test: let the OS choose the vitest browser fixture's server port

[wan9chi]

Motivation

vitest_browser_cache::vitest_browser_caches_inputs_and_restores_outputs fails intermittently on Windows runners in the Test (windows-ignored) job:

Error: listen EACCES: permission denied ::1:63315

63315 is the fixed default port for Vitest browser mode's server. Windows reserves dynamic port ranges (Hyper-V/WinNAT excluded port ranges), and listening on a reserved port fails with EACCES. Vite only tries another port on EADDRINUSE, so the run fails, dist/result.json is never written, and the snapshot diverges. It depends on which runner the job lands on: it failed on #824 and #825 and passed on other runs of the same code.

Changes

The fixture's browser server now listens on port 0, so the OS chooses a free port. Vite supports server.listen(0) directly, but the config can't request it the normal way:

• test.api: { port: 0 }: Vitest only copies api.port when it is truthy, so 0 falls back to 63315.
• Setting test.api at all, even with a concrete port, adds an API started at http://localhost:<port>/ banner line that would change the snapshot. test.browser.api prints a deprecation warning in Vitest 5.

Instead, a small enforce: 'post' plugin sets test.api.port = 0 after Vitest resolves test.api. The banner stays unchanged, and the snapshot is identical.

🤖 Generated with Claude Code

[github-actions]

fspy benchmark

linux

dynamic/launch             change  +1.81%  [-13.90% .. +20.58%]  overhead   +58.39%
dynamic/access             change  -0.35%  [-15.53% .. +72.88%]  overhead   +11.12%
dynamic/access-relative    change  -0.39%  [ -6.64% ..  +5.03%]  overhead   +44.51%
dynamic/access-contended   change  +1.18%  [ -4.36% ..  +5.62%]  overhead    +4.88%
static/launch              change  +6.57%  [-21.10% .. +43.68%]  overhead  +168.19%
static/access              change  -0.67%  [-18.52% .. +18.87%]  overhead  +852.64%
static/access-relative     change  -2.92%  [-10.28% ..  +5.22%]  overhead +1228.54%
static/access-contended    change  +2.79%  [ -5.63% .. +10.34%]  overhead +2220.67%

macos

dynamic/launch             change  +0.14%  [ -4.03% ..  +4.79%]  overhead  +234.18%
dynamic/access             change  -0.33%  [-56.44% .. +13.08%]  overhead    +5.47%
dynamic/access-relative    change  -0.87%  [-15.90% .. +16.35%]  overhead  +248.98%
dynamic/access-contended   change  +2.38%  [-50.83% .. +637.48%]  overhead    +2.72%

windows

dynamic/launch             change  +0.51%  [ -2.85% ..  +3.89%]  overhead   +26.13%
dynamic/access             change  +0.00%  [ -1.23% ..  +0.93%]  overhead    +1.15%
dynamic/access-relative    change  +0.19%  [ -0.92% ..  +0.96%]  overhead    +0.95%
dynamic/access-contended   change  +0.00%  [ -1.06% ..  +1.31%]  overhead    +1.31%