fix(codex): render plans in approval UI

[MattPua]

Problem

Codex plan output renders as regular chat markdown instead of the dedicated plan approval UI used by Claude.

BEfore:

After:

Changes

• Buffer Codex plan deltas instead of adding them to the transcript.
• Emit a structured plan tool call for approval and persist its final status.
• Show rejected Codex plans correctly in the shared plan view.

How did you test this?

• pnpm --filter @posthog/agent exec vitest run src/adapters/codex-app-server/mapping.test.ts src/adapters/codex-app-server/codex-app-server-agent.test.ts
• pnpm --filter @posthog/ui exec vitest run src/features/sessions/components/session-update/PlanApprovalView.test.tsx
• pnpm --filter @posthog/agent typecheck
• pnpm --filter @posthog/ui typecheck
• Commit hook full pnpm typecheck

Automatic notifications

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

---

Created with PostHog Code

[trunk-io]

😎 Merged successfully - details.

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 5f9dfbf.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix(codex): render plans in approval UI" | Re-trigger Greptile}

[greptile-apps]

_{Reviews (2): Last reviewed commit: "fix(codex): harden plan approval lifecyc..." | Re-trigger Greptile}

[veria-ai]

PR overview

All previously flagged issues have been addressed. No open security concerns remain on this pull request.

Security review

No open security issues remain on this pull request.

Fixed/addressed: 1 · PR risk: 0/10

[github-actions]

All bot-raised concerns (cancellation timing, stuck terminal status, misleading rejection copy, unbounded plan snapshots) are demonstrably addressed in the current diff with targeted fixes and matching tests. No unresolved review comments, no security or data-model concerns.