feat: add support for user message events from Codex

Add sendUserMessage() method to ApiSessionClient and CodexSession to handle
user_message events from Codex. Updates CodexConversionResult type and
convertCodexEvent() to process user_message payloads, with test coverage.

cli/src/codex/utils/codexEventConverter.test.ts

@@ -23,6 +23,15 @@ describe('convertCodexEvent', () => {
         });
     });
 
+    it('converts user_message events', () => {
+        const result = convertCodexEvent({
+            type: 'event_msg',
+            payload: { type: 'user_message', message: 'hello user' }
+        });
+
+        expect(result?.userMessage).toBe('hello user');
+    });
+
     it('converts reasoning events', () => {
         const result = convertCodexEvent({
             type: 'event_msg',

cli/src/codex/utils/codexEventConverter.ts

@@ -41,6 +41,7 @@ export type CodexMessage = {
 export type CodexConversionResult = {
     sessionId?: string;
     message?: CodexMessage;
+    userMessage?: string;
 };
 
 function asRecord(value: unknown): Record<string, unknown> | null {
@@ -118,7 +119,15 @@ export function convertCodexEvent(rawEvent: unknown): CodexConversionResult | nu
         }
 
         if (eventType === 'user_message') {
-            return null;
+            const message = asString(payloadRecord.message)
+                ?? asString(payloadRecord.text)
+                ?? asString(payloadRecord.content);
+            if (!message) {
+                return null;
+            }
+            return {
+                userMessage: message
+            };
         }
 
         if (eventType === 'agent_message') {