fix: enforce XOR between agent and custom source in online eval config

Author: notgitika

src/cli/commands/run/command.tsx

@@ -101,7 +101,7 @@ export const registerRun = (program: Command) => {
         json?: boolean;
       }) => {
         const isArnMode = !!(cliOptions.runtimeArn && cliOptions.evaluatorArn);
-        const isCustomMode = !!cliOptions.customServiceName;
+        const isCustomMode = !!(cliOptions.customServiceName && cliOptions.customLogGroupName);
         const isInputMode = !!cliOptions.inputPath;
         if (!isArnMode && !isCustomMode && !isInputMode) {
           requireProject();

src/schema/schemas/primitives/__tests__/online-eval-config.test.ts

@@ -118,13 +118,13 @@ describe('OnlineEvalConfigSchema', () => {
     expect(OnlineEvalConfigSchema.safeParse(config).success).toBe(true);
   });
 
-  it('accepts config with both agent and custom log source fields', () => {
+  it('rejects config with both agent and custom log source fields', () => {
     const config = {
       ...validConfig,
       customLogGroupName: '/custom/log-group',
       customServiceName: 'custom-service',
     };
-    expect(OnlineEvalConfigSchema.safeParse(config).success).toBe(true);
+    expect(OnlineEvalConfigSchema.safeParse(config).success).toBe(false);
   });
 
   it('rejects config with neither agent nor custom log source fields', () => {

src/schema/schemas/primitives/online-eval-config.ts

@@ -50,24 +50,25 @@ export const OnlineEvalConfigSchema = z
   })
   .refine(
     data => {
-      const hasAgent = data.agent !== undefined;
-      const hasCustom = data.customLogGroupName !== undefined && data.customServiceName !== undefined;
-      return hasAgent || hasCustom;
+      // Custom fields must be provided together
+      const hasLogGroup = data.customLogGroupName !== undefined;
+      const hasServiceName = data.customServiceName !== undefined;
+      return hasLogGroup === hasServiceName;
     },
     {
-      message:
-        'Either "agent" must be provided (for project agents) or both "customLogGroupName" and "customServiceName" (for external agents)',
+      message: 'Both "customLogGroupName" and "customServiceName" must be provided together',
     }
   )
   .refine(
     data => {
-      // If one custom field is set, the other must also be set
-      const hasLogGroup = data.customLogGroupName !== undefined;
-      const hasServiceName = data.customServiceName !== undefined;
-      return hasLogGroup === hasServiceName;
+      const hasAgent = data.agent !== undefined;
+      const hasCustom = data.customLogGroupName !== undefined && data.customServiceName !== undefined;
+      // Exactly one source must be specified, not both
+      return (hasAgent || hasCustom) && !(hasAgent && hasCustom);
     },
     {
-      message: 'Both "customLogGroupName" and "customServiceName" must be provided together',
+      message:
+        'Specify either "agent" (for project agents) or both "customLogGroupName" and "customServiceName" (for external agents), but not both',
     }
   );