docs: update DEBUGGING.md with config race condition fix

DEBUGGING.md

@@ -62,8 +62,37 @@ console.log("[Tauri Listener] message");
 - Config file gets reset to defaults
 - Settings don't persist between sessions
 - Model selection is lost
+- Config appears to work, then randomly resets
 
-**POTENTIAL CAUSES:**
+**ACTUAL ROOT CAUSE (FIXED!):**
+
+The config store had a **critical race condition bug** in `src/lib/stores/config.ts`. The pattern used everywhere was:
+
+```typescript
+// ❌ BUGGY CODE
+let currentConfig = defaultConfig;
+config.subscribe((c) => (currentConfig = c))();  // <-- Immediate unsubscribe!
+return currentConfig;
+```
+
+**Why this caused config loss:**
+- The `()` at the end immediately unsubscribes from the store
+- This creates a race condition - sometimes you get the value, sometimes you don't
+- When it fails, it returns `defaultConfig` instead of your actual config
+- This is why your settings would randomly disappear!
+
+**The fix:**
+```typescript
+// ✅ CORRECT CODE
+function getCurrentConfig(): HikariConfig {
+  let currentConfig: HikariConfig = defaultConfig;
+  const unsubscribe = config.subscribe((c) => (currentConfig = c));
+  unsubscribe();  // <-- Proper cleanup after getting value
+  return currentConfig;
+}
+```
+
+**POTENTIAL CAUSES (if the above is fixed):**
 
 ### 1. Missing `#[serde(default)]` Attribute