- Snapshot delete: make agent RPC failure a hard error so DB record is
not removed when files cannot be deleted from disk
- Snapshot overwrite: call agent to delete old files before removing the
DB record, preventing stale memfile.{uuid} generations from accumulating
on disk across repeated overwrites
- Sandbox destroy: only swallow CodeNotFound from the agent (sandbox
already gone / TTL-reaped); any other error now propagates to the caller
instead of being silently ignored
Moves business logic from API handlers into internal/service/ so that
both the REST API and the upcoming dashboard can share the same operations
without duplicating code. API handlers now delegate to the service layer
and only handle HTTP-specific concerns (request parsing, response formatting).
