Add attendee cap with required login for capped events

Hosts can optionally cap total attendance (RSVPs + plus-ones) when
creating an event. Capped events require guests to log in via the
existing email code flow; RSVPs are tied to accounts and deduped per
user. The event page shows spots left and replaces the form with a
full notice when the cap is reached; the server rejects over-cap
RSVPs and edits with 409 as a race backstop.

Also threads a safeNext-validated ?next= param through the login and
name-setup flow so guests land back on the event after signing in.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

auth.go

@@ -11,6 +11,7 @@ import (
 	"log"
 	"math/big"
 	"net/http"
+	"net/url"
 	"os"
 	"strings"
 	"time"
@@ -63,39 +64,62 @@ func (s *Server) sessionMiddleware(next http.Handler) http.Handler {
 func (s *Server) requireAuth(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if s.currentUser(r) == nil {
-			http.Redirect(w, r, "/login", http.StatusSeeOther)
+			dest := "/login"
+			if r.Method == http.MethodGet {
+				dest += "?next=" + url.QueryEscape(r.URL.RequestURI())
+			}
+			http.Redirect(w, r, dest, http.StatusSeeOther)
 			return
 		}
 		next.ServeHTTP(w, r)
 	})
 }
 
+// safeNext returns next if it is a safe local path, else "".
+func safeNext(next string) string {
+	if strings.HasPrefix(next, "/") && !strings.HasPrefix(next, "//") && !strings.ContainsAny(next, "\\\r\n") {
+		return next
+	}
+	return ""
+}
+
 // isEmail returns true if the input looks like an email address.
 func isEmail(s string) bool {
 	return strings.Contains(s, "@")
 }
 
 func (s *Server) handleLoginPage(w http.ResponseWriter, r *http.Request) {
+	next := safeNext(r.URL.Query().Get("next"))
 	if s.currentUser(r) != nil {
-		http.Redirect(w, r, "/dashboard", http.StatusSeeOther)
+		dest := "/dashboard"
+		if next != "" {
+			dest = next
+		}
+		http.Redirect(w, r, dest, http.StatusSeeOther)
 		return
 	}
 	pageTmpl["login"].ExecuteTemplate(w, "layout", map[string]any{
 		"Step":        "identify",
+		"Next":        next,
 		"AuthEnabled": true,
 	})
 }
 
 func (s *Server) handleLoginSubmit(w http.ResponseWriter, r *http.Request) {
+	next := safeNext(r.FormValue("next"))
+	loginURL := "/login"
+	if next != "" {
+		loginURL += "?next=" + url.QueryEscape(next)
+	}
 	raw := strings.TrimSpace(r.FormValue("identifier"))
 	if raw == "" {
-		http.Redirect(w, r, "/login", http.StatusSeeOther)
+		http.Redirect(w, r, loginURL, http.StatusSeeOther)
 		return
 	}
 
 	identifier := strings.ToLower(raw)
 	if !isEmail(identifier) {
-		http.Redirect(w, r, "/login", http.StatusSeeOther)
+		http.Redirect(w, r, loginURL, http.StatusSeeOther)
 		return
 	}
 
@@ -118,11 +142,13 @@ func (s *Server) handleLoginSubmit(w http.ResponseWriter, r *http.Request) {
 	pageTmpl["login"].ExecuteTemplate(w, "layout", map[string]any{
 		"Step":        "code",
 		"Identifier":  identifier,
+		"Next":        next,
 		"AuthEnabled": true,
 	})
 }
 
 func (s *Server) handleVerifyCode(w http.ResponseWriter, r *http.Request) {
+	next := safeNext(r.FormValue("next"))
 	identifier := strings.TrimSpace(r.FormValue("identifier"))
 	code := strings.TrimSpace(r.FormValue("code"))
 
