diff --git a/src/adapters/google.ts b/src/adapters/google.ts
index f152d91741..d3c1995f34 100644
--- a/src/adapters/google.ts
+++ b/src/adapters/google.ts
@@ -698,9 +698,10 @@ export function createGoogleAdapter(provider: OcxProviderConfig): ProviderAdapte
         // Antigravity use separate model namespaces so opaque provider state cannot cross routes.
         const replayModel = provider.googleMode === "cloud-code-assist" ? antigravityModel : vertexReplayModel;
         const replaySession = provider.googleMode === "cloud-code-assist" ? antigravitySession : vertexReplaySession;
+        let observedStreamThoughtSig = pendingStreamThoughtSig;
         if ((provider.googleMode === "cloud-code-assist" || provider.googleMode === "vertex")
           && parts && replayModel && replaySession) {
-          pendingStreamThoughtSig = observeAntigravityReplay(
+          observedStreamThoughtSig = observeAntigravityReplay(
             replayModel,
             replaySession,
             parts as unknown[],
@@ -747,6 +748,10 @@ export function createGoogleAdapter(provider: OcxProviderConfig): ProviderAdapte
               yield { type: "tool_call_end" };
             }
           }
+          // The observer scans the complete frame to populate replay state. Publish its carried
+          // signature only after emitting parts in source order, so a later thought part cannot
+          // supply fallback metadata to an earlier function call in the same frame.
+          pendingStreamThoughtSig = observedStreamThoughtSig;
         }
         return emittedContentEvent ? "content" : "continue";
       };
diff --git a/tests/google-signature-history-roundtrip.test.ts b/tests/google-signature-history-roundtrip.test.ts
index b40c21f074..67c72811c6 100644
--- a/tests/google-signature-history-roundtrip.test.ts
+++ b/tests/google-signature-history-roundtrip.test.ts
@@ -185,6 +185,24 @@ describe("#1735 thought signature survives history replay", () => {
       .toBe(SIGNATURE);
   });
 
+  test("streaming signatures only attach to function calls that follow them", async () => {
+    const adapter = createGoogleAdapter(provider);
+    await adapter.buildRequest(firstTurn());
+    const frame = `data: ${JSON.stringify(googleBody([
+      { functionCall: { name: "shell_command", args: { command: "pwd" } } },
+      { text: "thinking...", thought: true, thought_signature: SIGNATURE },
+      { functionCall: { name: "shell_command", args: { command: "ls" } } },
+    ]))}\n\n`;
+    const events: AdapterEvent[] = [];
+    for await (const event of adapter.parseStream(new Response(frame))) events.push(event);
+
+    const starts = events.filter((event): event is Extract<AdapterEvent, { type: "tool_call_start" }> =>
+      event.type === "tool_call_start");
+    expect(starts).toHaveLength(2);
+    expect(starts[0].providerMetadata?.google?.thoughtSignature).toBeUndefined();
+    expect(starts[1].providerMetadata?.google?.thoughtSignature).toBe(SIGNATURE);
+  });
+
   test("a signature replayed through Responses history reaches the rebuilt Google part", async () => {
     // No cache is warmed here: this is a cold process replaying client-supplied history.
     const parsed = parseRequestScoped({