Docs and test comments: correct the Rust duplicate-key citation, say what the TS and Rust duplicate tests pin

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

contracts/cultnet/interop/write-receipt.md

@@ -14,7 +14,7 @@ A put or delete today has two answers on the wire: nothing (admitted, or the ser
 
 **A `write_admitted` `messageId` is valid only if it contains at least one Unicode letter (`\p{L}`) or number (`\p{N}`) and no Default_Ignorable_Code_Point (DerivedCoreProperties).** The compare is raw: the id is echoed byte for byte, so a decoder never trims or normalizes it (`" a "` is valid; U+2800 is not, and neither is `a` followed by U+200B). Unlike the Required fields rule, this is not a White_Space test. The letters, numbers and Default_Ignorable code points are those of **Unicode 16.0** in every runtime, taken from tables embedded in each runtime and generated by `scripts/gen-unicode-messageid-tables.py` from `DerivedGeneralCategory.txt` (Lu Ll Lt Lm Lo Nd Nl No) and `DerivedCoreProperties.txt`; no runtime asks its platform's Unicode data, so a runtime's own Unicode version cannot change a result. Bumping the version is one coordinated change: regenerate the five tables and update the vectors that pin the version in the same commit. The rule is on the decoded string, which must be well-formed Unicode: a lone surrogate refuses. A runtime whose MessagePack reader rejects invalid UTF-8 refuses the frame earlier; byte-level strictness is a property of the reader and is not required of a decoder. A frame with more than one `messageId` key is malformed: a decoder that can see the duplicate (the C# and Rust decoders) refuses it; a decoder that collapses the map (Python, TypeScript, Kotlin) judges the value it ends up with, the last key, and refuses if that value is invalid, so no decoder echoes an invalid id (vectors `admittedMessageIdDuplicates` declare each policy and every runner asserts its own). A decoder refuses an invalid id the way it refuses an empty or ill-typed one; the rule is for `write_admitted` only and `error.v1` is unchanged.
 
-**Where a received `messageId` decides, and what that relies on.** Beyond echoing it, a received `messageId` is used in exactly two places. On a server, the remembered-write key `(actor, messageId)` with the content hash, the per-session limit and the replay of rule 5 are taken from the id of the write frame the server itself parsed. On a client, the write tracker attributes a `write_admitted` or `error.v1` to a write by equality with the id of a write that client itself sent (a frame naming an id not in flight settles nothing), and attributes an id-less error by the count of unanswered writes, not by any id. Both rely on the receiver being the only parser of that frame: a decoder's `messageId` on a frame that carries more than one `messageId` key is not trusted for any authorization, dedupe, replay or ordering decision, and the map-collapsing runtimes (Python, TypeScript, Kotlin, and C#'s typed deserializer on write frames) cannot see the duplicate. If a frame is ever parsed by two runtimes in a chain (a relay, proxy or forwarder that re-reads it), or a consumer needs `messageId` for authorization, dedupe, replay or ordering beyond echo and equality with a self-sent id, all runtimes must first refuse a duplicate `messageId` key (a spec change plus byte-level duplicate detection in the runtimes that decode to a map) before that use lands. Today Rust refuses a repeated key on every raw schema frame, write frames included; C# does not on write frames (a duplicate-key write is deduped on its last id, while the id it names in a refusal for an unreadable frame is read from the first key), and the Python server (`cultmesh_py/server.py`) only echoes the id while the TypeScript and Kotlin code matches it by equality with a request it sent.
+**Where a received `messageId` decides, and what that relies on.** Beyond echoing it, a received `messageId` is used in exactly two places. On a server, the remembered-write key `(actor, messageId)` with the content hash, the per-session limit and the replay of rule 5 are taken from the id of the write frame the server itself parsed. On a client, the write tracker attributes a `write_admitted` or `error.v1` to a write by equality with the id of a write that client itself sent (a frame naming an id not in flight settles nothing), and attributes an id-less error by the count of unanswered writes, not by any id. Both rely on the receiver being the only parser of that frame: a decoder's `messageId` on a frame that carries more than one `messageId` key is not trusted for any authorization, dedupe, replay or ordering decision, and the map-collapsing runtimes (Python, TypeScript, Kotlin, and C#'s typed deserializer on write frames) cannot see the duplicate. If a frame is ever parsed by two runtimes in a chain (a relay, proxy or forwarder that re-reads it), or a consumer needs `messageId` for authorization, dedupe, replay or ordering beyond echo and equality with a self-sent id, all runtimes must first refuse a duplicate `messageId` key (a spec change plus byte-level duplicate detection in the runtimes that decode to a map) before that use lands. Today Rust refuses a repeated key on write frames and on `write_admitted` (serde's `duplicate field messageId`, and `refuse_duplicate_keys` for the raw-list frames such as `document_put_raw`), though its `readable_message_id` names the first key when it names an unreadable frame; C# does not on write frames (a duplicate-key write is deduped on its last id, while the id it names in a refusal for an unreadable frame is read from the first key), and the Python server (`cultmesh_py/server.py`) only echoes the id while the TypeScript and Kotlin code matches it by equality with a request it sent.
 
 **`cultnet.error.v1`**: `cultnet.error.v0` plus a required `messageId` (string or nil). The code enum is v0's plus `limit_reached` (see Remembered-write limits); `cultnet.error.v1.schema.json` is the authority for the closed set. Sent in place of `error.v0` to a receipt-capable connection. `messageId` is the id of the request the error answers; nil only when the frame was unreadable or carried no id.
 

packages/cultnet-rs/tests/write_receipt.rs

@@ -239,7 +239,8 @@ fn every_range_of_the_unicode_tables_is_pinned_at_both_ends() {
     assert!(failures.is_empty(), "{} failing:\n{}", failures.len(), failures.join("\n"));
 }
 
-/// Vectors `admittedMessageIdDuplicates`: Rust decodes a map it can see into, so a repeated messageId key is refused whatever the values.
+/// Vectors `admittedMessageIdDuplicates`: a repeated messageId key is refused whatever the values. This pins the outcome, not the
+/// cause (today serde's `duplicate field messageId` in the typed decode of write_admitted).
 #[test]
 fn a_repeated_message_id_key_is_refused_whatever_the_values() {
     let path = concat!(env!("CARGO_MANIFEST_DIR"), "/../../contracts/cultnet/interop/write-receipt-vectors.json");

packages/cultnet-ts/test/write-receipt.test.ts

@@ -325,6 +325,8 @@ test("write_admitted messageId: every range of the Unicode 16.0 tables is pinned
 });
 
 // TypeScript decodes the frame to an object, so it cannot see a duplicate key: it judges the last one (admittedMessageIdDuplicates).
+// This pins @msgpack/msgpack's last-key behaviour plus the id check on the decoded object, not a first-key or duplicate path in
+// cultnet-ts source: there is none, so a refuse-on-first mutation in src would not be killed.
 test("write_admitted messageId: a repeated key follows the last-key-wins policy", () => {
   const vectors = JSON.parse(readFileSync(join(__dirname, "..", "..", "..", "..", "contracts", "cultnet", "interop", "write-receipt-vectors.json"), "utf8"));
   const section = vectors.admittedMessageIdDuplicates;