CSS HMR restored; CSP violations fixed; collection references validated

Patch Changes

• #17612 7133730 Thanks @thelazylamaGit! - Fixes CSS hot module replacement after navigating between pages with ClientRouter

• #17628 4ada248 Thanks @astrobot-houston! - Fixes a CSP violation when using both security.csp and experimental.clientPrerender with data-astro-prefetch links. The dynamically injected <script type="speculationrules"> now uses a static "source": "document" approach with a CSS selector, producing a deterministic payload that is hashed and included in the CSP script-src directive at build time.

• #17605 89e4647 Thanks @ashleigh-yeoman! - Fixes middleware HMR not responding to changes in imported modules. Previously, only direct edits to the middleware file would trigger a reload.

• #17582 bd2c1a5 Thanks @astrobot-houston! - Fixes a regression where content collection reference() fields silently accepted entry IDs that don't exist, such as an ID that doesn't match a loader's slugified version of it. Astro now logs an error for references that point to a missing entry after all loaders finish syncing.

• #17661 97b0cc7 Thanks @ArmandPhilippot! - Improves Markdown options documentation with links to the Markdown guide and official processors.

• #17349 4328c73 Thanks @astrobot-houston! - Fixes an issue where requests handled by the dev prerender environment (e.g. /_image with @astrojs/cloudflare's prerenderEnvironment: 'node') returned a 500 when a prerendered catch-all route existed, because non-prerendered route modules were imported in an environment where their runtime-specific APIs are unavailable

• #17603 722eed6 Thanks @astrobot-houston! - Fixes <video> and <audio> elements being non-functional after navigating via view transitions (<ClientRouter />)

• #17616 3a890d2 Thanks @lazerg! - Fixes experimental.incrementalBuild re-rendering unchanged routes that import more than one asset. The route's dependency hash depended on the order the assets finished building, so two builds of identical sources could produce different hashes. The hash is now based on the file name each asset resolves to.

• #17547 fba468c Thanks @dmgawel! - Improves getCollection() and getEntry() performance for entries without local image references

• #17602 16e0d9d Thanks @astrobot-houston! - Fixes a build error caused by hash collisions in generated content collection image import identifiers