Keep auto paused instances paused

Every RCON command makes an auto paused Factorio server run one tick, so
subspace_storage's 1 s inventory update and 5 s ping, plus a
statistics_exporter gather on every Prometheus scrape, kept a server with
nobody online running at about 1.3 ticks per second.

The instance now records the auto_pause server setting it was started
with and exposes autoPaused, true while that setting is on and no players
are online, along with an autoPauseChanged hook. subspace_storage skips
its timers while paused and sends a ping and inventory as soon as a player
joins. statistics_exporter gathers once after the game pauses and keeps
serving those values until it resumes.

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

test/host/Instance.js

@@ -418,6 +418,42 @@ describe("class Instance", function() {
 		});
 	});
 
+	describe(".autoPaused", function() {
+		let changes;
+		beforeEach(function() {
+			changes = [];
+			instance.hooks.autoPauseChanged.attach("test", async paused => { changes.push(paused); });
+		});
+
+		it("should be false when auto_pause is off", function() {
+			assert.equal(instance.autoPaused, false);
+			instance._recordPlayerJoin("player");
+			instance._recordPlayerLeave("player", "quit");
+			assert.equal(instance.autoPaused, false);
+			assert.deepEqual(changes, []);
+		});
+		it("should follow players online when auto_pause is on", function() {
+			instance._autoPause = true;
+			assert.equal(instance.autoPaused, true);
+			instance._recordPlayerJoin("a");
+			instance._recordPlayerJoin("b");
+			assert.equal(instance.autoPaused, false);
+			instance._recordPlayerLeave("a", "quit");
+			assert.equal(instance.autoPaused, false);
+			instance._recordPlayerLeave("b", "quit");
+			assert.equal(instance.autoPaused, true);
+			assert.deepEqual(changes, [false, true]);
+		});
+		it("should not invoke the hook on exit", function() {
+			instance._autoPause = true;
+			instance._recordPlayerJoin("player");
+			instance._saveStats = async () => {};
+			instance.notifyExit();
+			assert.equal(instance.autoPaused, false);
+			assert.deepEqual(changes, [false]);
+		});
+	});
+
 	describe("._checkOnlinePlayers()", function() {
 		it("should do nothing on empty server", async function() {
 			await instance._checkOnlinePlayers();

test/integration/clusterio.js

@@ -1332,6 +1332,55 @@ describe("Integration of Clusterio", function() {
 			});
 		});
 
+		describe("auto pause", function() {
+			requiresFactorio(this);
+			async function getTick() {
+				return Number(await getControl().sendTo(
+					{ instanceId: 44 }, new lib.InstanceSendRconRequest("/sc rcon.print(game.tick)")
+				));
+			}
+			async function sendPlayerEvent(type) {
+				const json = JSON.stringify({ type, name: "auto_pause_player", reason: "quit" });
+				await getControl().sendTo(
+					{ instanceId: 44 },
+					new lib.InstanceSendRconRequest(`/sc print("\\f$ipc:player_event?j${lib.escapeString(json)}")`),
+				);
+			}
+			let started = false;
+			before(async function() {
+				slowTest(this);
+				this.timeout(60000);
+				started = true;
+				await execCtl("instance stop test");
+				await execCtl("instance config set-prop test factorio.settings auto_pause true");
+				await execCtl("instance start test");
+			});
+			after(async function() {
+				if (!started) {
+					return;
+				}
+				this.timeout(60000);
+				await execCtl("instance stop test");
+				await execCtl("instance config set-prop test factorio.settings auto_pause false");
+				await execCtl("instance start test");
+			});
+			it("does not tick the game while no players are online", async function() {
+				slowTest(this);
+				const start = await getTick();
+				await wait(6000);
+				assert.equal(await getTick() - start, 1);
+			});
+			it("resumes plugin work when a player joins", async function() {
+				slowTest(this);
+				const start = await getTick();
+				await sendPlayerEvent("join");
+				await wait(6000);
+				const ticks = await getTick() - start;
+				await sendPlayerEvent("leave");
+				assert(ticks > 3, `game ran ${ticks} ticks`);
+			});
+		});
+
 		describe("instance stop", function() {
 			it("stops the instance", async function() {
 				slowTest(this);

test/mock.js

@@ -129,6 +129,7 @@ export class MockInstance extends lib.Link {
 		this.name = "test";
 		this.id = 7357;
 		this.status = "running";
+		this.autoPaused = false;
 		this.hooks = new InstanceHooks(this.logger);
 		this.loadedPlugins = new Set();
 		this.mockConfigEntries = new Map([