Bug type

Regression (worked before, now fails)

Beta release blocker

No

Summary

In OpenClaw v2026.5.2, the webchat session JSONL transcript is overwritten on every turn — only the latest message exchange survives. On page refresh, all previous messages are gone. This worked correctly on v2026.4.29.

Root cause

mirrorCodexAppServerTranscript (in run-attempt-*.js) receives the full conversation history via messagesSnapshot (built from readMirroredSessionHistoryMessages at line 3264) and rewrites ALL messages to the JSONL every turn. Each message is written via appendCodexAppServerTranscriptMessage, which calls migrateLinearTranscriptToParentLinked — a function that reads the entire file and rewrites it via fs.writeFile (not append).

The per-turn idempotencyScope (codex-app-server:${threadId}:${turnId}) changes every turn, so old messages get new keys and bypass the idempotency check. The rewrite creates new entries with different parentId chains, causing selectBoundedActiveTailRecords (the tree walk) to follow the newest branch and orphan previous entries.

In v4.29, SessionManager.open().appendMessage() truly appended to the file. The SessionManager was removed in 5.2 and replaced with this read-migrate-rewrite cycle.

Steps to reproduce

1. Open webchat on v2026.5.2
2. Send message 1, receive response
3. Send message 2, receive response
4. Check the session JSONL — message 1's assistant response is gone
5. Refresh page — only message 2 and its response are visible

Evidence

Controlled test on macOS arm64, v2026.5.2 (8b2a6e5), stock dist (no patches except prewarm skip):

• Took a JSONL snapshot between turns
• Diffed after the next turn
• The previous assistant response (id 44b4ec62, parentId d3471f25) was replaced by the new user message (id 9f4b19a1, parentId d3471f25) — same parent, sibling branch
• The tree walk follows the new branch, orphaning the old assistant entry
• 9 minutes between turns — no race condition, purely the mirror rewrite logic

Contributing factors

1. migrateLinearTranscriptToParentLinked rewrites via writeFile — any concurrent access or stale read loses data
2. Per-turn turnId in idempotency scope — old messages get new keys, bypassing dedup
3. Write lock race (fix: session write lock race — async release can delete newly-acquired lock #57019) — releaseHeldLock deletes HELD_LOCKS before async cleanup, allowing concurrent acquirers on macOS
4. appendCodexAppServerTranscriptMessage calls migration inside the lock but mirrorCodexAppServerTranscript takes a separate lock per batch — interleaving between the webchat write path and the mirror write path can race

Code references (v2026.5.2 dist)

• run-attempt-CektiLYp.js:3264 — finalMessages = readMirroredSessionHistoryMessages(sessionFile) (full history)
• run-attempt-CektiLYp.js:3598 — idempotencyScope: codex-app-server:${threadId}:${turnId} (per-turn keys)
• run-attempt-CektiLYp.js:2082 — appendCodexAppServerTranscriptMessage triggers migration
• transcript-C_uDP9Gl.js:121 — migrateLinearTranscriptToParentLinked rewrites file via writeFile
• transcript-C_uDP9Gl.js:156 — fs.writeFile(transcriptPath, ...) — destructive overwrite
• session-utils.fs-W0CAUUsv.js:564 — selectBoundedActiveTailRecords tree walk follows one branch

What changed (4.29 → 5.2)

Environment

• OpenClaw: v2026.5.2 (8b2a6e5), npm global install
• OS: macOS 26.4.0 arm64 (Mac Mini M4 Pro)
• Node: 22
• Channels affected: WebChat (Telegram and BlueBubbles unaffected — different write path)

Related issues

• fix: session write lock race — async release can delete newly-acquired lock #57019 — Write lock race (contributing factor, not root cause)
• WebChat: assistant text responses not persisted to session transcript (5.2 regression) #76804 — Assistant text not persisted (separate issue, PR feat(gateway/transcript): add silent option to assistant transcript append helper #76819 merged)
• [Bug]: Control UI Chat History Display Issues #76892, [Bug]:the messages often disspear #76763, [Bug]: Control UI: chat history intermittently shows only the latest message in 2006.5.2 #76384 — Duplicate reports of history loss
• [Bug]: WebChat loses message queue, conversation history, and draft on browser refresh #51549 — Architectural gap in webchat persistence