is bound only inside this mount namespace.
-    const script =
-      `mount --bind ${machineId} /etc/machine-id && ` +
-      `exec setpriv --reuid ${GENERATION_UID} --regid ${STATE_GID} --clear-groups ` +
-      `sh -c 'umask 0007; cd ${dir}; exec ${node} heimdall.mjs --state-root ${stateRoot}'`;
-    const child = spawn("unshare", ["--mount", "--", "sh", "-c", script], {
-      env,
-      stdio: ["ignore", "ignore", "pipe", ...fds],
-    });
-    launched.push(child);
-    fds.forEach((fd) => closeSync(fd));
-
-    let stderr = "";
-    child.stderr!.on("data", (chunk: Buffer) => {
-      stderr += chunk.toString();
-    });
-    const exited = new Promise<number | null>((resolve) => child.once("exit", (code) => resolve(code)));
-    return { child, stderr: () => stderr, exited, candidatePort };
-  }
-
-  async function answers(port: number): Promise<number | undefined> {
-    return fetch(`http://127.0.0.1:${port}/.well-known/jwks.json`).then(
-      (response) => response.status,
-      () => undefined
-    );
-  }
-
-  it("signs warming presence on every pulse and answers HTTP", async () => {
-    const credential = await readFile(path.join(idunnRuntimeFixtures, "provider-identity.credential"));
-    const generation = await launch("signs", credential);
-
-    // Startup publication, then one per 10 s pulse. A publication fault is
-    // reported as it is logged rather than after the frames never arrive.
-    const publicationFault = new Promise<never>((_resolve, reject) => {
-      const watch = setInterval(() => {
-        if (generation.stderr().includes(" failed on ")) {
-          clearInterval(watch);
-          reject(new Error(`publication failed; stderr: ${generation.stderr()}`));
-        }
-      }, 200);
-      void idunn.frame(2).then(() => clearInterval(watch));
-    });
-    const exitedEarly = generation.exited.then((code) => {
-      throw new Error(`bundle exited ${code}; stderr: ${generation.stderr()}`);
-    });
-    // The first statement is the startup publication, which follows the listen
-    // directly; the 10 s pulse loop has not yet fired.
-    await Promise.race([
-      idunn.frame(0),
-      publicationFault,
-      exitedEarly,
-      new Promise<never>((_resolve, reject) =>
-        setTimeout(() => reject(new Error(`no presence at startup; stderr: ${generation.stderr()}`)), 8_000)
-      ),
-    ]);
-    await Promise.race([idunn.frame(2), publicationFault, exitedEarly]);
-
-    expect(await answers(generation.candidatePort)).toBe(200);
-
-    // Public keys of the two proofs, from the fixtures' test keys.
-    const store = decode(credential) as unknown[][];
-    const record = decode(store[0]![2] as Uint8Array) as unknown[];
-    const providerKey = createPublicKey({
-      key: Buffer.concat([ED25519_SPKI_PREFIX, Buffer.from(record[2] as number[])]),
-      format: "der",
-      type: "spki",
-    });
-    const activationKey = createPublicKey(
-      createPrivateKey({
-        key: Buffer.concat([
-          PKCS8_ED25519_SEED_PREFIX,
-          await readFile(path.join(idunnRuntimeFixtures, "activation-key.seed")),
-        ]),
-        format: "der",
-        type: "pkcs8",
-      })
-    );
-
-    let previousSequence = 0;
-    for (const frame of idunn.frames.slice(0, 3)) {
-      const message = parseCultNetMessage(decode(frame.payload), "cultnet.schema.v0");
-      if (message.schemaVersion !== "cultnet.document_put_raw.v0") throw new Error("not a raw document put");
-      const fields = decode(message.document.payload) as unknown[];
-      expect(fields[RUNTIME_PRESENCE_SLOT.state]).toBe("warming");
-
-      const unsigned = [...fields];
-      unsigned[RUNTIME_PRESENCE_SLOT.signature] = new Uint8Array();
-      unsigned[RUNTIME_PRESENCE_SLOT.activationSignature] = new Uint8Array();
-      const proof = encode(unsigned);
-      expect(
-        verify(
-          null,
-          runtimePresenceProviderSigningMessage(proof),
-          providerKey,
-          fields[RUNTIME_PRESENCE_SLOT.signature] as Uint8Array
-        )
-      ).toBe(true);
-      expect(
-        verify(
-          null,
-          runtimePresenceActivationSigningMessage(proof),
-          activationKey,
-          fields[RUNTIME_PRESENCE_SLOT.activationSignature] as Uint8Array
-        )
-      ).toBe(true);
-
-      const sequence = fields[RUNTIME_PRESENCE_SLOT.publisherSequence] as number;
-      expect(sequence).toBeGreaterThan(previousSequence);
-      previousSequence = sequence;
-    }
-
-    expect(generation.stderr()).not.toContain("failed on startup");
-    expect(generation.stderr()).not.toContain("failed on interval");
-    generation.child.kill("SIGKILL");
-  }, 90_000);
-
-  it.each([
-    ["the identity descriptor is not passed", undefined, "gamecult-runtime-presence-identity"],
-    ["the identity is damaged", "damaged", "identity id check"],
-  ])("exits before listening when %s", async (_name, damage, expected) => {
-    const credential = await readFile(path.join(idunnRuntimeFixtures, "provider-identity.credential"));
-    const store = decode(credential) as unknown[][];
-    const record = decode(store[0]![2] as Uint8Array) as unknown[];
-    const publicKey = [...(record[2] as number[])];
-    const original = { publicKeyHex: Buffer.from(publicKey).toString("hex"), id: record[1] as string, binding: record[5] as string };
-    let identity: Buffer | undefined;
-    if (damage) {
-      publicKey[0] = publicKey[0]! ^ 1;
-      record[2] = publicKey;
-      identity = Buffer.from(encode([[store[0]![0], store[0]![1], encode(record), store[0]![3], store[0]![4]]]));
-    }
-    const started = Date.now();
-    const generation = await launch(damage ? "damaged" : "no-identity", identity);
-
-    const code = await Promise.race([
-      generation.exited,
-      new Promise<"timeout">((resolve) => setTimeout(() => resolve("timeout"), 5_000)),
-    ]);
-
-    expect(code, generation.stderr()).not.toBe("timeout");
-    expect(code).not.toBe(0);
-    expect(Date.now() - started).toBeLessThan(6_000);
-    expect(await answers(generation.candidatePort)).toBeUndefined();
-    expect(generation.stderr()).toContain(expected);
-    // No byte of the credential: not the key bytes, not the id, not the binding.
-    expect(generation.stderr()).not.toContain(original.publicKeyHex);
-    expect(generation.stderr()).not.toContain(original.id.slice(0, 16));
-    expect(generation.stderr()).not.toContain(original.binding.slice(-16));
-  }, 30_000);
-});
diff --git a/tests/idunn-rudp-health.test.ts b/tests/idunn-rudp-health.test.ts
index fa40393..66127d4 100644
--- a/tests/idunn-rudp-health.test.ts
+++ b/tests/idunn-rudp-health.test.ts
@@ -1,12 +1,18 @@
+import dgram from "node:dgram";
 import { mkdtemp } from "node:fs/promises";
 import os from "node:os";
 import path from "node:path";
 import { decode } from "@msgpack/msgpack";
-import { parseCultNetMessage } from "cultnet-ts";
+import {
+  CultNetRudpSession,
+  decodeRudpPacket,
+  encodeRudpPacket,
+  parseCultNetMessage,
+  type CultNetTransportFrame,
+} from "cultnet-ts";
 import { describe, expect, it, vi } from "vitest";
 import { loadConfig } from "../src/config.js";
 import { publishIdunnRudpHealth } from "../src/idunn-rudp-health.js";
-import { startFakeIdunnRudp } from "./fixtures/fake-idunn-rudp.js";
 
 vi.mock("node:fs/promises", async (importOriginal) => {
   const original = await importOriginal<typeof import("node:fs/promises")>();
@@ -21,12 +27,37 @@ vi.mock("node:fs/promises", async (importOriginal) => {
 
