Andrew Clark e3d634e0bc Fix isHeadPartial when hydrating from a static fallback shell (#96400) ...

When a static fallback shell is served as-is — e.g. from a CDN in a
deployed environment — the client can't hydrate from inline Flight data;
it fetches the full RSC payload separately and reconstructs the initial
payload on the client. During that reconstruction, the head's partiality
flag was accidentally set to the head itself. Since the head is always
truthy, the head was unconditionally treated as partial.

This happens to be unobservable today: the only flows that reach the
reconstruction are fallback-shell prerenders, where the server
pessimistically marks the head partial anyway, and when Cache Components
is enabled the client ignores the per-payload flag entirely in favor of
response-level partiality. But we're about to rework the RSC response
format so that head partiality has a single, load-bearing source of
truth, so the flag needs to survive the reconstruction correctly rather
than by coincidence.

While auditing the payload consumers, I also fixed the payload shape
check in segment prefetch generation (it used `&&` where `||` was
intended, so it accepted any shape) and deleted
`should-hard-navigate.ts`, which no longer has any callers on the
client.

Adds e2e coverage asserting that metadata survives hydrating a fallback
shell page: the title is correct after hydration, the head is included
in prefetched data, and a return navigation is served entirely from the
cache that was populated during initial hydration. In deployed
environments this exercises the client resume path, which is where the
reconstruction runs.

2026-07-31 00:37:15 -04:00

..

link-accordion.tsx

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