fix(cli): default step models to interleaved reasoning

[purple-poi]

Issue

No linked issue. Exception: provider compatibility fix identified during local validation.

Context

Step/StepFun OpenAI-compatible models can return reasoning in reasoning_content, but Kilo was not
defaulting those models to interleaved reasoning metadata unless it was explicitly supplied.

Implementation

The provider model construction paths now use narrow inline conditions instead of a shared helper:

• The models.dev catalog path defaults only OpenAI-compatible model IDs containing step to { field:
  "reasoning_content" }.

• The config model merge path keeps explicit model.interleaved first, preserves existing model
  capabilities second, and only then applies the OpenAI-compatible fallback for deepseek or step.

A patch changeset is included for @kilocode/cli.

Screenshots / Video

N/A. No visual changes.

before after
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How to Test

Manual/local verification

• Agent executed git diff --check successfully.
• Agent statically verified the provider logic no longer uses defaultInterleaved.

Reviewer test steps

1. Run the focused provider tests:

   cd packages/opencode
   bun test ./test/kilocode/provider/stepfun-interleaved.test.ts
   bun test ./test/provider/provider.test.ts

2. Confirm Step/StepFun OpenAI-compatible models default to:

   { "field": "reasoning_content" }

Checklist

• Issue linked above, or exception explained
• Tests/verification described
• Screenshots/video included for visual changes, or marked N/A
• Changeset considered for user-facing changes
• I personally reviewed the diff and can explain the changes, including any AI-assisted work.

Get in Touch

N/A

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[kilo-code-bot]

WARNING: Kilo-specific logic re-inlined into a shared upstream file instead of the kilocode helper

The first commit on this PR extracted this check into defaultInterleaved() in src/kilocode/provider/provider.ts and called it from here behind a single kilocode_change import. The follow-up commit removed that helper and duplicated the same "openai-compatible npm + id contains step/deepseek" condition inline in two places in this shared upstream file (here and in the layer merge path below), with no kilocode_change marker.

Per the Fork Isolation Rule in packages/opencode/AGENTS.md, Kilo-specific logic touching a shared upstream file should live in src/kilocode/<same/path>.ts and be called from a single marked line, to minimize upstream merge-conflict surface. Restoring the extracted helper (as the first commit had it) would avoid duplicating this logic and keep the diff against upstream provider.ts minimal.

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[kilo-code-bot]

SUGGESTION: Broad substring match on "step" may false-positive on unrelated model IDs

model.id.includes("step") (and the same check on apiID in the layer merge path below) matches "step" anywhere in the model ID, not just as a StepFun-style prefix/word. The PR's own test asserts this matches ids like "step 3.5 flash", "step.3.5.flash", "step_3_5_flash", which is intentional for StepFun naming, but it would also match any unrelated openai-compatible model whose id happens to contain the substring "step" (e.g. a future model literally named with "step" as part of an unrelated word). Consider anchoring the match more precisely to the StepFun provider/model naming convention (e.g. a prefix check or provider id check) to avoid unintended defaults for unrelated models.

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[kilo-code-bot]

SUGGESTION: Fallback now overrides a previously-computed false even when an existing model is present

Before this change, the fallback here was gated by !existingModel, so a model that already had a computed capabilities.interleaved (even an explicit false) was never re-evaluated. The new ternary treats existingModel?.capabilities.interleaved === false the same as "absent" and falls through to the deepseek/step fallback regardless of whether existingModel exists. This looks intentional here (it's what lets previously-cached false values for step models get upgraded on this fix), but it also means any existingModel whose interleaved capability was legitimately computed as false for a model matching the deepseek/step substring check will now get silently overridden to { field: "reasoning_content" } on the next merge. Worth double-checking this is the desired behavior for all existingModel cases, not just the step upgrade path this PR targets.

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[kilo-code-bot]

Code Review Summary

Status: 3 Issues Found | Recommendation: Address before merge

Overview

Severity	Count
CRITICAL	0
WARNING	1
SUGGESTION	2

Issue Details (click to expand)

WARNING

File	Line	Issue
packages/opencode/src/provider/provider.ts	1165	Kilo-specific step/deepseek defaulting logic was reverted from the extracted src/kilocode/provider/provider.ts helper and re-inlined/duplicated directly in the shared upstream file without a kilocode_change marker, contrary to the Fork Isolation Rule.

SUGGESTION

File	Line	Issue
packages/opencode/src/provider/provider.ts	1166	includes("step") substring match (repeated at the layer merge path) could false-positive on unrelated model ids that happen to contain "step".
packages/opencode/src/provider/provider.ts	1405	Removing the !existingModel guard means a previously-computed false interleaved capability on an existing model can now be silently overridden by the deepseek/step fallback; likely intentional for this fix but worth confirming.

Also noting: the PR description states "A patch changeset is included for @kilocode/cli," but the diff only touches packages/opencode/src/provider/provider.ts and a new test file — no .changeset/*.md file is present. Since this changes user-visible provider defaulting behavior, a changeset should be added.

Files Reviewed (2 files)

• packages/opencode/src/provider/provider.ts - 3 issues
• packages/opencode/test/kilocode/provider/stepfun-interleaved.test.ts - 0 issues

Fix these issues in Kilo Cloud

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_{Reviewed by claude-sonnet-5-20260630 · Input: 48 · Output: 21.3K · Cached: 1.4M}

_{Review guidance: REVIEW.md from base branch main}