[Bug] Opus 4.7 with extended thinking intermittently emits unparseable tool_use blocks

Bug Description
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Title: Opus 4.7 + extended thinking intermittently emits unparseable tool_use blocks (small calls too)

Body:
Frequent "The model's tool call could not be parsed (retry also failed)" hard-stops.
CLI 2.1.150 (latest). Model: claude-opus-4-7.

Findings from my local session logs (~/.claude/projects/.../*.jsonl), 5/24-5/26:

• ~20 "malformed and could not be parsed" retry prompts across 6 sessions;

one session (83889c9d) hit it 8 times.

• The failing assistant turns have stop_reason="tool_use" but NO parseable

tool_use block — only a thinking block is present.

• NOT caused by size: failing turns were only 164-1093 output tokens.
• NOT caused by special chars: a plain 119-char single-line SQL

(SELECT ... FROM information_schema.columns ...) triggered it.

• Affects multiple tools: Read, Bash, mcp execute_sql.
• Common factor: every failing turn is Opus 4.7 with an extended-thinking block.

Looks like a tool_use serialization defect when extended thinking is active.
Auto-retry sometimes recovers; "retry also failed" is when the retry repeats it.

Environment Info

• Platform: darwin
• Terminal: ghostty
• Version: 2.1.150
• Feedback ID: 59d64386-04ba-4c37-ace9-f2c3a0830f55

Errors

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