fix: HEIC vips fallback, DB pool exhaustion, auth session persistence

HEIC thumbnails:
- Switch fallback from ffmpeg to vips for HEIC files that pillow-heif
  rejects. ffmpeg decoded gain map tiles instead of the primary image,
  producing inverted/negative thumbnails. vips uses libheif's item
  references correctly and extracts the full-resolution primary image.

Database pool exhaustion:
- Add idle_in_transaction_session_timeout=60s so Postgres auto-kills
  leaked connections from disconnected thumbnail requests.
- Add pool_timeout=10 so new requests fail fast instead of hanging.
- Bump pool from 5+5 to 10+10 for thumbnail concurrency headroom.
- get_db rolls back on exception before closing.

Auth session persistence:
- Narrow 401 interceptor exclusion to only /auth/refresh and /auth/login
  (was excluding all /auth/* including /auth/me, preventing token refresh
  on boot).
- fetchMe only clears tokens on 401/403, not network errors.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/config.py

@@ -26,8 +26,8 @@ class PerformanceSettings(BaseModel):
     """Performance tuning settings"""
     max_concurrent_thumbnails: int = 10
     cache_ttl: int = 3600
-    db_pool_size: int = 5
-    db_pool_max_overflow: int = 5
+    db_pool_size: int = 10
+    db_pool_max_overflow: int = 10
     db_pool_recycle: int = 3600
 
 class EmbedderSettings(BaseModel):

backend/app/database.py

@@ -76,6 +76,10 @@ else:
         max_overflow=settings.performance.db_pool_max_overflow,
         pool_recycle=settings.performance.db_pool_recycle,
         pool_pre_ping=True,
+        pool_timeout=10,          # fail fast if pool exhausted (default 30)
+        # Kill connections idle in a transaction for >60s. Prevents leaked
+        # sessions from thumbnail requests that disconnect mid-flight.
+        connect_args={"server_settings": {"idle_in_transaction_session_timeout": "60000"}},
     )
 
 # Create async session factory
@@ -89,10 +93,17 @@ AsyncSessionLocal = async_sessionmaker(
 Base = declarative_base()
 
 async def get_db() -> AsyncSession:
-    """Dependency to get database session"""
+    """Dependency to get database session.
+
+    Rolls back any uncommitted transaction before closing so a client
+    disconnect doesn't leave idle-in-transaction connections in the pool.
+    """
     async with AsyncSessionLocal() as session:
         try:
             yield session
+        except Exception:
+            await session.rollback()
+            raise
         finally:
             await session.close()
 

backend/app/tasks/thumbs.py

@@ -114,23 +114,27 @@ def process_heic_image(filepath: str) -> Image.Image:
             img = img.convert('RGB')
         return img
     except Exception as e:
-        logger.warning(f"pillow-heif failed for {filepath}: {e} — trying ffmpeg")
+        logger.warning(f"pillow-heif failed for {filepath}: {e} — trying vips")
 
-    # ffmpeg fallback: decode HEIC to PNG in memory.
-    import subprocess
-    from io import BytesIO
+    # vips fallback: handles tiled Apple HEIC files (bursts, HDR gain
+    # maps, depth maps) that pillow-heif/libheif rejects due to too many
+    # auxiliary image references.
+    import subprocess, tempfile
     try:
+        with tempfile.NamedTemporaryFile(suffix='.png', delete=False) as tmp:
+            tmp_path = tmp.name
         result = subprocess.run(
-            ['ffmpeg', '-i', filepath, '-frames:v', '1',
-             '-f', 'image2pipe', '-vcodec', 'png', 'pipe:1'],
-            capture_output=True, timeout=30, stdin=subprocess.DEVNULL,
+            ['vips', 'heifload', filepath, tmp_path],
+            capture_output=True, timeout=60, stdin=subprocess.DEVNULL,
         )
-        if result.returncode == 0 and result.stdout:
-            img = Image.open(BytesIO(result.stdout)).convert('RGB')
+        if result.returncode == 0:
+            img = Image.open(tmp_path).convert('RGB')
+            os.unlink(tmp_path)
             return img
-        logger.error(f"ffmpeg HEIC decode failed for {filepath}: {result.stderr.decode()[-200:]}")
+        logger.error(f"vips HEIC decode failed for {filepath}: {result.stderr.decode()[-200:]}")
+        os.unlink(tmp_path)
     except Exception as e2:
-        logger.error(f"ffmpeg fallback failed for {filepath}: {e2}")
+        logger.error(f"vips fallback failed for {filepath}: {e2}")
     raise RuntimeError(f"Cannot decode HEIC: {filepath}")
 
 def process_video_thumbnail(filepath: str) -> Image.Image:

frontend/src/contexts/AuthContext.tsx

@@ -72,9 +72,14 @@ export function AuthProvider({ children }: { children: ReactNode }) {
     try {
       const res = await api.get('/auth/me')
       setUser(res.data)
-    } catch {
-      clearTokens()
-      setUser(null)
+    } catch (err: any) {
+      // Only clear tokens on auth failure (401/403), not network errors.
+      if (err?.response?.status === 401 || err?.response?.status === 403) {
+        clearTokens()
+        setUser(null)
+      }
+      // Network errors: leave tokens in place, user stays on login screen
+      // but can retry without re-entering credentials.
     }
   }, [])
 
@@ -136,7 +141,8 @@ export function AuthProvider({ children }: { children: ReactNode }) {
         if (
           error.response?.status === 401 &&
           !original._retry &&
-          !original.url?.includes('/auth/')
+          !original.url?.includes('/auth/refresh') &&
+          !original.url?.includes('/auth/login')
         ) {
           original._retry = true
           const rt = getStoredRefreshToken()