fix return type of fireSessionStartEvent to defaultHookOutput (#16833)

packages/cli/src/gemini.tsx

@@ -648,18 +648,22 @@ export async function main() {
     const sessionStartSource = resumedSessionData
       ? SessionStartSource.Resume
       : SessionStartSource.Startup;
-    const result = await config
-      .getHookSystem()
-      ?.fireSessionStartEvent(sessionStartSource);
 
-    if (result?.finalOutput) {
-      if (result.finalOutput.systemMessage) {
-        writeToStderr(result.finalOutput.systemMessage + '\n');
-      }
-      const additionalContext = result.finalOutput.getAdditionalContext();
-      if (additionalContext) {
-        // Prepend context to input (System Context -> Stdin -> Question)
-        input = input ? `${additionalContext}\n\n${input}` : additionalContext;
+    const hookSystem = config?.getHookSystem();
+    if (hookSystem) {
+      const result = await hookSystem.fireSessionStartEvent(sessionStartSource);
+
+      if (result) {
+        if (result.systemMessage) {
+          writeToStderr(result.systemMessage + '\n');
+        }
+        const additionalContext = result.getAdditionalContext();
+        if (additionalContext) {
+          // Prepend context to input (System Context -> Stdin -> Question)
+          input = input
+            ? `${additionalContext}\n\n${input}`
+            : additionalContext;
+        }
       }
     }
 

packages/cli/src/ui/AppContainer.tsx

@@ -300,18 +300,18 @@ export const AppContainer = (props: AppContainerProps) => {
         .getHookSystem()
         ?.fireSessionStartEvent(sessionStartSource);
 
-      if (result?.finalOutput) {
-        if (result.finalOutput?.systemMessage) {
+      if (result) {
+        if (result.systemMessage) {
           historyManager.addItem(
             {
               type: MessageType.INFO,
-              text: result.finalOutput.systemMessage,
+              text: result.systemMessage,
             },
             Date.now(),
           );
         }
 
-        const additionalContext = result.finalOutput.getAdditionalContext();
+        const additionalContext = result.getAdditionalContext();
         const geminiClient = config.getGeminiClient();
         if (additionalContext && geminiClient) {
           await geminiClient.addHistory({

packages/cli/src/ui/commands/clearCommand.ts

@@ -29,7 +29,10 @@ export const clearCommand: SlashCommand = {
       .getChatRecordingService();
 
     // Fire SessionEnd hook before clearing
-    await config?.getHookSystem()?.fireSessionEndEvent(SessionEndReason.Clear);
+    const hookSystem = config?.getHookSystem();
+    if (hookSystem) {
+      await hookSystem.fireSessionEndEvent(SessionEndReason.Clear);
+    }
 
     if (geminiClient) {
       context.ui.setDebugMessage('Clearing terminal and resetting chat.');
@@ -48,9 +51,10 @@ export const clearCommand: SlashCommand = {
     }
 
     // Fire SessionStart hook after clearing
-    const result = await config
-      ?.getHookSystem()
-      ?.fireSessionStartEvent(SessionStartSource.Clear);
+    let result;
+    if (hookSystem) {
+      result = await hookSystem.fireSessionStartEvent(SessionStartSource.Clear);
+    }
 
     // Give the event loop a chance to process any pending telemetry operations
     // This ensures logger.emit() calls have fully propagated to the BatchLogRecordProcessor
@@ -65,11 +69,11 @@ export const clearCommand: SlashCommand = {
     uiTelemetryService.setLastPromptTokenCount(0);
     context.ui.clear();
 
-    if (result?.finalOutput?.systemMessage) {
+    if (result?.systemMessage) {
       context.ui.addItem(
         {
           type: MessageType.INFO,
-          text: result.finalOutput.systemMessage,
+          text: result.systemMessage,
         },
         Date.now(),
       );

packages/core/src/hooks/hookSystem.ts

@@ -94,11 +94,12 @@ export class HookSystem {
    */
   async fireSessionStartEvent(
     source: SessionStartSource,
-  ): Promise<AggregatedHookResult | undefined> {
+  ): Promise<DefaultHookOutput | undefined> {
     if (!this.config.getEnableHooks()) {
       return undefined;
     }
-    return this.hookEventHandler.fireSessionStartEvent(source);
+    const result = await this.hookEventHandler.fireSessionStartEvent(source);
+    return result.finalOutput;
   }
 
   async fireSessionEndEvent(