fix: handle compaction boundaries without metadata

[MattPua]

Problem

Codex emits _posthog/compact_boundary without Claude's optional trigger, preTokens, and contextSize metadata. The UI treated those fields as required, so Codex compactions rendered as Conversation compacted · undefined · ~NaNK tokens.

With Codex

Changes

• Make compaction metadata optional through the conversation builder and render types.
• Render only metadata that exists while preserving the existing detailed Claude output.
• Share the compaction boundary types instead of repeating the payload shape.
• Add coverage for metadata-free Codex boundaries and both UI label formats.

How did you test this?

• pnpm --dir packages/ui exec vitest run src/features/sessions/components/session-update/CompactBoundaryView.test.ts src/features/sessions/components/buildConversationItems.test.ts
• pnpm --filter @posthog/ui typecheck
• Commit hook: pnpm typecheck
• Biome checks on touched files

Automatic notifications

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

---

Created with PostHog Code

[trunk-io]

😎 Merged successfully - details.

[github-actions]

React Doctor found 2 issues in 1 file · 2 warnings.

2 warnings

src/features/sessions/components/session-update/CompactBoundaryView.tsx

• ⚠️ src/features/sessions/components/session-update/CompactBoundaryView.tsx:34 Non-component export in component file only-export-components
• ⚠️ src/features/sessions/components/session-update/CompactBoundaryView.tsx:50 Non-component export in component file only-export-components

_{Reviewed by React Doctor for commit ddf618d.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix: handle compaction boundaries withou..." | Re-trigger Greptile}

[greptile-apps]

_{Reviews (2): Last reviewed commit: "fix: handle compaction boundaries withou..." | Re-trigger Greptile}

[github-actions]

Contained UI fix making compaction-boundary metadata optional so Codex's boundary events render correctly; diff matches the description, includes new tests, and touches no risky territory.

• Author wrote 0% of the modified lines and has 11 merged PRs in these paths (familiarity MODERATE).
• 👍 on the PR from greptile-apps[bot].

Gate mechanics and policy version

Gate		Result
prerequisites	✓	all clear
deny-list	✓	no deny categories matched
size	✓	127L, 4F substantive, 210L/6F incl. docs/generated/snapshots — within ceiling
tier	✓	T1-agent / T1c-medium (210L, 6F, single-area, fix)
stamphog 2.0.0b3		.stamphog/policy.yml @ cf1c82e · reviewed head ddf618d