fix(core): fill Bedrock endpoint region from provider settings (#58538)

packages/core/src/model-resolver.ts

@@ -278,7 +278,7 @@ function prepareProviderSettings(
 ): Effect.Effect<Readonly<Record<string, unknown>>, UnresolvedProviderVariablesError> {
   const baseURL = settings.baseURL
   if (typeof baseURL !== "string") return Effect.succeed(settings)
-  return prepareProviderURL(model, baseURL).pipe(
+  return prepareProviderURL(model, baseURL, settings).pipe(
     Effect.map((prepared) => (prepared === baseURL ? settings : { ...settings, baseURL: prepared })),
   )
 }
@@ -286,9 +286,15 @@ function prepareProviderSettings(
 function prepareProviderURL(
   model: RuntimeInfo,
   baseURL: string,
+  settings: Readonly<Record<string, unknown>>,
 ): Effect.Effect<string, UnresolvedProviderVariablesError> {
   if (!baseURL.includes("${")) return Effect.succeed(baseURL)
-  const prepared = baseURL.replace(/\$\{([^}]+)\}/g, (placeholder, name: string) => process.env[name] ?? placeholder)
+  // Catalog Bedrock URLs are model settings while `region` is a provider setting, so they only meet here.
+  const prepared = baseURL.replace(
+    /\$\{([^}]+)\}/g,
+    (placeholder, name: string) =>
+      (name === "AWS_REGION" && typeof settings.region === "string" ? settings.region : process.env[name]) ?? placeholder,
+  )
   const failure = unresolvedProviderVariables(model, prepared)
   return failure ? Effect.fail(failure) : Effect.succeed(prepared)
 }

packages/core/test/model-resolver.test.ts

@@ -242,6 +242,24 @@ describe("ModelResolver", () => {
     ),
   )
 
+  it.effect("fills Mantle catalog URLs from the provider region", () =>
+    withEnv({ AWS_REGION: undefined, AWS_DEFAULT_REGION: undefined }, () =>
+      Effect.gen(function* () {
+        const catalog = model(Provider.aisdk("@ai-sdk/amazon-bedrock/mantle"), {
+          providerID: Provider.ID.amazonBedrock,
+          modelID: "openai.gpt-5.5",
+          settings: { baseURL: "https://bedrock-mantle.${AWS_REGION}.api.aws/openai/v1" },
+        })
+        const resolved = yield* ModelResolver.fromCatalogModel({
+          ...catalog,
+          settings: Provider.mergeOverlay({ region: "us-west-2" }, catalog.settings),
+        })
+
+        expect(resolved.route.endpoint.baseURL).toBe("https://bedrock-mantle.us-west-2.api.aws/openai/v1")
+      }),
+    ),
+  )
+
   it.effect("prefers the configured Mantle region over the environment", () =>
     withEnv({ AWS_REGION: "us-east-1" }, () =>
       Effect.gen(function* () {