What Changed

Adds in-thread find to the chat timeline, on the new chat.find keybinding command (mod+f, when: !terminalFocus, so it stays out of the terminal's own find). Enter / Shift+Enter step forward and back, Esc closes.

Scope is deliberately narrow: conversation content only — user messages, assistant messages and proposed plans. Work-log/tool rows are not searched.

• apps/web/src/components/chat/threadFind.ts — pure match model over timeline entries
• apps/web/src/components/chat/threadFindHighlights.ts — CSS Custom Highlight API painting
• apps/web/src/components/chat/FindInThreadBar.tsx — the bar
• apps/web/src/lib/visibleMessageText.ts — the "what does this user message display?" derivation, extracted from MessagesTimeline so the row and find share one source

Why

Requested in #1486. Three earlier attempts (#1501, #3539, #3779) stalled; #1501 was closed with "it should restart as a smaller focused change". This is that smaller change, built to avoid the specific defects reviewers found in the earlier ones:

Highlighting never touches the DOM. Earlier attempts injected <mark> tags into message text before markdown parsing, which rendered literal <mark class=...> inside fenced code blocks and corrupted copied source, and desynchronized the AST offsets that task-list checkbox toggling derives from message text. This uses the CSS Custom Highlight API instead: ranges are painted, the DOM is unmodified. Code blocks keep their syntax highlighting and their exact copy text. Browsers without the API render no highlights but keep working counting and navigation.

Matches are counted against timeline entries, not rendered nodes. LegendList virtualizes the timeline, so DOM-derived counts change as you scroll. Counting from entries keeps the total stable, and navigation uses scrollToIndex on the row model rather than document.querySelector, so a match in an unmounted row is reachable.

Folded turns unfold on navigation. A settled turn hides everything but its terminal assistant message. Those hidden messages are still counted, and stepping to one expands its turn first, then scrolls (screenshot below).

Only one occurrence is ever active. The active style applies to a single range, not to the whole row, so advancing within a long message moves the marker instead of lighting up every match in it.

The counter cannot show an impossible position. The index is clamped against the live match count on every render, so a streaming edit that removes matches cannot leave 5/2 on screen. Occurrence scanning advances by the needle length, so aa in aaa counts once — the count matches what a left-to-right highlighter can actually paint.

Find searches what the timeline shows. User prompts carry appended <terminal_context> / <element_context> / preview-annotation blocks that are stripped before rendering. Searching raw message.text counted invisible text; the display derivation is now shared between the row and the search index, so they cannot drift.

Known limitation, called out rather than hidden: an occurrence split across text nodes by inline markup (**bo**ld) is counted but not painted. The row is authoritative for navigation and the occurrence index within a row is clamped, so this degrades to "scrolls to the right message, paints fewer highlights than it counts" rather than breaking.

UI Changes

Find bar with match count, live highlighting across markdown, inline code and fenced code blocks (light):

Dark:

Stepping onto a match inside a folded turn unfolds the turn and reveals it (the "Worked for 2m" fold above has expanded, and the commentary message it was hiding now shows the active match):

No results:

Verification

Unit tests:

vp test run apps/web/src/components/chat/threadFind.test.ts apps/web/src/components/chat/threadFindHighlights.test.ts
# 17 passed

vp test run apps/web/src/keybindings.test.ts \
  apps/web/src/components/settings/KeybindingsSettings.logic.test.ts \
  apps/web/src/components/chat/MessagesTimeline.test.tsx \
  apps/web/src/components/chat/MessagesTimeline.logic.test.ts \
  packages/contracts/src/settings.test.ts
# 116 passed

Static checks:

vp check apps/web/src packages/contracts/src packages/shared/src   # 0 errors
pnpm --filter @t3tools/web run typecheck                           # clean
pnpm --filter @t3tools/contracts run typecheck                     # clean
pnpm --filter @t3tools/shared run typecheck                        # clean

Driven in a real browser against an isolated local environment seeded with a 17-turn thread (folded turns, a fenced code block, and enough filler to force virtualization). Confirmed there: Ctrl+F opens and focuses; deploy reports 1/12, matching a hand count that includes the folded commentary and the code block; Enter at 1/12 unfolds the folded turn and mounts the hidden message; wrap-around forward and back (12/12 → 1/12); the code block's textContent is unchanged with zero <mark> elements in the DOM; a no-match query reports 0/0 and paints nothing; Esc closes and unregisters both highlights.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes