Tests swapped the package-level newTimerFn hook while async goroutines
leaked from earlier tests (backup-cleanup and stop-command paths) were
still reading it in waitForAsyncDelay, tripping the race detector on CI.
Replace the global with a per-Agent newTimerFn seam (nil defaults to
time.NewTimer), make waitForContextDelay an Agent method, and inject the
immediate timer into the tests that previously swapped the global.
Verified with go test ./internal/dockeragent/ -race -count=20.
Contract-Neutral: test seam refactor to fix data race, no public contract delta
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
courtmanr@gmail.com
8e5ef365d4