Add missing sessionStart hook properties (#311109)

extensions/copilot/src/extension/intents/node/toolCallingLoop.ts

@@ -196,6 +196,11 @@ export abstract class ToolCallingLoop<TOptions extends IToolCallingLoopOptions =
 		return this.options.conversation.getLatestTurn();
 	}
 
+	protected get agentName(): string | undefined {
+		return (this.options.request as { subAgentName?: string }).subAgentName
+			?? (this.options.request as { participant?: string }).participant;
+	}
+
 	constructor(
 		protected readonly options: TOptions,
 		@IInstantiationService private readonly _instantiationService: IInstantiationService,
@@ -685,6 +690,8 @@ export abstract class ToolCallingLoop<TOptions extends IToolCallingLoopOptions =
 			if (isFirstTurn) {
 				const startHookResult = await this.executeSessionStartHook({
 					source: 'new',
+					model: this.options.request.model?.id ?? 'unknown',
+					agent_type: this.agentName,
 				}, sessionId, outputStream, token);
 				if (startHookResult.additionalContext) {
 					this.additionalHookContext = startHookResult.additionalContext;
@@ -701,9 +708,7 @@ export abstract class ToolCallingLoop<TOptions extends IToolCallingLoopOptions =
 	}
 
 	public async run(outputStream: ChatResponseStream | undefined, token: CancellationToken): Promise<IToolCallLoopResult> {
-		const agentName = (this.options.request as { subAgentName?: string }).subAgentName
-			?? (this.options.request as { participant?: string }).participant
-			?? 'GitHub Copilot Chat';
+		const agentName = this.agentName ?? 'GitHub Copilot Chat';
 
 		// Extract custom mode name for debug logging (kept separate from agentName to avoid metric cardinality)
 		const modeInstructions = (this.options.request as { modeInstructions2?: { name?: string; isBuiltin?: boolean } }).modeInstructions2;

extensions/copilot/src/extension/intents/test/node/toolCallingLoopHooks.spec.ts

@@ -197,7 +197,10 @@ describe('ToolCallingLoop SessionStart hook', () => {
 	describe('SessionStart hook execution conditions', () => {
 		it('should execute SessionStart hook on the first turn of regular sessions', async () => {
 			const conversation = createTestConversation(1); // First turn
-			const request = createMockChatRequest();
+			const request = createMockChatRequest({
+				model: { id: 'test-model-id' } as ChatRequest['model'],
+				participant: 'test-agent',
+			} as unknown as Partial<ChatRequest>);
 
 			const loop = instantiationService.createInstance(
 				TestToolCallingLoop,
@@ -216,7 +219,12 @@ describe('ToolCallingLoop SessionStart hook', () => {
 
 			const sessionStartCalls = mockChatHookService.getCallsForHook('SessionStart');
 			expect(sessionStartCalls).toHaveLength(1);
-			expect((sessionStartCalls[0].input as SessionStartHookInput).source).toBe('new');
+			const input = sessionStartCalls[0].input as SessionStartHookInput;
+			expect(input).toMatchObject({
+				source: 'new',
+				model: 'test-model-id',
+				agent_type: 'test-agent',
+			});
 		});
 
 		it('should NOT execute SessionStart hook on subsequent turns', async () => {

extensions/copilot/src/platform/chat/common/chatHookService.ts

@@ -172,6 +172,14 @@ export interface SessionStartHookInput {
 	 * The source of the session start. Always "new".
 	 */
 	readonly source: 'new';
+	/**
+	 * The model identifier (e.g. "claude-sonnet-4-6").
+	 */
+	readonly model: string;
+	/**
+	 * The agent or mode name, if applicable.
+	 */
+	readonly agent_type?: string;
 }
 
 /**