cultnet-ts: the registry sizes the reply that would serve a raw put

CultNetDocumentRegistry.createRawSnapshotResponseForPut(put, messageId)
returns the snapshot response that would serve the put's document alone:
the envelope applyRawDocumentPutMessage stores, as createRawSnapshotResponse
serves it. A server can judge a put by the size it would be served at.

applyRawDocumentPutMessage and the new method share one envelope builder,
and the served record comes from the snapshot path's own record builder,
so the size and the stored record cannot drift.

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

packages/cultnet-ts/src/replication.ts

@@ -246,17 +246,46 @@ export class CultNetDocumentRegistry {
     cache: CultCache,
     message: CultNetDocumentPutRawMessage,
   ): Promise<unknown> {
+    const { binding, envelope } = this.#rawPutEnvelope(message);
+    return cache.putEnvelope(binding.definition, envelope);
+  }
+
+  /**
+   * The snapshot response that would serve this raw put's document alone: the
+   * record `applyRawDocumentPutMessage` would store, as `createRawSnapshotResponse`
+   * would serve it. A server uses it to judge a put by the size it would be
+   * served at. Throws, as the put would, when no binding accepts the document.
+   */
+  createRawSnapshotResponseForPut(
+    message: CultNetDocumentPutRawMessage,
+    messageId: string,
+  ): CultNetSnapshotResponseRawMessage {
+    const { envelope } = this.#rawPutEnvelope(message);
+    return {
+      schemaVersion: "cultnet.snapshot_response_raw.v0",
+      messageId,
+      documents: [this.#createRawDocumentRecord(envelope)],
+    };
+  }
+
+  #rawPutEnvelope(message: CultNetDocumentPutRawMessage): {
+    binding: CultNetDocumentBinding;
+    envelope: CultCacheEnvelope;
+  } {
     const resolution = this.#resolveRawDocumentBinding(message.document);
     const { binding } = resolution;
-    return cache.putEnvelope(binding.definition, {
-      key: message.document.recordKey,
-      type: binding.definition.type,
-      schemaId: resolution.preserveIncomingSchemaId
-        ? message.document.schemaId
-        : schemaIdForBinding(binding),
-      payload: new Uint8Array(message.document.payload),
-      storedAt: message.document.storedAt,
-    });
+    return {
+      binding,
+      envelope: {
+        key: message.document.recordKey,
+        type: binding.definition.type,
+        schemaId: resolution.preserveIncomingSchemaId
+          ? message.document.schemaId
+          : schemaIdForBinding(binding),
+        payload: new Uint8Array(message.document.payload),
+        storedAt: message.document.storedAt,
+      },
+    };
   }
 
   async applySnapshotResponse(