fix(frames): drain records when a fragment reveals into an adopted region (#2978 follow-up)

[brenelz]

Follow-up to #2978. A <Loading> inside a server component now reveals correctly, but the first refetch after that reveal crashes the page:

TypeError: Cannot read properties of undefined (reading 'text2')
[REACTIVITY_HALTED] An uncaught error halted the reactive system.

Repro

examples/playground, a server component whose slot is invoked inside its own <Loading>:

export const getServerComp = async (count: number) => {
  "use server";
  return (props: { text: (p: { text2: number }) => any }) => {
    const test = createMemo(async () => {
      await new Promise(r => setTimeout(r, 1000));
      return Math.random();
    });
    return (
      <div>
        <h1>Playground2</h1>
        <Loading fallback={<div>loading new value…</div>}>
          <props.text text2={test()} />
        </Loading>
      </div>
    );
  };
};

Load the page, wait for the value, click a button that switches the call's args. The reactive system halts.

Root cause: the delivery disarms its own pickup

A slot invoked inside a server <Loading> ships its sc:slot: args record with the deferred fragment — about the async's own delay after the boundary adopted, long after adoptBoundary's drain ran. (Confirmed on the wire: in the document the record's script sits at byte 2708, its $df(...) reveal at 2785 — the record is present and unread.)

Nothing ever picks it up:

• drainRecords() runs at adopt time — too early, the fragment hasn't streamed.
• The only other re-drain is inside the Server component slot callback is invoked without props during hydration #2968 classification defer loop, which arms on _$HY.fr.pending().
• Post-<Loading> inside a server component never reveals on document SSR — held-fragment policy and frames adoption deadlock (no claimant path) #2978, a revealed fragment is no longer pending — so the very reveal that delivers the record is what flips recordsPending() false.

The event that makes the record available is the event that disarms the mechanism that would fetch it. The record strands in _$HY.r for the life of the page, and the next full sync — a refetch's stream apply — finds a recordless occurrence, classifies the region's render prop as a direct-insert value, and hands it to insert as a zero-arg accessor. props.text2 on undefined halts everything.

Fix

The reveal callback already exists in adoptBoundary for the nested-placeholder cascade; it now drains there too. A revealed fragment brings its occurrences' records with it, so the reveal is exactly the right moment. drainRecords is re-drainable by design (each key applies once), so this is a cheap no-op once caught up. The subscription is also no longer gated on fr.claim — the drain is useful whether or not the ledger exposes claiming.

Verification

• New test in frames-adopted-region-fragments.spec.tsx, red without the fix and green with it: a record delivered alongside its fragment reaches the frame, so the region's render prop keeps its args.
• @solidjs/web suite: 400/400. dom-expressions runtime suite: 1114/1114.
• Live playground: before, every increment halted the page; after, five consecutive increments run clean.

Note two things this does not fix, both filed/PR'd separately:

1. The render prop's async arg (text2={test()}) is the DR-2 value tier, and the frame-client mishandles it on repeat responses — fix(frames): wait for a slot record's data refs; async refs compare by identity ryansolid/dom-expressions#565.
2. The document's occurrence counter drifts across render attempts (doc ships text#1, a fresh stream ships text#0), so the first switch re-mounts instead of updating and blanks for the server's wait. $key on the slot avoids it entirely; the underlying determinism question looks like a design call.

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: db8cdd3

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 10 packages

Name	Type
@solidjs/web	Patch
@solidjs/element	Patch
@solidjs/h	Patch
@solidjs/html	Patch
test-integration	Patch
chat-example	Patch
solid-js	Patch
babel-preset-solid	Patch
@solidjs/universal	Patch
@solidjs/signals	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR