Bug Description

When a long-running session (e.g., Discord channel) accumulates many messages and goes through compaction, orphaned tool_result blocks can be sent to the Anthropic API without their matching tool_use. This causes a 400 invalid_request_error that permanently bricks the session — the bot can never respond again in that channel.

Root Cause

Observed in a Discord channel session (6,724 JSONL entries, 23 compactions):

1. An assistant request is aborted mid-tool-call (stopReason: "aborted")
2. The toolCall block and its toolResult message are both recorded in the JSONL
3. When compaction runs, the conversation is summarized — but the toolResult entry survives into the post-compaction message window while its matching toolCall does not
4. On the next API call, Anthropic receives a tool_result referencing a tool_use_id that doesn't exist in the conversation
5. API returns: messages.166.content.1: unexpected tool_use_id found in tool_result blocks
6. Every subsequent API call fails with the same error — the session is bricked

Reproduction

This happened naturally in a Discord channel session after ~2 weeks of continuous use. The JSONL had:

• Line 6716: Assistant message with toolCall (stopReason: "aborted")
• Line 6717: toolResult message referencing that tool call
• Line 6719: Compaction entry (parentId chain includes both 6716 and 6717)
• Line 6721: Next assistant message → 400 error

Expected Behavior

Compaction should ensure tool_use/tool_result pairs are always kept or removed together. If a toolCall is summarized away, its corresponding toolResult must also be excluded from the API request.

Suggested Fix

When building the API message array from the JSONL:

1. After compaction, validate that every tool_result has a matching tool_use in the message array
2. Strip orphaned tool_result blocks before sending to the API
3. Consider also handling orphaned tool_use blocks (tool_use without a following tool_result)

Alternatively, during compaction:

• Ensure aborted tool calls and their results are either both kept or both summarized
• Never split a tool_use/tool_result pair across a compaction boundary

Workaround

Manually clearing the session transcript (.jsonl file) restores functionality but loses all conversation history.

Environment

• OpenClaw: 2026.2.22-2
• Provider: Anthropic (Claude Opus 4.6)
• Session type: Discord channel (long-running, continuous)
• OS: macOS 15.7.3