fix(vscode): allow removing provider reasoning

[marius-kilocode]

Edit Provider omits a model's reasoning field when it is disabled, but provider updates are deep-merged with the existing global config. The previously saved reasoning: true therefore survived and reappeared when the provider was reloaded.

Emit the same explicit null deletion sentinel already used for removed models and variants when reasoning is cleared, and accept that sentinel through the config update schema. Existing provider fields remain intact, including sibling models and model variants, while the persisted reasoning override is removed.

Regression coverage exercises the extension save path and the real global config add, persist, remove, and reload lifecycle.

Fixes #11193

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

The only change since the previous review at d3ce281 is a cosmetic line-wrap in a test assertion (custom-provider.test.ts). No logic, types, or behavior changed.

Files Reviewed (6 files)

• .changeset/calm-models-forget.md
• packages/kilo-vscode/src/shared/custom-provider.ts
• packages/kilo-vscode/tests/unit/custom-provider.test.ts
• packages/kilo-vscode/tests/unit/provider-actions-save.test.ts
• packages/opencode/src/config/provider.ts
• packages/opencode/test/kilocode/config/config.test.ts

Previous Review Summary (commit d3ce281)

Current summary above is authoritative. Previous snapshots are kept for context only.

Previous review (commit d3ce281)

Status: No Issues Found | Recommendation: Merge

The fix is correct and well-scoped. The deep-merge/stripNulls pattern is already in use for model and variant deletions; this PR extends it consistently to the reasoning field.

Key observations:

• ProviderPatch type correctly widens reasoning to true | null for the intermediate patch, and the as SanitizedProviderConfig cast at line 200 is intentional — callers receive null sentinels that stripNulls will eliminate on the CLI side.
• The guard oldModel.reasoning !== undefined && newModel.reasoning === undefined correctly captures the "was set, now removed" case, including when the prior value was null.
• The Schema.NullOr(Schema.Boolean) change in provider.ts is the minimal schema change needed to let the null sentinel pass through the CLI's update endpoint without being rejected.
• Test coverage exercises the extension save path (unit), the withCustomProviderDeletions helper directly (unit), and the real global config add/persist/remove/reload lifecycle (integration) — solid regression coverage.

Files Reviewed (5 files)

• .changeset/calm-models-forget.md
• packages/kilo-vscode/src/shared/custom-provider.ts
• packages/kilo-vscode/tests/unit/custom-provider.test.ts
• packages/kilo-vscode/tests/unit/provider-actions-save.test.ts
• packages/opencode/src/config/provider.ts
• packages/opencode/test/kilocode/config/config.test.ts

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_{Reviewed by claude-4.6-sonnet-20260217 · 131,810 tokens}

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