fix: post-merge breakage (Gemini, idle timeout, sharp cache) (#1138)

* fix: add gemini-3-flash to validModels array

The model was defined in the type union and RPM limits but missing from
the runtime validModels array, causing silent fallback to gemini-2.5-flash.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: skip processing when Gemini returns empty observation response

Empty responses were silently consuming messages from the queue via
processAgentResponse. Now skips processing on empty content, leaving
the message in processing status for stale recovery.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: prevent idle timeout from triggering infinite restart loop

When a session hits the 3-minute idle timeout, the finally block was
seeing stale processing messages and restarting the generator endlessly.
Now tracks idle timeout as a distinct exit reason via session flag,
resets stale messages, and skips restart.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: clear stale Bun native module cache on update

Bun's global cache retains sharp/libvips native binaries with broken
dylib references after version upgrades. Clear ~/.bun/install/cache/@img/
before install in both the end-user (smart-install) and dev (sync-marketplace)
paths to prevent ERR_DLOPEN_FAILED errors in Chroma sync.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: address PR review feedback (empty summary response, session-scoped reset, shell injection)

- Apply same empty-response guard to summary path as observation path in GeminiAgent
- Add optional sessionDbId param to resetStaleProcessingMessages for session-scoped resets
- Use JSON.stringify for gitignore pattern escaping, filter negation patterns

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

scripts/smart-install.js

@@ -5,7 +5,7 @@
  * Ensures Bun runtime and uv (Python package manager) are installed
  * (auto-installs if missing) and handles dependency installation when needed.
  */
-import { existsSync, readFileSync, writeFileSync } from 'fs';
+import { existsSync, readFileSync, writeFileSync, rmSync } from 'fs';
 import { execSync, spawnSync } from 'child_process';
 import { join } from 'path';
 import { homedir } from 'os';
@@ -260,6 +260,15 @@ function installDeps() {
 
   console.error('📦 Installing dependencies with Bun...');
 
+  // Clear stale native module cache (sharp/libvips) to prevent broken dylib references.
+  // Bun's cache can retain native binaries that reference companion libraries at
+  // broken relative paths after version upgrades.
+  const bunCacheImgDir = join(homedir(), '.bun', 'install', 'cache', '@img');
+  if (existsSync(bunCacheImgDir)) {
+    console.error('   Clearing stale native module cache (@img/sharp)...');
+    rmSync(bunCacheImgDir, { recursive: true, force: true });
+  }
+
   // Quote path for Windows paths with spaces
   const bunCmd = IS_WINDOWS && bunPath.includes(' ') ? `"${bunPath}"` : bunPath;