fix(opencode): support interleaved reasoning_content for anthropic protocol non-Claude models

[llc1123]

Issue for this PR

Closes #14638

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

When non-Claude models (e.g. kimi-k2.5) are used via the Anthropic SDK with interleaved reasoning enabled, reasoning content from previous assistant turns is silently dropped because the Anthropic SDK has no mechanism to pass arbitrary message-level fields (like reasoning_content) through to the HTTP body.

This PR makes the interleaved reasoning path for Anthropic SDK models use providerOptions.anthropic — the same pattern the openai-compatible provider already uses with providerOptions.openaiCompatible.

Dependencies

Blocked by: vercel/ai#12760 — Adds support for spreading providerOptions.anthropic onto assistant messages in @ai-sdk/anthropic.

This PR is not ready for review until the upstream change lands and is released.

How did you verify your code works?

• Typecheck passes (bun turbo typecheck)
• 108 tests pass (including 5 new tests for this feature)
• Tested with kimi-k2.5 via Anthropic SDK: reasoning content round-trips correctly across turns

Screenshots / recordings

N/A — no UI changes.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate Found:

• PR fix(opencode): support interleaved reasoning_content for anthropic protocol non-Claude models #14637: fix(opencode): support interleaved reasoning_content for anthropic protocol non-Claude models #14637
  • Same title: "fix(opencode): support interleaved reasoning_content for anthropic protocol non-Claude models"
  • Relationship: This appears to be a duplicate or closely related PR addressing the same issue. Both PRs have identical titles and are targeting the same fix for supporting reasoning content with non-Claude models via the Anthropic SDK.

Since PR #14641 (current PR) and PR #14637 share the exact same title and appear to address the same issue, you should check if one is a duplicate of the other and consider closing one while consolidating efforts on the other.