[Bug] Thinking blocks in latest assistant message are immutable

Bug Description
getting thinking or redacted_thinking blocks in the latest assistant message cannot be modified. These blocks must remain as they were in the original response.

Environment Info

• Platform: linux
• Terminal: ghostty
• Version: 2.1.153
• Feedback ID: 7ba9663b-3019-414e-a3cf-5e7ff31d0bdc

Errors

[{"error":"Error: 400 {\"type\":\"error\",\"error\":{\"type\":\"invalid_request_error\",\"message\":\"messages.3.content.11: `thinking` or `redacted_thinking` blocks in the latest assistant message cannot be modified. These blocks must remain as they were in the original response.\"},\"request_id\":\"req_011CbVJR3DSpsq426RyQ7HJ2\"}\n    at generate (/$bunfs/root/src/entrypoints/cli.js:11:63519)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:51:7694)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-05-28T16:42:35.214Z"}]