diff --git a/apps/api/app/routes/session.ts b/apps/api/app/routes/session.ts
index 1868f300..293c5e15 100644
--- a/apps/api/app/routes/session.ts
+++ b/apps/api/app/routes/session.ts
@@ -476,6 +476,11 @@ export namespace SessionApi {
 				description:
 					'Adds a launch to a run that its host has taken on and that is not being stopped; the host starts it in the box without stopping what already runs there. Answers with the launch: its `id` is what the launched game’s window carries, and what to stop when that window closes. A run that is waiting for a host, stopping or over is 409: ask for a new run instead. So is a run on a host that does not handle launches, with code `host_too_old`: stop the run and ask for a new one, as before launches. The run is still what is billed and what the allowance counts, so adding a launch asks nothing of either.',
 				responses: {
+					200: {
+						content: { 'application/json': { schema: Result(Launch.Info) } },
+						description:
+							'That game already has a launch in this run that is not over: it is answered instead of a second one'
+					},
 					201: {
 						content: { 'application/json': { schema: Result(Launch.Info) } },
 						description: 'The launch has been requested'
@@ -537,6 +542,8 @@ export namespace SessionApi {
 						conflict('That run is not running, so it cannot take another launch');
 					case 'hostTooOld':
 						hostTooOld();
+					case 'existing':
+						return c.json({ data: result.launch }, 200);
 					default:
 						return c.json({ data: result.launch }, 201);
 				}
diff --git a/apps/api/test/launch.test.ts b/apps/api/test/launch.test.ts
index a22ba4c6..251179af 100644
--- a/apps/api/test/launch.test.ts
+++ b/apps/api/test/launch.test.ts
@@ -226,6 +226,16 @@ describe('launches', () => {
 		expect(run.launches.map((l: any) => l.state)).toEqual(['running', 'running']);
 	});
 
+	test('the same game added twice is one launch', async () => {
+		const { s, id, second } = await liveRun('launch-dedupe', 7109);
+		const [a, b] = await Promise.all([addLaunch(s, id, second), addLaunch(s, id, second)]);
+		const statuses = [a.status, b.status].sort();
+		expect(statuses).toEqual([200, 201]);
+		const ids = [((await a.json()) as any).data.id, ((await b.json()) as any).data.id];
+		expect(ids[0]).toBe(ids[1]);
+		expect((await read(s, id)).launches.length).toBe(2);
+	});
+
 	test('a run that is not running takes no launch', async () => {
 		const s = await scene('launch-notrunning', 7102);
 		const { body } = await requestSession(s);
diff --git a/packages/core/src/session/index.ts b/packages/core/src/session/index.ts
index 1025e77b..bb1b4ffb 100644
--- a/packages/core/src/session/index.ts
+++ b/packages/core/src/session/index.ts
@@ -1230,7 +1230,8 @@ export namespace Session {
 		| { outcome: 'notFound' }
 		| { outcome: 'notRunning'; session: Info }
 		| { outcome: 'hostTooOld' }
-		| { outcome: 'created'; launch: Launch.Info };
+		| { outcome: 'created'; launch: Launch.Info }
+		| { outcome: 'existing'; launch: Launch.Info };
 
 	/**
 	 * Add a launch to a run that is going. The library and account checks are
@@ -1266,6 +1267,16 @@ export namespace Session {
 					return { outcome: 'notRunning', session: serialize(run) };
 				}
 				if (!(await Launch.hostTakesLaunches(run.id))) return { outcome: 'hostTooOld' };
+				// The same game asked for twice (two windows, or a retry after a
+				// lost reply) is one launch: under the run's lock the first add
+				// has committed, so the second finds it and gets it back.
+				const open = (await Launch.listForSession(run.id)).find(
+					(l) =>
+						l.gameId === input.gameId &&
+						(Launch.OPEN as readonly string[]).includes(l.state) &&
+						l.timeStopRequested === null
+				);
+				if (open) return { outcome: 'existing', launch: open };
 				const launch = await Launch.insert({
 					id: Identifier.ascending('launch'),
 					sessionId: run.id,