[Juliusolsson05]

Summary

Closes #291.

This implements the Codex side of the existing Claude-style subagent rendering path:

• filters Codex <subagent_notification> runtime messages out of normal user prompt rendering
• builds SubAgentState for Codex by joining parent spawn_agent calls to child rollout files via function_call_output.agent_id
• routes Codex spawn_agent blocks through TaskSubagentRow, including adjacent spawn grouping
• suppresses the raw spawn_agent result row because it is just {agent_id,nickname} join metadata
• adds focused tests for notification filtering and Codex subagent state extraction/building

Evidence

The implementation is based on the saved debug bundle noted as "Not handling codex subagents at all." The parent rollout stores spawn_agent function calls and synthetic user <subagent_notification> messages, while the child rollouts store session_meta.payload.source.subagent.thread_spawn with the parent thread id, nickname, and role.

Verification

• npm test -- --run src/renderer/src/workspace/codex/rollout.test.ts src/main/subagents/codexSubagentState.test.ts
• npx tsc --noEmit

npm test and npm run build:app are blocked in this worktree because packages/claude-code-headless/src/... files, including src/proxy/mitmAddon.py, are missing from the worktree checkout. The new targeted suites pass before that unrelated package-source failure is hit.