diff --git a/packages/data-provider/src/resolve-llm-delivery-path.spec.ts b/packages/data-provider/src/resolve-llm-delivery-path.spec.ts
index 5d316578f5..09999f8bf0 100644
--- a/packages/data-provider/src/resolve-llm-delivery-path.spec.ts
+++ b/packages/data-provider/src/resolve-llm-delivery-path.spec.ts
@@ -189,6 +189,15 @@ describe('resolveDefaultLLMDeliveryPath', () => {
     );
   });
 
+  it('keeps the system default when the provider is unresolved (agents container)', () => {
+    expect(resolveDefaultLLMDeliveryPath('audio/mpeg', undefined, undefined, 'agents')).toBe(
+      'provider',
+    );
+    expect(resolveDefaultLLMDeliveryPath('application/pdf', undefined, undefined, 'agents')).toBe(
+      'provider',
+    );
+  });
+
   it('should export SYSTEM_LLM_DELIVERY_DEFAULTS with correct shape', () => {
     expect(SYSTEM_LLM_DELIVERY_DEFAULTS.fallback).toBe('text');
     expect(SYSTEM_LLM_DELIVERY_DEFAULTS.overrides).toEqual({
diff --git a/packages/data-provider/src/resolve-llm-delivery-path.ts b/packages/data-provider/src/resolve-llm-delivery-path.ts
index f6e9ebb597..02392182d6 100644
--- a/packages/data-provider/src/resolve-llm-delivery-path.ts
+++ b/packages/data-provider/src/resolve-llm-delivery-path.ts
@@ -70,7 +70,12 @@ export function resolveDefaultLLMDeliveryPath(
   /** Only the system default is capability-gated: an explicit config above is the
    *  admin's decision. A known endpoint that cannot encode documents or media would
    *  otherwise accept the upload and hand the model nothing at all. */
-  if (systemDefault === 'provider' && endpoint != null && !isProviderCapable(mimeType, endpoint)) {
+  /** `agents` is a container, not a provider: it is what an upload reports when the
+   *  agent's real provider could not be resolved, as for ephemeral agents. Judging
+   *  capability from it would downgrade media the actual provider can deliver, so an
+   *  unresolved provider keeps the system default. */
+  const providerKnown = endpoint != null && endpoint !== EModelEndpoint.agents;
+  if (systemDefault === 'provider' && providerKnown && !isProviderCapable(mimeType, endpoint)) {
     return 'text';
   }