opencode: quote Windows spawn arguments

[Siddhesh2377]

wally opencode's Spawn has the same Windows bug the codex review (#70) found:
the _spawn* family joins argv into a command line without quoting, so a
passthrough argument containing a space arrives at opencode split in two. On
POSIX execvp passes argv verbatim, so only the Windows branch is affected.

Adds the same MSVCRT-rule quoting used in the codex fix (double the backslash
run before a quote or the closing quote; backslash-escape embedded quotes),
applied to each argument on the Windows path only. Algorithm verified against
spaces, embedded quotes, trailing backslashes, and empty; POSIX path unchanged.

Summary by CodeRabbit

• Bug Fixes
  • Improved Windows process launching when executable paths or arguments contain spaces or quotation marks.
  • Preserved arguments correctly during application startup and command execution on Windows.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: 1b105362-9636-4252-aea8-03b6a7455570

📥 Commits

Reviewing files that changed from the base of the PR and between 61191dc and c9c5ed2.

📒 Files selected for processing (1)

• src/harness/opencode.cpp

Included review availability: Your plan provides up to 4 included reviews per hour; 1 remains after this review.

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📝 Walkthrough

Walkthrough

Windows process spawning now quotes the executable and arguments according to MSVCRT rules. The POSIX spawning path remains unchanged.

Changes

Windows spawn argument handling

Layer / File(s)	Summary
Quote and pass Windows spawn arguments src/harness/opencode.cpp	Adds QuoteWindowsArg for whitespace and quote escaping. The Windows Spawn path applies it to the executable and each argument, while the POSIX path retains its existing behavior.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~15–30 minutes

Merge Risk: ⚪ Minimal · up to c9c5e

Windows passthrough arguments with spaces, quotes, trailing backslashes, or empty values are preserved when launching OpenCode, without changing POSIX behavior. No current merge-blocking risk remains.

Suggested reviewers: sanchitmonga22

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: quoting Windows spawn arguments in opencode.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

• Fix all pre-merge checks with AI

✨ Finishing Touches 💡 1

📝 Generate docstrings 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch siddhesh/opencode-win-quote

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