Fix non-atomic ref update race and options spread signal override

- ProviderRegistry: Use Ref.modify for atomic read-modify-write in
  upsertProviders to prevent concurrent provider data loss when
  multiple fibers update providersRef simultaneously.

- Desktop main: Reorder spread in waitForBackendHttpReady so the
  internal abort controller signal always takes precedence over
  any signal passed via options.

Author: cursoragent

apps/desktop/src/main.ts

@@ -365,8 +365,8 @@ async function waitForBackendHttpReady(
 
   try {
     await waitForHttpReady(baseUrl, {
-      signal: controller.signal,
       ...options,
+      signal: controller.signal,
     });
   } finally {
     if (backendReadinessAbortController === controller) {

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

@@ -108,17 +108,21 @@ export const ProviderRegistryLive = Layer.effect(
         readonly publish?: boolean;
       },
     ) {
-      const previousProviders = yield* Ref.get(providersRef);
-      const mergedProviders = new Map(
-        previousProviders.map((provider) => [provider.provider, provider] as const),
-      );
+      const [previousProviders, providers] = yield* Ref.modify(
+        providersRef,
+        (previousProviders) => {
+          const mergedProviders = new Map(
+            previousProviders.map((provider) => [provider.provider, provider] as const),
+          );
 
-      for (const provider of nextProviders) {
-        mergedProviders.set(provider.provider, provider);
-      }
+          for (const provider of nextProviders) {
+            mergedProviders.set(provider.provider, provider);
+          }
 
-      const providers = orderProviderSnapshots([...mergedProviders.values()]);
-      yield* Ref.set(providersRef, providers);
+          const providers = orderProviderSnapshots([...mergedProviders.values()]);
+          return [[previousProviders, providers] as const, providers];
+        },
+      );
 
       if (haveProvidersChanged(previousProviders, providers)) {
         yield* Effect.forEach(nextProviders, persistProvider, {