diff --git a/src/vs/platform/agentHost/node/copilot/copilotAgentSession.ts b/src/vs/platform/agentHost/node/copilot/copilotAgentSession.ts
index 0d4a1dcbe41aa..da814dff103eb 100644
--- a/src/vs/platform/agentHost/node/copilot/copilotAgentSession.ts
+++ b/src/vs/platform/agentHost/node/copilot/copilotAgentSession.ts
@@ -6098,14 +6098,26 @@ export class CopilotAgentSession extends Disposable {
 			this._logService.trace(`[Copilot:${sessionId}] Subagent selected: ${e.data.agentName}`);
 		}));
 
+		const subagentIdsByStopHook = new Map<string, string>();
 		this._register(wrapper.onHookStart(e => {
 			this._logService.trace(`[Copilot:${sessionId}] Hook started: ${e.data.hookType} (${e.data.hookInvocationId})`);
+			if (e.data.hookType === 'subagentStop') {
+				// Some SDK stop hooks identify the subagent only in the start event's input.
+				const input = e.data.input;
+				const inputAgentId = input !== null && typeof input === 'object' && !Array.isArray(input) ? input.agentId : undefined;
+				const agentId = e.agentId ?? (isString(inputAgentId) ? inputAgentId : undefined);
+				if (agentId) {
+					subagentIdsByStopHook.set(e.data.hookInvocationId, agentId);
+				}
+			}
 		}));
 
 		this._register(wrapper.onHookEnd(e => {
 			this._logService.trace(`[Copilot:${sessionId}] Hook ended: ${e.data.hookType} (${e.data.hookInvocationId}), success=${e.data.success}`);
-			if (e.data.hookType === 'agentStop') {
-				this._completeSubagentTurn(e.agentId);
+			const agentId = e.agentId ?? subagentIdsByStopHook.get(e.data.hookInvocationId);
+			subagentIdsByStopHook.delete(e.data.hookInvocationId);
+			if (e.data.hookType === 'agentStop' || e.data.hookType === 'subagentStop') {
+				this._completeSubagentTurn(agentId);
 			}
 		}));
 
diff --git a/src/vs/platform/agentHost/test/node/copilotAgentSession.test.ts b/src/vs/platform/agentHost/test/node/copilotAgentSession.test.ts
index fb2f47119a59e..6f6a3740c8d55 100644
--- a/src/vs/platform/agentHost/test/node/copilotAgentSession.test.ts
+++ b/src/vs/platform/agentHost/test/node/copilotAgentSession.test.ts
@@ -8541,6 +8541,135 @@ Use the attached image as context.
 			]);
 		});
 
