fix(sub): keep the spider settings in a reality spiderX seed's query (#6694)

* fix(sub): keep the spider settings in a reality spiderX seed's query

xray's REALITY client reads p, c, t, i and r from the spiderX query as
its spider's own settings (padding, concurrency, times, interval,
return). deriveSpiderX hashes the whole seed into a bare /path per
client, so any query set on the inbound was dropped from every share
link and JSON subscription, and the spider always ran with defaults.

Keep the seed's query after the derived path. The hash input is
unchanged, so every existing client's spx stays the same; only seeds
that carry a query gain it. The frontend mirror and the cross-language
vectors are updated together.

* docs(sub): keep the deriveSpiderX comments within two lines

Review feedback on #6694: the added lines pushed both doc blocks past the two-line cap.

internal/sub/service.go

@@ -2016,14 +2016,18 @@ func subKey(c model.Client) string {
 	return c.Email
 }
 
-// deriveSpiderX maps the inbound's spiderX seed plus a stable client key to a
-// deterministic per-client "/path"; frontend/src/lib/xray/spider-x.ts mirrors it.
+// deriveSpiderX maps the seed and a stable client key to a per-client "/path" plus the seed's
+// query, where xray reads its spider settings (#6693); frontend/src/lib/xray/spider-x.ts mirrors it.
 func deriveSpiderX(seed, clientKey string) string {
 	if seed == "" && clientKey == "" {
 		return "/" + random.Seq(15)
 	}
 	sum := sha256.Sum256([]byte(seed + "|" + clientKey))
-	return "/" + hex.EncodeToString(sum[:])[:15]
+	path := "/" + hex.EncodeToString(sum[:])[:15]
+	if _, query, _ := strings.Cut(seed, "?"); query != "" {
+		return path + "?" + query
+	}
+	return path
 }
 
 func buildVmessLink(obj map[string]any) string {

internal/sub/service_sharelink_test.go

@@ -143,6 +143,23 @@ func TestGenVlessLink_RealitySpiderXPerClientStable(t *testing.T) {
 	}
 }
 
+// A seed's spider settings (p, c, t, i, r) ride along in the share link's spx,
+// escaped so they stay inside that one parameter.
+func TestGenVlessLink_RealitySpiderXKeepsSpiderSettings(t *testing.T) {
+	s := &SubService{}
+	inbound := realityTwoClientInbound()
+	inbound.StreamSettings = strings.Replace(inbound.StreamSettings, `"spiderX":"/seed"`, `"spiderX":"/seed?p=40-400&r=500-2000"`, 1)
+
+	link := s.genVlessLink(inbound, "alice")
+	if got, want := spxParam(t, link), "/09dd00b3f8c01f5?p=40-400&r=500-2000"; got != want {
+		t.Fatalf("spx = %q, want %q", got, want)
+	}
+	u, _ := url.Parse(link)
+	if u.Query().Get("p") != "" || u.Query().Get("r") != "" {
+		t.Fatalf("spider settings leaked out of spx into the link's own query: %q", link)
+	}
+}
+
 func TestDeriveSpiderX(t *testing.T) {
 	if got := deriveSpiderX("seed", "clientA"); got != deriveSpiderX("seed", "clientA") {
 		t.Fatalf("deriveSpiderX not deterministic: %q", got)
@@ -168,6 +185,10 @@ func TestDeriveSpiderXMatchesFrontendVectors(t *testing.T) {
 	vectors := map[string]struct{ seed, clientKey, want string }{
 		"seed and subId": {"/seed", "subAlice", "/c252fbc3ecd3e3c"},
 		"seed only":      {"/", "", "/d08ed99bd9afc60"},
+		// xray reads p, c, t, i and r from the spiderX query as the spider's
+		// own settings, so the seed's query must survive the derivation.
+		"seed with spider settings": {"/seed?p=40-400&r=500-2000", "subAlice", "/09dd00b3f8c01f5?p=40-400&r=500-2000"},
+		"spider settings only":      {"/?p=40-400&c=1-4&t=1-3&i=1500-6000&r=500-2000", "", "/ac2cb268d22908e?p=40-400&c=1-4&t=1-3&i=1500-6000&r=500-2000"},
 	}
 	for name, v := range vectors {
 		t.Run(name, func(t *testing.T) {