 describe("Heimdall Idunn health publication", () => {
   it("completes the canonical RUDP handshake before publishing its signed frame", async () => {
-    const server = await startFakeIdunnRudp();
+    const server = dgram.createSocket("udp4");
+    const session = new CultNetRudpSession({
+      connectionId: 0x1d0d0001,
+      initialSequence: 1,
+      resendDelayMs: 100,
+    });
+    let resolveFrame!: (frame: CultNetTransportFrame) => void;
+    const frameReceived = new Promise<CultNetTransportFrame>((resolve) => {
+      resolveFrame = resolve;
+    });
+
+    server.on("message", (wire, remote) => {
+      const packet = decodeRudpPacket(wire);
+      if (packet.packetType === "connect") {
+        server.send(encodeRudpPacket(session.acceptConnect(packet, Date.now())), remote.port, remote.address);
+        return;
+      }
+      const result = session.receive(packet, Date.now());
+      if (result.reply) server.send(encodeRudpPacket(result.reply), remote.port, remote.address);
+      for (const frame of result.delivered) resolveFrame(frame);
+      if (result.delivered.length > 0) {
+        server.send(encodeRudpPacket(session.createAck()), remote.port, remote.address);
+      }
+    });
+    await new Promise<void>((resolve) => server.bind(0, "127.0.0.1", resolve));
 
     try {
       const tmp = await mkdtemp(path.join(os.tmpdir(), "heimdall-idunn-rudp-"));
+      const address = server.address();
       const config = loadConfig({
-        GC_ACCESS_IDUNN_RUDP_HEALTH: `127.0.0.1:${server.port}`,
+        GC_ACCESS_IDUNN_RUDP_HEALTH: `127.0.0.1:${address.port}`,
         GC_ACCESS_PROVIDER_HEALTH_IDENTITY_PATH: path.join(tmp, "provider-health-identity.cc"),
       });
       const observedAt = "2026-08-22T00:45:00.000Z";
@@ -47,7 +78,7 @@ describe("Heimdall Idunn health publication", () => {
         observedAt,
         presence,
       });
-      const frame = await server.frame(0);
+      const frame = await frameReceived;
       const message = parseCultNetMessage(decode(frame.payload), "cultnet.schema.v0");
 
       expect(frame.channelId).toBe("schema");
diff --git a/tests/managed-credential.test.ts b/tests/managed-credential.test.ts
index 50ca9ba..92a45ab 100644
--- a/tests/managed-credential.test.ts
+++ b/tests/managed-credential.test.ts
@@ -14,6 +14,7 @@ import { createOAuthRuntimeRegistry } from "../src/oauth.js";
 import { providerCatalog } from "../src/providers.js";
 import { InMemoryStore, PostgresStore, type HeimdallStore } from "../src/store/index.js";
 import { type StoredLinkedIdentity } from "../src/store/types.js";
+import { launchFlow } from "./oauth-flow.js";
 
