fix(host): restart Ace Helper by itself when Tailscale starts or changes tailnet

.lane/memory/apps/host/src/catalog.ts/01M52ZT4QFXW6G0AFQFZNG86B1-channel-names-stay-unique-ac.md

@@ -4,9 +4,9 @@ anchor: function draft
 created: 2026-10-16T18:32:55Z
 norm: '1'
 sig: 9775c8890db42443
-body_hash: 715d3c6a84062b19
-raw_hash: 4ac416bc7ff419f2
-vouched: 2026-10-21T21:54:51Z
+body_hash: 6918a46a3994c088
+raw_hash: 8984d6500c60a112
+vouched: 2026-10-22T21:42:37Z
 lines: 133-155
 ---
 

.lane/memory/apps/host/src/gateway.ts/01M4YT9Z8YJ2ZWZCVB752WDCFF-workers-and-agent-shells-fin.md

@@ -4,9 +4,9 @@ anchor: function serve
 created: 2026-10-15T03:39:45Z
 norm: '1'
 sig: 171797818ef4d836
-body_hash: 0f15dc30991bf467
-raw_hash: aa609814e48a6d89
-vouched: 2026-10-22T21:10:47Z
+body_hash: f0a0ef2c205726cc
+raw_hash: a98db292f7a9e13d
+vouched: 2026-10-22T21:42:37Z
 lines: 668-751
 ---
 

.lane/memory/apps/host/src/gateway.ts/01M4ZH1NMBK54TCB970R3AJ1X1-a-loopback-host-must-not-cal.md

@@ -4,9 +4,9 @@ anchor: function serve
 created: 2026-10-15T10:17:10Z
 norm: '1'
 sig: 171797818ef4d836
-body_hash: 0f15dc30991bf467
-raw_hash: aa609814e48a6d89
-vouched: 2026-10-22T21:10:47Z
+body_hash: f0a0ef2c205726cc
+raw_hash: a98db292f7a9e13d
+vouched: 2026-10-22T21:42:37Z
 lines: 830-948
 supersedes: 01M4Z2R1HEVDKEA8VEJ7XRJQ8F
 ---

.lane/memory/apps/host/src/gateway.ts/01M5D4BXMERGZ1EZ3EYAFM3YC4-worker-requests-worker-never.md

@@ -4,9 +4,9 @@ anchor: '@file'
 created: 2026-10-20T17:04:56Z
 norm: '1'
 sig: 1acdc0f6a0895ac5
-body_hash: 734539b04f3c9fb5
-raw_hash: faceff1158ed3942
-vouched: 2026-10-22T21:30:21Z
+body_hash: 94af0091ce8ea05b
+raw_hash: 43d4d53a6b1fecd9
+vouched: 2026-10-22T21:42:37Z
 lines: 1-1153
 ---
 

.lane/memory/apps/host/src/gateway.ts/01M5HYM54QCSF4ESXJSWZK588G-every-project-op-that-change.md

@@ -4,9 +4,9 @@ anchor: '@file'
 created: 2026-10-22T14:00:47Z
 norm: '1'
 sig: 1acdc0f6a0895ac5
-body_hash: 734539b04f3c9fb5
-raw_hash: faceff1158ed3942
-vouched: 2026-10-22T21:30:21Z
+body_hash: 94af0091ce8ea05b
+raw_hash: 43d4d53a6b1fecd9
+vouched: 2026-10-22T21:42:37Z
 lines: 1-1309
 ---
 

.lane/memory/apps/host/src/gateway.ts/01M5JQ79TQ8E8R693FQD7PF3RP-only-a-command-line-host-pri.md

@@ -4,8 +4,9 @@ anchor: function serve
 created: 2026-10-22T21:10:40Z
 norm: '1'
 sig: 171797818ef4d836
-body_hash: 0f15dc30991bf467
-raw_hash: aa609814e48a6d89
+body_hash: f0a0ef2c205726cc
+raw_hash: a98db292f7a9e13d
+vouched: 2026-10-22T21:42:37Z
 lines: 1191-1341
 ---
 

.lane/memory/apps/host/src/gateway.ts/01M5JS1HEWX8RK77BQVSA9XQZG-ace-helper-s-tailnet-self-re.md

@@ -0,0 +1,12 @@
+---
+id: 01M5JS1HEWX8RK77BQVSA9XQZG
+anchor: function serve
+created: 2026-10-22T21:42:29Z
+norm: '1'
+sig: 171797818ef4d836
+body_hash: f0a0ef2c205726cc
+raw_hash: a98db292f7a9e13d
+lines: 1200-1357
+---
+
+Ace Helper's tailnet self-restart exits non-zero because launchd's KeepAlive relaunches only a failed exit