@@ -134,6 +160,7 @@ func (s *Server) handleVerifyCode(w http.ResponseWriter, r *http.Request) {
 		pageTmpl["login"].ExecuteTemplate(w, "layout", map[string]any{
 			"Step":        "code",
 			"Identifier":  identifier,
+			"Next":        next,
 			"Error":       "Invalid or expired code. Try again.",
 			"AuthEnabled": true,
 		})
@@ -174,10 +201,18 @@ func (s *Server) handleVerifyCode(w http.ResponseWriter, r *http.Request) {
 
 	// If user has no name, send them to set it
 	if user.Name == "" {
-		http.Redirect(w, r, "/account/name", http.StatusSeeOther)
+		dest := "/account/name"
+		if next != "" {
+			dest += "?next=" + url.QueryEscape(next)
+		}
+		http.Redirect(w, r, dest, http.StatusSeeOther)
 		return
 	}
 
+	if next != "" {
+		http.Redirect(w, r, next, http.StatusSeeOther)
+		return
+	}
 	http.Redirect(w, r, "/dashboard", http.StatusSeeOther)
 }
 
@@ -215,21 +250,31 @@ func (s *Server) handleNamePage(w http.ResponseWriter, r *http.Request) {
 	user := s.currentUser(r)
 	pageTmpl["name"].ExecuteTemplate(w, "layout", map[string]any{
 		"User":        user,
+		"Next":        safeNext(r.URL.Query().Get("next")),
 		"AuthEnabled": true,
 	})
 }
 
 func (s *Server) handleNameSubmit(w http.ResponseWriter, r *http.Request) {
 	user := s.currentUser(r)
+	next := safeNext(r.FormValue("next"))
 	name := strings.TrimSpace(r.FormValue("name"))
 	if name == "" {
-		http.Redirect(w, r, "/account/name", http.StatusSeeOther)
+		dest := "/account/name"
+		if next != "" {
+			dest += "?next=" + url.QueryEscape(next)
+		}
+		http.Redirect(w, r, dest, http.StatusSeeOther)
 		return
 	}
 	s.q.UpdateUserName(r.Context(), db.UpdateUserNameParams{
 		Name: name,
 		ID:   user.ID,
 	})
+	if next != "" {
+		http.Redirect(w, r, next, http.StatusSeeOther)
+		return
+	}
 	http.Redirect(w, r, "/dashboard", http.StatusSeeOther)
 }
 

db/models.go

@@ -26,6 +26,7 @@ type Event struct {
 	Location    string
 	AdminToken  string
 	Description string
+	AttendeeCap int64
 	UserID      sql.NullInt64
 	CreatedAt   time.Time
 }
@@ -36,6 +37,7 @@ type Rsvp struct {
 	Name      string
 	Note      string
 	PlusOne   int64
+	UserID    sql.NullInt64
 	CreatedAt time.Time
 }
 

db/queries.sql

@@ -5,8 +5,8 @@ SELECT * FROM events WHERE slug = ?;
 SELECT * FROM events WHERE admin_token = ?;
 
 -- name: CreateEvent :one
-INSERT INTO events (slug, title, date, time, location, admin_token, description)
+INSERT INTO events (slug, title, date, time, location, admin_token, description, attendee_cap)
-VALUES (?, ?, ?, ?, ?, ?, ?)
+VALUES (?, ?, ?, ?, ?, ?, ?, ?)
 RETURNING *;
 
 -- name: UpdateEventDescription :exec
@@ -65,8 +65,8 @@ SELECT COUNT(*) FROM claims WHERE slot_id = ?;
 SELECT * FROM rsvps WHERE event_id = ? ORDER BY created_at;
 
 -- name: CreateRsvp :one
-INSERT INTO rsvps (event_id, name, note, plus_one)
+INSERT INTO rsvps (event_id, name, note, plus_one, user_id)
-VALUES (?, ?, ?, ?)
+VALUES (?, ?, ?, ?, ?)
 RETURNING *;
 
 -- name: DeleteRsvp :exec
@@ -78,6 +78,12 @@ SELECT COUNT(*) FROM rsvps WHERE event_id = ?;
 -- name: GetRsvpByName :one
 SELECT * FROM rsvps WHERE event_id = ? AND name = ? COLLATE NOCASE LIMIT 1;
 
