[niteshseram]

In-app navigation can trigger a full page reload when a shared cache returns HTML instead of page data.

For example, opening /blog directly returns HTML. Following an in-app link to /blog requests the same URL with X-VoidPages: true, expecting JSON. If a cache returns the earlier HTML response, Void falls back to a full page load.

Cause

HTML responses were missing Vary: X-VoidPages, which tells caches that requests with and without this header receive different responses.

JSON and streamed NDJSON responses already included it, but HTML and streamed HTML did not.

Fix

Move the existing Vary handling to a shared location so all four response formats include the header. Also cover pages rendered after an action.

Preserve existing Vary values without adding duplicates, and respect Vary: *. Island pages remain unchanged because they always return HTML.

[cpojer]

Thanks for the fix!