fix: state persistence diagnostics + fallback write

- loadState: logs DATA_DIR path, writability check, lists files, shows
  radio_favorites count on load
- saveState: read-back verification after atomic write, fallback to
  direct write if rename fails
- /api/health: shows state diagnostics (file exists, file size, keys,
  favorites count in memory vs disk, lastSaveOk)
- Helps diagnose why favorites are not persisting across deploys

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

server/src/core/persistence.ts

@@ -7,19 +7,45 @@ const backupFile = stateFile + '.bak';
 const tmpFile = stateFile + '.tmp';
 
 let state: Record<string, any> = {};
+let lastSaveOk = false;
 
 export function loadState(): void {
+  console.log(`[State] DATA_DIR=${DATA_DIR}, stateFile=${stateFile}`);
+
+  // Check if DATA_DIR exists and is writable
+  try {
+    fs.mkdirSync(DATA_DIR, { recursive: true });
+    const testFile = path.join(DATA_DIR, '.write-test');
+    fs.writeFileSync(testFile, 'ok');
+    fs.unlinkSync(testFile);
+    console.log(`[State] DATA_DIR is writable`);
+  } catch (e) {
+    console.error(`[State] ⚠ DATA_DIR is NOT writable:`, e);
+  }
+
+  // List existing files in DATA_DIR for diagnostics
+  try {
+    const files = fs.readdirSync(DATA_DIR);
+    console.log(`[State] Files in DATA_DIR: ${files.join(', ') || '(empty)'}`);
+  } catch (e) {
+    console.error(`[State] Cannot list DATA_DIR:`, e);
+  }
+
   // Try main file first, fall back to backup if corrupted
   for (const file of [stateFile, backupFile]) {
     try {
       if (fs.existsSync(file)) {
-        state = JSON.parse(fs.readFileSync(file, 'utf-8'));
+        const raw = fs.readFileSync(file, 'utf-8');
+        state = JSON.parse(raw);
         const keys = Object.keys(state);
-        console.log(`[State] Loaded from ${path.basename(file)} (${keys.length} keys: ${keys.join(', ')})`);
+        const favCount = Array.isArray(state.radio_favorites) ? state.radio_favorites.length : 0;
+        console.log(`[State] ✓ Loaded from ${path.basename(file)} (${keys.length} keys: ${keys.join(', ')})`);
+        console.log(`[State]   radio_favorites: ${favCount} entries`);
         // Create backup on successful load from main file
         if (file === stateFile) {
           try { fs.copyFileSync(stateFile, backupFile); } catch {}
         }
+        lastSaveOk = true;
         return;
       }
     } catch (e) {
@@ -32,12 +58,29 @@ export function loadState(): void {
 export function saveState(): void {
   try {
     fs.mkdirSync(path.dirname(stateFile), { recursive: true });
+    const json = JSON.stringify(state, null, 2);
     // Atomic write: write to tmp file, then rename
-    // rename() is atomic on POSIX filesystems, prevents corruption on crash
-    fs.writeFileSync(tmpFile, JSON.stringify(state, null, 2));
+    fs.writeFileSync(tmpFile, json);
     fs.renameSync(tmpFile, stateFile);
+    // Verify write by reading back
+    const verify = fs.readFileSync(stateFile, 'utf-8');
+    if (verify.length !== json.length) {
+      console.error(`[State] ⚠ Write verification FAILED: wrote ${json.length} bytes, read back ${verify.length}`);
+      lastSaveOk = false;
+    } else {
+      lastSaveOk = true;
+    }
   } catch (e) {
-    console.error('[State] Failed to save:', e);
+    console.error('[State] ✗ Failed to save:', e);
+    lastSaveOk = false;
+    // Fallback: try direct write if rename failed
+    try {
+      fs.writeFileSync(stateFile, JSON.stringify(state, null, 2));
+      console.log('[State] Fallback direct write succeeded');
+      lastSaveOk = true;
+    } catch (e2) {
+      console.error('[State] ✗ Fallback write also failed:', e2);
+    }
   }
 }
 
@@ -53,3 +96,33 @@ export function setState(key: string, value: any): void {
 export function getFullState(): Record<string, any> {
   return { ...state };
 }
+
+/** Diagnostic info for health endpoint */
+export function getStateDiag(): Record<string, any> {
+  let fileExists = false;
+  let fileSize = 0;
+  let fileKeys: string[] = [];
+  let fileFavCount = 0;
+  try {
+    if (fs.existsSync(stateFile)) {
+      fileExists = true;
+      const stat = fs.statSync(stateFile);
+      fileSize = stat.size;
+      const parsed = JSON.parse(fs.readFileSync(stateFile, 'utf-8'));
+      fileKeys = Object.keys(parsed);
+      fileFavCount = Array.isArray(parsed.radio_favorites) ? parsed.radio_favorites.length : 0;
+    }
+  } catch {}
+  const memKeys = Object.keys(state);
+  const memFavCount = Array.isArray(state.radio_favorites) ? state.radio_favorites.length : 0;
+  return {
+    stateFile,
+    fileExists,
+    fileSize,
+    fileKeys,
+    fileFavCount,
+    memoryKeys: memKeys,
+    memoryFavCount: memFavCount,
+    lastSaveOk,
+  };
+}