docs: update Firebase Hosting caching examples

[kevmoo]

Updates the Firebase Hosting caching guidance in the Web FAQ (sites/docs/src/content/platform-integration/web/faq.md) and adds a 404.html negative-cache rule to both sites/docs/firebase.json (docs.flutter.dev) and sites/www/firebase.json (flutter.dev):

• Drop no-op s-maxage on static files: On Firebase Hosting, static files are cached at the CDN edge via internal surrogate controls purged on deploy; Cache-Control governs the browser cache only.
• Revalidate all entry points and manifests ("source": "**"): Use max-age=0, must-revalidate instead of extension-only rules that previously left index.html at the default max-age=3600 (causing up to 1-hour stale shells after deploy).
• Prevent cached 404s ("source": "404.html"): Add explicit max-age=0, must-revalidate rules to the FAQ example, sites/docs/firebase.json (docs.flutter.dev), and sites/www/firebase.json (flutter.dev) so missing assets (such as /assets/*.png) do not inherit wildcard TTLs (max-age=604800 / max-age=3600) at the CDN edge.
• Guard SPA rewrites ("!(/assets/**|/canvaskit/**|/icons/**|/main.dart.*)"): Exclude asset directories and root compiled entry points (main.dart.wasm, main.dart.mjs, main.dart.js) from /index.html catch-all rewrites so missing assets and bundles return a real 404 status rather than 200 OK HTML.
• Clarify service worker behavior: Note that newer Flutter releases emit a self-cleaning stub to remove legacy service workers rather than a caching service worker.

[gemini-code-assist]

Code Review

This pull request updates the Firebase Hosting configuration and the web FAQ documentation to optimize caching headers for Flutter web applications, particularly for hashed assets and 404 pages. Feedback on these changes highlights a potential cache poisoning issue where the rewrite exclusion pattern fails to match root files like main.dart.*.js due to a trailing wildcard. Additionally, the 404.html source patterns in both the configuration and documentation are missing a leading slash, which could prevent the cache-control headers from being applied correctly.

[flutter-website-bot]

Staged preview of the updated flutter.dev site (updated for commit f91d4a3):

https://flutter-dev-230821--www-pr13909-audit-firebase-docs-u5mlpicq.web.app

[flutter-website-bot]

Staged preview of the updated docs.flutter.dev site (updated for commit f91d4a3):

https://flutter-docs-prod--docs-pr13909-audit-firebase-docs-cktehg15.web.app

[kevmoo]

/gemini review

[gemini-code-assist]

Code Review

This pull request updates the Firebase Hosting configuration in firebase.json and the web FAQ documentation to optimize caching behavior, prevent caching of 404 responses, and clarify service worker behavior. Feedback on these changes suggests using a leading slash for the 404.html source pattern in firebase.json for consistency, and refining the cache-control configuration in the FAQ documentation to target only entry points and compiled code instead of all assets (**) to avoid performance degradation.

[gemini-code-assist]

Code Review

This pull request updates the Firebase Hosting configuration and documentation to ensure proper caching behavior and prevent the caching of missing assets. Specifically, it sets Cache-Control to max-age=0, must-revalidate for all files and the 404.html page, and adds rewrite exclusions for SPA routing. The review feedback suggests using a leading slash for the 404.html source pattern (i.e., /404.html) in both configuration files and the documentation to precisely target the root 404 page. Additionally, for the documentation example, it is recommended to exclude critical root files like flutter_bootstrap.js, flutter.js, and manifest.json from the SPA rewrite rule to avoid syntax errors when these files are missing.

[sfshaza2]

lgtm. @kevmoo, I leave it to you to decide how to handle the bot's comments. But I'm approving, just to expedite...