Final step of the virtualization plan. Turns the virtualized render
path on in production behind a row-count threshold, and adds regression
tests covering every gate.
- `VIRTUALIZATION_ROW_THRESHOLD = 60`. Short lists stay on the direct
render path (no wrapper, no position: absolute, no measurement
churn). Above the threshold the virtualizer takes over. Threshold is
sized so conversations under ~one session of activity don't pay the
virtualization cost; it activates once scrolling through a longer
history.
- `shouldVirtualize` now requires `renderRows.length >= threshold` in
addition to the existing opt-in and scroll-ref checks.
- `MessagesPanel` opts into virtualization for every layout it wires
(inline / sidebar / bottom-sheet). The internal threshold then
decides when to actually enable it, so callers don't need per-layout
heuristics.
- Tests: adds a new `ActivityTimeline virtualization threshold` block
covering (a) below-threshold list stays on the direct path,
(b) no viewport → direct path regardless of count, (c) above
threshold + viewport with `virtualizationEnabled` flips to the
virtualized render path (simulated by clicking "show all" past
pagination).
With this in, #70 → #74 combine to deliver:
- correct IntersectionObserver roots in scroll containers
- atomic render rows with stable keys
- windowed rendering with DOM-measured scrollMargin and measureElement
- auto-on when the cost of direct rendering actually shows up
Third step of the virtualization plan. Pure refactor — no UI change, no
virtualization yet. Prepares the timeline for row-level windowing.
- Introduces `TimelineRow`, a discriminated union of `session-separator`,
`lead-thought-group` (pinned and non-pinned), `compaction-divider`,
and `message-row`. Each row maps 1:1 to a single visual element.
- Adds a `renderRows` useMemo that walks `timelineItems` once and emits
atomic rows, hoisting session separators out of the Fragment bundle
that used to pair them with their owning item. This is the shape a
windowing layer needs: each row measurable and addressable
independently.
- Extracts a `renderTimelineRow(row)` helper that switches on `row.kind`
and returns the same JSX the previous inline render produced. Logic
per kind is identical — keys, memoization, collapse props, pinned
thought "live" semantics — so there is no visual diff.
- The render body collapses from two blocks (pinned + `.slice().map()`)
into a single `renderRows.map(renderTimelineRow)` call.
Follow-ups will virtualize `renderRows` with measured row heights and
tighten observer/animation wiring; pagination, collapse state, zebra
striping, and `groupTimelineItems` are untouched.
Second step of the virtualization plan. No virtualization yet. This PR
makes IntersectionObserver-based visibility tracking correct inside
scroll containers (sidebar, bottom-sheet), which is a prerequisite for
virtualizing the timeline.
- Introduces `TimelineViewport` — a grouped contract passed as a single
`viewport` prop on `ActivityTimeline`. Holds `scrollElementRef`,
`observerRoot`, `scrollMargin`, and `virtualizationEnabled`.
- `MessageRowWithObserver` and `LeadThoughtsGroupRow` now create their
`IntersectionObserver` with `root = observerRoot?.current ?? null`
instead of defaulting to the document viewport. Unread marking now
fires when rows enter their real scroll parent.
- `MessagesPanel` resolves the active scroll owner from `position`
(inline from parent ref, sidebar from `sidebarScrollRef`, bottom-sheet
from `bottomSheetScrollRef`) and passes it into ActivityTimeline.
- Tests: stubs `IntersectionObserver` to capture `options.root` and
asserts null when no viewport is passed, and the provided element when
`viewport.observerRoot` is set.
`scrollMargin` and `virtualizationEnabled` are included in the contract
but not consumed yet — they land in follow-up PRs (#4/#5).
- Introduced caching mechanism with expiration for message feeds to improve performance.
- Added logging for cache expiration events to aid in debugging.
- Updated MessagesPanel to reopen search bar when participant filters are active.
- Added test cases for handling tmux server errors and message panel behavior with filters.
