feat(mtproto): add domain-fronting and essential mtg options

Expose mtg's [domain-fronting] section (ip/port/proxy-protocol) plus
proxy-protocol-listener, prefer-ip, and debug on MTProto inbounds. Each
key is written to the generated mtg-<id>.toml only when set, so mtg's own
defaults apply otherwise. The instance fingerprint now covers these
fields, so editing an option restarts the sidecar.

Since MTProto is mtg-served (not Xray), sniffing does not apply: hide the
Sniffing tab and the Advanced sniffing sub-editor, drop it from the
Advanced "All" JSON view, and emit empty sniffing in the wire payload,
all gated by a new canEnableSniffing predicate.

frontend/src/test/__snapshots__/protocol-capabilities.test.ts.snap

@@ -672,6 +672,174 @@ exports[`protocol capability predicates > mtproto-basic :: xhttp/tls 1`] = `
 }
 `;
 
+exports[`protocol capability predicates > mtproto-domain-fronting :: grpc/none 1`] = `
+{
+  "canEnableReality": false,
+  "canEnableStream": false,
+  "canEnableTls": false,
+  "canEnableTlsFlow": false,
+  "canEnableVisionSeed": false,
+  "isSS2022": false,
+  "isSSMultiUser": true,
+}
+`;
+
+exports[`protocol capability predicates > mtproto-domain-fronting :: grpc/reality 1`] = `
+{
+  "canEnableReality": false,
+  "canEnableStream": false,
+  "canEnableTls": false,
+  "canEnableTlsFlow": false,
+  "canEnableVisionSeed": false,
+  "isSS2022": false,
+  "isSSMultiUser": true,
+}
+`;
+
+exports[`protocol capability predicates > mtproto-domain-fronting :: grpc/tls 1`] = `
+{
+  "canEnableReality": false,
+  "canEnableStream": false,
+  "canEnableTls": false,
+  "canEnableTlsFlow": false,
+  "canEnableVisionSeed": false,
+  "isSS2022": false,
+  "isSSMultiUser": true,
+}
+`;
+
+exports[`protocol capability predicates > mtproto-domain-fronting :: httpupgrade/none 1`] = `
+{
+  "canEnableReality": false,
+  "canEnableStream": false,
+  "canEnableTls": false,
+  "canEnableTlsFlow": false,
+  "canEnableVisionSeed": false,
+  "isSS2022": false,
+  "isSSMultiUser": true,
+}
+`;
+
+exports[`protocol capability predicates > mtproto-domain-fronting :: httpupgrade/tls 1`] = `
+{
+  "canEnableReality": false,
+  "canEnableStream": false,
+  "canEnableTls": false,
+  "canEnableTlsFlow": false,
+  "canEnableVisionSeed": false,
+  "isSS2022": false,
+  "isSSMultiUser": true,
+}
+`;
+
+exports[`protocol capability predicates > mtproto-domain-fronting :: kcp/none 1`] = `
+{
+  "canEnableReality": false,
+  "canEnableStream": false,
+  "canEnableTls": false,
+  "canEnableTlsFlow": false,
+  "canEnableVisionSeed": false,
+  "isSS2022": false,
+  "isSSMultiUser": true,
+}
+`;
+
+exports[`protocol capability predicates > mtproto-domain-fronting :: tcp/none 1`] = `
+{
+  "canEnableReality": false,
+  "canEnableStream": false,
+  "canEnableTls": false,
+  "canEnableTlsFlow": false,
+  "canEnableVisionSeed": false,
+  "isSS2022": false,
+  "isSSMultiUser": true,
+}
+`;
+
+exports[`protocol capability predicates > mtproto-domain-fronting :: tcp/reality 1`] = `
+{
+  "canEnableReality": false,
+  "canEnableStream": false,
+  "canEnableTls": false,
+  "canEnableTlsFlow": false,
+  "canEnableVisionSeed": false,
+  "isSS2022": false,
+  "isSSMultiUser": true,
+}
+`;
+
+exports[`protocol capability predicates > mtproto-domain-fronting :: tcp/tls 1`] = `
+{
+  "canEnableReality": false,
+  "canEnableStream": false,
+  "canEnableTls": false,
+  "canEnableTlsFlow": false,
+  "canEnableVisionSeed": false,
+  "isSS2022": false,
+  "isSSMultiUser": true,
+}
+`;
+
+exports[`protocol capability predicates > mtproto-domain-fronting :: ws/none 1`] = `
+{
+  "canEnableReality": false,
+  "canEnableStream": false,
+  "canEnableTls": false,
+  "canEnableTlsFlow": false,
+  "canEnableVisionSeed": false,
+  "isSS2022": false,
+  "isSSMultiUser": true,
+}
+`;
+
+exports[`protocol capability predicates > mtproto-domain-fronting :: ws/tls 1`] = `
+{
+  "canEnableReality": false,
+  "canEnableStream": false,
+  "canEnableTls": false,
+  "canEnableTlsFlow": false,
+  "canEnableVisionSeed": false,
+  "isSS2022": false,
+  "isSSMultiUser": true,
+}
+`;
+
+exports[`protocol capability predicates > mtproto-domain-fronting :: xhttp/none 1`] = `
+{
+  "canEnableReality": false,
+  "canEnableStream": false,
+  "canEnableTls": false,
+  "canEnableTlsFlow": false,
+  "canEnableVisionSeed": false,
+  "isSS2022": false,
+  "isSSMultiUser": true,
+}
+`;
+
+exports[`protocol capability predicates > mtproto-domain-fronting :: xhttp/reality 1`] = `
+{
+  "canEnableReality": false,
+  "canEnableStream": false,
+  "canEnableTls": false,
+  "canEnableTlsFlow": false,
+  "canEnableVisionSeed": false,
+  "isSS2022": false,
+  "isSSMultiUser": true,
+}
+`;
+
+exports[`protocol capability predicates > mtproto-domain-fronting :: xhttp/tls 1`] = `
+{
+  "canEnableReality": false,
+  "canEnableStream": false,
+  "canEnableTls": false,
+  "canEnableTlsFlow": false,
+  "canEnableVisionSeed": false,
+  "isSS2022": false,
+  "isSSMultiUser": true,
+}
+`;
+
 exports[`protocol capability predicates > shadowsocks-2022 :: grpc/none 1`] = `
 {
   "canEnableReality": false,

