Merge pull request #845 from MatthieuBizien/fix/issue-841-openrouter-gemini

Agents: sanitize OpenRouter Gemini thoughtSignature

CHANGELOG.md

@@ -144,6 +144,7 @@
 ### Fixes
 - Packaging: include `dist/memory/**` in the npm tarball (fixes `ERR_MODULE_NOT_FOUND` for `dist/memory/index.js`).
 - Agents: persist sub-agent registry across gateway restarts and resume announce flow safely. (#831) — thanks @roshanasingh4.
+- Agents: strip invalid Gemini thought signatures from OpenRouter history to avoid 400s. (#841, #845) — thanks @MatthieuBizien.
 
 ## 2026.1.12-1
 

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

@@ -9,26 +9,65 @@ import type { EmbeddedContextFile } from "./types.js";
 
 type ContentBlockWithSignature = {
   thought_signature?: unknown;
+  thoughtSignature?: unknown;
   [key: string]: unknown;
 };
 
+type ThoughtSignatureSanitizeOptions = {
+  allowBase64Only?: boolean;
+  includeCamelCase?: boolean;
+};
+
+function isBase64Signature(value: string): boolean {
+  const trimmed = value.trim();
+  if (!trimmed) return false;
+  const compact = trimmed.replace(/\s+/g, "");
+  if (!/^[A-Za-z0-9+/=_-]+$/.test(compact)) return false;
+  const isUrl = compact.includes("-") || compact.includes("_");
+  try {
+    const buf = Buffer.from(compact, isUrl ? "base64url" : "base64");
+    if (buf.length === 0) return false;
+    const encoded = buf.toString(isUrl ? "base64url" : "base64");
+    const normalize = (input: string) => input.replace(/=+$/g, "");
+    return normalize(encoded) === normalize(compact);
+  } catch {
+    return false;
+  }
+}
+
 /**
  * Strips Claude-style thought_signature fields from content blocks.
  *
  * Gemini expects thought signatures as base64-encoded bytes, but Claude stores message ids
  * like "msg_abc123...". We only strip "msg_*" to preserve any provider-valid signatures.
  */
-export function stripThoughtSignatures<T>(content: T): T {
+export function stripThoughtSignatures<T>(
+  content: T,
+  options?: ThoughtSignatureSanitizeOptions,
+): T {
   if (!Array.isArray(content)) return content;
+  const allowBase64Only = options?.allowBase64Only ?? false;
+  const includeCamelCase = options?.includeCamelCase ?? false;
+  const shouldStripSignature = (value: unknown): boolean => {
+    if (!allowBase64Only) {
+      return typeof value === "string" && value.startsWith("msg_");
+    }
+    return typeof value !== "string" || !isBase64Signature(value);
+  };
   return content.map((block) => {
     if (!block || typeof block !== "object") return block;
     const rec = block as ContentBlockWithSignature;
-    const signature = rec.thought_signature;
+    const stripSnake = shouldStripSignature(rec.thought_signature);
-    if (typeof signature !== "string" || !signature.startsWith("msg_")) {
+    const stripCamel = includeCamelCase
+      ? shouldStripSignature(rec.thoughtSignature)
+      : false;
+    if (!stripSnake && !stripCamel) {
       return block;
     }
-    const { thought_signature: _signature, ...rest } = rec;
+    const next = { ...rec };
-    return rest;
+    if (stripSnake) delete next.thought_signature;
+    if (stripCamel) delete next.thoughtSignature;
+    return next;
   }) as T;
 }
 

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

@@ -23,6 +23,7 @@ export { sanitizeGoogleTurnOrdering };
 type GeminiToolCallBlock = {
   type?: unknown;
   thought_signature?: unknown;
+  thoughtSignature?: unknown;
   id?: unknown;
   toolCallId?: unknown;
   name?: unknown;
@@ -118,7 +119,8 @@ export function downgradeGeminiHistory(messages: AgentMessage[]): AgentMessage[]
         const blockRecord = block as GeminiToolCallBlock;
         const type = blockRecord.type;
         if (type === "toolCall" || type === "functionCall" || type === "toolUse") {
-          const hasSignature = Boolean(blockRecord.thought_signature);
+          const signature = blockRecord.thought_signature ?? blockRecord.thoughtSignature;
+          const hasSignature = Boolean(signature);
           if (!hasSignature) {
             const id =
               typeof blockRecord.id === "string"

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

@@ -34,6 +34,10 @@ export async function sanitizeSessionMessagesImages(
     sanitizeToolCallIds?: boolean;
     enforceToolCallLast?: boolean;
     preserveSignatures?: boolean;
+    sanitizeThoughtSignatures?: {
+      allowBase64Only?: boolean;
+      includeCamelCase?: boolean;
+    };
   },
 ): Promise<AgentMessage[]> {
   // We sanitize historical session messages because Anthropic can reject a request
@@ -82,7 +86,7 @@ export async function sanitizeSessionMessagesImages(
       if (Array.isArray(content)) {
         const strippedContent = options?.preserveSignatures
           ? content // Keep signatures for Antigravity Claude
-          : stripThoughtSignatures(content); // Strip for Gemini
+          : stripThoughtSignatures(content, options?.sanitizeThoughtSignatures); // Strip for Gemini
 
         const filteredContent = strippedContent.filter((block) => {
           if (!block || typeof block !== "object") return true;

src/agents/pi-embedded-runner.google-sanitize-thinking.test.ts

@@ -145,6 +145,65 @@ describe("sanitizeSessionHistory (google thinking)", () => {
     expect(assistant.content?.[1]?.text).toBe("internal note");
   });
 
