Keep a trailing AS set out of the origin and the peerings (closes #75)

A path ending in an AS set, such as [64496, 64497, [64498, 64499]], was
flattened into the sequence, so the route was stored as originated by the
last set member and the peering handler recorded peerings the path does not
show. ASPath now keeps the sequence and a trailing set of several members
apart; Origin() gives the last AS of the sequence, or 0 (no known origin)
for such a set. The handlers use it; peerings come from the sequence only.
The pages show origin 0 as no known origin, and the IP lookup asks no WHOIS
lookup for it. Empty paths are unchanged.

Model: opus-5-5

internal/server/handlers_internal_test.go

@@ -331,6 +331,63 @@ func TestPrefixDetailShowsOriginNames(t *testing.T) {
 	}
 }
 
+// TestPagesSayOriginZeroIsNoKnownOrigin stores a route with origin 0, as the
+// prefix handler stores a route whose AS path ends in an AS set of several
+// members, and checks that the prefix page and the prefix length page say it
+// has no known origin, without a link to AS0 or the description of the
+// reserved AS 0 (https://git.eeqj.de/sneak/routewatch/issues/75).
+func TestPagesSayOriginZeroIsNoKnownOrigin(t *testing.T) {
+	t.Parallel()
+
+	db, err := database.New(&config.Config{StateDir: t.TempDir()}, logger.New())
+	if err != nil {
+		t.Fatalf("database.New: %v", err)
+	}
+
+	t.Cleanup(func() { _ = db.Close() })
+
+	err = db.UpsertLiveRouteBatch([]*database.LiveRoute{{
+		ID: uuid.New(), Prefix: testPrefixV4, MaskLength: 24, IPVersion: 4,
+		OriginASN: 0, PeerIP: testPeerV4, ASPath: []int{64500, 64501, 64502},
+		NextHop: testPeerV4, LastUpdated: time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC),
+	}})
+	if err != nil {
+		t.Fatalf("UpsertLiveRouteBatch: %v", err)
+	}
+
+	reserved, ok := asinfo.Get(0)
+	if !ok {
+		t.Fatal("AS0 is not in the AS info data")
+	}
+
+	s := New(db, streamer.New(logger.New(), metrics.New()), logger.New(), &config.Config{})
+
+	for _, path := range []string{"/prefix/" + testPrefixV4, "/prefixlength/24"} {
+		rec := httptest.NewRecorder()
+		s.router.ServeHTTP(rec, httptest.NewRequestWithContext(
+			t.Context(), http.MethodGet, path, nil))
+
+		if rec.Code != http.StatusOK {
+			t.Fatalf("%s: status %d, want %d; body %s",
+				path, rec.Code, http.StatusOK, rec.Body)
+		}
+
+		page := rec.Body.String()
+
+		if !strings.Contains(page, "No known origin") {
+			t.Errorf("%s does not say the route has no known origin", path)
+		}
+
+		if strings.Contains(page, `href="/as/0"`) {
+			t.Errorf("%s links to AS0", path)
+		}
+
+		if strings.Contains(page, html.EscapeString(reserved.Description)) {
+			t.Errorf("%s shows AS0's description %q", path, reserved.Description)
+		}
+	}
+}
+
 // shortRequestDeadline is the deadline the tests below give a request. The
 // server's 30-second limit and the stats handlers' 4-second limit inherit it,
 // so the tests do not wait for either.