Reap the log aggregator's tail processes

[Sayan-]

Summary

tailFile starts tail -n +1 -F <path> and reads its stdout, but never calls Wait. When that tail exits, nothing collects its status, so it stays a zombie.

The wrapper is pid 1 in both the container (ENTRYPOINT) and the unikernel (Kraftfile cmd), so there is no other init to clean up after it. On a long-lived instance whose services restart repeatedly, these accumulate for the life of the instance and each one holds a pid slot.

A clean scan ends exactly when tail closes its stdout, which is when it has exited, so that is where the wait belongs. A scan that ends on a read error instead is a different case: bufio.Scanner also stops on ErrTooLong, and there tail is still alive, so waiting would park the goroutine forever. Kill it first in that path.

Testing

go build, go vet, gofmt and go test -race pass on server/cmd/wrapper.

No test added here. tail -F does not exit on its own and tailFile keeps no handle to the process, so there is no seam to drive it from a test without reshaping the function. The reaper PR stacked on this one carries tests that cover the same defect class directly.

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Note

Low Risk
Localized change to log tailing cleanup in the wrapper; no auth, data, or API surface impact.

Overview
tailFile in the wrapper supervisord log aggregator previously started tail -F and read lines but never Wait() on the child. Because the wrapper runs as pid 1 in container and unikernel, exited tails became zombies that could pile up when services restart.

After the scan loop, the change always **Wait()**s to reap the process. If scanner.Err() is set (e.g. a line exceeds the 1MB scanner limit while tail is still running), it **Kill()**s tail first so Wait() does not block forever.

^{Reviewed by Cursor Bugbot for commit 20a0f55. Bugbot is set up for automated code reviews on this repo. Configure here.}

[masnwilliams]

reviewed — looks good. the cleanup follows os/exec's pipe lifecycle correctly, handles scanner failure without blocking, and ensures the tail process is always reaped.