+-- name: GetRsvpByUser :one
+SELECT * FROM rsvps WHERE event_id = ? AND user_id = ? LIMIT 1;
+
+-- name: CountGoing :one
+SELECT CAST(COALESCE(SUM(1 + plus_one), 0) AS INTEGER) FROM rsvps WHERE event_id = ?;
+
 -- name: DeleteDuplicateRsvps :exec
 DELETE FROM rsvps WHERE id NOT IN (
   SELECT MIN(id) FROM rsvps GROUP BY event_id, name COLLATE NOCASE

db/queries.sql.go

@@ -22,6 +22,17 @@ func (q *Queries) CountClaimsBySlot(ctx context.Context, slotID int64) (int64, e
 	return count, err
 }
 
+const countGoing = `-- name: CountGoing :one
+SELECT CAST(COALESCE(SUM(1 + plus_one), 0) AS INTEGER) FROM rsvps WHERE event_id = ?
+`
+
+func (q *Queries) CountGoing(ctx context.Context, eventID int64) (int64, error) {
+	row := q.db.QueryRowContext(ctx, countGoing, eventID)
+	var column_1 int64
+	err := row.Scan(&column_1)
+	return column_1, err
+}
+
 const countRsvps = `-- name: CountRsvps :one
 SELECT COUNT(*) FROM rsvps WHERE event_id = ?
 `
@@ -59,9 +70,9 @@ func (q *Queries) CreateClaim(ctx context.Context, arg CreateClaimParams) (Claim
 }
 
 const createEvent = `-- name: CreateEvent :one
-INSERT INTO events (slug, title, date, time, location, admin_token, description)
+INSERT INTO events (slug, title, date, time, location, admin_token, description, attendee_cap)
-VALUES (?, ?, ?, ?, ?, ?, ?)
+VALUES (?, ?, ?, ?, ?, ?, ?, ?)
-RETURNING id, slug, title, date, time, location, admin_token, description, user_id, created_at
+RETURNING id, slug, title, date, time, location, admin_token, description, attendee_cap, user_id, created_at
 `
 
 type CreateEventParams struct {
@@ -72,6 +83,7 @@ type CreateEventParams struct {
 	Location    string
 	AdminToken  string
 	Description string
+	AttendeeCap int64
 }
 
 func (q *Queries) CreateEvent(ctx context.Context, arg CreateEventParams) (Event, error) {
@@ -83,6 +95,7 @@ func (q *Queries) CreateEvent(ctx context.Context, arg CreateEventParams) (Event
 		arg.Location,
 		arg.AdminToken,
 		arg.Description,
+		arg.AttendeeCap,
 	)
 	var i Event
 	err := row.Scan(
@@ -94,6 +107,7 @@ func (q *Queries) CreateEvent(ctx context.Context, arg CreateEventParams) (Event
 		&i.Location,
 		&i.AdminToken,
 		&i.Description,
+		&i.AttendeeCap,
 		&i.UserID,
 		&i.CreatedAt,
 	)
@@ -101,9 +115,9 @@ func (q *Queries) CreateEvent(ctx context.Context, arg CreateEventParams) (Event
 }
 
 const createRsvp = `-- name: CreateRsvp :one
-INSERT INTO rsvps (event_id, name, note, plus_one)
+INSERT INTO rsvps (event_id, name, note, plus_one, user_id)
-VALUES (?, ?, ?, ?)
+VALUES (?, ?, ?, ?, ?)
-RETURNING id, event_id, name, note, plus_one, created_at
+RETURNING id, event_id, name, note, plus_one, user_id, created_at
 `
 
 type CreateRsvpParams struct {
@@ -111,6 +125,7 @@ type CreateRsvpParams struct {
 	Name    string
 	Note    string
 	PlusOne int64
+	UserID  sql.NullInt64
 }
 