frontend/src/test/__snapshots__/protocols.test.ts.snap

@@ -69,6 +69,24 @@ exports[`InboundSettingsSchema fixtures > parses mtproto-basic byte-stably 1`] =
 }
 `;
 
+exports[`InboundSettingsSchema fixtures > parses mtproto-domain-fronting byte-stably 1`] = `
+{
+  "protocol": "mtproto",
+  "settings": {
+    "debug": true,
+    "domainFronting": {
+      "ip": "127.0.0.1",
+      "port": 9443,
+      "proxyProtocol": true,
+    },
+    "fakeTlsDomain": "www.cloudflare.com",
+    "preferIp": "prefer-ipv4",
+    "proxyProtocolListener": true,
+    "secret": "ee0123456789abcdef0123456789abcdef7777772e636c6f7564666c6172652e636f6d",
+  },
+}
+`;
+
 exports[`InboundSettingsSchema fixtures > parses shadowsocks-2022 byte-stably 1`] = `
 {
   "protocol": "shadowsocks",

frontend/src/test/golden/fixtures/inbound/mtproto-domain-fronting.json

@@ -0,0 +1,15 @@
+{
+  "protocol": "mtproto",
+  "settings": {
+    "fakeTlsDomain": "www.cloudflare.com",
+    "secret": "ee0123456789abcdef0123456789abcdef7777772e636c6f7564666c6172652e636f6d",
+    "proxyProtocolListener": true,
+    "preferIp": "prefer-ipv4",
+    "debug": true,
+    "domainFronting": {
+      "ip": "127.0.0.1",
+      "port": 9443,
+      "proxyProtocol": true
+    }
+  }
+}

frontend/src/test/inbound-form-adapter.test.ts

@@ -142,6 +142,17 @@ describe('formValuesToWirePayload', () => {
     expect(payload.streamSettings).toBe('');
   });
 
+  it('emits empty sniffing for mtproto (mtg-served, not Xray)', () => {
+    const values = rawInboundToFormValues({
+      ...vlessRow,
+      protocol: 'mtproto',
+      settings: { fakeTlsDomain: 'www.cloudflare.com', secret: 'ee00' },
+    });
+    const payload = formValuesToWirePayload(values);
+    expect(payload.protocol).toBe('mtproto');
+    expect(payload.sniffing).toBe('');
+  });
+
   it('omits nodeId when null', () => {
     const values = rawInboundToFormValues({ ...vlessRow, nodeId: null });
     const payload = formValuesToWirePayload(values);