fix(opencode): wait for shell output capture

[MaartenBaert]

Issue for this PR

Closes#36795

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Retains and joins the shell output-capture fiber after the process closes or is terminated. This prevents scope cleanup from interrupting output capture before the result is constructed.

How did you verify your code works?

I can't reliably reproduce the issue so I'm not sure whether this actually fixes it. I just ran the local tests to catch obvious regressions.

Screenshots / recordings

N/A

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, here are potentially related PRs that address similar shell output issues:

Related PRs:

1. fix: normalize carriage-return shell output #36684 - fix: normalize carriage-return shell output

   • Related to shell output handling and formatting

2. fix: prevent UTF-8 corruption when stdout and stderr interleave #36665 - fix: prevent UTF-8 corruption when stdout and stderr interleave

   • Addresses shell output capture issues when stdout/stderr overlap

3. fix(core): preserve shell output tail #36554 - fix(core): preserve shell output tail

   • Directly related to preserving shell output

4. fix(shell): drain stdout before reading output to avoid "(no output)" on exit 0 #35543 - fix(shell): drain stdout before reading output to avoid "(no output)" on exit 0

   • Addresses output capture timing issues similar to the scope cleanup problem in PR fix(opencode): wait for shell output capture #36796

These PRs are all related to shell output capture and handling. PR #35543 is particularly relevant since it also deals with timing issues between process exit and output capture completion—a concern similar to what #36796 addresses with fiber joining.

[github-actions]

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[MaartenBaert]

Yes, I think this was closed incorrectly. I get that you guys are volunteers but really - this is an obvious bug, it has an obvious solution, I run into this race condition almost daily and it creates real issues, multiple people have independently reported this and submitted a PR with a fix for this ... clearly this is a real issue.