feat(tier2): smarter fraud detection — Block G

Per-event fraud tuning. Hosts can now dial the medium / high / block
boundaries, allowlist trusted networks, and feed verdicts back on
flagged accesses — the seed corpus for a future ML model.

Schema (migration 0011)
- events.fraud_{medium,high,block}_threshold default 30/60/85 so
  existing events behave identically until a host changes them
- access_logs.geo_{country,city,lat,lon} for future enrichment
- fraud_feedback table — verdict ('legitimate' | 'suspicious') + note,
  PK on access_log_id so re-mark is an upsert
- event_allowlists table — (event_id, ip_cidr) primary key, inet column
  so containment checks use the native >>= operator (indexed lookup)

Domain
- FraudThresholds with Valid() + Band() helpers; Default trio echoed
  through GET responses so the frontend doesn't duplicate constants
- ParseAllowlistCIDR accepts bare IPs (auto-widens to /32 or /128) and
  canonicalises the output (203.0.113.42 → 203.0.113.42/32)
- Event.Thresholds() falls back to defaults if columns weren't
  populated yet, so the API never wedges every score into "low"

Storage
- AllowlistRepo: List / Add / Remove + Matches() — the latter pushes
  CIDR containment into Postgres rather than streaming rows back
- FeedbackRepo: Record (upserts) + ListForEvent (joined through guests)
- EventRepo.GetThresholds + UpdateThresholds, plus the threshold
  columns baked into scanEvent so every event load carries them
- AccessLogRepo.BelongsToEvent — stops a hostile editor on event A
  from marking event B's access logs

API
- GET/PUT /events/{id}/security/thresholds (viewer/editor)
- GET/POST/DELETE /events/{id}/security/allowlist
- POST /events/{id}/access-logs/{log_id}/feedback (editor)
- GET /events/{id}/security/feedback
- RSVP scoring path: allowlist short-circuit fires before the fraud
  engine; the engine's score is then re-banded against the event's
  thresholds (engine.Risk becomes advisory — API is the source of
  truth for "what counts as block here")
- CORS Allow-Methods already includes PUT (Block D fix)

Fraud engine
- Single-signal cap: it now takes ≥2 sub-scores of ≥70 to push the
  final into HIGH. Fixes the well-known "second visit with a slightly
  shifted fingerprint scores 60+" false positive
- Engine band remains advisory; API re-bands using per-event
  thresholds before deciding to block

Frontend
- SecurityCard.vue: visual band ribbon (proportional to thresholds),
  three sliders with mutual clamping so dragging medium past high
  pushes high (not an invalid ordering), reset-to-defaults button,
  CIDR allowlist with inline add + per-row remove, verdict-history
  inbox. Toast feedback on save/add/remove
- "Security" tab added to the event-detail tab nav (5th tab,
  right of Analytics)
- Viewer role hides write affordances; server enforces too

Tests
- Domain: ThresholdsBand, ThresholdsValid, ParseAllowlistCIDR (bare
  IP widening + traversal/typo rejection), FraudFeedbackValid
- Integration: thresholds round-trip + invalid ordering rejection,
  allowlist CRUD + duplicate 409 + invalid CIDR 400 + IP auto-widen,
  feedback record + upsert + cross-tenant 404 + invalid verdict 400,
  viewer can read / editor can write / outsider gets 404
- Full integration suite green (315.8s, all 36 top-level tests pass)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/api/fraud_v2.go

