fix: sync stderr after command completion to fix CI flake#95
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Adds a __HERMES_STDBUF_N__ marker written to stderr after each user command in the execution frame. Run() spins until the marker appears in stderrBuf before reading the stderr delta. This fixes a race where the END marker on stdout signals completion before the stderr pipe has finished delivering the command's output. On CI (no TTY), bash -i echoes the input frame to stderr, which arrives via a separate pipe — the sync marker ensures captureStderr has flushed everything before Run reads the buffer. Fixes TestRunStderrScopedPerCommand flake on GitHub Actions runners. Signed-off-by: Blasius Patrick <blasius.patrick@gmail.com>
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Problem
TestRunStderrScopedPerCommandflakes on GitHub Actions CI (no TTY) becausebash -iechoes the input frame to stderr while stdout/stderr are separate pipes. The END marker on stdout can signal completion before the stderr pipe has finished delivering the command's output, causing stderr from cmd1 to leak into cmd2's captured stderr.Fix
__HERMES_STDBUF_N__marker to the execution frame, written to stderr after every user commandstderrBufbefore reading the stderr deltaTesting
TestRunStderrScopedPerCommandpasses 10/10 runs locallyinternal/exec/suite passes