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feat(chat): load older messages on scroll-to-top (history pagination) (v1.11.0+15)

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Repository keeps one live Timeline per room and re-yields on its
onUpdate callback (fires for both live events AND requestHistory),
not just onSync which never fires for pagination. loadMoreMessages
now paginates that same instance; added canLoadMore.

Timeline widget requests older history when scrolled within 400px of
the oldest end, guarded against re-entry, with a top loading spinner.

Verified: widget test drives a drag-to-top and asserts loadMoreMessages
fires; live smoke test confirms the onUpdate delivery path (reused by
history) still shows new messages after the refactor.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
help4bis
2026-07-04 08:44:38 +10:00
parent f9c21fddc4
commit e4aa5277d7
6 changed files with 194 additions and 17 deletions
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help4bis-claude-notes/decisions.md
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@@ -123,3 +123,13 @@
- Scroll-to-latest: the Flutter CanvasKit surface would NOT accept synthetic scroll input from Playwright (mouse wheel and drag both no-op on the canvas; input field steals focus). Verified instead with a deterministic widget test (test/scroll_to_latest_test.dart): 40 messages, starts at offset 0, drag up → offset > 400 + button appears, tap → offset back to 0. Passes.
- **Note for future:** getTimeline() only yields the ~10-event sync window and there is no scroll-back history pagination, so on a normal phone the timeline rarely exceeds ~1 screen and the jump button seldom shows in practice. Wiring requestHistory() on near-top scroll would make both the button and long-scrollback genuinely useful. Flagged, not built.
- **Status:** built + deployed app2.m8chat.au v1.10.0+14 (backup pre1100 tarball). Analyze clean, 4 tests pass.
### 2026-07-04 08:50 — Scroll-back history pagination (v1.11.0+15)
- **What:** wired requestHistory() so older messages load as you scroll toward the top. Completes the scroll-to-latest feature (previously the timeline only ever held the ~10-event sync window).
- **Repository (chat_repository.dart v1.5.0):** now keeps one live Timeline per room in `_timelines` map. watchTimeline creates it with an onUpdate callback that drives a StreamController signal, re-yielding the mapped list on BOTH live events and history pagination (the old code only re-yielded on onSync, which does NOT fire for requestHistory). loadMoreMessages paginates that stored instance (old code called requestHistory on a throwaway getTimeline() — wrong instance). Added canLoadMore(roomId) → timeline.canRequestHistory. Timeline cancelled + removed in the stream's finally.
- **UI (chat_screen.dart v1.7.0):** _TimelineState._onScroll detects near-top (reverse list: pixels >= maxScrollExtent - 400) and calls _loadOlder, guarded by _loadingMore + canLoadMore. Top-centre spinner while loading. Prepended older content grows maxScrollExtent while pixels stays put, so the viewport stays anchored and you move out of the trigger band (no infinite loop).
- **Verified:**
- Widget test test/history_pagination_test.dart: 40 msgs, fake repo, drag to top → loadMoreMessages called (with offset/override assertions). Passes. 5 tests total green.
- Live smoke test on production: room displays the synced window correctly after the refactor, and a newly-sent message appears at the bottom — proving the onUpdate→remap→display path (which history reuses) works.
- NOT screenshot-verified: older messages (1-5) materialising on scroll-to-top, because the CanvasKit surface rejects synthetic scroll in headless Chromium. Trigger (widget test) + delivery path (live message) are both proven; the SDK calls onUpdate after requestHistory (timeline.dart:115), same path.
- **Status:** built + deployed app2.m8chat.au v1.11.0+15 (backup pre1110 tarball). Analyze clean, 5 tests pass.