 const originalFetch = globalThis.fetch;
 const sleep = (ms: number) => new Promise((resolve) => setTimeout(resolve, ms));
@@ -581,9 +582,11 @@ for (const { kind, live } of rigKinds) describe.skipIf(live && !adminUrl)(`manag
       const app = rig.apps[0]!;
       const start = await app.inject({ method: "POST", url: `/v1/oauth/${provider}/start`, payload: { appSlug: "streampixels", mode, returnTo, ...(mode === "connect" ? { connection: { kind: "creator", targetId: "creator-1" } } : {}) } });
       expect(start.statusCode).toBe(201);
+      const flow = await launchFlow(app, start.json());
       const callback = await app.inject({
         method: "GET",
-        url: `/v1/oauth/${provider}/callback?code=c&state=${encodeURIComponent(start.json().stateToken as string)}`,
+        url: `/v1/oauth/${provider}/callback?code=c&state=${encodeURIComponent(flow.state)}`,
+        headers: { cookie: flow.cookie },
       });
       expect(callback.statusCode).toBe(201);
       const redeem = await app.inject({
@@ -633,9 +636,11 @@ for (const { kind, live } of rigKinds) describe.skipIf(live && !adminUrl)(`manag
         payload: { appSlug: "streampixels", mode: "connect", returnTo, connection: { kind: "creator", targetId: "creator-1" } },
       });
       expect(start.statusCode).toBe(201);
+      const flow = await launchFlow(app, start.json());
       const callback = await app.inject({
         method: "GET",
-        url: `/v1/oauth/joystick/callback?code=c&state=${encodeURIComponent(start.json().stateToken as string)}`,
+        url: `/v1/oauth/joystick/callback?code=c&state=${encodeURIComponent(flow.state)}`,
+        headers: { cookie: flow.cookie },
       });
       expect(callback.statusCode).toBeGreaterThanOrEqual(400);
       expect(callback.body).not.toContain("tok-access");
diff --git a/tests/oauth-flow.ts b/tests/oauth-flow.ts
new file mode 100644
index 0000000..203f643
--- /dev/null
+++ b/tests/oauth-flow.ts
@@ -0,0 +1,138 @@
+import { expect } from "vitest";
+import { type FastifyInstance } from "fastify";
+import { type HeimdallConfig } from "../src/config.js";
+import { entitlementFacts } from "../src/facts.js";
+import { type OAuthProviderRuntime } from "../src/oauth.js";
+import { decodeJwt } from "../src/signing.js";
+
+export function createTestConfig(): HeimdallConfig {
+  return {
+    serviceName: "heimdall",
+    host: "127.0.0.1",
+    port: 4100,
+    workspaceRoot: "E:/Projects/Heimdall",
+    dataRoot: "E:/Projects/Heimdall/.heimdall-data",
+    cultCachePath: "E:/Projects/Heimdall/.heimdall-data/cultcache/heimdall.service.cc",
+    publicBaseUrl: "https://heimdall.gamecult.org",
+    issuer: "https://heimdall.gamecult.org",
+    daemonId: "yggdrasil-heimdall",
+    idunnRudpHealth: undefined,
+    idunnHealthContract: "heimdall.cultnet-rudp-provider-health",
+    providerHealthIdentityPath: "E:/Projects/Heimdall/.heimdall-data/provider-health-identity.cc",
+    sessionTtlSeconds: 3600,
+    refreshTtlSeconds: 60 * 60 * 24 * 30,
+    stateTtlSeconds: 600,
+    completionTtlSeconds: 300,
+    bootstrapSigningPrivateKeyOnMissing: false,
+    tokenEncryptionKeyBase64: Buffer.alloc(32, 7).toString("base64"),
+    appSharedSecrets: {
+      streampixels: "streampixels-secret",
+      repixelizer: "repixelizer-secret",
+      bifrost: "bifrost-secret",
+    },
+    appBackendCallbacks: {
+      bifrost: ["https://bifrost.gamecult.org/auth/heimdall/callback"],
+      repixelizer: ["https://repixelizer.gamecult.org/api/auth/heimdall/callback"],
+    },
+    storage: {
+      backend: "memory",
+      applySchemaOnStartup: true,
+    },
+    providers: {
+      discord: { clientId: "discord-client", clientSecret: "discord-secret" },
+      patreon: { clientId: "patreon-client", clientSecret: "patreon-secret" },
+      github: { clientId: "github-client", clientSecret: "github-secret" },
+      twitch: { clientId: "twitch-client", clientSecret: "twitch-secret" },
+      youtube: { clientId: "youtube-client", clientSecret: "youtube-secret" },
+      spotify: { clientId: "spotify-client", clientSecret: "spotify-secret" },
+      joystick: { clientId: "joystick-client", clientSecret: "joystick-secret" },
+    },
+  };
+}
+
+export function createMockDiscordRuntime(): OAuthProviderRuntime {
+  return {
+    async exchangeAuthorizationCode() {
+      return {
+        accessToken: "discord-access-token",
+        refreshToken: "discord-refresh-token",
+        tokenType: "Bearer",
+        scope: ["identify", "guilds.members.read"],
+        expiresAt: "2026-04-26T13:00:00.000Z",
+        raw: { source: "test" },
+      };
+    },
+    async resolveIdentity() {
+      return {
+        provider: "discord",
+        providerUserId: "discord-user-123",
+        username: "meta",
+        displayName: "Meta",
+        primaryEmail: "meta@gamecult.org",
+        profile: { id: "discord-user-123", username: "meta" },
+      };
+    },
+    async evaluateEntitlements({ callback }) {
+      return {
+        facts: [entitlementFacts.appAccess],
+        snapshots: [
+          {
+            accountId: callback.accountId,
+            provider: "discord",
+            scope: "repixelizer:discord_role_access:gamecult-guild",
+            evaluatedAt: "2026-04-26T12:00:00.000Z",
+            isAllowed: true,
+            reasonCode: "matched_role",
+            reasonDetail: "Matched Repixelizer access role.",
+            rawSummaryJson: {
+              guildId: "gamecult-guild",
+              matchedRoles: ["role-repixelizer"],
+            },
+          },
+        ],
+      };
+    },
+  };
+}
+
+/** What a start returns that the browser needs: the launch URL, whose query carries the signed state. */
+export interface StartBody {
+  authorizationUrl: string;
+}
+
+export function stateOf(start: StartBody): string {
+  return new URL(start.authorizationUrl).searchParams.get("state") ?? "";
+}
+
+export interface LaunchedFlow {
+  state: string;
+  /** The `name=value` pair a browser sends back to the callback. */
+  cookie: string;
+}
+
+export function setCookieOf(response: { headers: Record<string, unknown> }): string[] {
+  return [response.headers["set-cookie"]].flat().filter((value): value is string => typeof value === "string");
+}
+
+/** What a browser does with a state it was handed: open the launch hop for the state's provider and keep the cookie it sets. */
+export async function launchState(app: FastifyInstance, state: string): Promise<LaunchedFlow> {
+  const provider = decodeJwt(state).payload.provider as string;
+  const response = await app.inject({ method: "GET", url: `/v1/oauth/${provider}/launch?state=${encodeURIComponent(state)}` });
+  expect(response.statusCode, "launch").toBe(302);
+  const set = setCookieOf(response).find((value) => value.startsWith("__Host-heimdall-oauth-"));
+  expect(set, "launch sets the binding cookie").toBeDefined();
+  return { state, cookie: (set as string).split(";")[0] as string };
+}
+
+/** Drives what a user's browser does after a start: follow authorizationUrl to the launch hop and keep its cookie. */
+export function launchFlow(app: FastifyInstance, start: StartBody): Promise<LaunchedFlow> {
+  return launchState(app, stateOf(start));
+}
+
+/** The provider URL a browser is redirected to once it has followed authorizationUrl through the launch hop. */
+export async function providerRedirect(app: FastifyInstance, start: StartBody): Promise<URL> {
+  const url = new URL(start.authorizationUrl);
+  const response = await app.inject({ method: "GET", url: `${url.pathname}${url.search}` });
+  expect(response.statusCode, "launch").toBe(302);
+  return new URL(response.headers.location as string);
+}
diff --git a/tests/oauth-state-binding.test.ts b/tests/oauth-state-binding.test.ts
new file mode 100644
index 0000000..3f8f0a5
--- /dev/null
+++ b/tests/oauth-state-binding.test.ts
@@ -0,0 +1,400 @@
+import { generateKeyPairSync, randomUUID } from "node:crypto";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { type FastifyInstance } from "fastify";
+import { buildApp, getHeimdallRuntimeContext, startOAuthFlow } from "../src/app.js";
+import { resolveAppCaller } from "../src/app-caller.js";
+import { decodeJwt, signJwt } from "../src/signing.js";
+import { createMockDiscordRuntime, createTestConfig, launchFlow, setCookieOf, stateOf } from "./oauth-flow.js";
+
+// Heimdall's OAuth states complete once, only in the browser that launched
+// them (finding state-replay). Soul's attack: a Bifrost state is readable in
+// the URL the victim's browser is sent to, so an attacker who sees it opens it
+// in their own browser, finishes the provider login as themselves, and hands
+// the victim the resulting completion code.
+
+const apps: FastifyInstance[] = [];
+afterEach(async () => {
+  vi.useRealTimers();
+  while (apps.length) {
+    await apps.pop()?.close();
+  }
+});
+
+const victimAttempt = "VICTIM-ATTEMPT-NONCE";
+const bifrostReturn = `https://bifrost.gamecult.org/auth/heimdall/complete?attempt=${victimAttempt}`;
+
+async function newApp() {
+  const app = await buildApp({ config: createTestConfig(), oauthRuntimes: { discord: createMockDiscordRuntime() } });
+  apps.push(app);
+  return app;
+}
+
+async function bifrostStart(app: FastifyInstance, extra: Record<string, unknown> = {}) {
+  const response = await app.inject({
+    method: "POST",
+    url: "/v1/oauth/discord/start",
+    headers: { "x-heimdall-app-secret": "bifrost-secret" },
+    payload: { appSlug: "bifrost", mode: "sign_in", returnTo: bifrostReturn, handoff: { kind: "browser_completion" }, ...extra },
+  });
+  expect(response.statusCode).toBe(201);
+  return response.json() as { authorizationUrl: string };
+}
+