@@ -0,0 +1,280 @@
+package api
+
+import (
+	"encoding/json"
+	"errors"
+	"log/slog"
+	"net/http"
+
+	"github.com/alchemistkay/guestguard/internal/domain"
+	"github.com/alchemistkay/guestguard/internal/storage"
+)
+
+// securityHandler bundles the Tier 2 Block G endpoints: per-event fraud
+// thresholds, the CIDR allowlist, and the fraud-feedback inbox.
+type securityHandler struct {
+	logger    *slog.Logger
+	events    *storage.EventRepo
+	collabs   *storage.CollaboratorRepo
+	allowlist *storage.AllowlistRepo
+	feedback  *storage.FeedbackRepo
+	access    *storage.AccessLogRepo
+}
+
+// --- thresholds ---
+
+type thresholdsResponse struct {
+	domain.FraudThresholds
+	// Defaults are echoed so the slider can show "reset" affordances
+	// without a hardcoded duplicate in the frontend.
+	Defaults domain.FraudThresholds `json:"defaults"`
+}
+
+// GET /events/{id}/security/thresholds — viewer+.
+func (h *securityHandler) getThresholds(w http.ResponseWriter, r *http.Request) {
+	hostID, ok := hostFromContext(w, r)
+	if !ok {
+		return
+	}
+	eventID, ok := parseIDParam(w, r, "id")
+	if !ok {
+		return
+	}
+	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleViewer); !ok {
+		return
+	}
+	th, err := h.events.GetThresholds(r.Context(), eventID)
+	if err != nil && !errors.Is(err, domain.ErrEventNotFound) {
+		writeError(w, http.StatusInternalServerError, "failed to load thresholds")
+		return
+	}
+	writeJSON(w, http.StatusOK, thresholdsResponse{
+		FraudThresholds: th,
+		Defaults:        domain.DefaultThresholds(),
+	})
+}
+
+// PUT /events/{id}/security/thresholds — editor+.
+func (h *securityHandler) putThresholds(w http.ResponseWriter, r *http.Request) {
+	hostID, ok := hostFromContext(w, r)
+	if !ok {
+		return
+	}
+	eventID, ok := parseIDParam(w, r, "id")
+	if !ok {
+		return
+	}
+	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleEditor); !ok {
+		return
+	}
+	var req domain.FraudThresholds
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid json")
+		return
+	}
+	if err := req.Valid(); err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	if err := h.events.UpdateThresholds(r.Context(), eventID, req); err != nil {
+		if errors.Is(err, domain.ErrEventNotFound) {
+			writeError(w, http.StatusNotFound, "event not found")
+			return
+		}
+		h.logger.Error("update thresholds", "err", err)
+		writeError(w, http.StatusInternalServerError, "failed to update thresholds")
+		return
+	}
+	writeJSON(w, http.StatusOK, thresholdsResponse{
+		FraudThresholds: req,
+		Defaults:        domain.DefaultThresholds(),
+	})
+}
+
+// --- allowlist ---
+
+type addAllowlistRequest struct {
+	CIDR  string `json:"cidr"`
+	Label string `json:"label"`
+}
+
+// GET /events/{id}/security/allowlist — viewer+.
+func (h *securityHandler) listAllowlist(w http.ResponseWriter, r *http.Request) {
+	hostID, ok := hostFromContext(w, r)
+	if !ok {
+		return
+	}
+	eventID, ok := parseIDParam(w, r, "id")
+	if !ok {
+		return
+	}
+	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleViewer); !ok {
+		return
+	}
+	entries, err := h.allowlist.List(r.Context(), eventID)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to list allowlist")
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]any{"entries": entries})
+}
+
+// POST /events/{id}/security/allowlist — editor+.
+func (h *securityHandler) addAllowlist(w http.ResponseWriter, r *http.Request) {
+	hostID, ok := hostFromContext(w, r)
+	if !ok {
+		return
+	}
+	eventID, ok := parseIDParam(w, r, "id")
+	if !ok {
+		return
+	}
+	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleEditor); !ok {
+		return
+	}
+	var req addAllowlistRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid json")
+		return
+	}
+	canonical, _, err := domain.ParseAllowlistCIDR(req.CIDR)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	entry, err := h.allowlist.Add(r.Context(), storage.AddAllowlistParams{
+		EventID:   eventID,
+		CIDR:      canonical,
+		Label:     req.Label,
+		CreatedBy: hostID,
+	})
+	if err != nil {
+		if errors.Is(err, storage.ErrAllowlistExists) {
+			writeError(w, http.StatusConflict, "that CIDR is already allowlisted")
+			return
+		}
+		h.logger.Error("add allowlist", "err", err)
+		writeError(w, http.StatusInternalServerError, "failed to add allowlist entry")
+		return
+	}
+	writeJSON(w, http.StatusCreated, entry)
+}
+
+// DELETE /events/{id}/security/allowlist?cidr=... — editor+. CIDR comes in
+// on the query string so the URL stays RESTful without route-encoding the
+// slash in the path.
+func (h *securityHandler) removeAllowlist(w http.ResponseWriter, r *http.Request) {
+	hostID, ok := hostFromContext(w, r)
+	if !ok {
+		return
+	}
+	eventID, ok := parseIDParam(w, r, "id")
+	if !ok {
+		return
+	}
+	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleEditor); !ok {
+		return
+	}
+	cidr := r.URL.Query().Get("cidr")
+	if cidr == "" {
+		writeError(w, http.StatusBadRequest, "cidr query parameter required")
+		return
+	}
+	canonical, _, err := domain.ParseAllowlistCIDR(cidr)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	if err := h.allowlist.Remove(r.Context(), eventID, canonical); err != nil {
+		if errors.Is(err, domain.ErrAllowlistNotFound) {
+			writeError(w, http.StatusNotFound, "allowlist entry not found")
+			return
+		}
+		writeError(w, http.StatusInternalServerError, "failed to remove allowlist entry")
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}
+
+// --- feedback ---
+
+type feedbackRequest struct {
+	Verdict string `json:"verdict"` // "legitimate" | "suspicious"
+	Note    string `json:"note"`
+}
+
+// POST /events/{id}/access-logs/{log_id}/feedback — editor+. Records the
+// host's verdict on a specific access log. We re-verify the log belongs
+// to the event (a hostile editor on event A shouldn't be able to mark
+// event B's logs).
+func (h *securityHandler) recordFeedback(w http.ResponseWriter, r *http.Request) {
+	hostID, ok := hostFromContext(w, r)
+	if !ok {
+		return
+	}
+	eventID, ok := parseIDParam(w, r, "id")
+	if !ok {
+		return
+	}
+	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleEditor); !ok {
+		return
+	}
+	logID, ok := parseIDParam(w, r, "log_id")
+	if !ok {
+		return
+	}
+
+	// Confirm the access log is on this event.
+	belongs, err := h.access.BelongsToEvent(r.Context(), logID, eventID)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to verify access log")
+		return
+	}
+	if !belongs {
+		writeError(w, http.StatusNotFound, "access log not found")
+		return
+	}
+
+	var req feedbackRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid json")
+		return
+	}
+	if err := (domain.FraudFeedback{Verdict: req.Verdict}).Valid(); err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	f, err := h.feedback.Record(r.Context(), storage.RecordFeedbackParams{
+		AccessLogID: logID,
+		Verdict:     req.Verdict,
+		MarkedBy:    hostID,
+		Note:        req.Note,
+	})
+	if err != nil {
+		h.logger.Error("record feedback", "err", err)
+		writeError(w, http.StatusInternalServerError, "failed to record feedback")
+		return
+	}
+	writeJSON(w, http.StatusOK, f)
+}
+
+// GET /events/{id}/security/feedback — viewer+.
+func (h *securityHandler) listFeedback(w http.ResponseWriter, r *http.Request) {
+	hostID, ok := hostFromContext(w, r)
+	if !ok {
+		return
+	}
+	eventID, ok := parseIDParam(w, r, "id")
+	if !ok {
+		return
+	}
+	if _, _, ok := requireRole(w, r, h.events, h.collabs, eventID, hostID, domain.RoleViewer); !ok {
+		return
+	}
+	fb, err := h.feedback.ListForEvent(r.Context(), eventID)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to list feedback")
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]any{"feedback": fb})
+}

