feat: bridge-repeaters breakdown on the Scopes analytics tab

Adds bridgeRepeaters to /api/scope-stats: RepeatersByRegion inverted
into pubkey -> regions, keeping only repeaters that have relayed
traffic for MORE than one region. These are the mesh's literal
backbone nodes connecting otherwise-separate regional communities —
losing one is a more consequential failure than losing a
single-region repeater.

Computed inline while building RepeatersByRegion (reuses the same
byRegion map and role-filtered names lookup, no extra queries).

Frontend renders a small table under "Repeaters by Region": repeater
name (linked to its node detail page), region count, and the region
list.

cmd/server/routes.go

@@ -3568,6 +3568,35 @@ func (s *Server) handleScopeStats(w http.ResponseWriter, r *http.Request) {
 			}
 			sort.Slice(repeaters, func(i, j int) bool { return repeaters[i].Count > repeaters[j].Count })
 			resp.RepeatersByRegion = repeaters
+
+			// Bridge repeaters: invert byRegion into pubkey -> regions and
+			// keep only repeaters relaying for MORE than one region — the
+			// mesh's literal backbone nodes connecting separate regional
+			// communities. Same `names` existence-filter as above.
+			pubkeyRegions := make(map[string][]string)
+			for region, pks := range byRegion {
+				for _, pk := range pks {
+					if _, ok := names[pk]; !ok {
+						continue
+					}
+					pubkeyRegions[pk] = append(pubkeyRegions[pk], region)
+				}
+			}
+			bridges := make([]BridgeRepeater, 0)
+			for pk, regions := range pubkeyRegions {
+				if len(regions) < 2 {
+					continue
+				}
+				sort.Strings(regions)
+				bridges = append(bridges, BridgeRepeater{Name: names[pk], PublicKey: pk, Regions: regions, Count: len(regions)})
+			}
+			sort.Slice(bridges, func(i, j int) bool {
+				if bridges[i].Count != bridges[j].Count {
+					return bridges[i].Count > bridges[j].Count
+				}
+				return bridges[i].Name < bridges[j].Name
+			})
+			resp.BridgeRepeaters = bridges
 		}
 	}
 

cmd/server/routes_test.go

@@ -4424,6 +4424,74 @@ func TestHandleScopeStats_RepeatersByRegion(t *testing.T) {
 	}
 }
 
+// TestHandleScopeStats_BridgeRepeaters verifies the RepeatersByRegion
+// inversion: a repeater that relayed traffic for TWO distinct regions must
+// appear in BridgeRepeaters with both region names, while a repeater that
+// only ever relayed one region must be excluded.
+func TestHandleScopeStats_BridgeRepeaters(t *testing.T) {
+	srv, _ := setupTestServer(t)
+	if _, err := srv.db.conn.Exec(`ALTER TABLE transmissions ADD COLUMN scope_name TEXT DEFAULT NULL`); err != nil {
+		t.Fatalf("add scope_name column: %v", err)
+	}
+	srv.db.hasScopeName = true
+
+	if _, err := srv.db.conn.Exec(
+		`INSERT INTO nodes (public_key, name, role) VALUES ('bbbbccdd0011', 'BridgeNode', 'repeater')`,
+	); err != nil {
+		t.Fatalf("seed bridge node: %v", err)
+	}
+	if _, err := srv.db.conn.Exec(
+		`INSERT INTO nodes (public_key, name, role) VALUES ('ccccccdd0011', 'SingleRegionNode', 'repeater')`,
+	); err != nil {
+		t.Fatalf("seed single-region node: %v", err)
+	}
+
+	pt5 := 5
+	txBelgium := &StoreTx{ID: 1, Hash: "tx1", FirstSeen: time.Now().UTC().Add(-5 * time.Minute).Format(time.RFC3339Nano), PayloadType: &pt5, ScopeName: "#belgium"}
+	txFrance := &StoreTx{ID: 2, Hash: "tx2", FirstSeen: time.Now().UTC().Add(-5 * time.Minute).Format(time.RFC3339Nano), PayloadType: &pt5, ScopeName: "#france"}
+	txBelgium2 := &StoreTx{ID: 3, Hash: "tx3", FirstSeen: time.Now().UTC().Add(-5 * time.Minute).Format(time.RFC3339Nano), PayloadType: &pt5, ScopeName: "#belgium"}
+
+	srv.store = &PacketStore{
+		byPathHop: map[string][]*StoreTx{
+			"bbbbccdd0011": {txBelgium, txFrance}, // relayed BOTH regions — a bridge
+			"ccccccdd0011": {txBelgium2},          // relayed only #belgium — not a bridge
+		},
+	}
+
+	req := httptest.NewRequest("GET", "/api/scope-stats?window=24h", nil)
+	w := httptest.NewRecorder()
+	srv.handleScopeStats(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200; body: %s", w.Code, w.Body.String())
+	}
+	var resp ScopeStatsResponse
+	if err := json.NewDecoder(w.Body).Decode(&resp); err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	if len(resp.BridgeRepeaters) != 1 {
+		t.Fatalf("bridgeRepeaters = %v, want 1 entry", resp.BridgeRepeaters)
+	}
+	br := resp.BridgeRepeaters[0]
+	if br.Name != "BridgeNode" || br.PublicKey != "bbbbccdd0011" || br.Count != 2 {
+		t.Errorf("bridgeRepeaters[0] = %+v, want {BridgeNode bbbbccdd0011 2 [...]}", br)
+	}
+	wantRegions := []string{"#belgium", "#france"}
+	if len(br.Regions) != len(wantRegions) {
+		t.Fatalf("bridgeRepeaters[0].Regions = %v, want %v", br.Regions, wantRegions)
+	}
+	for i, r := range wantRegions {
+		if br.Regions[i] != r {
+			t.Errorf("bridgeRepeaters[0].Regions[%d] = %q, want %q", i, br.Regions[i], r)
+		}
+	}
+	for _, b := range resp.BridgeRepeaters {
+		if b.PublicKey == "ccccccdd0011" {
+			t.Errorf("SingleRegionNode should not appear in bridgeRepeaters (only relayed 1 region)")
+		}
+	}
+}
+
 // TestHandleScopeStats_OriginatingNodesByRegion verifies the complementary
 // breakdown to RepeatersByRegion: nodes whose OWN default_scope (#899) is a
 // given region, i.e. nodes actually configured with/running that region

cmd/server/types.go

@@ -154,6 +154,11 @@ type ScopeStatsResponse struct {
 	// channel chat specifically (payload_type=5), window-scoped like
 	// Summary above — see ChannelScopeStats doc.
 	ChannelMessages *ChannelScopeStats `json:"channelMessages,omitempty"`
+	// BridgeRepeaters is the RepeatersByRegion data inverted: repeaters
+	// that have relayed traffic for MORE than one region are the mesh's
+	// literal backbone nodes connecting separate regional communities.
+	// All-time, like RepeatersByRegion (same source data, same caveats).
+	BridgeRepeaters []BridgeRepeater `json:"bridgeRepeaters,omitempty"`
 }
 
 type RepeaterRef struct {
@@ -167,6 +172,13 @@ type ScopeRegionRepeaters struct {
 	Repeaters []RepeaterRef `json:"repeaters"`
 }
 
+type BridgeRepeater struct {
+	Name      string   `json:"name"`
+	PublicKey string   `json:"publicKey"`
+	Regions   []string `json:"regions"`
+	Count     int      `json:"count"`
+}
+
 // ─── Health ────────────────────────────────────────────────────────────────────
 
 type MemoryStats struct {