API Error 400: tool_use ids must be unique - occurs consistently

Description

When using Claude Code CLI with --print --output-format json, the API consistently returns a 400 error indicating duplicate tool_use IDs are being sent in the request.

Environment

• Platform: macOS (Darwin 25.2.0)
• Model: claude-opus-4-5-20251101

Error

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.1.content.1: `tool_use` ids must be unique"},"request_id":"req_011CXYMdu1vaiqC69uftUr9D"}

Observed Behavior

• The CLI exits with code 0 (success)
• JSON response has is_error: true but subtype: "success"
• The error occurs consistently, not just occasionally
• num_turns: 2 suggests it fails early in the conversation

Expected Behavior

1. Tool use IDs should be unique in all API requests
2. CLI should exit with non-zero code when API returns an error
3. subtype should reflect the error state

Additional Context

The error messages.1.content.1: tool_use ids must be unique suggests tool_use blocks are being duplicated with the same ID somewhere in conversation serialization.