Bound sandbox-gh-wrapper.cjs's stdin read so it can't hang forever

[nananek]

Summary

• Reported from real use in another project's sandboxed session: gh pr create --base develop --title "..." --body "$(cat <<'BODY' ...multi-line markdown... BODY)" hung inside a ccserver sandbox. Switching to --body-file <path> worked around it.
• Investigated sandbox-gh-wrapper.cjs's readStdin() (added in Scope gh CLI through the git broker instead of disabling it #5) and found a real, independent bug: it has no timeout at all and relies entirely on process.stdin.isTTY to decide whether to skip reading. That's not a hard guarantee -- whatever invokes gh inside the sandbox may hand this process a non-TTY stdin (e.g. an fd shared with a longer-lived shell/pty) that was never going to send EOF on its own, and the vast majority of gh invocations don't read stdin at all (title/body/etc. come in as flags).
• Note: this may or may not be the exact root cause of the reported hang (switching to --body-file should still go through the same unconditional readStdin() call, which is a bit inconsistent with that being the fix that worked -- the original hang could equally have been a Bash-tool/pty issue with typing a large heredoc, unrelated to this code). Fixing this regardless since it's a real latent hang risk in code I own here.

Fix

readStdin() now:

• gives up after 200ms if nothing arrives at all (the common case: no stdin intended), instead of blocking forever
• once real data starts flowing, allows a generous-but-bounded 2s inactivity window to finish, rather than waiting indefinitely for the stream to close

Test plan

• npm test -- 66 tests passing (63 existing + 3 new)
• New server/ws/sandbox-gh-wrapper.test.js: spawns the real wrapper against a real broker + fake gh, with stdin left open and never written to -- completes in ~300ms instead of hanging (this is the exact regression scenario)
• Same test also covers stdin closed immediately with no data, and real piped content (--body-file -) still being forwarded correctly -- the timeout doesn't break legitimate piped input

🤖 Generated with Claude Code

https://claude.ai/code/session_01YNFA5BLgmig7RswZypScjX