.lane/memory/apps/host/src/tailnet.ts/01M5JS1HGCGP3SEXKET1EFDJ87-tailscale-stopping-must-not.md

@@ -0,0 +1,12 @@
+---
+id: 01M5JS1HGCGP3SEXKET1EFDJ87
+anchor: function watch
+created: 2026-10-22T21:42:29Z
+norm: '1'
+sig: 6c1e8049ae309bc1
+body_hash: 8530c8fc8dec8e95
+raw_hash: 03c20bc7ed33888a
+lines: 113-125
+---
+
+Tailscale stopping must not restart the host; only a running tailnet other than the one the host started on does

apps/host/src/catalog.ts

@@ -199,12 +199,13 @@ export function fork(source: Listing, model: ModelRef | undefined, branches: Set
 /** A new channel's record, not yet saved: a hosted channel saves it once the service has it. */
 export function draft(project: string, model?: ModelRef, name?: string, hosted?: string): Listing {
 	if (!tailnet) {
-		// The tailnet is read once at startup, so Tailscale started later needs a restart.
-		const host = config.helper ? "Ace Helper" : "ace serve";
+		// The tailnet is read once at startup; Ace Helper restarts itself when Tailscale starts later.
 		throw new Error(
-			identity().tailnet
-				? `Restart ${host}: it started before Tailscale was running.`
-				: "Start Tailscale first: every channel belongs to a tailnet.",
+			!identity().tailnet
+				? "Start Tailscale first: every channel belongs to a tailnet."
+				: config.helper
+				? "Ace Helper is restarting to use Tailscale. Try again in a moment."
+				: "Restart ace serve: it started before Tailscale was running.",
 		);
 	}
 	const names = taken();

apps/host/src/gateway.ts

@@ -51,7 +51,7 @@ import {
 	projectId,
 	type WorkerRequest,
 } from "./protocol";
-import { type Machine, self, whois } from "./tailnet";
+import { type Machine, self, watch as tailscale, whois } from "./tailnet";
 import {
 	checkKey,
 	forgetKey,
@@ -1231,7 +1231,7 @@ export async function serve(port: number, loopback = false, script?: string): Pr
 		tick = now;
 	}, 1000);
 	cleanup.push(() => clearInterval(stalls));
-	async function stop() {
+	async function stop(code = 0) {
 		if (closing) return;
 		closing = true;
 		log("info", "host.stop", { pending: pending.size });
@@ -1244,10 +1244,17 @@ export async function serve(port: number, loopback = false, script?: string): Pr
 				log("error", "host.shutdown.failed", failure(result.reason));
 			}
 		}
-		process.exit(results.some((result) => result.status === "rejected") ? 1 : 0);
+		process.exit(results.some((result) => result.status === "rejected") ? 1 : code);
 	}
 	process.on("SIGTERM", () => void stop());
 	process.on("SIGINT", () => void stop());
+	// The owner's login, the channels' tailnet, and every tailnet listener are read once at startup.
+	cleanup.push(tailscale(catalog.tailnet, (tailnet) => {
+		log("info", "host.tailnet.moved", { from: catalog.tailnet, to: tailnet });
+		// launchd starts Ace Helper again after a failed exit, which picks up the new tailnet.
+		if (config.helper) void stop(75);
+		else console.log(`Tailscale is on ${tailnet} now. Restart ace serve to use it.`);
+	}));
 	console.log(`Ace on http://${server.hostname}:${server.port}`);
 	// Ace Helper's console is its log file, which must not hold the token.
 	if (!config.helper) {

apps/host/src/tailnet.ts

@@ -106,6 +106,24 @@ export async function diagnostics(started?: string): Promise<Diagnostics["tailsc
 	}
 }
 
+/**
+ * Calls `moved` once Tailscale has run on a tailnet other than `started` for two checks in a row.
+ * Tailscale stopping never counts: the host's channels stay on the tailnet it started on.
+ */
+export function watch(started: string | undefined, moved: (tailnet: string) => void): () => void {
+	let seen: string | undefined;
+	const timer = setInterval(async () => {
+		const now = (await status())?.MagicDNSSuffix;
+		if (!now || now === started) seen = undefined;
+		else if (now !== seen) seen = now;
+		else {
+			clearInterval(timer);
+			moved(now);
+		}
+	}, 10_000);
+	return () => clearInterval(timer);
+}
+
 /** Online machines owned by people; tagged nodes are servers, not participants. */
 export async function peers(): Promise<Machine[]> {
 	const value = await status();