Address review comments

Author: andrewheard

FirebaseAI/Sources/Extensions/Internal/GenerationSchema+Gemini.swift

@@ -40,8 +40,11 @@ extension FirebaseAI.GenerationSchema {
     #endif // canImport(FoundationModels)
 
     // TODO: Implement FirebaseAI.GenerationSchema encoding for for iOS < 26.
-    assertionFailure("TODO: \(Self.self).#\(#function) not yet implemented for iOS < 26.")
-    return [:]
+    throw GenerativeModelSession.GenerationError.decodingFailure(
+      GenerativeModelSession.GenerationError.Context(debugDescription: """
+      \(Self.self).#\(#function): `GenerationSchema` encoding is not yet implemented for iOS < 26.
+      """)
+    )
   }
 
   private struct SchemaCodingKey: CodingKey {

FirebaseAI/Tests/TestApp/Tests/Integration/GenerativeModelSessionTests.swift

@@ -254,7 +254,6 @@
       #expect(isComplete, "The stream finished, but the final snapshot was not marked as complete.")
 
       let response = try await stream.collect()
-      print(response.rawContent.isComplete)
       let content = response.content
       #expect(!content.isEmpty)
       #expect(response.rawContent.isComplete, "The final response was not marked as complete.")