fix(chat): kick load-older from items effect when viewport cannot scroll

[vellum-apollo-bot]

Problem

A user reported the chat transcript stuck at the top of a short conversation with no way to load older history. Captured via window._vellumDebug.chat.getScrollState():

{
  "scrollTop": 0,
  "scrollHeight": 1370,
  "clientHeight": 1370,
  "distanceFromBottom": 0,
  "distanceFromTop": 0,
  "isPinnedToLatest": true,
  "showScrollToLatest": false,
  "hasMore": true,
  "isLoadingOlder": false,
  "itemCount": 2,
  "shouldLoadOlder": true,
  "diagnosis": "NEAR TOP (distanceFromTop=0px) and shouldLoadOlder=true but NOT loading — scroll handler may be stuck. itemCount=2"
}

scrollHeight === clientHeight is the smoking gun: the user cannot scroll because the content doesn't overflow the viewport.

Root Cause

use-transcript-scroll.ts has two places that read scroll metrics and classify position:

1. handleScroll — fires on user scroll events. Acts on every classification field including shouldLoadOlder.
2. The items-change useLayoutEffect — runs after every items render. Acts on isPinned and showScrollToLatest, but silently discards shouldLoadOlder.

When initial layout puts scrollHeight === clientHeight:

• No scroll event will ever fire (nothing to scroll).
• handleScroll never runs.
• onLoadOlder() is never called.
• The transcript sits stuck with hasMore=true && shouldLoadOlder=true forever.

The debug API's diagnosis ("scroll handler may be stuck") was a red herring — the handler isn't stuck, it just has nothing to fire on.

Fix

The items effect now also acts on classification.shouldLoadOlder, mirroring the scroll handler's anchor-save + onLoadOlder() pattern.

Anchor handling differs by context:

• Inside the auto-pin window (conversation switch / "Go to Newest" / user submit): skip the anchor save. The content resize observer is about to re-pin to latest after the prepend lands, and a saved anchor would otherwise restore scrollTop to where the old first-item used to be, fighting auto-pin.
• Outside the window: save the anchor exactly like handleScroll does, so the reader's row stays visually stable across the prepend.

The cascade self-terminates without extra gating: classification.shouldLoadOlder already requires hasMore && !isLoadingOlder && hasConversation. Once any of those flips false (history exhausted, request in flight, or viewport finally overflows the 200 px threshold), the kick stops.

Tests

Adds 5 regression tests in a new integration — items-effect dispatch on underfilled viewport describe block, locking in:

• The exact bug-report metrics classify as shouldLoadOlder=true.
• Items-effect-style dispatch fires onLoadOlder when classify says so.
• The dispatch is correctly gated by isLoadingOlder, hasMore, and viewport overflow — so the cascade terminates cleanly in every termination scenario.

33 pass (file)
123 pass across 8 adjacent test files

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Use current loading flags before chaining underfilled loads

This new items-effect load kick can stall after the first page because it relies on classification computed from latestRef.current (which is only refreshed in a later useEffect). In the common sequence isLoadingOlder: false -> true -> false while prepended items arrive, the layout effect on the prepend render still sees the previous isLoadingOlder=true snapshot, so shouldLoadOlder is false and no second kick fires even if the viewport is still unscrollable and hasMore remains true. That leaves the transcript stuck again for conversations that need multiple older pages to overflow.

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[vellum-apollo-bot]

Good catch — addressed in e021b2c.

The items effect now reads hasMore, isLoadingOlder, conversationKey, items, and onLoadOlder from the closure instead of latestRef.current, and those flags are in the dep array. The stale-snapshot window you described (the prepend render runs the layout effect before the latestRef-refreshing useEffect fires) was a real bug — confirmed by tracing the false → true → false sequence.

Added a regression test (chain-load: false→true→false sequence kicks again when still underfilled) that walks the three-step sequence and asserts a second kick fires on step 3 when the viewport is still underfilled. Would have caught this exact issue if the dispatch read from a stale ref.