Bug type

Behavior bug (incorrect output/state without crash)

Beta release blocker

No

Summary

Every assistant turn in WebChat writes a second identical message(role=assistant) record as a child of the openclaw.cache-ttl session entry, causing WebChat to render each reply twice.

Steps to reproduce

1. Open WebChat (Control UI, default port 18789) with any agent
2. Send any text message
3. Observe the assistant reply appears twice in the chat view
4. (Optional) Verify in the session JSONL:
   Path: ~/.openclaw/agents/main/sessions/.jsonl
   Expected: two consecutive message records with role: "assistant",
   identical content, timestamps within ~1 second, and different
   parentId values — one being the id of an openclaw.cache-ttl record.

Expected behavior

One assistant message per turn in WebChat.

Actual behavior

Two identical assistant messages rendered per turn. Session JSONL confirms this is not a client-side rendering issue: the JSONL itself contains two message(role=assistant) entries per turn, forming the tree:

message(user) id=bfcafeb6
message(assistant) id=29dc915b ts=10:05:13.618Z ← primary reply
custom(cache-ttl) id=28ed4f69 ts=10:05:13.701Z ← 83ms later
message(assistant) id=d8566daf-8796-… ts=10:05:14.413Z ← duplicate (UUID format)
message(user) id=b712f6e7 ← next user turn

The duplicate (B) has a different id format (full UUID vs short hex for the primary), a different parentId, and idempotencyKey: null. Pattern observed on every turn in the session — 6 confirmed pairs.

OpenClaw version

2026.6.8 (844f405)

Operating system

macOS 25.5.0 Darwin arm64 (Apple M4)

Install method

npm global

Model

claude-sonnet-4-6

Provider / routing chain

openclaw → meridian (local OAuth proxy) → Anthropic

Additional provider/model setup details

No response

Logs, screenshots, and evidence

All 6 duplicate pairs from session 3ad55650-86b7-4028-b3a3-091c92776fb2:

PAIR 1:  A id=29dc915b  parent=bfcafeb6  ts=10:05:13.618Z  len=330
         B id=d8566daf-8796-4ded-a6e1-f222380b4de5  parent=28ed4f69  ts=10:05:14.413Z  len=330

PAIR 2:  A id=7a98a048  parent=4478f66b  ts=10:19:26.345Z  len=623
         B id=7838f911-c874-4b22-969a-16fefeaaa652  parent=bf13e59d  ts=10:19:39.422Z  len=623

PAIR 3:  A id=f9c13c38  parent=0a31d550  ts=10:23:40.840Z  len=1088
         B id=e720048d-48ff-4a1d-91cd-70e762e04bc2  parent=4e59e4f8  ts=10:23:42.432Z  len=1088

PAIR 4:  A id=be98e1a7  parent=59d6cd84  ts=10:25:32.038Z  len=1613
         B id=5b435097-ca71-491a-beb4-b91aafc03e96  parent=fa1c8d57  ts=10:25:33.155Z  len=1613

PAIR 5:  A id=c71ecced  parent=b70a0105  ts=10:29:56.159Z  len=401
         B id=f1a40b40-060f-487c-b6a3-475fc24a917a  parent=3a0ba6f2  ts=10:29:57.087Z  len=401

PAIR 6:  A id=f55093ea  parent=a2240660  ts=10:30:55.783Z  len=1193
         B id=72b29193-fe0c-4436-a372-198b1c8287b6  parent=0f29a1f4  ts=10:30:56.945Z  len=1193

All B records: idempotencyKey=null, content identical to A.
Telegram channel unaffected (only primary message A is delivered).
streaming.mode tested: "off" and "partial" — both produce duplicates.
Plugins: lossless-claw 0.13.1, openclaw-amem, openshell, browser-automation, brave, diffs (all official).

Impact and severity

• Affected: All WebChat users on 2026.6.8 (reproduced 100% of turns in one session)

• Severity: High — every reply is visually doubled, degrading chat usability

• Frequency: Always (every assistant turn)

• Consequence: User sees every response twice; Telegram users unaffected

Additional information

Not a duplicate of #5964: In #5964, the session JSONL contained no duplicate entries (pure client-side rendering race condition). In this report, the JSONL itself contains two message(role=assistant) entries per turn — the root cause is in session-tree write logic, not rendering.

Not a duplicate of #85771: Same symptom, different root cause. #85771 is a UI rendering bug. This is a backend session-tree write bug where the JSONL itself stores two assistant messages per turn.

Related to #28491: The openclaw.cache-ttl custom entry has a known history of bypassing guards. The duplicate assistant message is appended as a child of this entry and may share the same insertion logic.