From 12e07f646f4283500686f6a888693e437582c0f5 Mon Sep 17 00:00:00 2001
From: Ingwannu <ingwannu@users.noreply.github.com>
Date: Sun, 9 Aug 2026 04:41:29 +0000
Subject: [PATCH] fix(vertex): scope replay by client thread

---
 src/adapters/google.ts                        |  4 +-
 tests/google-vertex-thought-signature.test.ts | 38 +++++++++++++++++++
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/src/adapters/google.ts b/src/adapters/google.ts
index 91f8bc0994..f8709714a7 100644
--- a/src/adapters/google.ts
+++ b/src/adapters/google.ts
@@ -54,8 +54,8 @@ function resolveVertexApiKey(optKey?: string): string | undefined {
 /** Prefer Codex's stable opaque thread key; retain the existing deterministic fallback for clients
  * that omit it. The replay store hashes this value and never retains the raw session identifier. */
 function vertexReplaySessionId(parsed: OcxParsedRequest): string {
-  const promptCacheKey = parsed.options.promptCacheKey?.trim();
-  return promptCacheKey || antigravitySessionId(parsed);
+  const threadId = parsed._clientThreadId?.trim();
+  return threadId || antigravitySessionId(parsed);
 }
 
 /**
diff --git a/tests/google-vertex-thought-signature.test.ts b/tests/google-vertex-thought-signature.test.ts
index f24a33f7c5..5761462da8 100644
--- a/tests/google-vertex-thought-signature.test.ts
+++ b/tests/google-vertex-thought-signature.test.ts
@@ -55,6 +55,16 @@ const continuation = () => request([
   },
 ], false);
 
+function scopedReplayRequest(
+  parsed: OcxParsedRequest,
+  threadId: string | undefined,
+  promptCacheKey: string | undefined,
+): OcxParsedRequest {
+  if (threadId !== undefined) parsed._clientThreadId = threadId;
+  if (promptCacheKey !== undefined) parsed.options.promptCacheKey = promptCacheKey;
+  return parsed;
+}
+
 function vertexResponseBody(): Record<string, unknown> {
   return {
     candidates: [{
@@ -107,6 +117,34 @@ describe("Vertex thought-signature continuation (#1254)", () => {
     expect(replayedFunctionCall(followup.body as string).thoughtSignature).toBe(SIGNATURE);
   });
 
+  test("#1312: shared prompt cache keys cannot cross client-thread replay namespaces", async () => {
+    const first = scopedReplayRequest(firstTurn(false), "thread-a", "shared-cache-cohort");
+    const firstAdapter = createGoogleAdapter(provider);
+    await firstAdapter.buildRequest(first);
+    await firstAdapter.parseResponse!(new Response(JSON.stringify(vertexResponseBody())));
+
+    const otherThread = await createGoogleAdapter(provider).buildRequest(
+      scopedReplayRequest(continuation(), "thread-b", "shared-cache-cohort"),
+    );
+    expect(replayedFunctionCall(otherThread.body as string).thoughtSignature).toBeUndefined();
+
+    const originalThread = await createGoogleAdapter(provider).buildRequest(
+      scopedReplayRequest(continuation(), "thread-a", "different-cache-cohort"),
+    );
+    expect(replayedFunctionCall(originalThread.body as string).thoughtSignature).toBe(SIGNATURE);
+  });
+
+  test("#1312: threadless clients keep deterministic replay regardless of prompt cache key", async () => {
+    const firstAdapter = createGoogleAdapter(provider);
+    await firstAdapter.buildRequest(scopedReplayRequest(firstTurn(false), undefined, "cohort-a"));
+    await firstAdapter.parseResponse!(new Response(JSON.stringify(vertexResponseBody())));
+
+    const followup = await createGoogleAdapter(provider).buildRequest(
+      scopedReplayRequest(continuation(), undefined, "cohort-b"),
+    );
+    expect(replayedFunctionCall(followup.body as string).thoughtSignature).toBe(SIGNATURE);
+  });
+
   test("Vertex signatures cannot enter the Antigravity replay namespace", async () => {
     const first = firstTurn(false);
     const adapter = createGoogleAdapter(provider);