 func (q *Queries) CreateRsvp(ctx context.Context, arg CreateRsvpParams) (Rsvp, error) {
@@ -119,6 +134,7 @@ func (q *Queries) CreateRsvp(ctx context.Context, arg CreateRsvpParams) (Rsvp, e
 		arg.Name,
 		arg.Note,
 		arg.PlusOne,
+		arg.UserID,
 	)
 	var i Rsvp
 	err := row.Scan(
@@ -127,6 +143,7 @@ func (q *Queries) CreateRsvp(ctx context.Context, arg CreateRsvpParams) (Rsvp, e
 		&i.Name,
 		&i.Note,
 		&i.PlusOne,
+		&i.UserID,
 		&i.CreatedAt,
 	)
 	return i, err
@@ -328,7 +345,7 @@ func (q *Queries) GetClaimByID(ctx context.Context, id int64) (Claim, error) {
 }
 
 const getEventByAdminToken = `-- name: GetEventByAdminToken :one
-SELECT id, slug, title, date, time, location, admin_token, description, user_id, created_at FROM events WHERE admin_token = ?
+SELECT id, slug, title, date, time, location, admin_token, description, attendee_cap, user_id, created_at FROM events WHERE admin_token = ?
 `
 
 func (q *Queries) GetEventByAdminToken(ctx context.Context, adminToken string) (Event, error) {
@@ -343,6 +360,7 @@ func (q *Queries) GetEventByAdminToken(ctx context.Context, adminToken string) (
 		&i.Location,
 		&i.AdminToken,
 		&i.Description,
+		&i.AttendeeCap,
 		&i.UserID,
 		&i.CreatedAt,
 	)
@@ -350,7 +368,7 @@ func (q *Queries) GetEventByAdminToken(ctx context.Context, adminToken string) (
 }
 
 const getEventBySlug = `-- name: GetEventBySlug :one
-SELECT id, slug, title, date, time, location, admin_token, description, user_id, created_at FROM events WHERE slug = ?
+SELECT id, slug, title, date, time, location, admin_token, description, attendee_cap, user_id, created_at FROM events WHERE slug = ?
 `
 
 func (q *Queries) GetEventBySlug(ctx context.Context, slug string) (Event, error) {
@@ -365,6 +383,7 @@ func (q *Queries) GetEventBySlug(ctx context.Context, slug string) (Event, error
 		&i.Location,
 		&i.AdminToken,
 		&i.Description,
+		&i.AttendeeCap,
 		&i.UserID,
 		&i.CreatedAt,
 	)
@@ -372,7 +391,7 @@ func (q *Queries) GetEventBySlug(ctx context.Context, slug string) (Event, error
 }
 
 const getRsvp = `-- name: GetRsvp :one
-SELECT id, event_id, name, note, plus_one, created_at FROM rsvps WHERE id = ?
+SELECT id, event_id, name, note, plus_one, user_id, created_at FROM rsvps WHERE id = ?
 `
 
 func (q *Queries) GetRsvp(ctx context.Context, id int64) (Rsvp, error) {
@@ -384,13 +403,14 @@ func (q *Queries) GetRsvp(ctx context.Context, id int64) (Rsvp, error) {
 		&i.Name,
 		&i.Note,
 		&i.PlusOne,
+		&i.UserID,
 		&i.CreatedAt,
 	)
 	return i, err
 }
 
 const getRsvpByName = `-- name: GetRsvpByName :one
-SELECT id, event_id, name, note, plus_one, created_at FROM rsvps WHERE event_id = ? AND name = ? COLLATE NOCASE LIMIT 1
+SELECT id, event_id, name, note, plus_one, user_id, created_at FROM rsvps WHERE event_id = ? AND name = ? COLLATE NOCASE LIMIT 1
 `
 