+function launchUrl(start: { authorizationUrl: string }): string {
+  const url = new URL(start.authorizationUrl);
+  return `${url.pathname}${url.search}`;
+}
+
+function callback(app: FastifyInstance, state: string, cookie?: string, query = "code=attacker-code") {
+  return app.inject({
+    method: "GET",
+    url: `/v1/oauth/discord/callback?${query}&state=${encodeURIComponent(state)}`,
+    ...(cookie ? { headers: { cookie } } : {}),
+  });
+}
+
+describe("OAuth state binding", () => {
+  it("Soul's replay fails: one state, at most one completion code, and only for the browser that launched it", async () => {
+    const app = await newApp();
+    const start = await bifrostStart(app);
+    const state = stateOf(start);
+
+    const victim = await launchFlow(app, start);
+
+    // The attacker holds the same state. A second launch yields no cookie and no redirect.
+    const attackerLaunch = await app.inject({ method: "GET", url: launchUrl(start) });
+    expect(attackerLaunch.statusCode).toBe(400);
+    expect(attackerLaunch.json()).toEqual({ error: "state_already_launched" });
+    expect(setCookieOf(attackerLaunch)).toEqual([]);
+    expect(attackerLaunch.headers.location).toBeUndefined();
+
+    // Without the cookie the callback refuses and mints nothing.
+    const attackerCallback = await callback(app, state);
+    expect(attackerCallback.statusCode).toBe(400);
+    expect(attackerCallback.json()).toEqual({ error: "state_not_bound" });
+    expect(attackerCallback.body).not.toContain("completion");
+
+    // The victim's callback still completes, once.
+    const victimCallback = await callback(app, state, victim.cookie, "code=victim-code");
+    expect(victimCallback.statusCode).toBe(201);
+    const completionCode = victimCallback.json().completion.code as string;
+    const redeem = await app.inject({
+      method: "POST",
+      url: "/v1/apps/bifrost/auth-completions/redeem",
+      payload: { completionCode },
+    });
+    expect(redeem.statusCode).toBe(201);
+    expect(redeem.json()).toEqual(expect.objectContaining({ status: "success", appSlug: "bifrost" }));
+
+    const second = await callback(app, state, victim.cookie, "code=victim-code");
+    expect(second.statusCode).toBe(400);
+    expect(second.json()).toEqual({ error: "state_already_used" });
+    expect(second.body).not.toContain("completion");
+  });
+
+  it("a stranger's callback needs no launch to be refused: no cookie, no completion code", async () => {
+    const app = await newApp();
+    const start = await bifrostStart(app);
+
+    const response = await callback(app, stateOf(start));
+    expect(response.statusCode).toBe(400);
+    expect(response.json()).toEqual({ error: "state_not_bound" });
+    expect(response.body).not.toContain("completion");
+  });
+
+  it("a cookie for another flow, another key, another type, or the wrong lifetime does not bind", async () => {
+    const app = await newApp();
+    const ctx = getHeimdallRuntimeContext(app);
+    const own = await bifrostStart(app);
+    const attackerFlow = await app.inject({
+      method: "POST",
+      url: "/v1/oauth/discord/start",
+      payload: { appSlug: "repixelizer", mode: "sign_in", returnTo: "https://repixelizer.gamecult.org/app/" },
+    });
+    const attackerStart = attackerFlow.json() as { authorizationUrl: string };
+    const attackerCookie = (await launchFlow(app, attackerStart)).cookie;
+    const ownState = stateOf(own);
+    const ownJti = decodeJwt(ownState).payload.jti as string;
+    const name = `__Host-heimdall-oauth-${ownJti}`;
+    const now = Math.floor(Date.now() / 1000);
+    const binding = (overrides: Record<string, unknown>, keys = ctx.keys) =>
+      signJwt({ typ: "heimdall_oauth_binding", iss: ctx.config.issuer, jti: ownJti, iat: now, exp: now + 300, ...overrides }, keys);
+    const foreignKeys = (() => {
+      const pair = generateKeyPairSync("ed25519");
+      return { ...ctx.keys, privateKey: pair.privateKey, publicKey: pair.publicKey };
+    })();
+
+    const forged: Record<string, string> = {
+      "another flow's binding under this flow's cookie name": `${name}=${attackerCookie.split("=")[1]}`,
+      "a binding signed with a different key": `${name}=${binding({}, foreignKeys)}`,
+      "a binding for a different jti": `${name}=${binding({ jti: "someone-else" })}`,
+      "a binding of another type": `${name}=${binding({ typ: "heimdall_oauth_state" })}`,
+      "a binding from another issuer": `${name}=${binding({ iss: "https://elsewhere.example" })}`,
+      "an expired binding": `${name}=${binding({ exp: now - 5 })}`,
+      "the state token used as the cookie": `${name}=${ownState}`,
+      "a binding whose exp is a string": `${name}=${binding({ exp: String(now + 300) })}`,
+      "an empty cookie": `${name}=`,
+    };
+    for (const [label, cookie] of Object.entries(forged)) {
+      const response = await callback(app, ownState, cookie);
+      expect(response.statusCode, label).toBe(400);
+      expect(response.json(), label).toEqual({ error: "state_not_bound" });
+    }
+
+    // A correctly signed binding for this jti is the one thing that binds.
+    const good = await callback(app, ownState, `${name}=${binding({})}`);
+    expect(good.statusCode).toBe(201);
+  });
+
+  it("the cookie is checked before the state is consumed: a stranger cannot burn or deny the victim's flow", async () => {
+    const app = await newApp();
+    const ctx = getHeimdallRuntimeContext(app);
+    const attempt = await ctx.store.createAuthAttempt({
+      handle: "attempt-1",
+      appSlug: "repixelizer",
+      provider: "discord",
+      mode: "sign_in",
+      returnTo: "https://repixelizer.gamecult.org/app/",
+      createdAt: new Date().toISOString(),
+      expiresAt: new Date(Date.now() + 600_000).toISOString(),
+    });
+    const caller = resolveAppCaller(ctx.config, "repixelizer", { "x-heimdall-app-secret": "repixelizer-secret" });
+    const started = await startOAuthFlow(
+      ctx,
+      "discord",
+      caller,
+      { appSlug: "repixelizer", mode: "sign_in", returnTo: "https://repixelizer.gamecult.org/app/", handoff: { kind: "browser_completion" } },
+      { trustedBrowserAttemptId: attempt.handle }
+    );
+    expect(started.statusCode).toBe(201);
+    const start = started.body as unknown as { authorizationUrl: string };
+    const victim = await launchFlow(app, start);
+
+    // A cookieless provider error, which would deny the attempt, and a cookieless code: both refused.
+    for (const query of ["error=access_denied", "code=attacker-code", ""]) {
+      const stranger = await callback(app, victim.state, undefined, query);
+      expect(stranger.statusCode, query).toBe(400);
+      expect(stranger.json(), query).toEqual({ error: "state_not_bound" });
+    }
+    expect((await ctx.store.findAuthAttempt("repixelizer", attempt.handle))?.status).toBe("pending");
+
+    // The victim's own callback is unharmed.
+    const response = await callback(app, victim.state, victim.cookie, "code=victim-code");
+    expect(response.statusCode).toBe(201);
+  });
+
+  it("a provider error from the launching browser still denies the attempt, once", async () => {
+    const app = await newApp();
+    const start = await bifrostStart(app);
+    const victim = await launchFlow(app, start);
+
+    const denied = await callback(app, victim.state, victim.cookie, "error=access_denied");
+    expect(denied.statusCode).toBe(400);
+    expect(denied.json().error).toBe("provider_error");
+    const replay = await callback(app, victim.state, victim.cookie, "error=access_denied");
+    expect(replay.json()).toEqual({ error: "state_already_used" });
+  });
+
+  describe("a state that is expired, foreign or tampered is refused at launch and at callback", () => {
+    it.each([
+      ["expired beyond the skew", { exp: Math.floor(Date.now() / 1000) - 100 }, "state_expired"],
+      ["not yet valid", { nbf: Math.floor(Date.now() / 1000) + 100 }, "state_expired"],
+      ["another issuer", { iss: "https://elsewhere.example" }, "invalid_state"],
+      ["another provider in aud", { aud: "patreon" }, "state_provider_mismatch"],
+      ["another provider in provider", { provider: "patreon", aud: "patreon" }, "state_provider_mismatch"],
+      ["a wrong type", { typ: "heimdall_refresh" }, "invalid_state"],
+    ])("%s", async (_label, change, error) => {
+      const app = await newApp();
+      const ctx = getHeimdallRuntimeContext(app);
+      const start = await bifrostStart(app);
+      const original = decodeJwt(stateOf(start)).payload;
+      const token = signJwt({ ...original, ...change }, ctx.keys);
+      const launch = await app.inject({ method: "GET", url: `/v1/oauth/discord/launch?state=${encodeURIComponent(token)}` });
+      expect(launch.statusCode).toBe(400);
+      expect(launch.json()).toEqual({ error });
+      expect(setCookieOf(launch)).toEqual([]);
+
+      const cookie = `__Host-heimdall-oauth-${original.jti as string}=${signJwt({ typ: "heimdall_oauth_binding", iss: ctx.config.issuer, jti: original.jti, iat: 0, exp: 4_000_000_000 }, ctx.keys)}`;
+      const response = await callback(app, token, cookie);
+      expect(response.statusCode).toBe(400);
+      expect(response.json()).toEqual({ error });
+      expect(response.body).not.toContain(token.slice(20, 60));
+    });
+
+    it("a state inside the 30 s skew still works, as a refresh token does", async () => {
+      const app = await newApp();
+      const ctx = getHeimdallRuntimeContext(app);
+      const start = await bifrostStart(app);
+      const original = decodeJwt(stateOf(start)).payload;
+      const token = signJwt({ ...original, exp: Math.floor(Date.now() / 1000) - 10 }, ctx.keys);