+  it("strips non-base64 thought signatures for OpenRouter Gemini", async () => {
+    const sessionManager = SessionManager.inMemory();
+    const input = [
+      {
+        role: "user",
+        content: "hi",
+      },
+      {
+        role: "assistant",
+        content: [
+          { type: "text", text: "hello", thought_signature: "msg_abc123" },
+          { type: "thinking", thinking: "ok", thought_signature: "c2ln" },
+          {
+            type: "toolCall",
+            id: "call_1",
+            name: "read",
+            arguments: { path: "/tmp/foo" },
+            thoughtSignature: "{\"id\":1}",
+          },
+          {
+            type: "toolCall",
+            id: "call_2",
+            name: "read",
+            arguments: { path: "/tmp/bar" },
+            thoughtSignature: "c2ln",
+          },
+        ],
+      },
+    ] satisfies AgentMessage[];
+
+    const out = await sanitizeSessionHistory({
+      messages: input,
+      modelApi: "openrouter",
+      provider: "openrouter",
+      modelId: "google/gemini-1.5-pro",
+      sessionManager,
+      sessionId: "session:openrouter-gemini",
+    });
+
+    const assistant = out.find((msg) => (msg as { role?: string }).role === "assistant") as {
+      content?: Array<{ type?: string; thought_signature?: string; thoughtSignature?: string }>;
+    };
+    expect(assistant.content).toEqual([
+      { type: "text", text: "hello" },
+      { type: "text", text: "ok" },
+      {
+        type: "text",
+        text: "[Tool Call: read (ID: call_1)]\nArguments: {\n  \"path\": \"/tmp/foo\"\n}",
+      },
+      {
+        type: "toolCall",
+        id: "call_2",
+        name: "read",
+        arguments: { path: "/tmp/bar" },
+        thoughtSignature: "c2ln",
+      },
+    ]);
+  });
+
   it("downgrades only unsigned thinking blocks when mixed with signed ones", async () => {
     const sessionManager = SessionManager.inMemory();
     const input = [

src/agents/pi-embedded-runner/compact.ts

@@ -308,6 +308,7 @@ export async function compactEmbeddedPiSession(params: {
               messages: session.messages,
               modelApi: model.api,
               modelId,
+              provider,
               sessionManager,
               sessionId: params.sessionId,
             });

src/agents/pi-embedded-runner/google.ts

@@ -185,17 +185,26 @@ export async function sanitizeSessionHistory(params: {
   messages: AgentMessage[];
   modelApi?: string | null;
   modelId?: string;
+  provider?: string;
   sessionManager: SessionManager;
   sessionId: string;
 }): Promise<AgentMessage[]> {
   const isAntigravityClaudeModel = isAntigravityClaude(params.modelApi, params.modelId);
+  const provider = (params.provider ?? "").toLowerCase();
+  const modelId = (params.modelId ?? "").toLowerCase();
+  const isOpenRouterGemini =
+    (provider === "openrouter" || provider === "opencode") && modelId.includes("gemini");
+  const isGeminiLike = isGoogleModelApi(params.modelApi) || isOpenRouterGemini;
   const sanitizedImages = await sanitizeSessionMessagesImages(params.messages, "session:history", {
     sanitizeToolCallIds: shouldSanitizeToolCallIds(params.modelApi),
     enforceToolCallLast: params.modelApi === "anthropic-messages",
     preserveSignatures: params.modelApi === "google-antigravity" && isAntigravityClaudeModel,
+    sanitizeThoughtSignatures: isOpenRouterGemini
+      ? { allowBase64Only: true, includeCamelCase: true }
+      : undefined,
   });
   const repairedTools = sanitizeToolUseResultPairing(sanitizedImages);
-  const shouldDowngradeGemini = isGoogleModelApi(params.modelApi) && !isAntigravityClaudeModel;
+  const shouldDowngradeGemini = isGeminiLike && !isAntigravityClaudeModel;
   // Gemini rejects unsigned thinking blocks; downgrade them before send to avoid INVALID_ARGUMENT.
   const downgradedThinking = shouldDowngradeGemini
     ? downgradeGeminiThinkingBlocks(repairedTools)

src/agents/pi-embedded-runner/run/attempt.ts

@@ -323,6 +323,7 @@ export async function runEmbeddedAttempt(
           messages: activeSession.messages,
           modelApi: params.model.api,
           modelId: params.modelId,
+          provider: params.provider,
           sessionManager,
           sessionId: params.sessionId,
         });