Record origin changes and show them on the prefix page (closes #161)

The routing table records each prefix and origin AS pair's origin changes:
when it gains its first peer and when it loses its last. Each row holds the
prefix, the origin AS, announced or withdrawn, the peer count and the time.
The prefix handler writes them to a new origin_changes table, and the database
maintainer prunes each prefix to its newest 500 rows and 72 hours. The prefix
page lists them newest first, at most 5,000.

Model: deepseek-v4-pro

internal/server/handlers.go

@@ -88,6 +88,10 @@ const (
 	ipVersionV6 = 6
 )
 
+// maxOriginChangesOnPage is the most origin changes the prefix page shows. A
+// prefix with more shows the newest ones and says so.
+const maxOriginChangesOnPage = 5000
+
 // HealthCheckResponse represents the health check response.
 type HealthCheckResponse struct {
 	Status    string            `json:"status"`
@@ -1534,27 +1538,24 @@ func (s *Server) handlePrefixDetail() http.HandlerFunc {
 
 		routes := prefixRoutes(parsed, origins)
 
-		// Prepare template data
-		data := struct {
-			Prefix      string
-			MaskLength  int
-			IPVersion   int
-			Routes      []EnhancedRoute
-			Origins     []*ASNInfo
-			PeerCount   int
-			OriginCount int
-			CSPNonce    string
-		}{
-			Prefix:      parsed.String(),
-			MaskLength:  parsed.Bits(),
-			IPVersion:   ipVersionOf(parsed),
-			Routes:      routesWithASPathHandles(routes),
-			Origins:     originInfos,
-			PeerCount:   len(routes),
-			OriginCount: len(originInfos),
-			CSPNonce:    cspNonce(r.Context()),
+		changes, moreChanges, err := s.prefixOriginChanges(r.Context(), parsed)
+		if deadlinePassed(r.Context()) {
+			http.Error(w, requestTimeoutMessage, http.StatusGatewayTimeout)
+
+			return
 		}
 
+		if err != nil {
+			s.logger.Error("Failed to get the origin changes", "error", err)
+			http.Error(w, internalErrorMessage, http.StatusInternalServerError)
+
+			return
+		}
+
+		// Prepare template data
+		data := newPrefixDetailData(parsed, routes, originInfos, changes,
+			moreChanges, cspNonce(r.Context()))
+
 		// Check if context is still valid before writing response
 		select {
 		case <-r.Context().Done():
@@ -1606,6 +1607,58 @@ func (s *Server) originASNs(
 	return infos, nil
 }
 
+// prefixOriginChanges returns prefix's origin changes for the page, newest
+// first, at most maxOriginChangesOnPage, and whether there are more.
+func (s *Server) prefixOriginChanges(
+	ctx context.Context, prefix netip.Prefix,
+) ([]routetable.OriginChange, bool, error) {
+	// One more is read to know whether there are more.
+	changes, err := s.db.GetOriginChanges(ctx, prefix, maxOriginChangesOnPage+1)
+	if err != nil {
+		return nil, false, err
+	}
+
+	more := len(changes) > maxOriginChangesOnPage
+	if more {
+		changes = changes[:maxOriginChangesOnPage]
+	}
+
+	return changes, more, nil
+}
+
+// prefixDetailData is what the prefix detail page is rendered with.
+type prefixDetailData struct {
+	Prefix            string
+	MaskLength        int
+	IPVersion         int
+	Routes            []EnhancedRoute
+	Origins           []*ASNInfo
+	PeerCount         int
+	OriginCount       int
+	OriginChanges     []routetable.OriginChange
+	MoreOriginChanges bool
+	CSPNonce          string
+}
+
+// newPrefixDetailData builds the prefix detail page's data.
+func newPrefixDetailData(
+	parsed netip.Prefix, routes []LiveRoute, originInfos []*ASNInfo,
+	changes []routetable.OriginChange, moreChanges bool, nonce string,
+) prefixDetailData {
+	return prefixDetailData{
+		Prefix:            parsed.String(),
+		MaskLength:        parsed.Bits(),
+		IPVersion:         ipVersionOf(parsed),
+		Routes:            routesWithASPathHandles(routes),
+		Origins:           originInfos,
+		PeerCount:         len(routes),
+		OriginCount:       len(originInfos),
+		OriginChanges:     changes,
+		MoreOriginChanges: moreChanges,
+		CSPNonce:          nonce,
+	}
+}
+
 // prefixRoutes returns one route for each peer that carries prefix, by origin
 // AS in the order of origins. Each origin's kept routes come first, newest
 // first, with their AS path, next hop and time. Its other peers follow without