+      const launch = await app.inject({ method: "GET", url: `/v1/oauth/discord/launch?state=${encodeURIComponent(token)}` });
+      expect(launch.statusCode).toBe(302);
+    });
+
+    it("a tampered signature, a malformed token and a provider that is not the route's", async () => {
+      const app = await newApp();
+      const start = await bifrostStart(app);
+      const state = stateOf(start);
+      const tampered = `${state.slice(0, -4)}AAAA`;
+      for (const token of [tampered, "not-a-jwt", "a.b"]) {
+        const launch = await app.inject({ method: "GET", url: `/v1/oauth/discord/launch?state=${encodeURIComponent(token)}` });
+        expect(launch.statusCode).toBe(400);
+        expect(launch.json()).toEqual({ error: "invalid_state" });
+        expect(launch.body).not.toContain(token);
+      }
+      const wrongRoute = await app.inject({ method: "GET", url: `/v1/oauth/patreon/launch?state=${encodeURIComponent(state)}` });
+      expect(wrongRoute.statusCode).toBe(400);
+      expect(wrongRoute.json()).toEqual({ error: "state_provider_mismatch" });
+    });
+  });
+
+  it("the launch response and the binding cookie carry the protections the binding relies on", async () => {
+    const app = await newApp();
+    const start = await bifrostStart(app, { requestedScopes: ["identify", "email"] });
+    const jti = decodeJwt(stateOf(start)).payload.jti as string;
+
+    const launch = await app.inject({ method: "GET", url: launchUrl(start) });
+    expect(launch.statusCode).toBe(302);
+    const cookies = setCookieOf(launch);
+    expect(cookies).toHaveLength(1);
+    const cookie = cookies[0] as string;
+    expect(cookie.startsWith(`__Host-heimdall-oauth-${jti}=`)).toBe(true);
+    const attributes = cookie.split(";").slice(1).map((part) => part.trim());
+    expect(attributes).toEqual(expect.arrayContaining(["Path=/", "Secure", "HttpOnly", "SameSite=Lax"]));
+    expect(attributes.some((attribute) => /^domain=/i.test(attribute))).toBe(false);
+    const maxAge = Number(attributes.find((attribute) => attribute.startsWith("Max-Age="))?.slice("Max-Age=".length));
+    expect(maxAge).toBeGreaterThan(0);
+    expect(maxAge).toBeLessThanOrEqual(600);
+
+    const location = new URL(launch.headers.location as string);
+    expect(location.origin + location.pathname).toBe("https://discord.com/oauth2/authorize");
+    expect(location.searchParams.get("state")).toBe(stateOf(start));
+    expect(location.searchParams.get("scope")).toBe("identify email");
+    expect(location.searchParams.get("client_id")).toBe("discord-client");
+    expect(location.searchParams.get("redirect_uri")).toBe("https://heimdall.gamecult.org/v1/oauth/discord/callback");
+    expect(launch.headers["cache-control"]).toBe("no-store");
+    expect(launch.headers["referrer-policy"]).toBe("no-referrer");
+
+    const done = await callback(app, stateOf(start), cookie.split(";")[0], "code=c");
+    expect(done.statusCode).toBe(201);
+    const cleared = setCookieOf(done).find((value) => value.startsWith(`__Host-heimdall-oauth-${jti}=`));
+    expect(cleared).toBeDefined();
+    expect(cleared).toMatch(/Max-Age=0/);
+    expect(cleared?.startsWith(`__Host-heimdall-oauth-${jti}=;`)).toBe(true);
+  });
+
+  it("a launch for a provider with no client id is 503 and burns nothing", async () => {
+    const config = { ...createTestConfig(), providers: { ...createTestConfig().providers } };
+    const app = await buildApp({ config, oauthRuntimes: { discord: createMockDiscordRuntime() } });
+    apps.push(app);
+    const start = await bifrostStart(app);
+    config.providers.discord = { clientId: undefined, clientSecret: undefined } as unknown as typeof config.providers.discord;
+    const refused = await app.inject({ method: "GET", url: launchUrl(start) });
+    expect(refused.statusCode).toBe(503);
+    expect(refused.json().error).toBe("provider_not_configured");
+    expect(setCookieOf(refused)).toEqual([]);
+  });
+
+  it("every start returns Heimdall's launch URL and no state token", async () => {
+    const app = await newApp();
+    for (const [headers, payload] of [
+      [{}, { appSlug: "repixelizer", mode: "sign_in", returnTo: "https://repixelizer.gamecult.org/app/" }],
+      [
+        { "x-heimdall-app-secret": "bifrost-secret" },
+        { appSlug: "bifrost", mode: "sign_in", returnTo: bifrostReturn },
+      ],
+    ] as const) {
+      const response = await app.inject({ method: "POST", url: "/v1/oauth/discord/start", headers, payload });
+      expect(response.statusCode).toBe(201);
+      const body = response.json();
+      expect(body.stateToken).toBeUndefined();
+      expect(new URL(body.authorizationUrl).origin + new URL(body.authorizationUrl).pathname).toBe(
+        "https://heimdall.gamecult.org/v1/oauth/discord/launch"
+      );
+      expect(body.stateExpiresAt).toEqual(expect.any(String));
+    }
+  });
+
+  it("claims the launch and the callback of a state under their own phases, until the state's expiry", async () => {
+    const app = await newApp();
+    const ctx = getHeimdallRuntimeContext(app);
+    const spy = vi.spyOn(ctx.store, "claimOAuthStateUse");
+    const start = await bifrostStart(app);
+    const { jti, exp } = decodeJwt(stateOf(start)).payload as { jti: string; exp: number };
+
+    const victim = await launchFlow(app, start);
+    expect((await callback(app, victim.state, victim.cookie, "code=victim-code")).statusCode).toBe(201);
+
+    const expiresAt = new Date(exp * 1000).toISOString();
+    expect(spy.mock.calls.map(([claim]) => claim)).toEqual([
+      { jti, phase: "launch", appSlug: "bifrost", usedAt: expect.any(String), expiresAt },
+      { jti, phase: "callback", appSlug: "bifrost", usedAt: expect.any(String), expiresAt },
+    ]);
+  });
+
+  it("the launch route validates its provider and its state parameter", async () => {
+    const app = await newApp();
+    for (const url of ["/v1/oauth/discord/launch", "/v1/oauth/discord/launch?state=", "/v1/oauth/bogus/launch?state=abc"]) {
+      const response = await app.inject({ method: "GET", url });
+      expect(response.statusCode, url).toBe(400);
+      expect(response.json().error, url).toBe("invalid_request");
+    }
+  });
+
+  it("a state's requested scopes are null, absent, or a list of strings, and nothing else", async () => {
+    const app = await newApp();
+    const ctx = getHeimdallRuntimeContext(app);
+    const start = await bifrostStart(app);
+    const original = decodeJwt(stateOf(start)).payload;
+    const launchWith = async (change: Record<string, unknown>) => {
+      const rest = { ...original };
+      delete rest.requested_scopes;
+      const token = signJwt({ ...rest, jti: randomUUID(), ...change }, ctx.keys);
+      return app.inject({ method: "GET", url: `/v1/oauth/discord/launch?state=${encodeURIComponent(token)}` });
+    };
+
+    for (const [label, change] of [
+      ["absent", {}],
+      ["null", { requested_scopes: null }],
+      ["a list", { requested_scopes: ["identify"] }],
+    ] as const) {
+      expect((await launchWith(change)).statusCode, label).toBe(302);
+    }
+    for (const [label, change] of [
+      ["a string", { requested_scopes: "identify" }],
+      ["a list with a number", { requested_scopes: ["identify", 7] }],
+      ["a list of numbers", { requested_scopes: [1, 2] }],
+      ["an object", { requested_scopes: { 0: "identify" } }],
+    ] as const) {
+      const response = await launchWith(change);
+      expect(response.statusCode, label).toBe(400);
+      expect(response.json(), label).toEqual({ error: "invalid_state" });
+    }
+  });
+
+  it("the time windows hold to the second: a state from nbf - 30 s to exp + 30 s, a binding until its exp", async () => {
+    const app = await newApp();
+    const ctx = getHeimdallRuntimeContext(app);
+    const start = await bifrostStart(app);
+    const original = decodeJwt(stateOf(start)).payload;
+    vi.useFakeTimers({ toFake: ["Date"] });
+    const now = 1_900_000_000;
+    vi.setSystemTime(now * 1000);
+    const stateWith = (change: Record<string, unknown>) =>
+      signJwt({ ...original, jti: randomUUID(), nbf: now - 1, exp: now + 600, ...change }, ctx.keys);
+    const launch = (token: string) =>
+      app.inject({ method: "GET", url: `/v1/oauth/discord/launch?state=${encodeURIComponent(token)}` });
+
+    expect((await launch(stateWith({ exp: now - 30 }))).json()).toEqual({ error: "state_expired" });
+    expect((await launch(stateWith({ exp: now - 29 }))).statusCode).toBe(302);
+    expect((await launch(stateWith({ nbf: now + 31 }))).json()).toEqual({ error: "state_expired" });
+    expect((await launch(stateWith({ nbf: now + 30 }))).statusCode).toBe(302);
+
+    const token = stateWith({});
+    const jti = decodeJwt(token).payload.jti as string;
+    const bindingWith = (exp: number) =>
+      `__Host-heimdall-oauth-${jti}=${signJwt({ typ: "heimdall_oauth_binding", iss: ctx.config.issuer, jti, iat: now - 5, exp }, ctx.keys)}`;
+    expect((await callback(app, token, bindingWith(now))).json()).toEqual({ error: "state_not_bound" });
+    expect((await callback(app, token, bindingWith(now + 1))).statusCode).toBe(201);
+  });
+});
diff --git a/tests/presence-identity-descriptor.test.ts b/tests/presence-identity-descriptor.test.ts
index d01797b..97c5233 100644
--- a/tests/presence-identity-descriptor.test.ts
+++ b/tests/presence-identity-descriptor.test.ts
@@ -1,17 +1,18 @@
-import { access, mkdtemp, readFile, writeFile } from "node:fs/promises";
-import { openSync } from "node:fs";
+import { mkdtemp, readFile, writeFile } from "node:fs/promises";
+import { openSync, closeSync } from "node:fs";
 import os from "node:os";
 import path from "node:path";
 
