feat(delegate-task): add resolveMetadataModel helper for model fallback

Add helper that picks primary model with fallback to a secondary model

(e.g., categoryModel → parentContext.model). Enforces consistent

{providerID, modelID} shape.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/tools/delegate-task/resolve-metadata-model.test.ts

@@ -0,0 +1,50 @@
+const { describe, test, expect } = require("bun:test")
+
+import { resolveMetadataModel } from "./resolve-metadata-model"
+
+const PRIMARY = { providerID: "openai", modelID: "gpt-5.4" }
+const FALLBACK = { providerID: "anthropic", modelID: "claude-sonnet-4-6" }
+
+describe("resolveMetadataModel", () => {
+  describe("#given primary and fallback are both present", () => {
+    test("#when resolving #then returns primary", () => {
+      const result = resolveMetadataModel(PRIMARY, FALLBACK)
+
+      expect(result).toEqual(PRIMARY)
+    })
+  })
+
+  describe("#given only fallback is present", () => {
+    test("#when resolving #then returns fallback", () => {
+      const result = resolveMetadataModel(undefined, FALLBACK)
+
+      expect(result).toEqual(FALLBACK)
+    })
+  })
+
+  describe("#given only primary is present", () => {
+    test("#when resolving #then returns primary", () => {
+      const result = resolveMetadataModel(PRIMARY, undefined)
+
+      expect(result).toEqual(PRIMARY)
+    })
+  })
+
+  describe("#given both are undefined", () => {
+    test("#when resolving #then returns undefined", () => {
+      const result = resolveMetadataModel(undefined, undefined)
+
+      expect(result).toBeUndefined()
+    })
+  })
+
+  describe("#given primary has extra fields", () => {
+    test("#when resolving #then strips to providerID and modelID only", () => {
+      const extended = { providerID: "openai", modelID: "gpt-5.4", variant: "high", temperature: 0.7 } as const
+
+      const result = resolveMetadataModel(extended, undefined)
+
+      expect(result).toEqual({ providerID: "openai", modelID: "gpt-5.4" })
+    })
+  })
+})

src/tools/delegate-task/resolve-metadata-model.ts

@@ -0,0 +1,21 @@
+import type { DelegatedModelConfig } from "./types"
+
+export interface MetadataModel {
+  providerID: string
+  modelID: string
+}
+
+type ModelLike = Pick<DelegatedModelConfig, "providerID" | "modelID"> | MetadataModel
+
+export function resolveMetadataModel(
+  primary: ModelLike | undefined,
+  fallback: ModelLike | undefined,
+): MetadataModel | undefined {
+  if (primary) {
+    return { providerID: primary.providerID, modelID: primary.modelID }
+  }
+  if (fallback) {
+    return { providerID: fallback.providerID, modelID: fallback.modelID }
+  }
+  return undefined
+}