fix(opencode): ignore tool calls emitted inside reasoning blocks

[danmaxis]

Issue for this PR

Closes #6708

(Same underlying behavior was also reported in #8851 and #10996, now closed.)

Type of change

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

What does this PR do?

Reasoning models (Qwen, Kimi K2, GLM, ...) sometimes emit tool-call markup inside their <think> reasoning while still thinking. The inference server promotes that to a structured tool call, and since opencode's tools carry an execute, streamText runs it — firing a side effect and ending the turn before the model produces its real answer.

By the time the assistant message exists, the tool call is already a structured tool_calls entry with no trace of where it came from. The ordering is still visible at the provider stream level, so the fix is a small LanguageModelV3 wrapStream middleware (reasoning-tool-guard.ts) added next to the existing transformParams middleware in session/llm.ts. It runs over the stream before streamText interprets tool calls and:

• drops any tool call that begins while a reasoning block is still open (plus that call's tool-input-* / tool-result parts), and
• downgrades a resulting tool-calls finish reason to stop, so the session loop doesn't wait on a tool that never runs.

It only touches calls that begin before reasoning-end. Calls emitted after reasoning closes pass through, a mixed turn keeps its tool-calls finish reason, and it's a no-op for any stream without reasoning parts. Opt out per model with options.suppressToolCallsInReasoning: false.

How did you verify your code works?

Added test/session/reasoning-tool-guard.test.ts (5 cases: in-reasoning call suppressed + finish downgraded; post-reasoning call preserved; mixed turn keeps tool-calls; plain text passes through; suppressed even when the model stops mid-<think>). bun test, oxlint, prettier --check, and tsgo --noEmit pass; the existing llm.test.ts is unchanged.

Screenshots / recordings

N/A — not a UI change.

Checklist

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

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Thanks for taking a look — happy to adjust the gating, naming, or placement if you'd prefer it done differently.

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