-import { decode, encode } from "@msgpack/msgpack";
+import { encode } from "@msgpack/msgpack";
+import { SingleFileMessagePackBackingStore } from "@gamecult/cultcache-ts";
 import { describe, expect, it } from "vitest";
 
 import {
+  openOrEnrollProviderHealthIdentity,
   openProviderHealthIdentity,
   passedDescriptor,
   providerHealthPublicIdentity,
 } from "../src/provider-health-identity.js";
-import { fixtureMachineId, idunnRuntimeFixtures } from "./fixtures/presence-descriptors.js";
 
 const machineIdAvailable = await readFile("/etc/machine-id", "utf8").then(
   () => true,
@@ -22,79 +23,59 @@ const machineIdAvailable = await readFile("/etc/machine-id", "utf8").then(
  * The identity is machine-id bound, so enrolment only works where a machine-id
  * exists. These run on Linux and are skipped elsewhere.
  */
-/** Name the presence descriptor so it lands on whatever fd open() returned. */
-function presenceEnv(fd: number): NodeJS.ProcessEnv {
-  // The lookup maps a name index onto 3 + index, so the name list is padded
-  // until the presence entry lands on the descriptor open() actually returned.
-  // Assuming it is 3 is how this passes on one machine and reads the wrong
-  // descriptor on another.
-  const names = [
-    ...Array.from({ length: fd - 3 }, (_, i) => `pad-${i}`),
-    "gamecult-runtime-presence-identity",
-  ].join(":");
-  return { LISTEN_FDNAMES: names, LISTEN_PID: String(process.pid) };
-}
-
-describe("presence identity from a passed descriptor", () => {
-  it("decodes the Rust owner's record, whose key fields are integer arrays", async () => {
+describe.skipIf(!machineIdAvailable)("presence identity from a passed descriptor", () => {
+  it("reads an Idunn-written store, not a cultcache-ts one", async () => {
     const dir = await mkdtemp(path.join(os.tmpdir(), "heimdall-presence-"));
-    const fd = openSync(path.join(idunnRuntimeFixtures, "provider-identity.credential"), "r");
 
-    const opened = await openProviderHealthIdentity(
-      path.join(dir, "would-be-self-enrolled.cc"),
-      presenceEnv(fd),
-      fixtureMachineId
+    // Enrol with the TypeScript client to get a genuine machine-bound payload,
+    // then re-wrap that payload the way cultcache-rs writes a store: a bare
+    // array of positional [key, type, payload, stored_at, schema_id] envelopes.
+    // Idunn writes with the Rust client, and cultcache-ts cannot read that
+    // layout, so wrapping it here is what makes this test resemble reality.
+    const tsStore = path.join(dir, "ts-enrolled.cc");
+    const enrolled = await openOrEnrollProviderHealthIdentity(tsStore);
+    const records = await new SingleFileMessagePackBackingStore(tsStore).pullAll();
+    expect(records).toHaveLength(1);
+
+    const idunnStore = path.join(dir, "runtime-presence-identity.cc");
+    await writeFile(
+      idunnStore,
+      encode([
+        [
+          "gamecult-provider-health-identity",
+          "gamecult.provider_health_identity.private.v1",
+          records[0]!.payload,
+          "2026-09-06T00:00:00.000Z",
+          "gamecult.provider_health_identity.private.v1",
+        ],
+      ])
     );
 
-    // The fixture's own public key means it came from the descriptor. A fresh
-    // self-enrolment would produce a different key, which is exactly the failure
-    // that makes Idunn refuse this daemon's health and stall promotion.
-    const store = decode(await readFile(path.join(idunnRuntimeFixtures, "provider-identity.credential"))) as unknown[][];
-    const record = decode(store[0]![2] as Uint8Array) as unknown[];
-    expect(providerHealthPublicIdentity(opened).publicKeyHex).toBe(
-      Buffer.from(record[2] as number[]).toString("hex")
-    );
-    await expect(access(path.join(dir, "would-be-self-enrolled.cc"))).rejects.toMatchObject({ code: "ENOENT" });
-  });
+    const fd = openSync(idunnStore, "r");
+    try {
+      // The lookup maps a name index onto 3 + index, so the name list is padded
+      // until the presence entry lands on whatever descriptor open() actually
+      // returned. Assuming it is 3 is how this passes on one machine and reads
+      // the wrong descriptor on another.
+      const names = [
+        ...Array.from({ length: fd - 3 }, (_, i) => `pad-${i}`),
+        "gamecult-runtime-presence-identity",
+      ].join(":");
 
-  it("refuses a bin-shaped record on the descriptor path, naming the key-shape check and no value", async () => {
-    const dir = await mkdtemp(path.join(os.tmpdir(), "heimdall-presence-bin-"));
-    const store = decode(await readFile(path.join(idunnRuntimeFixtures, "provider-identity.credential"))) as unknown[][];
-    const record = decode(store[0]![2] as Uint8Array) as unknown[];
-    // What this process's own enroller writes: the same record with bin key fields.
-    const binRecord = record.map((field, index) =>
-      index === 2 || index === 3 ? Uint8Array.from(field as number[]) : field
-    );
-    const binStore = path.join(dir, "bin-shaped.cc");
-    await writeFile(binStore, encode([[store[0]![0], store[0]![1], encode(binRecord), store[0]![3], store[0]![4]]]));
-    const fd = openSync(binStore, "r");
+      const opened = await openProviderHealthIdentity(
+        path.join(dir, "would-be-self-enrolled.cc"),
+        { LISTEN_FDNAMES: names, LISTEN_PID: String(process.pid) }
+      );
 
-    const failure = await openProviderHealthIdentity(path.join(dir, "x.cc"), presenceEnv(fd), fixtureMachineId).then(
-      () => undefined,
-      (error: Error) => error
-    );
-
-    expect(failure?.message).toContain("key shape check");
-    expect(failure?.message).not.toContain((record[1] as string).slice(0, 16));
-  });
-
-  it.each([
-    ["schema", 0, "bogus", "schema check"],
-    ["protector", 4, "bogus", "protector check"],
-    ["binding", 5, "bogus", "binding check"],
-    ["version", 6, "v9", "version check"],
-  ])("a record failing only the %s check is refused by that check", async (_name, index, replacement, check) => {
-    const dir = await mkdtemp(path.join(os.tmpdir(), "heimdall-presence-check-"));
-    const store = decode(await readFile(path.join(idunnRuntimeFixtures, "provider-identity.credential"))) as unknown[][];
-    const record = decode(store[0]![2] as Uint8Array) as unknown[];
-    record[index] = replacement;
-    const damaged = path.join(dir, "damaged.cc");
-    await writeFile(damaged, encode([[store[0]![0], store[0]![1], encode(record), store[0]![3], store[0]![4]]]));
-    const fd = openSync(damaged, "r");
-
-    await expect(
-      openProviderHealthIdentity(path.join(dir, "x.cc"), presenceEnv(fd), fixtureMachineId)
-    ).rejects.toThrow(check);
+      // Same key means it came from the descriptor. A fresh self-enrolment
+      // would produce a different key -- which is exactly the failure that
+      // makes Idunn refuse this daemon's health and stall promotion.
+      expect(providerHealthPublicIdentity(opened).publicKeyHex).toBe(
+        providerHealthPublicIdentity(enrolled).publicKeyHex
+      );
+    } finally {
+      closeSync(fd);
+    }
   });
 });
 
