fix(bonjour): truncate mDNS service name and hostname to 63-byte DNS label limit

When the system hostname exceeds 63 bytes (common with Kubernetes pod
names), the @homebridge/ciao DNS label encoder throws an AssertionError
that crashes the gateway on startup.

Add truncateToDnsLabel() that safely truncates UTF-8 strings at byte
boundaries, applied to both the service instance name and hostname
before passing them to ciao.

Closes #37705

AI-assisted (built with Hermes orchestration).

extensions/bonjour/src/advertiser.test.ts

@@ -735,6 +735,54 @@ describe("gateway bonjour advertiser", () => {
     await started.stop();
   });
 
+  it("truncates service name exceeding 63-byte DNS label limit", async () => {
+    const longHostname = "app-41627eae5842473f9e05f139ea307277-7f9477f4d6-lqqzf";
+    enableAdvertiserUnitMode(longHostname);
+
+    const destroy = vi.fn().mockResolvedValue(undefined);
+    const advertise = vi.fn().mockResolvedValue(undefined);
+    mockCiaoService({ advertise, destroy });
+
+    const started = await startAdvertiser({
+      gatewayPort: 18789,
+      sshPort: 2222,
+    });
+
+    const [gatewayCall] = createService.mock.calls as Array<[ServiceCall]>;
+    const serviceName = gatewayCall?.[0]?.name as string;
+    const hostname = gatewayCall?.[0]?.hostname as string;
+
+    // Both name and hostname must be within the 63-byte DNS label limit
+    expect(new TextEncoder().encode(serviceName).byteLength).toBeLessThanOrEqual(63);
+    expect(new TextEncoder().encode(hostname).byteLength).toBeLessThanOrEqual(63);
+
+    await started.stop();
+  });
+
+  it("truncates multi-byte hostname within DNS label byte limit", async () => {
+    // 21 CJK characters = 63 bytes in UTF-8, adding " (OpenClaw)" pushes over
+    const cjkHostname = "你".repeat(21);
+    enableAdvertiserUnitMode(cjkHostname);
+
+    const destroy = vi.fn().mockResolvedValue(undefined);
+    const advertise = vi.fn().mockResolvedValue(undefined);
+    mockCiaoService({ advertise, destroy });
+
+    const started = await startAdvertiser({
+      gatewayPort: 18789,
+      sshPort: 2222,
+    });
+
+    const [gatewayCall] = createService.mock.calls as Array<[ServiceCall]>;
+    const serviceName = gatewayCall?.[0]?.name as string;
+
+    expect(new TextEncoder().encode(serviceName).byteLength).toBeLessThanOrEqual(63);
+    // Should not end with a replacement character from incomplete multi-byte truncation
+    expect(serviceName).not.toMatch(/\uFFFD$/);
+
+    await started.stop();
+  });
+
   it("uses system hostname when OPENCLAW_MDNS_HOSTNAME is unset", async () => {
     // Allow advertiser to run in unit tests.
     delete process.env.VITEST;

extensions/bonjour/src/advertiser.ts

@@ -183,9 +183,24 @@ function resolveSystemMdnsHostname(): string | null {
   return firstLabel;
 }
 
+const MAX_DNS_LABEL_BYTES = 63;
+
+function truncateToDnsLabel(name: string): string {
+  const encoder = new TextEncoder();
+  const encoded = encoder.encode(name);
+  if (encoded.byteLength <= MAX_DNS_LABEL_BYTES) {
+    return name;
+  }
+  // Truncate at byte boundary, then decode back (TextDecoder handles incomplete sequences)
+  const truncated = encoded.slice(0, MAX_DNS_LABEL_BYTES);
+  const decoded = new TextDecoder("utf-8", { fatal: false }).decode(truncated);
+  // Strip any replacement character from incomplete multi-byte sequence at the end
+  return decoded.replace(/\uFFFD$/, "").trim() || "OpenClaw";
+}
+
 function safeServiceName(name: string) {
   const trimmed = name.trim();
-  return trimmed.length > 0 ? trimmed : "OpenClaw";
+  return trimmed.length > 0 ? truncateToDnsLabel(trimmed) : "OpenClaw";
 }
 
 function prettifyInstanceName(name: string) {
@@ -353,11 +368,12 @@ export async function startGatewayBonjourAdvertiser(
 
     const hostnameRaw =
       process.env.OPENCLAW_MDNS_HOSTNAME?.trim() || resolveSystemMdnsHostname() || "openclaw";
-    const hostname =
+    const hostname = truncateToDnsLabel(
       hostnameRaw
         .replace(/\.local$/i, "")
         .split(".")[0]
-        .trim() || "openclaw";
+        .trim() || "openclaw",
+    );
     const instanceName =
       typeof opts.instanceName === "string" && opts.instanceName.trim()
         ? opts.instanceName.trim()