[lbarrosby]

What this PR does / why we need it:

RunProcess wraps stdout and stderr in an io.MultiReader, so stderr is only read after stdout reaches EOF. A command that writes more than a pipe buffer (64 KiB on Linux) to stderr while stdout is still open blocks on the write, and ct hangs forever. helm install --debug, helm dependency build or kubectl logs with a chatty container can hit this.

Two more problems in the same function:

• bufio.Scanner stops at lines longer than 64 KiB. The reader goroutine then exits and closes the pipes, and the command dies with SIGPIPE (failed waiting for process: signal: broken pipe).
• cmd.Wait() can run before the goroutine has finished reading, and the os/exec docs say Wait must not be called before all reads from the pipe are done, so the end of the output can be lost.

This change passes the same writer as Stdout and Stderr, so os/exec uses one pipe for both and copies it to stdout as is. WaitDelay stops reading one second after the command exits, so background processes that inherited the pipe cannot keep ct waiting, and a failed write to stdout closes the read end so the command gets EPIPE instead of blocking. Write errors are returned.

pkg/exec/exec_test.go covers 1 MiB on stderr before stdout, a 1 MiB line, a command that leaves a background process holding the pipe (both with exit 0 and a failing exit status), and a broken stdout with 2 MiB of output. Each case runs under a timeout. go test -race ./... and golangci-lint pass.

Which issue this PR fixes: fixes #471

Special notes for your reviewer:

#471 was closed by the stale bot, but the cause is still in RunProcess.

AI disclosure: written with the help of an AI coding assistant, reviewed and tested by me.

[cpanato]

This addresses a real deadlock: the added large-stderr test times out against the original implementation, and local go test ./... passes with the fix. However, I reproduced two additional hangs introduced by the new pipe lifecycle. Please address the inline findings and add regression coverage before merging.