[Bug] Claude Opus 4.8: Tool call parsing fails when extended thinking is triggered

Bug Description
Claude Opus 4.8 frequently fails with "The model's tool call could not be parsed (retry also failed)" whenever extended thinking is triggered. Repro: - Happens on plain conversational turns, not just tool-heavy workflows - Triggered whenever the model enters extended/adaptive thinking - Reproducible across multiple separate terminal sessions today - Same prompts on Opus 4.7 work fine — issue is specific to 4.8 Frequency: very high, most thinking-triggered turns fail Notes: - Opus 4.8 also tends to hang silently in the thinking phase (no token output visible) before producing this error - Adaptive thinking can't be disabled via budget_tokens on 4.8, so users have no way to avoid triggering this path - Issue #61133 describes the same parse failure on Opus 4.7 (1M); appears to have regressed / re-emerged on 4.8

Environment Info

• Platform: darwin
• Terminal: pycharm
• Version: 2.1.156
• Feedback ID: 951e763a-7846-4bab-a9e8-3f83b2b77322

Errors

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