The models page was slow because the work itself is slow, not because of routing:
cached-models walks the HF/GGUF cache doing per-model capability detection, and
cache-stats walks every file summing sizes — many seconds each on a large cache.

- routes.py: cached-models + cache-stats are now stale-while-revalidate (TTL 25s).
  First call computes; afterwards they return the last result instantly and refresh
  in a background thread. Mutating ops (clear-cache, delete cached model, free-disk)
  force the next refresh. The coderai-system worker pre-warms both scans on startup,
  so even the first page load is fast.
- gpu_detect.gpu_stats(): short 1.5s TTL cache — the Tasks page polls it ~every
  second and nvidia-smi is slow on a saturated GPU, so collapse repeats.

Verified: _cached returns stale instantly and refreshes in the background
(2 underlying calls across first+expire); all modules compile.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011DDv7BchtZQWsnPG6Jm49m