fix: race condition in resolvedPathname

[ascorbic]

Changes

Fixes a race condition in the dev server that could cause TypeError: Missing parameter errors when handling concurrent requests to dynamic routes.

The resolvedPathname was stored as shared instance state on AstroServerApp and DevApp, so concurrent requests could overwrite each other's pathname, causing a mismatch between the matched route and the pathname used to extract params.

This PR changes it to use a local variable per-request.

Claude was involved in the diagnosis of this bug and the creaiton of the fix.

Testing

Added a test

Docs

[changeset-bot]

🦋 Changeset detected

Latest commit: 4092385

The changes in this PR will be included in the next version bump.

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[codspeed-hq]

Merging this PR will improve performance by 12.16%

⚡ 1 improved benchmark
✅ 8 untouched benchmarks

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	Build: hybrid site (static + server)	8.6 s	7.7 s	+12.16%

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_{Comparing resolve-path-race (4092385) with main (6c60b05)¹}

Footnotes

1. No successful run was found on main (4c9f918) during the generation of this report, so 6c60b05 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