feat(codex): enable verified native conversation rewind

[rynfar]

Codex could not safely use Pylon's rewind actions through relative turn counts. Eligible completed turns now capture immutable native forks and support the existing restore-files/keep-files saga, idempotent application, compensation and same-incarnation restart recovery.

Proof covers complete native JSONL context and inactive native goal state, including hidden context and unknown fields. Fresh forks defer goal continuation until the next explicit send. Original checkpoints remain distinct from compacted current sources. Private cursors and lifecycle fences preserve ordinary Stop/resume and prevent retired callbacks from changing the selected conversation.

Native limits remain explicit: active or uninspectable goals, paginated forks, external history bases, unsupported file shapes, histories over 16 MiB/100,000 records or lines over 1 MiB, and uncaptured old/root bindings cannot claim exact rewind. No live model/account test was performed.

Validation: independent adversarial native-source and adapter review; 360 focused tests, server typecheck and scoped lint from the saved implementation. After integration onto #531, the reviewed native code was preserved except for removing an unused export on the unchanged history size limit, identified by CI. All 85 history-helper tests and scoped lint passed after that fix. The shared capability conflict preserves OpenCode and changes only Codex to absolute. Integration capability regression and server typecheck passed. All ten final-head CI jobs passed in run 34709776527; merge CI34710265069 and relay34710265062 succeeded. The optional Vercel marketing preview hit its daily deployment quota.

Part of #526, extending #513 for upstream fd5553f1afcef4f410a067687faa991743b5034c and efccda9ac9230db22b36990cffabdad218fa41b0. Claude follows separately. Includes user/internals eligibility documentation and the compact disposition record.

Model: GPT-6. Harness: Codex.

[vercel]

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Project	Deployment	Actions	Updated
pylon-marketing	Ready	Preview	Sep 12, 2026 5:54pm UTC

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.9 KiB	13.9 KiB	−23 B (−0.2%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.2 KiB	7.2 KiB	−5 B (−0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.7 KiB	6.7 KiB	−18 B (−0.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	58.0 KiB	58.0 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	8	8	0 (0.0%)	21	✅
Claude	Total thread wire	13.9 KiB	13.9 KiB	+9 B (+0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.2 KiB	7.2 KiB	+10 B (+0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.7 KiB	6.7 KiB	−1 B (−0.0%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	58.8 KiB	58.8 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	8	8	0 (0.0%)	21	✅

Baseline: 9764d77 · PR result: f2b305d · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 115.6 KiB
• Claude decoded thread snapshot: 116.4 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.