test(register-hook): take ports from the kernel instead of picking one at random

[bompus]

Two register-hook tests picked a random port in 20000-40000 and started a server there. A busy port failed the run with EADDRINUSE, which happened once on PR #128's first CI run (the rerun passed).

Those two tests now bind port 0 and read the assigned port. The test that must start its server after a first failed attempt asks the kernel for a free port before it starts.

Checked: bun test test/register-hook.test.js three times (28 pass each) and bun run check.

Summary by CodeRabbit

• Tests
  • Updated test server setup to use operating-system-assigned ports, reducing reliance on randomly selected ports.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Repository YAML (base), Organization UI (inherited)
• Review profile: CHILL
• Plan: Advanced
• Run ID: 316c89ac-4f86-4c40-a820-1b94984e03e4

---

📥 Commits

Reviewing files that changed from the base of the PR and between 5356317 and 21e46ec.

---

📒 Files selected for processing (1)

• test/register-hook.test.js

---

Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 1 remain after this review.

---

---

📝 Walkthrough

Walkthrough

The register-hook tests now obtain ports from the operating system for the retry, headless, and session-start test cases.

Changes

Test port allocation

Layer / File(s)	Summary
Port setup in register-hook tests test/register-hook.test.js	A new freePort() helper starts a temporary server on port 0, stops it, and returns its assigned port. The retry test uses that port. The headless and session-start tests start servers on port 0 and use each running server’s assigned port.

---

Priority: ⬇️ Low

Merge Risk: ⚪ Minimal · up to 21e46

The port-allocation changes do not introduce an actionable test failure: the retry test retains a pre-existing collision window, while the other changed tests use their servers’ assigned ports and clean up. No merge-blocking risk remains.

Pre-merge checks | 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: tests now obtain ports from the kernel instead of selecting random ports.
Description check		The description explains the failure cause, the implementation change, and the validation performed. The changelog requirement is not applicable because this pull request changes tests only.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Suppressions Explained		PASS. The pull request changes only test/register-hook.test.js. Added lines define freePort() and replace random port selection with kernel-assigned ports. No lint, type-check, formatter, or confi…
Interface Changes Documented		The pull request changes only test/register-hook.test.js. It adds freePort() and changes test server ports from random values to kernel-assigned ports. It does not add, remove, or rename an MCP to…

---

✨ Finishing Touches

📝 Generate docstrings

• Commit to this branch
• Create a new PR

---

---

🧪 Generate unit tests (beta)

• Commit to this branch
• Create a new PR

---

• Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

---

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