feat(web): scroll to the matched message on a palette search hit

[xiaogwu]

Summary

Pressing Enter on a command palette content match used to open the thread at the live edge. On a long thread that lands nowhere near the text you searched for, so you have to scroll and re-read to find it. This makes the thread scroll to the matched message and flash it briefly.

The search result carried no message identity, so the first part is plumbing: OrchestrationThreadSearchMatch now carries messageId. The ranked CTE in ProjectionSnapshotQuery was already reading messages.message_id for its ROW_NUMBER tiebreaker, so this is one extra column in the result set and no new index. The field is required rather than optional, since the server is the only producer and always has the id.

On the client, a small zustand store holds one nullable reveal request with a monotonic requestId, mirroring the revealLine pattern in rightPanelStore. The monotonic id is what makes repeat requests work: searching inside the thread you are already viewing produces no route change and no other state diff, so without it the second search would be a no-op. The palette fires the request after navigate() resolves, because requesting earlier means a thread switch is still in flight and ChatView's thread-change reset would wipe the anchor out from under it.

ChatView consumes the request in one effect that sits immediately after that reset effect. Effects run in declaration order, so an earlier declaration would have its anchor cleared whenever a reveal and a thread switch land in the same commit. The effect does not add a second scroll path: it reuses the existing timeline anchor, so the matched message is pinned near the top through the same anchoredEndSpace / onAnchorReady / scrollToIndex flow the send flow already uses.

The part that took the most iteration is the scroll mode. The reveal runs under a new TimelineScrollMode, "anchoring-reveal", because none of the three existing modes work. "following-end" lets live-follow drag the view back to the bottom. "free-scrolling" fails the mode guard in onTimelineAnchorReady, so the positioning silently never runs and the thread just opens (this was the actual bug during testing). "anchoring-new-turn" would pass the guard but also pull in the streaming turn-metrics adjustments, which assume a response is arriving below the anchor. The new mode passes the anchor-ready guard, is ignored by the turn-metrics pass, suppresses the isAtEnd handler while the scroll is in flight, and hands the list back to "free-scrolling" once the anchor settles.

Two guards are worth pointing out. The effect clears positionedTimelineAnchorRef and settledTimelineAnchorRef, so revealing the same message twice re-runs the positioning instead of returning early on the "already positioned" check. And a 5s timer drops the pending anchor back to following-end if the row never resolves, which happens when the message was deleted or compacted away between the search and the Enter. Without that timer pendingTimelineAnchorRef stays set and live-follow is suppressed for the rest of that thread's life, which reads as "the chat stopped auto-scrolling".

The matched row pulses twice with a box-shadow ring, mirroring the settings search target pulse, and goes quiet under prefers-reduced-motion.

Scope

The server returns at most one match per thread (WHERE thread_match_rank = 1), so this reveals that single best match. It is not find-next / find-prev; cycling matches would mean changing the query shape and the palette result model.

Mobile renders search matches through its own list and navigation and keeps today's behavior. The contract change is additive, so it still compiles.

Verification

• Manually verified in a local (test) desktop build off this branch: jump to an early user message, jump to an early agent message, plain thread row still opens at the live edge, repeat the same search twice, and live-follow resumes normally after a reveal.
• vp test run on the five touched test files: 73 passed.
• Typecheck across @t3tools/contracts, @t3tools/client-runtime, @t3tools/web, and t3: zero errors.
• vp lint on the touched source files and vp fmt --check both clean.

Design notes: docs/specs/2026-08-16-command-palette-message-reveal-design.md.