fix(provider): preserve reasoning_content on second interleaved pass (#24146 follow-up)

[claudianus]

Issue for this PR

Closes #24442

Type of change

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

What does this PR do?

Fixes a regression from PR #24146 where reasoning_content is lost on the second pass through the interleaved transform.

Root cause: The interleaved transform runs on every request. First pass extracts reasoning from content → stores in providerOptions ✅. Second pass (after DB round-trip) finds no reasoning in content (already extracted), so reasoningText = "" → unconditionally overwrites providerOptions.reasoning_content → DeepSeek 400 error.

Changes

1. transform.ts: When reasoningText is empty, fall back to existing providerOptions[sdk][field] value before defaulting to empty string. This preserves non-empty reasoning from the first pass.

const existingField = msg.providerOptions?.[sdk]?.[field]
const resolvedText = reasoningText || existingField || ""

2. provider.ts: Default interleaved: { field: "reasoning_content" } for reasoning models in fromModelsDevModel() when models.dev has reasoning: true but no explicit interleaved config.

3. transform.ts: Use dynamic SDK key ([sdk]) instead of hardcoded openaiCompatible for non-standard providers (e.g., OpenRouter).

How did you verify your code works?

• Empty reasoning_content → still sent as "" (preserves fix: preserve empty reasoning_content for DeepSeek V4 thinking mode #24146 fix)
• Non-empty reasoning_content on second pass → preserved from providerOptions
• DeepSeek direct + OpenRouter-routed DeepSeek both covered
• Non-reasoning models unaffected (gated on reasoning checks)

Screenshots / recordings

N/A

Checklist

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

[claudianus]

cubic review 분석 (PRR_kwDOQheEEc749AeS, 2026-04-26 09:03Z)

결과: ✅ PR 변경 파일(provider.ts, transform.ts)에서 0개 이슈 발견

cubic이 "Auto-approval blocked by 1 unresolved issue"로 표시한 이슈는 src/agents/builtin-agents/resolve-file-uri.ts:22 (Windows drive-root non-terminating loop, P1) 입니다. 그러나 이 파일은 본 PR의 diff에 포함되지 않은 upstream 파일입니다:

$ git diff origin/dev...HEAD --name-only
packages/opencode/src/provider/provider.ts
packages/opencode/src/provider/transform.ts

따라서 이 unresolved 이슈는 본 PR(#24443, DeepSeek reasoning_content second-pass fix)의 scope가 아닌 upstream 관심사입니다. 본 PR의 실질적 변경사항(2개 파일, +53/-9 lines)에서는 cubic이 0개 신규 이슈를 발견했습니다.

조치: 별도 upstream PR이나 이슈로 resolve-file-uri.ts 버그를 리포팅하는 것이 적절하며, 본 PR 머지와는 무관합니다.

cc @cubic-dev-ai