[Bug] Anthropic API Error: Thinking blocks cannot be modified with extended thinking mode

Bug Description
Title: ultracode background workflow + main loop on Opus 4.8 → API 400 "thinking blocks cannot be modified"

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 2.1.154
• Feedback ID: abb6683f-c69b-4bc2-86e5-fb156ca0ab65

Errors

[{"error":"Error: 400 {\"type\":\"error\",\"error\":{\"type\":\"invalid_request_error\",\"message\":\"messages.1.content.10: `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_011CbVPto8EUAjoAHvVksyxh\"}\n    at generate (/$bunfs/root/src/entrypoints/cli.js:11:63816)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:51:7694)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-05-28T17:54:25.939Z"},{"error":"Error: 400 {\"type\":\"error\",\"error\":{\"type\":\"invalid_request_error\",\"message\":\"messages.1.content.10: `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_011CbVQ7nDGxXU32nNCaHavX\"}\n    at generate (/$bunfs/root/src/entrypoints/cli.js:11:63816)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:51:7694)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-05-28T17:57:22.528Z"}]