refactor(core): clarify small model selection

packages/core/src/catalog.ts

@@ -1,7 +1,7 @@
 export * as Catalog from "./catalog"
 
 import { makeLocationNode } from "@opencode-ai/util/effect/app-node"
-import { Array, Context, Effect, Layer, Option, Order, pipe } from "effect"
+import { Array, Context, Effect, Layer, Order, pipe } from "effect"
 import { Catalog } from "@opencode-ai/schema/catalog"
 import { ModelV2 } from "./model"
 import { ProviderV2 } from "./provider"
@@ -208,57 +208,24 @@ const layer = Layer.effect(
         }),
 
         small: Effect.fn("CatalogV2.model.small")(function* (providerID) {
-          const record = state.get().providers.get(providerID)
-          if (!record) return
-          const provider = record.provider
+          const catalog = state.get().providers.get(providerID)
+          if (!catalog) return
 
           // TODO: Remove these provider-specific assumptions once model syncing reliably reports available deployments.
-          if (providerID === ProviderV2.ID.azure || providerID === ProviderV2.ID.make("azure-cognitive-services")) {
-            return
-          }
+          const cannotDiscoverAvailableModels =
+            providerID === ProviderV2.ID.azure || providerID === ProviderV2.ID.make("azure-cognitive-services")
+          if (cannotDiscoverAvailableModels) return
 
-          if (providerID === ProviderV2.ID.opencode) {
-            const gpt5Nano = record.models.get(ModelV2.ID.make("gpt-5-nano"))
-            if (gpt5Nano?.enabled && gpt5Nano.status === "active") return projectModel(gpt5Nano, provider)
-          }
+          const designated =
+            providerID === ProviderV2.ID.opencode ? catalog.models.get(ModelV2.ID.make("gpt-5-nano")) : undefined
+          if (designated && isActive(designated)) return projectModel(designated, catalog.provider)
 
-          const candidates = pipe(
-            Array.fromIterable(record.models.values()),
-            Array.filter(
-              (model) =>
-                model.providerID === providerID &&
-                model.enabled &&
-                model.status === "active" &&
-                model.capabilities.input.some((item) => item.startsWith("text")) &&
-                model.capabilities.output.some((item) => item.startsWith("text")),
-            ),
-            Array.map((model) => ({
-              model,
-              cost: model.cost[0] ? model.cost[0].input + model.cost[0].output : 999,
-              age: (Date.now() - model.time.released) / (1000 * 60 * 60 * 24 * 30),
-              small: SMALL_MODEL_RE.test(`${model.id} ${model.family ?? ""} ${model.name}`.toLowerCase()),
-            })),
-            Array.filter((item) => item.cost > 0 && item.age <= 18),
-          )
-
-          const pick = (items: typeof candidates) => {
-            const maxCost = Math.max(...items.map((item) => item.cost), 0.01)
-            const maxAge = Math.max(...items.map((item) => item.age), 0.01)
-            return pipe(
-              items,
-              Array.sortWith((item) => (item.cost / maxCost) * 0.8 + (item.age / maxAge) * 0.2, Order.Number),
-              Array.map((item) => projectModel(item.model, provider)),
-              Array.head,
-            )
-          }
-
-          return Option.getOrUndefined(
-            pipe(
-              candidates,
-              Array.filter((item) => item.small),
-              (items) => (items.length > 0 ? pick(items) : pick(candidates)),
-            ),
-          )
+          const candidates = modelCandidates(catalog.models.values(), providerID)
+          const small = candidates.filter((candidate) => candidate.looksSmall)
+          const pool = small.length > 0 ? small : candidates
+          const selected = bestValue(pool)
+          if (!selected) return
+          return projectModel(selected.model, catalog.provider)
         }),
       },
     }
@@ -268,5 +235,48 @@ const layer = Layer.effect(
 )
 
 const SMALL_MODEL_RE = /\b(nano|flash|lite|mini|haiku|small|fast)\b/
+const MONTH_MS = 1000 * 60 * 60 * 24 * 30
+
+const isActive = (model: ModelV2.Info) => model.enabled && model.status === "active"
+
+const modelCandidates = (models: Iterable<ModelV2.Info>, providerID: ProviderV2.ID) => {
+  const now = Date.now()
+  return Array.fromIterable(models).flatMap((model) => {
+    if (
+      model.providerID !== providerID ||
+      !isActive(model) ||
+      !model.capabilities.input.some((item) => item.startsWith("text")) ||
+      !model.capabilities.output.some((item) => item.startsWith("text"))
+    )
+      return []
+
+    const cost = model.cost[0] ? model.cost[0].input + model.cost[0].output : 999
+    const age = (now - model.time.released) / MONTH_MS
+    if (cost <= 0 || age > 18) return []
+    return [
+      {
+        model,
+        cost,
+        age,
+        looksSmall: SMALL_MODEL_RE.test(`${model.id} ${model.family ?? ""} ${model.name}`.toLowerCase()),
+      },
+    ]
+  })
+}
+
+type Candidate = ReturnType<typeof modelCandidates>[number]
+
+const bestValue = (candidates: readonly Candidate[]) => {
+  if (!Array.isReadonlyArrayNonEmpty(candidates)) return
+  const maxCost = Math.max(...candidates.map((candidate) => candidate.cost), 0.01)
+  const maxAge = Math.max(...candidates.map((candidate) => candidate.age), 0.01)
+  return Array.min(
+    candidates,
+    Order.mapInput(
+      Order.Number,
+      (candidate: Candidate) => (candidate.cost / maxCost) * 0.8 + (candidate.age / maxAge) * 0.2,
+    ),
+  )
+}
 
 export const node = makeLocationNode({ service: Service, layer, deps: [EventV2.node, Integration.node] })