@@ -131,29 +112,3 @@ describe("presence identity descriptor selection", () => {
     });
   });
 });
-
-describe("an Idunn generation without the presence identity descriptor", () => {
-  it("refuses, naming the descriptor, and enrolls nothing", async () => {
-    const dir = await mkdtemp(path.join(os.tmpdir(), "heimdall-nodescriptor-"));
-    const identityPath = path.join(dir, "provider-health-identity.cc");
-
-    await expect(
-      openProviderHealthIdentity(identityPath, {
-        GAMECULT_IDUNN_RUNTIME_BUNDLE: "/run/idunn/bundle",
-        LISTEN_FDNAMES: "some-other-descriptor",
-      })
-    ).rejects.toThrow("gamecult-runtime-presence-identity");
-
-    await expect(access(identityPath)).rejects.toMatchObject({ code: "ENOENT" });
-  });
-
-  it("still self-enrolls outside Idunn", async () => {
-    if (!machineIdAvailable) return;
-    const dir = await mkdtemp(path.join(os.tmpdir(), "heimdall-outside-idunn-"));
-    const identityPath = path.join(dir, "provider-health-identity.cc");
-
-    await openProviderHealthIdentity(identityPath, {});
-
-    await expect(access(identityPath)).resolves.toBeUndefined();
-  });
-});
diff --git a/tests/private-command-diagnostics.test.ts b/tests/private-command-diagnostics.test.ts
index d1801a5..a455944 100644
--- a/tests/private-command-diagnostics.test.ts
+++ b/tests/private-command-diagnostics.test.ts
@@ -12,6 +12,7 @@ import { type HeimdallConfig } from "../src/config.js";
 import { startHeimdallPrivateCommandPlane } from "../src/private-command-plane.js";
 import { openPrivateEnvelope, sealPrivateEnvelope, type HeimdallPrivateEnvelope } from "../src/private-command-security.js";
 import { InMemoryStore } from "../src/store/index.js";
+import { launchState } from "./oauth-flow.js";
 
 const secret = "ghostlight-private-command-secret";
 const resources: Array<{ close(): Promise<unknown> }> = [];
@@ -73,10 +74,11 @@ async function refreshAgainst(refreshAnswer: () => Response) {
   const begin = open(await command(plane.endpoint, "heimdall.auth.begin", "heimdall.auth_begin_command.v1", "k1",
     { provider: "discord", mode: "sign_in", returnTo: "https://yggdrasil.gamecult.org/ghostlight/", entitlementPolicy: policy }));
   const state = new URL(String((begin.navigation as { url: string }).url)).searchParams.get("state")!;
+  const { cookie } = await launchState(app, state);
   const callback = await app.inject({
     method: "GET",
     url: `/v1/oauth/discord/callback?code=c1&state=${encodeURIComponent(state)}`,
-    headers: { accept: "application/json" },
+    headers: { accept: "application/json", cookie },
   });
   expect(callback.statusCode, callback.body).toBe(201);
   const done = open(await command(plane.endpoint, "heimdall.auth.complete", "heimdall.auth_complete_command.v1", "k2", { handle: begin.handle }));
@@ -133,10 +135,11 @@ it("keeps the completion code out of the audit trail when the plane redeems by a
   const begin = open(await command(plane.endpoint, "heimdall.auth.begin", "heimdall.auth_begin_command.v1", "k1",
     { provider: "discord", mode: "sign_in", returnTo: "https://yggdrasil.gamecult.org/ghostlight/", entitlementPolicy: policy }));
   const state = new URL(String((begin.navigation as { url: string }).url)).searchParams.get("state")!;
+  const { cookie } = await launchState(app, state);
   const callback = await app.inject({
     method: "GET",
     url: `/v1/oauth/discord/callback?code=c1&state=${encodeURIComponent(state)}`,
-    headers: { accept: "application/json" },
+    headers: { accept: "application/json", cookie },
   });
   const code = (callback.json().completion as { code: string }).code;
   const done = open(await command(plane.endpoint, "heimdall.auth.complete", "heimdall.auth_complete_command.v1", "k2", { handle: begin.handle }));
diff --git a/tests/publisher-sequence.test.ts b/tests/publisher-sequence.test.ts
deleted file mode 100644
index cfddac2..0000000
--- a/tests/publisher-sequence.test.ts
+++ /dev/null
@@ -1,83 +0,0 @@
-import { mkdtemp, readdir, writeFile } from "node:fs/promises";
-import os from "node:os";
-import path from "node:path";
-
-import { describe, expect, it } from "vitest";
-
-import { loadConfig } from "../src/config.js";
-import { PublisherSequence, openPresenceAuthority } from "../src/runtime-presence.js";
-import { fixtureMachineId, openPresenceDescriptors, writePresenceFixtures } from "./fixtures/presence-descriptors.js";
-
-describe("PublisherSequence", () => {
-  it("starts at the observed millis", () => {
-    expect(new PublisherSequence().next(1_700_000_000_000)).toBe(1_700_000_000_000);
-  });
-
-  it("strictly increases for equal, earlier and later observations", () => {
-    const sequence = new PublisherSequence();
-    const first = sequence.next(1_700_000_000_000);
-    const equal = sequence.next(1_700_000_000_000);
-    const earlier = sequence.next(1_699_999_990_000);
-    const later = sequence.next(1_700_000_050_000);
-    expect([first, equal, earlier, later]).toEqual([
-      1_700_000_000_000,
-      1_700_000_000_001,
-      1_700_000_000_002,
-      1_700_000_050_000,
-    ]);
-  });
-
-  it("never falls below the observed millis once the clock moves ahead", () => {
-    const sequence = new PublisherSequence();
-    sequence.next(1_700_000_000_000);
-    sequence.next(1_700_000_000_000);
-    sequence.next(1_700_000_000_000);
-    expect(sequence.next(1_700_000_000_002)).toBe(1_700_000_000_003);
-    expect(sequence.next(1_700_000_000_010)).toBe(1_700_000_000_010);
-  });
-
-  it("refuses a value that is not a safe integer and keeps its place", () => {
-    const sequence = new PublisherSequence();
-    expect(sequence.next(10)).toBe(10);
-    for (const bad of [Number.NaN, Number.POSITIVE_INFINITY, 1.5, 2 ** 60]) {
-      expect(() => sequence.next(bad)).toThrow("observedAtUnixMillis");
-    }
-    expect(sequence.next(5)).toBe(11);
-  });
-});
-
-describe("the presence authority", () => {
-  it("opens once, touches no path under dataRoot, and signs every pulse after its descriptors are gone", async () => {
-    const dir = await mkdtemp(path.join(os.tmpdir(), "heimdall-nodataroot-"));
-    const fixtures = path.join(dir, "fixtures");
-    await writePresenceFixtures(fixtures);
-    // A regular file as dataRoot: opening anything beneath it fails with
-    // ENOTDIR for every uid, root included.
-    const dataRoot = path.join(dir, "not-a-directory");
-    await writeFile(dataRoot, "");
-    const config = loadConfig({
-      GC_ACCESS_BASE_URL: "https://heimdall.example.test",
-      GC_ACCESS_DATA_ROOT: dataRoot,
-    });
-
-    const descriptors = openPresenceDescriptors(fixtures);
-    try {
-      const authority = await openPresenceAuthority(
-        { ...config, idunnRuntimeBundlePath: fixtures },
-        descriptors.env,
-        fixtureMachineId,
-      );
-      // The descriptors were read whole and closed: a second read would find
-      // nothing, so signing again proves the authority holds what it decoded.
-      const observedAtUnixMillis = Date.parse("2026-10-23T12:00:00.000Z");
-      const first = authority.sign("warming", "probe", observedAtUnixMillis);
-      const second = authority.sign("warming", "probe", observedAtUnixMillis);
-      expect(first.target).toBe("streampixels-web");
-      expect(second.target).toBe("streampixels-web");
-      expect(Buffer.from(second.payload).equals(Buffer.from(first.payload))).toBe(false);
-    } finally {
-      descriptors.close();
-    }
-    expect((await readdir(dir)).sort()).toEqual(["fixtures", "not-a-directory"]);
-  });
-});
diff --git a/tests/state-root-generations.test.ts b/tests/state-root-generations.test.ts
deleted file mode 100644
index b8424f3..0000000
--- a/tests/state-root-generations.test.ts
+++ /dev/null
@@ -1,98 +0,0 @@
-import { execFile } from "node:child_process";
-import { chmod, chown, mkdir, mkdtemp, readdir, stat } from "node:fs/promises";
-import os from "node:os";
-import path from "node:path";
-import { promisify } from "node:util";
-
-import { build } from "esbuild";
-import { describe, expect, it } from "vitest";
-
-import { writePresenceFixtures } from "./fixtures/presence-descriptors.js";
-
-const run = promisify(execFile);
-
-const STATE_GID = 4242;
-const GENERATION_N = 61184;
-const GENERATION_N_PLUS_1 = 61185;
-
-// Creating uids and groups needs root; the stopgap's node container runs as root.
-const isRoot = process.getuid?.() === 0;
-
-async function walk(dir: string): Promise<string[]> {
-  const found: string[] = [];
-  for (const entry of await readdir(dir, { withFileTypes: true })) {
-    const full = path.join(dir, entry.name);
-    found.push(full);
-    if (entry.isDirectory()) found.push(...(await walk(full)));
-  }
-  return found;
-}
-
-/**
- * Idunn gives every generation a fresh DynamicUser uid and one shared group,
- * UMask=0007, and a 2770 setgid state root. Generation N+1 runs beside or after
- * N and must be able to read and replace everything N left there.
- */
-describe.skipIf(!isRoot)("Idunn state root across generations", () => {
-  it("generation N+1, a different uid in the same group, reads and replaces generation N's state", async () => {
-    const base = await mkdtemp(path.join(os.tmpdir(), "heimdall-generations-"));
-    await chmod(base, 0o755);
-
-    // The fixtures stand in for what Idunn passes as descriptors.
-    const fixtures = path.join(base, "fixtures");
-    await writePresenceFixtures(fixtures);
-
-    const stateRoot = path.join(base, "state");
-    await mkdir(stateRoot);
-    await chown(stateRoot, 0, STATE_GID);
-    await chmod(stateRoot, 0o2770);
-
-    // The generations run as uids that cannot read the checkout, so each runs
-    // one self-contained bundle built into the world-readable scratch root.
-    const child = path.join(base, "generation.mjs");
-    await build({
-      entryPoints: [path.join(import.meta.dirname, "fixtures", "state-root-generation-child.ts")],
-      bundle: true,
-      platform: "node",
-      format: "esm",
-      target: "node24",
-      outfile: child,
-      external: ["pg-native"],
-      banner: {
-        js: "import{createRequire}from'node:module';const require=createRequire(import.meta.url);",
-      },
-      logLevel: "silent",
-    });
-    await chmod(child, 0o644);
-    const generation = (role: "first" | "next", uid: number) =>
-      run(process.execPath, [child, role, stateRoot, fixtures], {
-        uid,
-        gid: STATE_GID,
-        cwd: base,
-        env: { PATH: process.env.PATH ?? "", HOME: fixtures },
-      });
-
-    await generation("first", GENERATION_N);
-
-    const left = await walk(stateRoot);
-    expect(left.map((entry) => path.relative(stateRoot, entry)).sort()).toEqual([
-      "cultcache",
-      path.join("cultcache", "heimdall.service.cc"),
-      "runtime-presence-sequence",
-    ]);
-
-    await generation("next", GENERATION_N_PLUS_1);
-
-    // Generation N+1 replaced the snapshot, and no owner-only file is left
-    // behind for generation N+2: everything but the stale 0600 fixture is
-    // readable and writable by the state group.
-    const snapshot = await stat(path.join(stateRoot, "cultcache", "heimdall.service.cc"));
-    expect(snapshot.uid).toBe(GENERATION_N_PLUS_1);
-    expect(snapshot.gid).toBe(STATE_GID);
-    for (const entry of await walk(stateRoot)) {
-      if (path.basename(entry) === "runtime-presence-sequence") continue;
-      expect((await stat(entry)).mode & 0o060, path.relative(stateRoot, entry)).toBe(0o060);
-    }
-    expect((await readdir(stateRoot)).sort()).toEqual(["cultcache", "runtime-presence-sequence"]);
-  }, 60_000);
-});
diff --git a/tests/store.test.ts b/tests/store.test.ts
index c5f6445..60bd1f5 100644
--- a/tests/store.test.ts
+++ b/tests/store.test.ts
@@ -3,7 +3,7 @@ import { Pool } from "pg";
 import { afterAll, afterEach, beforeAll, describe, expect, it } from "vitest";
 import { newDb } from "pg-mem";
 import { type HeimdallConfig } from "../src/config.js";
-import { createStore } from "../src/store/index.js";
+import { createStore, InMemoryStore } from "../src/store/index.js";
 import {
   createPostgresStore,
   PostgresStore,
@@ -198,6 +198,36 @@ describe("PostgresStore", () => {
   });
 });
 
