feat(web): compact a thread from the context meter

[TheDarkPhantom]

#252 landed context compaction on the server, but the web client had no way to trigger it besides typing /compact, no timeline rendering for it, and no handling of Claude's resume prompt.

This ports the web parts of upstream pingdotgg#9293 and pingdotgg#8144, plus pingdotgg#4772 (ContextWindowMeter.logic.ts), pingdotgg#11103 (drafts survive compaction) and pingdotgg#9623 (compaction folds with a settled turn).

Context meter

• Adds a Compact context button to the meter popover. It sends /compact as its own turn start and leaves the draft and attachments where they are (fix(web): preserve drafts when compacting context pingdotgg/t3code#11103). It is disabled while work runs, before the thread has any conversation, while a question or approval is pending, or when the provider doesn't advertise /compact, and the popover says why.
• Draws a tick on the usage bar at autoCompactThreshold and adds the text "Compacts automatically at N tokens".
• The tooltip names the thread's model instead of its provider (fix(web): show selected model in context window tooltip pingdotgg/t3code#4772).

Timeline

• context-compaction activities get their own static divider row (for example "Compacted context 899K → 19K tokens"). They are never grouped into work rows.
• A lone compaction stays visible. When a settled turn folds other work, the compaction folds with it (fix(web,mobile): fold context compaction under settled turn folds pingdotgg/t3code#9623).
• While a /compact runs, the working row reads "Compacting context for Ns" with a static icon instead of the pulsing dots. The only repaint is the existing once-a-second timer text.
• provider.turn.start.failed rows ("Context compaction failed", "Queued message was not sent") still render as error work rows. They now also acknowledge the local send, so the composer stops waiting for a session change that never comes (upstream latestTurnStartFailureId).

Claude resume

• Adds upstream's "Resume with less context" banner for Claude threads idle for 70 minutes or more with at least 100k tokens. It schedules one timer for when the thread crosses the idle threshold; there is no minute clock. "Keep full history" dismisses it for that snapshot.
• Fork addition: when the pending user-input request is Claude's native resume question (isClaudeResumeCompactionQuestion), ComposerPendingUserInputPanel shows a dedicated prompt with Compact and continue, Keep full history and Don't ask again. Upstream shows the generic questionnaire here. The answers go through the same option-selection path, so the server-side mapping is unchanged.
• Answering "Don't ask again" silences the banner on this device (localStorage, per environment and provider instance).

Slash menu

• /compact (advertised by the server) is offered only as the whole message, with no attachments or contexts, on a thread that can compact. composer-logic.ts itself is unchanged; the filter lives in ChatComposer's menu items.

No server, contract or migration changes. The larger additions went into new files (ContextWindowMeter.logic.ts, contextCompaction.logic.ts, useResumeCompactionBanner.tsx, ClaudeResumeCompactionPrompt.tsx), and the edits to ChatView, ChatComposer and MessagesTimeline stay small and local.

Verification

• vp test run on the new and touched tests: meter logic and render, compaction state, timeline rows, local-dispatch acknowledgement, resume prompt, settings form, changelog. All pass.
• tsgo --noEmit -p apps/web, vp lint and vp fmt on the changed paths, and vp run check:avicode all pass.
• No dev server or client pass has been done yet (see manual checks below).

Manual checks

• On a Claude thread with conversation, hover the context meter and click Compact context. The divider should appear, and the draft should stay.
• Try Compact context on a Codex thread.
• Resume a Claude thread idle for over 70 minutes. Check the banner, and check the dedicated prompt when Claude asks.

Built by Claude Opus 5.5 in Claude Code.

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