diff --git a/packages/core/src/agents/registry.test.ts b/packages/core/src/agents/registry.test.ts
index 24a8cf65c3..8518efb5b8 100644
--- a/packages/core/src/agents/registry.test.ts
+++ b/packages/core/src/agents/registry.test.ts
@@ -942,28 +942,14 @@ describe('AgentRegistry', () => {
       );
     });
 
-    it('should maintain registration under canonical name even if overrides are applied', async () => {
+    it('should maintain registration under canonical name', async () => {
       const originalName = 'my-agent';
       const definition = { ...MOCK_AGENT_V1, name: originalName };
 
-      // Mock overrides in settings
-      vi.spyOn(mockConfig, 'getAgentsSettings').mockReturnValue({
-        overrides: {
-          [originalName]: {
-            enabled: true,
-            modelConfig: { model: 'overridden-model' },
-          },
-        },
-      });
-
       await registry.testRegisterAgent(definition);
 
       const registered = registry.getDefinition(originalName);
       expect(registered).toBeDefined();
-      expect((registered as LocalAgentDefinition).modelConfig.model).toBe(
-        'overridden-model',
-      );
-      // Ensure it is NOT registered under some other key
       expect(registry.getAllAgentNames()).toEqual([originalName]);
     });
 
diff --git a/packages/core/src/agents/registry.ts b/packages/core/src/agents/registry.ts
index 3b33539f2d..537b8040c1 100644
--- a/packages/core/src/agents/registry.ts
+++ b/packages/core/src/agents/registry.ts
@@ -345,7 +345,18 @@ export class AgentRegistry {
     }
 
     const mergedDefinition = this.applyOverrides(definition, settingsOverrides);
-    this.agents.set(definition.name, mergedDefinition);
+
+    // Ensure we don't accidentally overwrite an existing agent with a different canonical name
+    if (
+      mergedDefinition.name !== definition.name &&
+      this.agents.has(mergedDefinition.name)
+    ) {
+      throw new Error(
+        `Cannot register agent '${definition.name}' as '${mergedDefinition.name}': Name collision with an already registered agent.`,
+      );
+    }
+
+    this.agents.set(mergedDefinition.name, mergedDefinition);
 
     this.registerModelConfigs(mergedDefinition);
     this.addAgentPolicy(mergedDefinition);