fix(provider): make small model fallback optional (#27405)

packages/opencode/src/provider/provider.ts

@@ -1707,7 +1707,9 @@ const layer = Layer.effect(
 
       if (cfg.small_model) {
         const parsed = parseModel(cfg.small_model)
-        return yield* getModel(parsed.providerID, parsed.modelID).pipe(Effect.orDie)
+        return yield* getModel(parsed.providerID, parsed.modelID).pipe(
+          Effect.catchTag("ProviderModelNotFoundError", () => Effect.succeed(undefined)),
+        )
       }
 
       const s = yield* InstanceState.get(state)
@@ -1735,22 +1737,22 @@ const layer = Layer.effect(
           const candidates = Object.keys(provider.models).filter((m) => m.includes(item))
 
           const globalMatch = candidates.find((m) => m.startsWith("global."))
-          if (globalMatch) return yield* getModel(providerID, ModelID.make(globalMatch)).pipe(Effect.orDie)
+          if (globalMatch) return provider.models[globalMatch]
 
           const region = provider.options?.region
           if (region) {
             const regionPrefix = region.split("-")[0]
             if (regionPrefix === "us" || regionPrefix === "eu") {
               const regionalMatch = candidates.find((m) => m.startsWith(`${regionPrefix}.`))
-              if (regionalMatch) return yield* getModel(providerID, ModelID.make(regionalMatch)).pipe(Effect.orDie)
+              if (regionalMatch) return provider.models[regionalMatch]
             }
           }
 
           const unprefixed = candidates.find((m) => !crossRegionPrefixes.some((p) => m.startsWith(p)))
-          if (unprefixed) return yield* getModel(providerID, ModelID.make(unprefixed)).pipe(Effect.orDie)
+          if (unprefixed) return provider.models[unprefixed]
         } else {
           for (const model of Object.keys(provider.models)) {
-            if (model.includes(item)) return yield* getModel(providerID, ModelID.make(model)).pipe(Effect.orDie)
+            if (model.includes(item)) return provider.models[model]
           }
         }
       }

packages/opencode/test/provider/provider.test.ts

@@ -1025,6 +1025,27 @@ test("getSmallModel respects config small_model override", async () => {
   })
 })
 
+test("getSmallModel ignores invalid config small_model", async () => {
+  await using tmp = await tmpdir({
+    init: async (dir) => {
+      await Bun.write(
+        path.join(dir, "opencode.json"),
+        JSON.stringify({
+          $schema: "https://opencode.ai/config.json",
+          small_model: "anthropic/not-a-real-model",
+        }),
+      )
+    },
+  })
+  await WithInstance.provide({
+    directory: tmp.path,
+    fn: async () => {
+      set("ANTHROPIC_API_KEY", "test-api-key")
+      expect(await getSmallModel(ProviderID.anthropic)).toBeUndefined()
+    },
+  })
+})
+
 test("provider.sort prioritizes preferred models", () => {
   const models = [
     { id: "random-model", name: "Random" },