[codex] Add conversation activity projection

[roackb2]

Summary

Adds the M9 shared conversation activity projection slice:

• introduces src/core/observability/conversation-activity.ts to project AgentLoopEvent, TraceEvent, and compaction status updates into host-agnostic ConversationActivity records
• adopts the shared projection in the TUI run-loop adapter and web session subscription hook
• keeps TUI wording in src/cli/chat/adapters/conversation-activity-adapter.ts instead of leaving the activity renderer in utils/format.ts
• exports the projection API for programmatic consumers
• adds focused unit coverage for assistant stream, tools, approvals, memory, compaction, nested trace events, run-finished, and shared tool summaries

Why

This gives future hosts and programmatic users a stable semantic activity layer without depending on React, Ink, SSE payload details, or duplicated trace parsing.

Validation

• yarn test:unit src/__tests__/unit/core/conversation-activity.test.ts
• yarn test:unit src/__tests__/unit/tui/chat-activity-format.test.ts
• yarn vitest run src/__tests__/integration/web/control-plane-sessions-state.test.tsx
• yarn vitest run src/__tests__/integration/chat/chat-runtime.test.ts
• yarn eslint
• yarn typecheck
• yarn build

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Validate trace payloads before projecting live activities

isAgentLoopEventLike now accepts any object with a string type, so a network payload like { type: 'trace' } (or a future trace event shape during frontend/backend version skew) is treated as a full AgentLoopEvent and passed to projectTraceEventToConversationActivities, which unconditionally invokes traceProjectors[event.type]. Because session SSE data is parsed from unknown without schema validation in subscribeToChatSessionEvents, this can throw at runtime and break live session updates instead of safely ignoring unsupported events as the previous handler path did.

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