Fix disabled instance check in text generation and empty registry fallback

- TextGenerationLive: Add enabled check in resolveInstance so disabled
  provider instances surface a TextGenerationError instead of silently
  executing text generation, matching the documented behavior.

- ProviderInstanceRegistryHydration: Fall back to DEFAULT_SERVER_SETTINGS
  instead of an empty ProviderInstanceConfigMap when the initial settings
  read fails, ensuring built-in driver default instances are materialized
  even on transient I/O errors during boot.

Author: cursoragent

apps/server/src/git/Layers/TextGenerationLive.ts

@@ -51,7 +51,14 @@ const resolveInstance = (
   registry.getInstance(instanceId).pipe(
     Effect.flatMap((instance) =>
       instance
-        ? Effect.succeed(instance.textGeneration)
+        ? instance.enabled
+          ? Effect.succeed(instance.textGeneration)
+          : Effect.fail(
+              new TextGenerationError({
+                operation,
+                detail: `Provider instance '${instanceId}' is disabled.`,
+              }),
+            )
         : Effect.fail(
             new TextGenerationError({
               operation,

apps/server/src/provider/Layers/ProviderInstanceRegistryHydration.ts

@@ -42,6 +42,7 @@
  * @module provider/Layers/ProviderInstanceRegistryHydration
  */
 import {
+  DEFAULT_SERVER_SETTINGS,
   defaultInstanceIdForDriver,
   type ProviderInstanceConfig,
   type ProviderInstanceConfigMap,
@@ -158,13 +159,10 @@ export const ProviderInstanceRegistryHydrationLive: Layer.Layer<
 > = Layer.unwrap(
   Effect.gen(function* () {
     const serverSettings = yield* ServerSettingsService;
-    const initialSettings: ServerSettings | undefined = yield* serverSettings.getSettings.pipe(
-      Effect.orElseSucceed(() => undefined),
+    const initialSettings: ServerSettings = yield* serverSettings.getSettings.pipe(
+      Effect.orElseSucceed(() => DEFAULT_SERVER_SETTINGS),
     );
-    const initialConfigMap =
-      initialSettings === undefined
-        ? ({} as ProviderInstanceConfigMap)
-        : deriveProviderInstanceConfigMap(initialSettings);
+    const initialConfigMap = deriveProviderInstanceConfigMap(initialSettings);
 
     const mutableLayer = ProviderInstanceRegistryMutableLayer({
       drivers: BUILT_IN_DRIVERS,