Bug

When replaying session history to Claude, requests fail with:

messages.3.content.0.thinking.signature: Field required

Root Cause

1. OpenClaw saves thinking blocks with thinkingSignature field
2. Some entries in session history have type: thinking but no signature at all
3. When context is sent back to Claude API, it rejects the malformed thinking blocks

Reproduction

Session JSONL has entries like:

{"type":"thinking","thinking":"..."}

Without the required signature field that Claude API now requires.

Suggested Fix

1. Sanitize session history before sending to API - strip or fix thinking blocks without signatures
2. Ensure all thinking blocks are saved with proper signature field

Workaround

User must run /new to start fresh session.

Environment

• OpenClaw 2026.2.2-3
• Model: claude-opus-4-5-thinking via google-antigravity

Note: Issue #8646 was created with the wrong account (hackathon bot) and should be disregarded.