+		test('completes a resumed subagent when its stop hook identifies the agent only in the input', async () => {
+			const { session, mockSession, signals } = await createAgentSession(disposables);
+			session.resetTurnState('turn-parent');
+
+			mockSession.fire('subagent.started', {
+				toolCallId: 'tc-subagent',
+				agentName: 'explore',
+				agentDisplayName: 'Explore',
+				agentDescription: 'Explore tests',
+			}, { agentId: 'agent-1' });
+			const completion = {
+				toolCallId: 'tc-subagent',
+				agentName: 'explore',
+				agentDisplayName: 'Explore',
+				durationMs: 1,
+				totalTokens: 0,
+				totalToolCalls: 0,
+			};
+			mockSession.fire('subagent.completed', completion, { agentId: 'agent-1' });
+			mockSession.fire('user.message', {
+				content: 'Review the follow-up',
+				source: 'agent-parent',
+			}, { agentId: 'agent-1' });
+			mockSession.fire('hook.end', {
+				hookInvocationId: 'agent-stop',
+				hookType: 'agentStop',
+				success: true,
+			});
+			mockSession.fire('hook.start', {
+				hookInvocationId: 'subagent-stop',
+				hookType: 'subagentStop',
+				input: { agentId: 'agent-1' },
+			});
+
+			const completions = () => signals
+				.filter(signal => signal.kind === 'subagent_completed')
+				.map(signal => signal.toolCallId);
+			const beforeHookEnd = completions();
+
+			mockSession.fire('hook.end', {
+				hookInvocationId: 'subagent-stop',
+				hookType: 'subagentStop',
+				success: true,
+			});
+			const afterHookEnd = completions();
+			mockSession.fire('subagent.completed', completion, { agentId: 'agent-1' });
+
+			assert.deepStrictEqual({
+				beforeHookEnd,
+				afterHookEnd,
+				afterDuplicateCompletion: completions(),
+				resumed: signals.filter(signal => signal.kind === 'subagent_resumed').map(signal => signal.toolCallId),
+				parentCompleted: signals.some(signal => isAction(signal, ActionType.ChatTurnComplete)),
+			}, {
+				beforeHookEnd: ['tc-subagent'],
+				afterHookEnd: ['tc-subagent', 'tc-subagent'],
+				afterDuplicateCompletion: ['tc-subagent', 'tc-subagent'],
+				resumed: ['tc-subagent'],
+				parentCompleted: false,
+			});
+		});
+
+		test('ignores subagent stop hook inputs without a string agent ID', async () => {
+			const { session, mockSession, signals } = await createAgentSession(disposables);
+			session.resetTurnState('turn-parent');
+			mockSession.fire('subagent.started', {
+				toolCallId: 'tc-subagent',
+				agentName: 'explore',
+				agentDisplayName: 'Explore',
+				agentDescription: 'Explore tests',
+			}, { agentId: 'agent-1' });
+
+			const inputs: SessionEventPayload<'hook.start'>['data']['input'][] = [
+				undefined, null, true, 1, 'agent-1', [], {}, { agentId: 1 }, { agentId: null }, { agentId: ['agent-1'] },
+			];
+			for (const input of inputs) {
+				mockSession.fire('hook.start', {
+					hookInvocationId: 'subagent-stop',
+					hookType: 'subagentStop',
+					input,
+				});
+				mockSession.fire('hook.end', {
+					hookInvocationId: 'subagent-stop',
+					hookType: 'subagentStop',
+					success: true,
+				});
+			}
+
+			assert.deepStrictEqual(signals.filter(signal => signal.kind === 'subagent_completed'), []);
+		});
+
+		test('matches overlapping subagent stop hooks to their own agents', async () => {
+			const { session, mockSession, signals } = await createAgentSession(disposables);
+			session.resetTurnState('turn-parent');
+
+			for (const id of ['first', 'second']) {
+				mockSession.fire('subagent.started', {
+					toolCallId: `tc-${id}`,
+					agentName: 'explore',
+					agentDisplayName: 'Explore',
+					agentDescription: 'Explore tests',
+				}, { agentId: `agent-${id}` });
+				mockSession.fire('hook.start', {
+					hookInvocationId: `stop-${id}`,
+					hookType: 'subagentStop',
+					input: { agentId: `agent-${id}` },
+				});
+			}
+
+			for (const id of ['second', 'first']) {
+				mockSession.fire('hook.end', {
+					hookInvocationId: `stop-${id}`,
+					hookType: 'subagentStop',
+					success: true,
+				});
+			}
+			mockSession.fire('user.message', { content: 'Another turn' }, { agentId: 'agent-first' });
+			mockSession.fire('hook.end', {
+				hookInvocationId: 'stop-first',
+				hookType: 'subagentStop',
+				success: true,
+			});
+
+			assert.deepStrictEqual(
+				signals.filter(signal => signal.kind === 'subagent_completed').map(signal => signal.toolCallId),
+				['tc-second', 'tc-first'],
+			);
+		});
+
 		test('history replay seeds turn id from the SDK envelope id, matching `turns.event_id`', async () => {
 			// Regression test: fork / truncate look up the SDK boundary
 			// event id via `getNextTurnEventId(turnId)`, which keys on