internal/api/rsvps.go

@@ -33,6 +33,7 @@ type rsvpHandler struct {
 	events     *storage.EventRepo
 	rsvps      *storage.RSVPRepo
 	accessLogs *storage.AccessLogRepo
+	allowlist  *storage.AllowlistRepo
 	scorer     fraudScorer
 	pub        rsvpPublisher
 }
@@ -322,6 +323,26 @@ func (h *rsvpHandler) scoreAccess(
 		h.logger.Error("create access log", "err", err)
 	}
 
+	// Block G: allowlist short-circuit. If the request IP matches a CIDR
+	// the host has explicitly trusted (office Wi-Fi, family network), we
+	// skip the fraud engine entirely — score 0, low band. Best-effort:
+	// any error reading the allowlist falls through to normal scoring so a
+	// dropped DB connection doesn't lock guests out of an event.
+	if h.allowlist != nil {
+		if matched, label, err := h.allowlist.Matches(r.Context(), event.ID, ip); err == nil && matched {
+			reason := "allowlisted"
+			if label != "" {
+				reason = "allowlisted: " + label
+			}
+			return fraud.Decision{
+				Score:   0,
+				Risk:    "low",
+				Reasons: []string{reason},
+				Used:    true,
+			}, fingerprint, ip, true
+		}
+	}
+
 	decision := h.scorer.Score(r.Context(), fraud.ScoreInput{
 		EventID:     event.ID,
 		GuestID:     guest.ID,
@@ -332,6 +353,14 @@ func (h *rsvpHandler) scoreAccess(
 		UserAgent:   r.UserAgent(),
 		Referrer:    r.Referer(),
 	})
+
+	// Block G: re-band the score using this event's thresholds. The
+	// engine's `Risk` field becomes advisory; the API is the source of
+	// truth for "what counts as block here". This lets a strict-event
+	// host set Block=70 while a casual-event host sets it to 95 without
+	// touching the engine.
+	decision.Risk = event.Thresholds().Band(decision.Score)
+
 	if fraud.IsBlock(decision) {
 		writeJSON(w, http.StatusForbidden, submitRSVPResponse{
 			Decision: decision,

