Summary

Fixes #1435 - Model switch via /model command reports success but doesn't actually switch.

Root Cause Analysis

In src/auto-reply/reply/directive-handling.impl.ts, the handleDirectiveOnly function has two separate code blocks:

Block 1 (lines 291-397): Session state persistence

if (sessionEntry && sessionStore && sessionKey) {
  // ... other directives ...
  if (modelSelection) {
    applyModelOverrideToSessionEntry({...});  // Actually saves the model
  }
  // ... persist to disk ...
}

Block 2 (lines 450-463): User feedback message generation

if (modelSelection) {
  parts.push(`Model set to ${label}.`);  // Always shown if modelSelection exists!
}

The bug: Block 2 runs regardless of whether Block 1 executed. So when sessionEntry, sessionStore, or sessionKey is missing:

• ❌ Model override is NOT persisted
• ✅ "Model set to X" message IS shown
• → User sees success, but /status still shows old model

The Fix

Track whether the persist actually happened:

+  let didPersistModel = false;
   if (sessionEntry && sessionStore && sessionKey) {
     ...
     if (modelSelection) {
       applyModelOverrideToSessionEntry({...});
+      didPersistModel = true;
     }
   }
   
   // User feedback - now conditional on actual persist
-  if (modelSelection) {
+  if (modelSelection && didPersistModel) {
     parts.push(`Model set to ${labelWithAlias}.`);
+  } else if (modelSelection && !didPersistModel) {
+    parts.push(`Model switch to ${provider}/${model} failed (session state unavailable).`);
   }

Behavior Change

Testing

Added unit tests covering all edge cases in directive-handling.impl.model-persist.test.ts:

✓ shows success message when session state is available
✓ shows error message when sessionEntry is missing  
✓ shows error message when sessionStore is missing
✓ shows no model message when no /model directive

Test Files  1 passed (1)
Tests       4 passed (4)

How to Verify

1. Apply this PR
2. Simulate missing session state (e.g., fresh session before store is initialized)
3. Run /model <some-model>
4. Before fix: "Model set to X" shown, but /status shows old model
5. After fix: "Model switch failed (session state unavailable)" shown

Files Changed

• src/auto-reply/reply/directive-handling.impl.ts - 5 lines changed (the fix)
• src/auto-reply/reply/directive-handling.impl.model-persist.test.ts - new file (174 lines, unit tests)

AI Disclosure

• 🤖 AI-assisted: Claude Opus 4.5 via Clawdbot
• 🧪 Testing: Fully tested - 4 unit tests added, all passing
• ✅ Code understanding: Yes, traced through the codebase to find root cause
• 📝 Prompts/context: Available on request

Minimal, surgical fix. No unrelated changes. Tests cover all edge cases.