Invalid `signature` in `thinking` block when switching Claude models (Copilot provider)

[mouadlotfi]

Summary

Switching from Claude Opus 4.5 to Claude Sonnet 4.5 within the same conversation (GitHub Copilot provider) fails with:

messages.3.content.0: Invalid `signature` in `thinking` block

Steps to Reproduce

1. Start a conversation using Claude Opus 4.5 via GitHub Copilot provider.
2. In the same conversation, switch to Claude Sonnet 4.5 (thinking enabled).
3. Send a new message.

Actual Behavior

Request fails with the error above.

Expected Behavior

Switching between Claude models in the same thread should work, or OpenCode should strip/normalize incompatible thinking blocks to avoid signature validation failures.

Notes

• Switching to OpenAI Codex medium in the same conversation works normally.
• Workaround: start a new conversation before switching Claude models.
• OpenCode version: (not provided).
• OS: (not provided).
• Provider: GitHub Copilot.

If you need additional logs or version info, I can follow up.

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Claude Models Thinking block error #10970: Claude Models Thinking block error - reports similar thinking block validation errors when writing tools or streaming
• Error: Invalid signature in thinking block #6418: Error: Invalid signature in thinking block - reports the exact same error message when switching models mid-session (GLM 4.7/MinMax 2.1 to Opus 4.5)

The error pattern appears to be a known issue with thinking block signature validation when switching between models with different thinking block implementations.

Feel free to ignore if these don't address your specific case.

[hchaudhary1]

seeing same issue..

[rekram1-node]

got a pr up with fixes, doing some touches and adding more tests.

The github copilot provider is non standard so we need to maintain a bit of logic ourselves