feat(web): the working row shows the agent's latest thought (upstream #16284) - #270

While an agent works, the live "Working for Xs" row at the bottom of the chat now shows the first sentence of the agent's latest thought, with a brain icon. A finding no longer hides behind the collapsed Thought row and the tool calls that follow it. Clicking the line opens that thought; an open thought hides the preview.

Note: upstream pingdotgg#16284 ("live row shows the agent's latest thought", Theo Browne) changes the chat timeline's live activity row, not a sidebar. Neither sidebar is touched here (see "Left out").

How it was ported

Upstream's thoughts are work-log entries inside a live tool group (work-live row). The fork keeps thoughts as reasoning role messages (ported in #259) and has no work-live row, so the change is re-expressed against the fork's working indicator row:

• liveThoughtLine (verbatim from upstream's client-runtime work-log/presentation.ts, which the fork lacks) lives in a new apps/web/src/components/chat/liveThoughtLine.ts. A bold-only opening line (the Codex summary heading) wins, otherwise the first sentence, markdown flattened.
• deriveMessagesTimelineRows attaches thought: { messageId, line } to the working row: the latest non-empty reasoning message since the last user message, so a steer starts fresh.
• LiveThoughtLine renders it above the working status in MessagesTimeline.tsx. It is hidden while compacting, like the rest of the status row.

Performance

• Client-only. Nothing new goes over the websocket. It reads the thread detail the timeline already has.
• The lookup walks backwards only through the current turn and stops at the last user message, so long threads cost nothing extra.
• Row stability compares the derived line, not the message, so the working row stops re-rendering once a streaming thought's first sentence is complete. A test covers this.
• No animation. Static icon and text, clamped to four lines.

Providers

Claude (including its between-step notes), Codex, and OpenCode emit reasoning, so they show the line. Cursor and Grok emit none, so the working row looks the same as before.

Left out

• Mobile (desktop-only fork) and upstream's WorkLog.tsx wrapLabel alignment tweak (the fork has no WorkLog.tsx; the new line handles its own alignment).
• Sidebars (v1 and SidebarV2). Upstream did not change them. Thread shells carry no thought data, so a sidebar line would need a new shell field broadcast to every client on every thought.
• No upstream follow-ups touch this feature (git log 95ccbf4066..upstream/main finds none).

Verification

• vp test run on liveThoughtLine.test.ts (4 passed), MessagesTimeline.logic.test.ts (50 passed), MessagesTimeline.test.tsx (23 passed). The render test fails when the line is removed.
• vp lint and vp fmt --check on changed files: clean.
• tsgo --noEmit -p apps/web/tsconfig.json: clean.
• vp run check:avicode: pass. vp run test:avicode: 7 passed.

🤖 Generated with Claude Code