feat(pipeline): add POST /backfill-refs endpoint to retroactively inject source back-references

ingestion/internal/api/handler.go

@@ -272,6 +272,18 @@ func (h *Handler) IngestPath(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, ingestResponse{Pages: allPages, Warnings: allWarnings})
 }
 
+// BackfillRefs handles POST /backfill-refs — injects source back-references
+// into all concept and entity pages based on existing wiki/sources/ pages.
+func (h *Handler) BackfillRefs(w http.ResponseWriter, r *http.Request) {
+	n, err := pipeline.BackfillRefs(r.Context(), h.brainDir)
+	if err != nil {
+		h.logger.Error("backfill-refs failed", "err", err)
+		writeError(w, http.StatusInternalServerError, "backfill error")
+		return
+	}
+	writeJSON(w, map[string]int{"updated": n})
+}
+
 func writeJSON(w http.ResponseWriter, v any) {
 	w.Header().Set("Content-Type", "application/json")
 	json.NewEncoder(w).Encode(v) //nolint:errcheck