[test] Enable goleak-based goroutine leak detection for daemon tests

[kangeunchan]

Enhancement Description

Add goleak-based leak detection to daemon/service tests to prevent resource leaks from silently shipping.

Background

Daemon/controller/runtime code is concurrency-heavy. Without leak detection, tests may pass while leaking goroutines, masking production resource issues.

Scope

Add goleak to TestMain for priority packages

• Files: internal/daemon/controller/**_test.go
• Files: internal/daemon/server/**_test.go
• Files: internal/daemon/runtime/**_test.go

Expand gradually to other packages

• Files: internal/** (as needed)

Document known safe leaks with explicit ignores

• Files: affected TestMain implementations

Non-Goals

• Fixing all existing leaks in the same PR (separate issues if widespread)
• Changing runtime behavior purely for test convenience
• Adding heavy integration tests

Risks and Open Questions

• Some third-party libs may spawn background goroutines; need explicit allowlist
• Risk of flaky tests if cleanup ordering is inconsistent
• Must ensure goleak is configured correctly for parallel tests

Validation Plan

Unit and Integration Checks

• go test ./... with goleak enabled
• Ensure tests clean up goroutines by stopping servers/controllers properly

End-to-End Checks

• Run focused daemon/controller tests repeatedly to ensure no flakiness
• Validate CI consistently detects introduced leaks (intentional leak test)

Evidence Required in Issue Updates

• Test output showing goleak active
• List of allowed leaks (if any) with justification
• CI evidence catching an intentional leak (optional)

Acceptance Criteria

• Goleak enabled for priority packages
• Tests fail on new goroutine leaks
• Known safe leaks are explicitly ignored with documented reasons
• CI consistently runs leak checks

Deliverables

• PR adding goleak harness and updating affected tests
• Notes listing any temporary allowlisted leaks

[kangeunchan]

pull request: #127