fix: let useConfig() inside UI components take precedence upon client-side navigation (vikejs/vike#3525)

[brillout]

Fixes the bug reported at vikejs/vike#3525.

Bug

Upon client-side navigation, a title set by useConfig() (or <Config>) inside a UI component briefly showed up, and then got overwritten by the title set by +data() (via useConfig()) or by +title.

Cause: useConfig-client.ts checked '_headAlreadySet' in pageContext instead of the flag's value. Since onRenderClient() always sets pageContext._headAlreadySet (to false upon client-side navigation), components always wrote to document.title directly while rendering. Then, after await renderPromise, onRenderClient() applied pageContext._configViaHook (values from +data()) or pageContext.config.title, overwriting the component's value.

Fix

• useConfig-client.ts checks !pageContext._headAlreadySet (like useConfig-server.ts and vike-vue do). While the page renders during client-side navigation, component values are now stored in pageContext._configViaHook and applied by onRenderClient(). They're stored after the values set by Vike hooks, so they take precedence, which matches SSR:
  1. useConfig() inside UI components
  2. useConfig() inside Vike hooks
  3. page settings
  4. global settings
• The client-side setPageContextConfigViaHook() skips undefined values, like the server-side version does. Otherwise config({ title: maybeUndefined }) in a component would now wipe the title set by +data().

Second fix: pageContext.config.stream mutated between requests

The new test surfaced an unrelated bug that the preview test +react.{server.client}.js had only passed by luck. resolveStreamSetting() called stream?.reverse(), which reverses the shared pageContext.config.stream array in place. In production, the precedence of +stream values therefore flips on every request: the landing page of examples/full (stream: false, while the global config has stream: true) was streamed on every other request. Fixed by copying before reversing, as getHeadSetting() already does. This is a separate commit.

Tests (examples/full)

• /images: <Image> now sets <Config title>, and a new +data() sets a title via useConfig(). Tests check that the component's title wins in the HTML, after hydration, and after client-side navigation. They also check that the title doesn't leak to the next page.
• +react.{server.client}.js now runs twice in a row, so it deterministically catches the stream mutation.
• Without the fixes, useConfig() in UI components upon client-side navigation fails with expected 'Images' to equal 'Image created by Romuald Brillout'. +react.{server.client}.js (request 1) fails in preview.
• Locally: all e2e tests pass (all examples, dev and preview), as do test:types, test:units and format:check.

Related PRs

• fix: let useConfig() inside UI components take precedence upon client-side navigation (vikejs/vike#3525) vike-solid#251: same bug, fixed there too
• test: useConfig() inside UI components takes precedence upon client-side navigation (vikejs/vike#3525) vike-vue#239: vike-vue already behaves correctly; adds the same test
• docs: useConfig() inside UI components takes precedence over useConfig() inside Vike hooks (#3525) vike#3526: docs, updates the precedence list

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