fix: show Codex subagent activity without streaming child output

[richardsolomou]

Problem

Codex app-server multiplexes parent and subagent notifications over one connection. Treating child-thread events as parent state interleaves delegated output into the conversation, pollutes parent usage and compaction state, and can mark the parent turn complete while work is still running. Simply dropping every subagent-related event would also hide useful delegation status.

Why: The conversation should behave like Claude: show compact parent-level delegation activity, let the parent model consume final results, and keep child transcripts out of the user-visible thread.

Changes

• Gate output, buffering, usage, compaction, and completion notifications by threadId while preserving child MCP tracking for approvals.
• Map actual spawn calls into dedicated subagent rows while keeping orchestration operations distinct and preserving Codex's terminal tool status.
• Render collaboration actions consistently, label grouped Codex spawn calls as subagents, and count only actual spawn calls.
• Cover parent activity plus child output, usage, compaction, and cloud completion isolation in focused tests.

The pinned Codex implementation returns final subagent messages to the parent through wait_agent, so genuine parent-context growth from those results remains unchanged. Child notification streams no longer affect parent context indicators or lifecycle state.

Cloud tasks run the published @posthog/agent from the sandbox image rather than the package checked out in the task workspace. Cloud validation therefore requires this agent change to merge, publish, and trigger the sandbox image rebuild. Existing logs produced by older agents cannot be repaired safely during replay because normalized ACP updates no longer identify the originating Codex thread.

Screenshots are not included because the behavior depends on live multi-agent event routing and is covered by adapter, mapping, and conversation-grouping tests.

How did you test this?

• Ran 116 focused Codex app-server adapter and mapping tests, including cloud task completion isolation.
• Ran 11 focused conversation-grouping, subagent-label, and tool-routing UI tests.
• Ran pnpm --filter @posthog/agent typecheck.
• Rebuilt the UI dependency graph and ran pnpm --filter @posthog/ui typecheck.
• Ran Biome checks on all changed files and git diff --check.

The full agent suite was also attempted, but unrelated tests that create temporary Git commits cannot run in this environment because unsigned git commit is intentionally blocked.

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code

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[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 12ec84a.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "Label Codex collaboration groups as suba..." | Re-trigger Greptile}

[github-actions]

Could not verify team-posthog-code membership (GitHub API error). Auto-release is limited to Team PostHog Code members, so this will ship with the next scheduled release instead.