Select desktop backend port by sequential scan

[juliusmarminge]

So that your host is more stable across restarts when doing remote

What Changed

Why

UI Changes

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

---

Note

Medium Risk
Changes desktop backend port selection during startup, which can affect app launch reliability and port-collision behavior if the preferred range is busy. Logic is straightforward and covered by new unit tests, but it touches the bootstrap path.

Overview
Desktop startup now selects the backend port by sequentially probing from a stable preferred port (default 3773) instead of reserving a random ephemeral loopback port.

This introduces resolveDesktopBackendPort (with validation and bounded scan) plus Vitest coverage, and updates main.ts bootstrap/logging to use the new resolver.

^{Reviewed by Cursor Bugbot for commit ca8118f. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Select desktop backend port by sequential scan from port 3773

• Replaces NetService.reserveLoopbackPort with a new resolveDesktopBackendPort function in backendPort.ts that scans ports sequentially from a start port until it finds one available via canListenOnHost.
• When T3CODE_PORT is unset, the desktop app now selects a backend port by scanning from DEFAULT_DESKTOP_BACKEND_PORT (3773) on the loopback host.
• Validates startPort and maxPort inputs and throws if no available port is found within the range.
• Behavioral Change: port selection now uses the first available port starting at 3773 rather than reserving an OS-assigned loopback port.

^{Macroscope summarized ca8118f.}

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on this repository. Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 53a1d1ab-b7f7-4d38-8c24-ef8214a0da6c

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feature/desktop-backend-port-scan

---

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

[macroscopeapp]

Approvability

Verdict: Approved

This PR refactors desktop backend port selection from ephemeral reservation to predictable sequential scanning starting at port 3773. The change is self-contained, includes comprehensive unit tests, and the author has recent ownership of the affected code. Low risk runtime behavior change with clear intent.

^{You can customize Macroscope's approvability policy. Learn more.}