Fix "undefined · ~NaNK tokens" in codex compaction boundary

[k11kirky]

Problem

A user on gpt-5.6-sol saw the transcript render "Conversation compacted · undefined · ~NaNK tokens" after an auto-compaction.

The codex-app-server adapter emitted the _posthog/compact_boundary notification with only sessionId, whereas the Claude adapter includes trigger, preTokens, and contextSize. With those fields missing, CompactBoundaryView rendered ${trigger} as "undefined" and Math.round(undefined / 1000) as NaN.

Changes

• UsageTracker retains the model context window and exposes contextSize().
• The codex compaction boundary now sends trigger: "auto" (codex only auto-compacts), preTokens from live context occupancy, and contextSize.
• CompactBoundaryView (and its type chain) treat trigger/preTokens as optional and omit each segment when absent — so a missing value can never render as undefined/NaN again.

Why

Reported by a user; the compaction marker was showing garbage text on codex models.

How did you test this?

• Extended the existing codex agent test to emit a token-usage update before compaction and assert the boundary carries trigger: "auto", preTokens: 185000, contextSize: 200000. All 75 codex agent tests pass.
• pnpm --filter @posthog/ui typecheck and @posthog/agent build pass; Biome lint clean on the changed files.

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 0222420.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "simplify compact boundary rendering and ..." | Re-trigger Greptile}

[github-actions]

This PR has had no activity for 7 days and has been marked stale. We are moving to the monorepo and tightening PR staleness in preparation, so it will be closed in 7 days if no further activity occurs.

[posthog]

🤖 CI You Later — rebased this branch onto main to clear the merge conflict (DIRTY → clean).

Conflicts were in 4 files. How each was resolved:

• packages/agent/.../usage-tracker.ts — both sides were additive and non-overlapping: main refactored lastTurn (added thoughtTokens/totalTokens), this PR added contextWindow tracking + contextSize(). Kept both.
• packages/ui/.../CompactBoundaryView.tsx, buildConversationItems.ts, SessionUpdateView.tsx — took main verbatim. main already landed the renderer-side fix this PR was making: CompactBoundaryMetadata (in types.ts) has optional trigger/preTokens, and getCompactBoundaryMetadata / formatCompactBoundaryLabel omit each segment when absent, so undefined / ~NaNK can no longer render. main also has a test file (CompactBoundaryView.test.ts) covering those exported helpers, and renamed markCompactingStatusComplete → markRuntimeStatusComplete(b, "compacting"), so keeping the PR's side would have broken compilation and dropped tests.

Net effect: the remaining diff vs main is agent-side only (26 insertions across 3 files) — the codex adapter now sends trigger: "auto", preTokens, and contextSize on the compaction boundary, plus the tracker/test support for it. The UI files are now byte-identical to main.

Verified locally before pushing: pnpm typecheck (24/24 packages), codex-app-server-agent.test.ts + usage-tracker.test.ts (113 passed), CompactBoundaryView.test.ts + buildConversationItems.test.ts (39 passed), Biome clean on changed files.

⚠️ For @k11kirky: the PR description still describes the renderer changes, which are now redundant with main — worth trimming before merge. Also note this rebase rewrote the two commits (8e9f3bf → 0222420).

[charlesvien]

Closing stale PRs ahead of Friday's monorepo migration. If this is a mistake, rebase and reopen for review.