fix: prevent hang on shutdown

[dobrac]

Try to prevent hang here:

2026-01-27T10:10:44.082Z  INFO  Shutdown signal received  {"service": "template-manager", "internal": true, "pid": 1943188}
2026-01-27T10:10:44.083Z  INFO  Service status changed  {"service": "template-manager", "internal": true, "pid": 1943188, "status": "Draining"}
2026-01-27T10:10:59.084Z  INFO  Waiting for all build jobs to finish  {"service": "template-manager", "internal": true, "pid": 1943188}
2026-01-27T10:10:59.084Z  INFO  Waiting for consumers to check build status  {"service": "template-manager", "internal": true, "pid": 1943188}
2026-01-27T10:11:14.085Z  INFO  Template build queue cleaned  {"service": "template-manager", "internal": true, "pid": 1943188}
2026-01-27T10:11:14.085Z  INFO  closing  {"service": "template-manager", "internal": true, "pid": 1943188, "service": "grpc server", "forced": false}
2026-01-27T10:11:14.085Z  INFO  Shutting down grpc server  {"service": "template-manager", "internal": true, "pid": 1943188}
2026-01-27T10:11:14.088Z  INFO  closing  {"service": "template-manager", "internal": true, "pid": 1943188, "service": "http server", "forced": false}
2026-01-27T10:11:14.089Z  INFO  closing  {"service": "template-manager", "internal": true, "pid": 1943188, "service": "cmux server", "forced": false}
2026-01-27T10:11:14.089Z  INFO  Shutting down cmux server  {"service": "template-manager", "internal": true, "pid": 1943188}
2026-01-27T10:11:14.089Z  INFO  closing  {"service": "template-manager", "internal": true, "pid": 1943188, "service": "template server", "forced": false}
2026-01-27T10:11:14.089Z  INFO  closing  {"service": "template-manager", "internal": true, "pid": 1943188, "service": "hyperloop server", "forced": false}
2026-01-27T10:11:14.090Z  INFO  closing  {"service": "template-manager", "internal": true, "pid": 1943188, "service": "template manager sandbox logger", "forced": false}
2026-01-27T10:11:14.090Z  INFO  closing  {"service": "template-manager", "internal": true, "pid": 1943188, "service": "network pool", "forced": false}
2026-01-27T10:11:14.090Z  INFO  Closing network pool  {"service": "template-manager", "internal": true, "pid": 1943188}
2026-01-27T10:11:21.702Z  INFO  closing  {"service": "template-manager", "internal": true, "pid": 1943188, "service": "device pool", "forced": false}
2026-01-27T10:11:21.702Z  INFO  Closing device pool  {"service": "template-manager", "internal": true, "pid": 1943188, "used_slots": 65}
2026-01-27T10:11:21.703Z  INFO  closing  {"service": "template-manager", "internal": true, "pid": 1943188, "service": "tcp egress firewall", "forced": false}
2026-01-27T10:11:21.703Z  INFO  closing  {"service": "template-manager", "internal": true, "pid": 1943188, "service": "sandbox proxy", "forced": false}
2026-01-27T10:11:21.704Z  INFO  closing  {"service": "template-manager", "internal": true, "pid": 1943188, "service": "sandbox observer", "forced": false}

Note

Improves shutdown reliability and observability.

• Adds 10s timeout when shutting down sandbox metrics meter exporter to avoid hangs
• Tracks active template builds using an atomic counter; increments/decrements around build goroutines and logs active_builds during Wait
• Logs start of drain phase with sandbox_count for better shutdown diagnostics

^{Written by Cursor Bugbot for commit d5cc2b6. This will update automatically on new commits. Configure here.}