feat(config): model pool - round-robin multi-model selection for categories

[kang-heewon]

Summary

Extends the model field in category config to accept a string array, enabling round-robin multi-model selection per category.

Usage

// .claude/oh-my-opencode.jsonc
{
  "categories": {
    "quick": {
      "model": ["claude-haiku-4-5", "claude-sonnet-4-5", "claude-opus-4"]
    },
    "deep": {
      "model": "claude-opus-4"  // single string still works as before
    }
  }
}

How It Works

1. Round-robin selection: cycles through the pool on each request
2. Availability check: skips unavailable models, tries the next one
3. Fallback chain: falls back to the existing fallbackChain if the entire pool is unavailable
4. 100% backward compatibility: existing single-string model configs continue to work unchanged

Changes

New Files

File	Description
src/tools/delegate-task/model-pool-utils.ts	Type utilities (isModelPool, normalizeModelToPool, extractSingleModel)
src/tools/delegate-task/model-pool-state.ts	Round-robin state manager (in-memory Map, per-category independent counter)

Modified Files

File	Change
src/config/schema/categories.ts	model: z.union([z.string(), z.array(z.string()).min(1)]).optional()
src/tools/delegate-task/model-selection.ts	Pool array handling + availability traversal logic
src/tools/delegate-task/categories.ts	Array model passthrough (skip resolveModel)
src/tools/delegate-task/category-resolver.ts	Split rawCategoryModel into string/pool branches
src/agents/agent-builder.ts	typeof === "string" guard (AgentConfig.model is string only)
src/agents/builtin-agents/agent-overrides.ts	Same type guard
src/agents/dynamic-agent-prompt-builder.ts	AvailableCategory.model?: string | string[]
src/plugin-handlers/prometheus-agent-config-builder.ts	Ignore array model (prometheus does not support pools)
assets/oh-my-opencode.schema.json	Schema updated to reflect model type change

Tests

✅ 41 tests pass, 0 fail (70 expect calls)
✅ TypeScript: 0 compile errors
✅ Build: success

Test File	Coverage
categories.test.ts	Schema extension, empty array rejection, type validation (5)
model-pool-utils.test.ts	isModelPool, normalizeModelToPool, extractSingleModel (10)
model-pool-state.test.ts	Round-robin cycling, per-category isolation, reset (6)
model-selection.test.ts	Pool selection, availability check, fallback (8)
categories.test.ts	Array passthrough, backward compatibility (5)
category-resolver.test.ts	Integration scenarios, error handling (7)

Design Decisions

• In-memory state: resets on process restart (intentional — no persistence needed)
• Safe modulo: handles pool size changes without index overflow
• Pool key: JSON.stringify(pool) — same array shares the same counter
• AgentConfig protection: SDK type (string | undefined) is immutable; arrays are handled exclusively at the category-resolver layer

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[github-actions]

All contributors have signed the CLA. Thank you! ✅
_{Posted by the CLA Assistant Lite bot.}

[cubic-dev-ai]

No issues found across 17 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Auto-approved: Comprehensive updates include schema validation, model pool support with thorough tests ensuring no regressions.}

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[kang-heewon]

I have read the CLA Document and I hereby sign the CLA