fix(core): harden model selection edges (#30987)

packages/core/test/catalog.test.ts

@@ -281,6 +281,34 @@ describe("CatalogV2", () => {
     }),
   )
 
+  it.effect("ignores a configured default on a disabled provider", () =>
+    Effect.gen(function* () {
+      const catalog = yield* Catalog.Service
+      const disabledProvider = ProviderV2.ID.make("disabled")
+      const enabledProvider = ProviderV2.ID.make("enabled")
+      const disabledModel = ModelV2.ID.make("configured")
+      const fallbackModel = ModelV2.ID.make("fallback")
+      const transform = yield* catalog.transform()
+
+      yield* transform((catalog) => {
+        catalog.provider.update(disabledProvider, (provider) => {
+          provider.enabled = false
+        })
+        catalog.model.update(disabledProvider, disabledModel, () => {})
+        catalog.provider.update(enabledProvider, (provider) => {
+          provider.enabled = { via: "custom", data: {} }
+        })
+        catalog.model.update(enabledProvider, fallbackModel, () => {})
+        catalog.model.default.set(disabledProvider, disabledModel)
+      })
+
+      expect(Option.getOrUndefined(yield* catalog.model.default())).toMatchObject({
+        providerID: enabledProvider,
+        id: fallbackModel,
+      })
+    }),
+  )
+
   it.effect("small model prefers small keyword candidates before cost scoring", () =>
     Effect.gen(function* () {
       const catalog = yield* Catalog.Service