Description

After compaction with truncateAfterCompaction: true, assistant messages are dropped from the rotated session transcript. This causes:

1. The Feishu (or any channel) reply briefly appears in webchat/Control UI (written by appendSessionTranscriptMessage before compaction)
2. When compaction rotates the session file via rotateTranscriptFileAfterCompaction, buildSuccessorEntries marks all messages before firstKeptEntryId as "removedIds" — including assistant replies
3. The rotated session now has: [user_msg_1], [compaction summary], [user_msg_2] — with NO assistant reply between them
4. The webchat UI refreshes and shows user messages consecutively without the reply
5. When the agent reads the session, it sees two unanswered user messages and processes them as one combined turn

Reproduction Steps

1. Send a message via any channel (e.g. Feishu)
2. Agent generates a reply — it appears in webchat temporarily
3. Session exceeds compaction threshold (token count or maxActiveTranscriptBytes)
4. Compaction runs → shouldRotateCompactionTranscript returns true → rotateTranscriptFileAfterCompaction creates new session file
5. In the new session file, the assistant reply is gone
6. Send a second message — agent processes both messages together (sees no intermediate reply)

Root Cause

In compaction-successor-transcript-ZByj7D6a.js, function buildSuccessorEntries:

for (const entry of allEntries) 
    if (summarizedBranchIds.has(entry.id) && entry.type === "message" 
        || staleStateEntryIds.has(entry.id) 
        || duplicateUserMessageIds.has(entry.id)) 
        removedIds.add(entry.id);

All messages before firstKeptEntryId are removed, regardless of role (user or assistant). User messages tend to survive because they are referenced by firstKeptEntryId, but the assistant replies to those user messages are dropped.

Session stats from the bug reproduction:

• Before compaction: user=8, assistant=167, total=556 entries, 1088KB
• After compaction rotation: user=6, assistant=30, total=278 entries, 455KB
• 137 assistant messages lost (82% reduction)

Impact

• All channels that share the embedded PI session experience this bug
• Users see replies "disappear" from webchat
• Multiple user messages get batched together as one LLM call
• Queue mode (steer/queue) can compound the issue by processing multiple items together

Suggested Fix

In buildSuccessorEntries, when determining which messages to remove, preserve the last assistant reply that precedes each surviving user message. This ensures that the rotated transcript maintains conversational structure (user → assistant → user → assistant) rather than collapsing into consecutive user messages.

Alternatively, ensure that compaction rotation preserves all assistant messages that are direct replies to surviving user messages.

Environment

• OpenClaw v2026.5.2
• compaction.truncateAfterCompaction: true
• compaction.maxActiveTranscriptBytes: 10mb
• Feishu channel + webchat/Control UI