fix: auto-recover from Gemini session corruption

Detect the Gemini API error 'function call turn comes immediately after
a user turn or after a function response turn' which indicates corrupted
session history.

When detected:
- Delete the corrupted transcript file
- Remove the session entry from the store
- Return a user-friendly message asking them to retry

This prevents the error loop where every subsequent message fails with
the same error until manual intervention.

Fixes #296

src/auto-reply/reply/agent-runner.ts

@@ -1,4 +1,5 @@
 import crypto from "node:crypto";
+import fs from "node:fs";
 import { lookupContextTokens } from "../../agents/context.js";
 import { DEFAULT_CONTEXT_TOKENS } from "../../agents/defaults.js";
 import { runWithModelFallback } from "../../agents/model-fallback.js";
@@ -8,6 +9,7 @@ import {
 } from "../../agents/pi-embedded.js";
 import {
   loadSessionStore,
+  resolveSessionTranscriptPath,
   type SessionEntry,
   saveSessionStore,
 } from "../../config/sessions.js";
@@ -346,6 +348,37 @@ export async function runReplyAgent(params: {
       const message = err instanceof Error ? err.message : String(err);
       const isContextOverflow =
         /context.*overflow|too large|context window/i.test(message);
+      const isSessionCorruption =
+        /function call turn comes immediately after|INVALID_ARGUMENT.*function/i.test(
+          message,
+        );
+
+      // Auto-recover from Gemini session corruption by resetting the session
+      if (isSessionCorruption && sessionKey && sessionStore && storePath) {
+        const corruptedSessionId = sessionEntry?.sessionId;
+        defaultRuntime.error(
+          `Session history corrupted (Gemini function call ordering). Resetting session: ${sessionKey}`,
+        );
+
+        // Delete transcript file if it exists
+        if (corruptedSessionId) {
+          const transcriptPath = resolveSessionTranscriptPath(corruptedSessionId);
+          try {
+            fs.unlinkSync(transcriptPath);
+          } catch {
+            // Ignore if file doesn't exist
+          }
+        }
+
+        // Remove session entry from store
+        delete sessionStore[sessionKey];
+        await saveSessionStore(storePath, sessionStore);
+
+        return finalizeWithFollowup({
+          text: "⚠️ Session history was corrupted. I've reset the conversation - please try again!",
+        });
+      }
+
       defaultRuntime.error(`Embedded agent failed before reply: ${message}`);
       return finalizeWithFollowup({
         text: isContextOverflow