feat(xray): add loopback sniffing and per-segment fragment masks

- Loopback outbound: add sniffing support (xray-core #6320)

- FinalMask fragment: support per-segment lengths/delays arrays with legacy length/delay migration (xray-core #6334)

- Consolidate sniffing into a shared SniffingFields component and the canonical SniffingSchema across inbound, VLESS reverse, and loopback

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

@@ -101,6 +101,29 @@ exports[`FinalMaskStreamSettingsSchema fixtures > parses salamander-gecko byte-s
 }
 `;
 
+exports[`FinalMaskStreamSettingsSchema fixtures > parses tcp-fragment-segments byte-stably 1`] = `
+{
+  "tcp": [
+    {
+      "settings": {
+        "delays": [
+          "5-10",
+          "0",
+        ],
+        "lengths": [
+          "10-20",
+          "50-100",
+        ],
+        "maxSplit": "0",
+        "packets": "tlshello",
+      },
+      "type": "fragment",
+    },
+  ],
+  "udp": [],
+}
+`;
+
 exports[`FinalMaskStreamSettingsSchema fixtures > parses tcp-mask byte-stably 1`] = `
 {
   "tcp": [

frontend/src/test/golden/fixtures/finalmask/tcp-fragment-segments.json

@@ -0,0 +1,13 @@
+{
+  "tcp": [
+    {
+      "type": "fragment",
+      "settings": {
+        "packets": "tlshello",
+        "lengths": ["10-20", "50-100"],
+        "delays": ["5-10", "0"],
+        "maxSplit": "0"
+      }
+    }
+  ]
+}

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

@@ -359,6 +359,39 @@ describe('outbound-form-adapter: round-trip', () => {
     expect(back.settings).toEqual({ inboundTag: 'tagged-inbound' });
   });
 
+  it('loopback omits sniffing when disabled', () => {
+    const form = rawOutboundToFormValues({
+      protocol: 'loopback',
+      settings: { inboundTag: 'tagged-inbound' },
+    });
+    if (form.protocol === 'loopback') {
+      expect(form.settings.sniffing.enabled).toBe(false);
+    }
+    const back = formValuesToWirePayload(form);
+    expect(back.settings).not.toHaveProperty('sniffing');
+  });
+
+  it('loopback round-trips sniffing when enabled', () => {
+    const wire = {
+      protocol: 'loopback',
+      settings: {
+        inboundTag: 'tagged-inbound',
+        sniffing: { enabled: true, destOverride: ['tls', 'http'], routeOnly: true },
+      },
+    };
+    const form = rawOutboundToFormValues(wire);
+    if (form.protocol === 'loopback') {
+      expect(form.settings.sniffing.enabled).toBe(true);
+      expect(form.settings.sniffing.destOverride).toEqual(['tls', 'http']);
+      expect(form.settings.sniffing.routeOnly).toBe(true);
+    }
+    const back = formValuesToWirePayload(form);
+    const sniffing = (back.settings as Record<string, unknown>).sniffing as Record<string, unknown>;
+    expect(sniffing.enabled).toBe(true);
+    expect(sniffing.destOverride).toEqual(['tls', 'http']);
+    expect(sniffing.routeOnly).toBe(true);
+  });
+
   it('unknown protocol falls back to vless without throwing', () => {
     const form = rawOutboundToFormValues({ protocol: 'mysterious', settings: {} });
     expect(form.protocol).toBe('vless');