feat: D3 foundation — retry schema, shared types, health client, backoff helper
- Add retry_count/next_retry_at to jobs table via guarded idempotent ALTER TABLE
(PRAGMA table_info existence check, try/catch for safety on restart)
- Add retryCount/nextRetryAt to Job type, rowToJob(), updateJob(), resetJob()
- Add getHealth() returning structured WhisperHealth (status, gpu_name,
vram_total_mb, model, queue_depth, model_state) distinct from
existing checkHealth() boolean helper
- Create retryWithBackoff() pure helper in src/lib/server/retry.ts with
exponential backoff + jitter and onAttempt callback — no persistence owned
- Tests: retry column read/write/reset, getHealth() smoke tests,
retryWithBackoff() edge cases (success, failure, backoff timing, onAttempt)
Giancarmine Salucci
9962a0fc0f