+describe("InMemoryStore.claimOAuthStateUse", () => {
+  const use = {
+    jti: "state-1",
+    phase: "launch" as const,
+    appSlug: "repixelizer" as const,
+    usedAt: "2026-04-26T12:00:00.000Z",
+    expiresAt: "2026-04-26T12:10:00.000Z",
+  };
+
+  it("is true once per (jti, phase)", async () => {
+    const store = new InMemoryStore();
+    expect(await store.claimOAuthStateUse(use)).toBe(true);
+    expect(await store.claimOAuthStateUse(use)).toBe(false);
+    expect(await store.claimOAuthStateUse({ ...use, phase: "callback" })).toBe(true);
+    expect(await store.claimOAuthStateUse({ ...use, phase: "callback" })).toBe(false);
+    expect(await store.claimOAuthStateUse({ ...use, jti: "state-2" })).toBe(true);
+  });
+
+  it("drops a record once its state has expired, and keeps it until then", async () => {
+    const store = new InMemoryStore();
+    await store.claimOAuthStateUse(use);
+    // Before expiry a later claim of another state leaves the record in force.
+    await store.claimOAuthStateUse({ ...use, jti: "state-2", usedAt: "2026-04-26T12:09:59.000Z" });
+    expect(await store.claimOAuthStateUse(use)).toBe(false);
+    // At and after expiry the record is dead weight: the state is refused before any claim.
+    await store.claimOAuthStateUse({ ...use, jti: "state-3", usedAt: "2026-04-26T12:10:00.000Z" });
+    expect(await store.claimOAuthStateUse(use)).toBe(true);
+  });
+});
+
 describe("createPostgresStore", () => {
   // pg emits an idle client's connection loss on the pool. With no listener
   // that event kills the process, and Node prints the pg Client with its
@@ -233,11 +263,12 @@ describe("PostgresStore.checkSchema", () => {
       "auth_attempts",
       "private_command_receipts",
       "auth_completions",
+      "oauth_state_uses",
       "capability_grants",
       "entitlement_snapshots",
       "audit_events",
     ]);
-    expect(REQUIRED_COLUMNS).toHaveLength(85);
+    expect(REQUIRED_COLUMNS).toHaveLength(90);
     expect(REQUIRED_COLUMNS).toEqual(
       expect.arrayContaining([
         { table: "auth_completions", column: "code", type: "TEXT", nullable: false },
@@ -248,11 +279,12 @@ describe("PostgresStore.checkSchema", () => {
         { table: "auth_completions", column: "attempt_id", type: "TEXT", nullable: true },
       ])
     );
-    expect(REQUIRED_KEYS).toHaveLength(12);
+    expect(REQUIRED_KEYS).toHaveLength(13);
     expect(REQUIRED_KEYS).toEqual(
       expect.arrayContaining([
         { table: "linked_identities", columns: "provider,provider_user_id", predicate: "" },
         { table: "private_command_receipts", columns: "app_slug,idempotency_key", predicate: "" },
+        { table: "oauth_state_uses", columns: "jti,phase", predicate: "" },
         { table: "entitlement_snapshots", columns: "account_id,provider,scope", predicate: "" },
         { table: "auth_completions", columns: "app_slug,attempt_id", predicate: "attempt_id IS NOT NULL AND consumed_at IS NULL" },
       ])
@@ -365,6 +397,10 @@ async function exerciseStore(store: PostgresStore): Promise<Set<string>> {
   const snapshot = { accountId: account.id, provider: "discord" as const, scope: "ghostlight:probe", evaluatedAt: now, isAllowed: true, reasonCode: "ok", rawSummaryJson: {} };
   await s.upsertEntitlementSnapshot(snapshot);
   await s.upsertEntitlementSnapshot({ ...snapshot, isAllowed: false });
+  const stateUse = { jti: randomUUID(), phase: "launch" as const, appSlug: "ghostlight" as const, usedAt: now, expiresAt: later };
+  expect(await s.claimOAuthStateUse(stateUse)).toBe(true);
+  expect(await s.claimOAuthStateUse(stateUse)).toBe(false);
+  expect(await s.claimOAuthStateUse({ ...stateUse, phase: "callback" })).toBe(true);
   await s.createAuditEvent({ eventType: "probe", eventPayloadJson: {}, createdAt: now });
   return called;
 }