kubectl-ate: keep client-go unhandled-error reports off stderr

[Yiqing Wang (YQ-Wang)]

Fixes #26

• Tests pass
• Appropriate changes to documentation are included in the PR

Summary

A successful kubectl ate create actor can print this:

E0520 15:40:33.154830 3507355 portforward.go:502] "Unhandled Error" err="error copying from local connection to remote stream: ... read: connection reset by peer"

The user never asked for port-forwarding — it is an implementation detail of this plugin — so a message naming portforward.go is not something they can act on.

client-go reports problems it cannot return to a caller through utilruntime.HandleError, whose default handler writes to stderr. This replaces that handler for kubectl-ate: those reports are dropped by default and printed under a new --verbose flag. klog is deliberately left alone, so warnings a user can act on directly — a missing kubeconfig, an exec credential plugin that failed to refresh — keep reaching the terminal. That is enough because every port-forward error that reaches a user goes through HandleError, while the package's direct klog calls are all V(4) or higher.

#539 proposes removing the localhost hop that produces this particular reset. That is a ~200 line transport change for one message, though, and the next HandleError call inside client-go would read just as strangely. Handling it here covers the class and leaves #539 to be weighed on its own merits.

Notes for reviewers

• Reflector and informer errors travel through the same channel. kubectl-ate makes one-shot RPCs today, so nothing actionable is lost, but a watch-based command should revisit this.
• The flag is --verbose rather than --v=N because -v is already cobra's --version shorthand here, and this does not wire klog verbosity. Happy to match that or the server binaries' --log-level if you prefer.

Validation

go test -race -count=5 ./cmd/kubectl-ate/... and the hack/verify scripts pass, with no changes to go.mod or vendor/modules.txt. New tests assert the exact text from #26 produces no output by default and is printed under --verbose, and the flag is documented in the CLI README.

The reset in #26 is timing-dependent and did not reproduce on macOS in 1,500 invocations against a kind cluster, so I forced the same code path by pointing the forwarder at a port with nothing listening. On main:

E0725 02:52:41.650594 63626 portforward.go:522] "Unhandled Error" err="an error occurred forwarding 54823 -> 9999: ... connect: connection refused" logger="UnhandledError"
Error: failed to list atespaces: rpc error: code = Unavailable ...

With this change only the second line is printed, and --verbose restores the first. A klog.Warning raised with the quiet handler installed still reaches stderr, and normal commands and error paths are identical to main.

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