internal/api/server.go

@@ -41,6 +41,7 @@ type Server struct {
 	analytics *analyticsHandler
 	branding  *brandingHandler
 	uploads   *uploadHandler
+	security  *securityHandler
 }
 
 type ServerDeps struct {
@@ -100,6 +101,8 @@ func NewServer(deps ServerDeps) (*Server, error) {
 	inviteRepo := storage.NewInviteRepo(deps.DB)
 	analyticsRepo := storage.NewAnalyticsRepo(deps.DB)
 	brandingRepo := storage.NewBrandingRepo(deps.DB)
+	allowlistRepo := storage.NewAllowlistRepo(deps.DB)
+	feedbackRepo := storage.NewFeedbackRepo(deps.DB)
 
 	// Branding image store. Empty UploadsDir leaves it nil and the upload
 	// + serve handlers report 503, so the rest of the service keeps
@@ -204,6 +207,7 @@ func NewServer(deps ServerDeps) (*Server, error) {
 			events:     eventRepo,
 			rsvps:      rsvpRepo,
 			accessLogs: accessRepo,
+			allowlist:  allowlistRepo,
 			scorer:     deps.FraudScorer,
 			pub:        deps.RSVPPublisher,
 		},
@@ -259,6 +263,14 @@ func NewServer(deps ServerDeps) (*Server, error) {
 			logger: deps.Logger,
 			store:  imageStore,
 		},
+		security: &securityHandler{
+			logger:    deps.Logger,
+			events:    eventRepo,
+			collabs:   collabRepo,
+			allowlist: allowlistRepo,
+			feedback:  feedbackRepo,
+			access:    accessRepo,
+		},
 		collabs: &collaboratorHandler{
 			logger:        deps.Logger,
 			events:        eventRepo,
@@ -356,6 +368,24 @@ func (s *Server) Handler() http.Handler {
 	mux.Handle("GET /events/{id}/analytics/export.csv",
 		authed(http.HandlerFunc(s.analytics.exportCSV)))
 
+	// Block G — smarter fraud detection. Per-event thresholds, CIDR
+	// allowlists, and the verdict feedback inbox. Reads are viewer+;
+	// writes are editor+ (matches the rest of the event-edit surface).
+	mux.Handle("GET /events/{id}/security/thresholds",
+		authed(http.HandlerFunc(s.security.getThresholds)))
+	mux.Handle("PUT /events/{id}/security/thresholds",
+		authed(http.HandlerFunc(s.security.putThresholds)))
+	mux.Handle("GET /events/{id}/security/allowlist",
+		authed(http.HandlerFunc(s.security.listAllowlist)))
+	mux.Handle("POST /events/{id}/security/allowlist",
+		authed(http.HandlerFunc(s.security.addAllowlist)))
+	mux.Handle("DELETE /events/{id}/security/allowlist",
+		authed(http.HandlerFunc(s.security.removeAllowlist)))
+	mux.Handle("GET /events/{id}/security/feedback",
+		authed(http.HandlerFunc(s.security.listFeedback)))
+	mux.Handle("POST /events/{id}/access-logs/{log_id}/feedback",
+		authed(http.HandlerFunc(s.security.recordFeedback)))
+
 	// Block D — event branding. Reads are viewer+; PUT is editor+. The
 	// upload endpoint is gated by auth only (any signed-in user can mint
 	// an image URL; the URL is no use without an event they can edit
@@ -470,7 +500,7 @@ func corsMiddleware(next http.Handler) http.Handler {
 			w.Header().Set("Access-Control-Allow-Origin", origin)
 			w.Header().Set("Access-Control-Allow-Credentials", "true")
 			w.Header().Set("Vary", "Origin")
-			w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PATCH, DELETE, OPTIONS")
+			w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, PATCH, DELETE, OPTIONS")
 			w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization, X-Device-Fingerprint")
 		}
 		if r.Method == http.MethodOptions {