Surface context window usage in the UI

[juliusmarminge]

Summary

• Adds provider normalization for token usage snapshots from Codex and Claude runtime events.
• Projects token usage and compaction state into orchestration thread activities.
• Renders a compact context window meter in the chat composer area.
• Displays context compaction markers as centered timeline chips.
• Adds coverage for adapter normalization, orchestration ingestion, and UI rendering behavior.

Testing

• Not run in this pass.
• Added/updated tests for ClaudeAdapter, CodexAdapter, ProviderRuntimeIngestion, contextWindow, MessagesTimeline, and session logic.
• Repository task requirements still call for bun fmt, bun lint, bun typecheck, and bun run test before merge.

Note

Surface context window usage and compaction events in the chat UI

• Adds a ContextWindowMeter circular ring meter to the chat composer that shows current token usage as a percentage, derived from a new deriveLatestContextWindowSnapshot utility that scans thread activities.
• Both the Claude and Codex adapters now emit structured thread.token-usage.updated events with a normalized ThreadTokenUsageSnapshot (including used/max tokens, per-slice counts, and compaction flags) at task progress, task completion, and turn boundaries.
• The orchestration layer maps thread.token-usage.updated events to context-window.updated thread activities, and thread.state.changed with state compacted to context-compaction activities.
• The messages timeline renders context-compaction activities as standalone centered chips labeled "Context compacted" and excludes context-window.updated activities from the work log feed.
• Risk: ThreadTokenUsageUpdatedPayload now requires a structured ThreadTokenUsageSnapshot; events that previously passed through untyped usage payloads will fail schema decoding.

^{Macroscope summarized b2a7fa3.}

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