fix(cli): honor port 0 in checkPortAvailable

[ChunkyMonkey11]

Summary

This PR fixes a bug in CLI preflight port handling by preserving port = 0 instead of incorrectly defaulting it to 18789.
In Node.js networking, 0 is a valid value that asks the OS to assign a temporary available port.
The fix changes null/default logic to keep valid explicit inputs while still applying the default when no port is provided.

Changes

• Updated checkPortAvailable in src/lib/preflight.ts:
  • Before: const p = port || 18789;
  • After: const p = port ?? 18789;
• This preserves:
  • undefined/null -> default 18789
  • 0 -> stays 0 (valid OS-assigned temporary available port request)
  • any explicit non-null value -> unchanged
• No CLI command surface changes.
• No docs changes required.

Type of Change

• Code change for a new feature, bug fix, or refactor.
• Code change with doc updates.
• Doc only. Prose changes without code sample modifications.
• Doc only. Includes code sample changes.

Testing

• npx prek run --all-files passes (or equivalently make check).
• npm test passes.
• make docs builds without warnings. (for doc-only changes)

Checklist

General

• I have read and followed the contributing guide.
• I have read and followed the style guide. (for doc-only changes)

Code Changes

• Formatters applied — npx prek run --all-files auto-fixes formatting (or make format for targeted runs).
• Tests added or updated for new or changed behavior.
• No secrets, API keys, or credentials committed.
• Doc pages updated for any user-facing behavior changes (new commands, changed defaults, new features, bug fixes that contradict existing docs).

Doc Changes

• Follows the style guide. Try running the update-docs agent skill to draft changes while complying with the style guide. For example, prompt your agent with "/update-docs catch up the docs for the new changes I made in this PR."
• New pages include SPDX license header and frontmatter, if creating a new page.
• Cross-references and links verified.

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Signed-off-by: Revant Patel revant.h.patel@gmail.com

Summary by CodeRabbit

• Bug Fixes
  • Corrected port configuration handling to properly respect explicitly set values instead of defaulting to the standard port.

[coderabbitai]

📝 Walkthrough

Walkthrough

The checkPortAvailable() function in src/lib/preflight.ts was updated to use nullish-coalescing (??) instead of logical-or (||) when defaulting the port parameter. This preserves an explicitly provided port value of 0 instead of replacing it with the default port 18789.

Changes

Cohort / File(s)	Summary
Port defaulting logic src/lib/preflight.ts	Changed port parameter handling from logical-or to nullish-coalescing operator to preserve explicit port value of 0 instead of replacing it with the default.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

A rabbit hops through code so small,
One operator fixes all!
From \|\| to ?? it goes,
Port zero now survives the flows! 🐰✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and concisely summarizes the main change: using nullish coalescing to preserve port 0 instead of replacing it with the default 18789.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[ChunkyMonkey11]

@cv I fixed the PR issue and this should be good now. Updated the PR body sign-off format, and checks are now passing on my side (npx prek run --all-files, npm test, make docs). Please take another look when you have a moment.