fix: handle URL changes before hydration starts

[brenelz]

Summary

Fixes #2313.

If the browser URL changes before the client router initializes, hydration currently tries to match the new route against the previous route’s server-rendered HTML. This can throw a hydration mismatch and leave the app blank. A query-only change can also silently reuse stale server data.

• Record the server-rendered pathname and query on the existing client entry script with data-start-url.
• Compare that URL with the current browser location in mount().
• If the path or query changed, mark hydration as done and disable queued hydration events before calling Solid’s existing client-render fallback. Late SSR fragments are discarded, and the requested route renders with fresh client data.
• Preserve normal hydration for hash-only changes.
• Include a patch changeset.

The guard handles the early URL change in the issue’s reproduction. A real link navigation while the initial route module is still loading is also covered by a control test. This works with the current Solid dependencies.

Regression coverage

The tests pin the timing by holding the client entry request, rather than sweeping machine-dependent delays:

• Pathname change before hydration.
• Pathname change while the original response is streaming.
• Query-only change while streaming, checking that the new query gets fresh data.
• Hash-only change, checking that the original DOM is hydrated rather than replaced.
• Real link navigation while the initial route module is pending.

They assert interactive content, a single layout and page, and no browser errors. The path and query cases failed before the fix; the hash-only control passed.

Verification

• Focused Playwright suite plus the existing hydration smoke test: 6 passed in standard dev and 6 passed in bundled dev.
• Production build: the four early-URL-change cases plus the hydration smoke test: 5 passed.
• pnpm --filter @solidjs/start test:ci: 114 tests passed.
• pnpm --filter @solidjs/start typecheck
• pnpm --filter @solidjs/start validate-imports
• pnpm --filter @solidjs/start build
• pnpm --filter tests build
• Formatting and git diff --check passed.

[changeset-bot]

🦋 Changeset detected

Latest commit: c3c46b0

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

This PR includes changesets to release 1 package

Name	Type
@solidjs/start	Patch

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