diff --git a/src/responses/parser.ts b/src/responses/parser.ts
index 2f1dd73dd4..9a503df53c 100644
--- a/src/responses/parser.ts
+++ b/src/responses/parser.ts
@@ -754,6 +754,23 @@ export function parseRequest(
   };
 }
 
+/**
+ * Restore provider-opaque signatures after routing has supplied the complete replay scope.
+ * The initial request parse necessarily happens before provider and credential selection, so
+ * production callers use this once the route-bound scope has been populated.
+ */
+export function hydrateReplayThoughtSignatures(parsed: OcxParsedRequest): void {
+  const scope = parsed._reasoningReplayScope;
+  for (const message of parsed.context.messages) {
+    if (message.role !== "assistant" || !Array.isArray(message.content)) continue;
+    for (const part of message.content) {
+      if (part.type !== "toolCall" || part.providerMetadata || !part.id) continue;
+      const remembered = replayThoughtSignatureMetadata(part.id, scope);
+      if (remembered) part.providerMetadata = remembered;
+    }
+  }
+}
+
 /**
  * The Responses `text.format` object when it requests structured output (json_schema or
  * json_object), undefined otherwise. Acceptance is identical to the boolean detector this
diff --git a/src/server/responses/core.ts b/src/server/responses/core.ts
index 8df2fc672d..294c634c6d 100644
--- a/src/server/responses/core.ts
+++ b/src/server/responses/core.ts
@@ -8,7 +8,7 @@ import {
   multiAgentGuidanceEnabled,
   resolveEnvValue,
 } from "../../config";
-import { parseRequest } from "../../responses/parser";
+import { hydrateReplayThoughtSignatures, parseRequest } from "../../responses/parser";
 import {
   bindReasoningReplayScope,
   reasoningReplayCodexCredentialIdentity,
@@ -2148,6 +2148,7 @@ async function handleResponsesInner(
     codexAuthContext: authCtx,
     forwardHeaders: selectedForwardHeaders,
   });
+  hydrateReplayThoughtSignatures(parsed);
   logCtx.providerAdapter = adapter.name;
   // Ordinary requests receive one durable attempt only after their final initial
   // adapter is resolved. Combo children own their attempt and retries keep it.
diff --git a/tests/google-signature-history-roundtrip.test.ts b/tests/google-signature-history-roundtrip.test.ts
index 049ea50f36..5441a826fc 100644
--- a/tests/google-signature-history-roundtrip.test.ts
+++ b/tests/google-signature-history-roundtrip.test.ts
@@ -8,7 +8,7 @@ import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { createGoogleAdapter as createGoogleAdapterProduction } from "../src/adapters/google";
 import { __resetAntigravityReplayCache } from "../src/adapters/google-antigravity-replay";
-import { parseRequest } from "../src/responses/parser";
+import { hydrateReplayThoughtSignatures, parseRequest } from "../src/responses/parser";
 import {
   flushThoughtSignatureReplayForTests,
   lookupReplayThoughtSignature,
@@ -179,6 +179,25 @@ describe("#1735 thought signature survives history replay", () => {
     expect(part?.thoughtSignature).toBe(SIGNATURE);
   });
 
+  test("the server can restore a signature after its route scope is bound", async () => {
+    const scope = scopeFor();
+    rememberThoughtSignatureForReplay("call_shell_late", SIGNATURE, scope);
+    const parsed = parseRequest({
+      model: MODEL,
+      input: [
+        { type: "function_call", call_id: "call_shell_late", name: "shell_command", arguments: "{}" },
+        { type: "function_call_output", call_id: "call_shell_late", output: "/workspace" },
+      ],
+    });
+
+    parsed._reasoningReplayScope = scope;
+    hydrateReplayThoughtSignatures(parsed);
+
+    const request = await createGoogleAdapter(provider).buildRequest(parsed);
+    const part = modelParts(request.body as string).find(candidate => "functionCall" in candidate);
+    expect(part?.thoughtSignature).toBe(SIGNATURE);
+  });
+
   test("a custom_tool_call replay is re-signed from the proxy-side store", async () => {
     rememberThoughtSignatureForReplay("call_custom_1", SIGNATURE_B, scopeFor());
     const parsed = parseRequestScoped({