Smooth scrolls toward the bottom (new-message arrival in Effect A and the
Jump-to-Present click) animate scrollTop over many frames. Each intermediate
handleScroll measurement saw a large distanceFromBottom and flipped
isAtBottomRef to false, closing the Effect B/C gates. Lazy media (avatars,
embeds, Spotify thumbs) finishing mid-animation grew scrollHeight while the
gate was closed, so the smooth scroll landed at its originally-computed
target — leaving the user above the new bottom by ~the height of what loaded.
Fix: typed smoothScrollIntentRef ('bottom' | 'message' | null) with an 800ms
deadline. handleScroll suppresses the at-bottom flip while intent is 'bottom'
and the user hasn't wheeled past the 5000px nearBottom threshold. Effect D
fires a final defensive instant pin via native scrollend (Chrome 114+,
Safari 18+) or a setTimeout(800) fallback. 'message' intent (jump-to-message
from search) does NOT suppress — the gate flips honestly so the user is left
at the targeted message.
Verified live on nova.ddns.net Orbit → general: Jump-to-Present
lands flush at bottom; new Spotify-link messages stay at bottom as embeds
arrive via WS. docs/systems/message-list.md updated.
Final-review reviewer flagged two minor staleness items:
- embeds.md §10 ImageEmbed bullets still described the pre-Task-1
shape (no wrapper, no aspect-ratio). Replaced with the actual
current shape, with an explicit pointer to the Dimension
reservation contract section that explains why the dims-null
branch deliberately has no fallback.
- message-list.md said VideoEmbed uses "padding-bottom" without
noting the direct-video branch uses aspectRatio. Now describes
both branches explicitly.
No code changes; both are documentation-only touch-ups.
Reviewer caught two small gaps after Task 3:
- Effect A's smooth-scroll path on new messages is intentionally NOT
instrumented with the sentinel (the animation lands asynchronously
across frames; no intermediate scrollTop is worth pinning to). The
doc now records this so the reader's intuition matches the code.
- The sentinel-branch comment in MessageList.tsx pointed at "spec §2",
which is the planning doc rather than the durable subsystem spec.
Pointed at docs/systems/message-list.md instead.
Jannis Braun