fix: strip only msg_* thought_signature (#805) (thanks @marcmarg)

CHANGELOG.md

@@ -28,6 +28,7 @@
 - Auto-reply: re-evaluate reasoning tag enforcement on fallback providers to prevent leaked reasoning. (#810 — thanks @mcinteerj)
 - Tools/Gemini: drop null-only union variants while cleaning tool schemas to avoid Cloud Code Assist schema errors. (#782 — thanks @AbhisekBasu1)
 - Connections UI: polish multi-account account cards in the Connections view. (#816 — thanks @steipete)
+- Gemini: strip Claude `msg_*` thought_signature fields from session history to avoid base64 decode errors. (#805 — thanks @marcmarg)
 
 ## 2026.1.12-3
 

src/agents/pi-embedded-helpers.test.ts

@@ -9,12 +9,13 @@ import {
   isCloudCodeAssistFormatError,
   isCompactionFailureError,
   isContextOverflowError,
+  isMessagingToolDuplicate,
   isFailoverErrorMessage,
+  normalizeTextForComparison,
   sanitizeGoogleTurnOrdering,
   sanitizeSessionMessagesImages,
   sanitizeToolCallId,
   stripThoughtSignatures,
-  validateGeminiTurns,
 } from "./pi-embedded-helpers.js";
 import {
   DEFAULT_AGENTS_FILENAME,
@@ -591,9 +592,9 @@ describe("sanitizeSessionMessagesImages - thought_signature stripping", () => {
     const content = (out[0] as { content?: unknown[] }).content;
     expect(content).toHaveLength(2);
     expect("thought_signature" in ((content?.[0] ?? {}) as object)).toBe(false);
-    expect((content?.[1] as { thought_signature?: unknown })?.thought_signature).toBe(
+    expect(
-      "AQID",
+      (content?.[1] as { thought_signature?: unknown })?.thought_signature,
-    );
+    ).toBe("AQID");
   });
 });