Bug: Stop-button abort races with compaction completion, causing model confusion

Description

When a user presses the stop button during an auto-compaction, the abort signal cancels the wait for compaction but the compaction LLM call continues in-flight and writes its result to the session transcript. This causes the model to receive only a compaction summary instead of the full context, leading to confused responses.

Note: The full transcript is preserved on disk — this is not data loss. The problem is model confusion, not user confusion.

Reproduction

1. Have a session with enough context to trigger auto-compaction (~200K+ estimated tokens)
2. Wait for auto-compaction to start (visible in logs as context overflow detected; attempting auto-compaction)
3. Press the stop button during compaction
4. Observe: compaction wait aborted + AbortError: This operation was aborted
5. But compaction result still gets written to session
6. Next message sees compacted session (e.g., 239 → 4 messages)

Evidence from logs

22:57:16 context overflow detected (attempt 1/3); attempting auto-compaction
22:57:17 [compaction-diag] start (compaction begins)
22:58:57 chat.abort → reply_operation_aborted
22:58:57 contextEngine.compact() threw during overflow recovery: AbortError: This operation was aborted
22:58:57 auto-compaction failed: AbortError
22:59:13 Auto-compaction failed. Preserving existing session mapping.
23:00:07 [compaction-diag] end outcome=compacted  ← compaction actually completed!
23:00:55 [context-diag] messages=4  ← model now sees only 4 messages

Root Cause

In selection-BMP-JCML.js:

• unsubscribe() (line ~5817) calls session.abortCompaction() but this only signals the session manager
• The LLM call for compaction summarization was already in-flight and completes independently
• The compaction end handler (line ~4685) checks wasAborted and skips incrementCompactionCount(), but the session file has already been modified by the session manager's compaction handler
• The main run's compaction-wait is aborted (line ~17277), but the compaction subprocess continues

Expected Behavior

When externalAbort=true and compaction was in-flight, the compaction result should be discarded (rolled back) rather than applied to the session. The session should remain in its pre-compaction state.

Impact

• Model confusion: Model receives only compaction summary instead of full context → loses track of ongoing work, instructions, and state
• Not data loss: The full transcript is preserved on disk. The Principal can read the original transcript. The problem is the model's confusion, not the Principal's.
• Stop-button mismatch: User presses stop expecting cancellation, but compaction still happens
• Degraded model context: Compaction summary generated from mid-turn state may be garbled

Environment

• OpenClaw version: 2026.5.28
• Model: xiaomi/mimo-v2.5-pro (but affects any model)