Wait for a start in progress before stopping an instance

A stop request sent while the instance was starting ran alongside the
start. During save preparation it did nothing and the instance came up
running anyway. Once Factorio was launched it put the server into the
stopping state, the start then failed with "Expected state running but
state is stopping" and its cleanup killed the server mid shutdown.

Stop and restart requests now wait for any start, stop or save in
progress to finish first, then stop the instance if it is running.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/host/Instance.js

@@ -268,6 +268,46 @@ describe("class Instance", function() {
 		});
 	});
 
+	describe(".handleInstanceStopRequest()", function() {
+		let calls;
+		beforeEach(function() {
+			calls = [];
+			instance.server._state = "running";
+			instance.server.stop = async () => { calls.push("stop"); instance.server._state = "stopping"; };
+			instance.server.kill = async () => { calls.push("kill"); };
+			instance.sendSaveListUpdate = async () => {};
+		});
+
+		it("should stop once a start in progress finishes", async function() {
+			instance.notifyStatus("starting");
+			let stopped = instance.handleInstanceStopRequest();
+			await wait(10);
+			assert.deepEqual(calls, [], "stopped while starting");
+			instance.notifyStatus("running");
+			await stopped;
+			assert.deepEqual(calls, ["stop"]);
+		});
+
+		it("should do nothing if a start in progress fails", async function() {
+			instance.notifyStatus("starting");
+			let stopped = instance.handleInstanceStopRequest();
+			await wait(10);
+			instance.notifyStatus("stopped");
+			await stopped;
+			assert.deepEqual(calls, []);
+		});
+
+		it("should not kill the server when stopped while stopping", async function() {
+			instance.notifyStatus("running");
+			let first = instance.handleInstanceStopRequest();
+			let second = instance.handleInstanceStopRequest();
+			await first;
+			instance.notifyStatus("stopped");
+			await second;
+			assert.deepEqual(calls, ["stop"]);
+		});
+	});
+
 	describe(".checkModPackVersion()", function() {
 		function modPack(factorioVersion) {
 			return lib.ModPack.fromJSON({ name: "pack", factorio_version: factorioVersion });