refactor(core): let plugins pin small models via catalog draft

Move copilot utility-model preference out of core selection into the
github-copilot plugin by exposing catalog.model.small set/get/remove on
the transform draft.

packages/core/src/catalog.ts

@@ -21,6 +21,7 @@ export const Event = Catalog.Event
 type Data = {
   providers: Map<ProviderV2.ID, ProviderRecord>
   defaultModel?: DefaultModel
+  smallModels: Map<ProviderV2.ID, ModelV2.ID>
 }
 
 export type Draft = {
@@ -38,6 +39,11 @@ export type Draft = {
       get: () => DefaultModel | undefined
       set: (providerID: ProviderV2.ID, modelID: ModelV2.ID) => void
     }
+    small: {
+      get: (providerID: ProviderV2.ID) => ModelV2.ID | undefined
+      set: (providerID: ProviderV2.ID, modelID: ModelV2.ID) => void
+      remove: (providerID: ProviderV2.ID) => void
+    }
   }
 }
 
@@ -83,7 +89,7 @@ const layer = Layer.effect(
 
     const state = State.create<Data, Draft>({
       name: "catalog",
-      initial: () => ({ providers: new Map() }),
+      initial: () => ({ providers: new Map(), smallModels: new Map() }),
       draft: (draft) => {
         const result: Draft = {
           provider: {
@@ -131,6 +137,15 @@ const layer = Layer.effect(
                 draft.defaultModel = { providerID, modelID }
               },
             },
+            small: {
+              get: (providerID) => draft.smallModels.get(providerID),
+              set: (providerID, modelID) => {
+                draft.smallModels.set(providerID, modelID)
+              },
+              remove: (providerID) => {
+                draft.smallModels.delete(providerID)
+              },
+            },
           },
         }
         return result
@@ -217,13 +232,11 @@ const layer = Layer.effect(
             return
           }
 
-          // GitHub exposes utility models for title generation without including them in the picker.
-          // They remain in the catalog with enabled=false, so prefer them before family selection.
-          if (providerID.startsWith("github-copilot")) {
-            for (const id of COPILOT_UTILITY_MODELS) {
-              const model = record.models.get(ModelV2.ID.make(id))
-              if (model?.status === "active") return projectModel(model, provider)
-            }
+          // Plugin transforms may pin a small model (for example picker-disabled utility models).
+          const configured = state.get().smallModels.get(providerID)
+          if (configured) {
+            const model = record.models.get(configured)
+            if (model?.status === "active") return projectModel(model, provider)
           }
 
           const priority = providerID.startsWith("opencode")
@@ -272,6 +285,5 @@ const layer = Layer.effect(
 )
 
 const SMALL_MODEL_FAMILY_PRIORITY = ["gemini-flash", "gpt-nano", "claude-haiku"]
-const COPILOT_UTILITY_MODELS = ["gpt-5.4-nano", "gpt-4.1", "gpt-4o", "gpt-4o-mini"]
 
 export const node = makeLocationNode({ service: Service, layer, deps: [EventV2.node, Integration.node] })

packages/core/src/plugin/host.ts

@@ -148,6 +148,12 @@ export const make = Effect.fn("PluginHost.make")(function* (plugin: PluginV2.Int
                 set: (providerID, modelID) =>
                   draft.model.default.set(ProviderV2.ID.make(providerID), ModelV2.ID.make(modelID)),
               },
+              small: {
+                get: (providerID) => draft.model.small.get(ProviderV2.ID.make(providerID)),
+                set: (providerID, modelID) =>
+                  draft.model.small.set(ProviderV2.ID.make(providerID), ModelV2.ID.make(modelID)),
+                remove: (providerID) => draft.model.small.remove(ProviderV2.ID.make(providerID)),
+              },
             },
           })
         }),

packages/core/src/plugin/provider/github-copilot.ts

@@ -119,6 +119,8 @@ function shouldUseResponses(modelID: string) {
   return Number(match[1]) >= 5 && !modelID.startsWith("gpt-5-mini")
 }
 
+const UTILITY_MODELS = ["gpt-5.4-nano", "gpt-4.1", "gpt-4o", "gpt-4o-mini"]
+
 export const GithubCopilotPlugin = define({
   id: "opencode.provider.github-copilot",
   effect: Effect.fn(function* (ctx) {
@@ -192,6 +194,13 @@ export const GithubCopilotPlugin = define({
           model.enabled = false
         })
       }
+      // GitHub exposes utility models for title generation without including them in the picker.
+      const utility = UTILITY_MODELS.map((id) => ModelV2.ID.make(id)).find((id) => {
+        const model = evt.model.get(item.provider.id, id)
+        return model?.status === "active"
+      })
+      if (utility) evt.model.small.set(item.provider.id, utility)
+      else evt.model.small.remove(item.provider.id)
     })
     const refresh = () => loading.withPermit(load().pipe(Effect.andThen(ctx.catalog.reload())))
     yield* events.subscribe(Integration.Event.ConnectionUpdated).pipe(

packages/core/test/catalog.test.ts

@@ -393,7 +393,7 @@ describe("CatalogV2", () => {
     }),
   )
 
-  it.effect("small model prefers picker-disabled copilot utility models", () =>
+  it.effect("small model prefers a plugin-configured small model override", () =>
     Effect.gen(function* () {
       const catalog = yield* Catalog.Service
       const providerID = ProviderV2.ID.githubCopilot
@@ -403,14 +403,11 @@ describe("CatalogV2", () => {
           model.family = ModelV2.Family.make("gpt-mini")
           model.time.released = Date.now()
         })
-        catalog.model.update(providerID, ModelV2.ID.make("gpt-4o-mini"), (model) => {
-          model.enabled = false
-          model.time.released = Date.now() - 1000
-        })
         catalog.model.update(providerID, ModelV2.ID.make("gpt-5.4-nano"), (model) => {
           model.enabled = false
           model.time.released = Date.now() - 2000
         })
+        catalog.model.small.set(providerID, ModelV2.ID.make("gpt-5.4-nano"))
       })
 
       expect((yield* catalog.model.small(providerID))?.id).toBe(ModelV2.ID.make("gpt-5.4-nano"))

packages/core/test/plugin/host.ts

@@ -178,6 +178,12 @@ export function catalogHost(catalog: Catalog.Interface): PluginContext["catalog"
               set: (providerID, modelID) =>
                 draft.model.default.set(ProviderV2.ID.make(providerID), ModelV2.ID.make(modelID)),
             },
+            small: {
+              get: (providerID) => draft.model.small.get(ProviderV2.ID.make(providerID)),
+              set: (providerID, modelID) =>
+                draft.model.small.set(ProviderV2.ID.make(providerID), ModelV2.ID.make(modelID)),
+              remove: (providerID) => draft.model.small.remove(ProviderV2.ID.make(providerID)),
+            },
           },
         }),
       ),

packages/plugin/src/v2/effect/catalog.ts

@@ -23,6 +23,11 @@ export interface CatalogDraft {
       get(): { providerID: string; modelID: string } | undefined
       set(providerID: string, modelID: string): void
     }
+    readonly small: {
+      get(providerID: string): string | undefined
+      set(providerID: string, modelID: string): void
+      remove(providerID: string): void
+    }
   }
 }