Replace the existing auto-destroy TTL behavior with auto-pause: when a
sandbox exceeds its timeout_sec of inactivity, the TTL reaper now pauses
it (snapshot + teardown) instead of destroying it, preserving the ability
to resume later.
Key changes:
- TTL reaper calls Pause instead of Destroy, with fallback to Destroy if
pause fails (e.g. Firecracker process already gone)
- New PingSandbox RPC resets the in-memory LastActiveAt timer
- New POST /v1/sandboxes/{id}/ping REST endpoint resets both agent memory
and DB last_active_at
- ListSandboxes RPC now includes auto_paused_sandbox_ids so the reconciler
can distinguish auto-paused sandboxes from crashed ones in a single call
- Reconciler polls every 5s (was 30s) and marks auto-paused as "paused"
vs orphaned as "stopped"
- Resume RPC accepts timeout_sec from DB so TTL survives pause/resume cycles
- Reaper checks every 2s (was 10s) and uses a detached context to avoid
incomplete pauses on app shutdown
- Default timeout_sec changed from 300 to 0 (no auto-pause unless requested)
- REST API (chi router): sandbox CRUD, exec, pause/resume, file write/read
- PostgreSQL persistence via pgx/v5 + sqlc (sandboxes table with goose migration)
- Connect RPC client to host agent for all VM operations
- Reconciler syncs host agent state with DB every 30s (detects TTL-reaped sandboxes)
- OpenAPI 3.1 spec served at /openapi.yaml, Swagger UI at /docs
- Added WriteFile/ReadFile RPCs to hostagent proto and implementations
- File upload via multipart form, download via JSON body POST
- sandbox_id propagated from control plane to host agent on create
