fix(agents): strip leaked tool call text from assistant messages

When replaying conversation history to Gemini, tool calls without
thought_signature are downgraded to text blocks like [Tool Call: ...].
This leaked internal technical info into user-facing chat messages.

Added stripDowngradedToolCallText filter alongside existing Minimax
filter to remove these text representations before extraction.

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

@@ -257,4 +257,105 @@ describe("extractAssistantText", () => {
     const result = extractAssistantText(msg);
     expect(result).toBe("First block.\nThird block.");
   });
+
+  it("strips downgraded Gemini tool call text representations", () => {
+    const msg: AssistantMessage = {
+      role: "assistant",
+      content: [
+        {
+          type: "text",
+          text: `[Tool Call: exec (ID: toolu_vrtx_014w1P6B6w4V92v4VzG7Qk12)]
+Arguments: { "command": "git status", "timeout": 120000 }`,
+        },
+      ],
+      timestamp: Date.now(),
+    };
+
+    const result = extractAssistantText(msg);
+    expect(result).toBe("");
+  });
+
+  it("strips multiple downgraded tool calls", () => {
+    const msg: AssistantMessage = {
+      role: "assistant",
+      content: [
+        {
+          type: "text",
+          text: `[Tool Call: read (ID: toolu_1)]
+Arguments: { "path": "/some/file.txt" }
+[Tool Call: exec (ID: toolu_2)]
+Arguments: { "command": "ls -la" }`,
+        },
+      ],
+      timestamp: Date.now(),
+    };
+
+    const result = extractAssistantText(msg);
+    expect(result).toBe("");
+  });
+
+  it("strips tool results for downgraded calls", () => {
+    const msg: AssistantMessage = {
+      role: "assistant",
+      content: [
+        {
+          type: "text",
+          text: `[Tool Result for ID toolu_123]
+{"status": "ok", "data": "some result"}`,
+        },
+      ],
+      timestamp: Date.now(),
+    };
+
+    const result = extractAssistantText(msg);
+    expect(result).toBe("");
+  });
+
+  it("preserves text around downgraded tool calls", () => {
+    const msg: AssistantMessage = {
+      role: "assistant",
+      content: [
+        {
+          type: "text",
+          text: `Let me check that for you.
+[Tool Call: browser (ID: toolu_abc)]
+Arguments: { "action": "act", "request": "click button" }`,
+        },
+      ],
+      timestamp: Date.now(),
+    };
+
+    const result = extractAssistantText(msg);
+    expect(result).toBe("Let me check that for you.");
+  });
+
+  it("handles multiple text blocks with tool calls and results", () => {
+    const msg: AssistantMessage = {
+      role: "assistant",
+      content: [
+        {
+          type: "text",
+          text: "Here's what I found:",
+        },
+        {
+          type: "text",
+          text: `[Tool Call: read (ID: toolu_1)]
+Arguments: { "path": "/test.txt" }`,
+        },
+        {
+          type: "text",
+          text: `[Tool Result for ID toolu_1]
+File contents here`,
+        },
+        {
+          type: "text",
+          text: "Done checking.",
+        },
+      ],
+      timestamp: Date.now(),
+    };
+
+    const result = extractAssistantText(msg);
+    expect(result).toBe("Here's what I found:\nDone checking.");
+  });
 });

src/agents/pi-embedded-utils.ts

@@ -21,6 +21,32 @@ function stripMinimaxToolCallXml(text: string): string {
   return cleaned;
 }
 
+/**
+ * Strip downgraded tool call text representations that leak into text content.
+ * When replaying history to Gemini, tool calls without `thought_signature` are
+ * downgraded to text blocks like `[Tool Call: name (ID: ...)]`. These should
+ * not be shown to users.
+ */
+function stripDowngradedToolCallText(text: string): string {
+  if (!text) return text;
+  if (!/\[Tool (?:Call|Result)/i.test(text)) return text;
+
+  // Remove [Tool Call: name (ID: ...)] blocks and their Arguments.
+  // Match until the next [Tool marker or end of string.
+  let cleaned = text.replace(
+    /\[Tool Call:[^\]]*\]\n?(?:Arguments:[\s\S]*?)?(?=\n*\[Tool |\n*$)/gi,
+    "",
+  );
+
+  // Remove [Tool Result for ID ...] blocks and their content.
+  cleaned = cleaned.replace(
+    /\[Tool Result for ID[^\]]*\]\n?[\s\S]*?(?=\n*\[Tool |\n*$)/gi,
+    "",
+  );
+
+  return cleaned.trim();
+}
+
 export function extractAssistantText(msg: AssistantMessage): string {
   const isTextBlock = (block: unknown): block is { type: "text"; text: string } => {
     if (!block || typeof block !== "object") return false;
@@ -31,7 +57,9 @@ export function extractAssistantText(msg: AssistantMessage): string {
   const blocks = Array.isArray(msg.content)
     ? msg.content
         .filter(isTextBlock)
-        .map((c) => stripMinimaxToolCallXml(c.text).trim())
+        .map((c) =>
+          stripDowngradedToolCallText(stripMinimaxToolCallXml(c.text)).trim(),
+        )
         .filter(Boolean)
     : [];
   return blocks.join("\n").trim();