 type GetRsvpByNameParams struct {
@@ -407,6 +427,31 @@ func (q *Queries) GetRsvpByName(ctx context.Context, arg GetRsvpByNameParams) (R
 		&i.Name,
 		&i.Note,
 		&i.PlusOne,
+		&i.UserID,
+		&i.CreatedAt,
+	)
+	return i, err
+}
+
+const getRsvpByUser = `-- name: GetRsvpByUser :one
+SELECT id, event_id, name, note, plus_one, user_id, created_at FROM rsvps WHERE event_id = ? AND user_id = ? LIMIT 1
+`
+
+type GetRsvpByUserParams struct {
+	EventID int64
+	UserID  sql.NullInt64
+}
+
+func (q *Queries) GetRsvpByUser(ctx context.Context, arg GetRsvpByUserParams) (Rsvp, error) {
+	row := q.db.QueryRowContext(ctx, getRsvpByUser, arg.EventID, arg.UserID)
+	var i Rsvp
+	err := row.Scan(
+		&i.ID,
+		&i.EventID,
+		&i.Name,
+		&i.Note,
+		&i.PlusOne,
+		&i.UserID,
 		&i.CreatedAt,
 	)
 	return i, err
@@ -569,7 +614,7 @@ func (q *Queries) ListClaimsBySlot(ctx context.Context, slotID int64) ([]Claim,
 }
 
 const listEventsByUser = `-- name: ListEventsByUser :many
-SELECT id, slug, title, date, time, location, admin_token, description, user_id, created_at FROM events WHERE user_id = ? ORDER BY created_at DESC
+SELECT id, slug, title, date, time, location, admin_token, description, attendee_cap, user_id, created_at FROM events WHERE user_id = ? ORDER BY created_at DESC
 `
 
 func (q *Queries) ListEventsByUser(ctx context.Context, userID sql.NullInt64) ([]Event, error) {
@@ -590,6 +635,7 @@ func (q *Queries) ListEventsByUser(ctx context.Context, userID sql.NullInt64) ([
 			&i.Location,
 			&i.AdminToken,
 			&i.Description,
+			&i.AttendeeCap,
 			&i.UserID,
 			&i.CreatedAt,
 		); err != nil {
@@ -607,7 +653,7 @@ func (q *Queries) ListEventsByUser(ctx context.Context, userID sql.NullInt64) ([
 }
 
 const listRsvps = `-- name: ListRsvps :many
-SELECT id, event_id, name, note, plus_one, created_at FROM rsvps WHERE event_id = ? ORDER BY created_at
+SELECT id, event_id, name, note, plus_one, user_id, created_at FROM rsvps WHERE event_id = ? ORDER BY created_at
 `
 
 func (q *Queries) ListRsvps(ctx context.Context, eventID int64) ([]Rsvp, error) {
@@ -625,6 +671,7 @@ func (q *Queries) ListRsvps(ctx context.Context, eventID int64) ([]Rsvp, error)
 			&i.Name,
 			&i.Note,
 			&i.PlusOne,
+			&i.UserID,
 			&i.CreatedAt,
 		); err != nil {
 			return nil, err

handlers.go

@@ -24,8 +24,18 @@ const (
 	maxRsvps     = 200
 	maxClaims    = 50
 	maxMaxClaims = 50
+
+	maxAttendeeCap = 1000
+	maxPlusOne     = 10
 )
 
+func plural(n int64) string {
+	if n == 1 {
+		return ""
+	}
+	return "s"
+}
+
 func sanitize(s string, maxLen int) string {
 	s = strings.TrimSpace(s)
 	if len(s) > maxLen {
@@ -73,10 +83,22 @@ func (s *Server) handleCreateEvent(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Capped events require login to RSVP, so the cap is only available when auth is on.
+	var attendeeCap int64
+	if s.features.Auth {
+		if v, err := strconv.ParseInt(r.FormValue("attendee_cap"), 10, 64); err == nil && v > 0 {
+			attendeeCap = v
+		}
+		if attendeeCap > maxAttendeeCap {
+			attendeeCap = maxAttendeeCap
+		}
+	}
+
 	slug := randomSlug()
 	token := randomToken()
 	event, err := s.q.CreateEvent(r.Context(), db.CreateEventParams{
 		Slug: slug, Title: title, Date: date, Time: time_, Location: location, AdminToken: token, Description: description,
+		AttendeeCap: attendeeCap,
 	})
 	if err != nil {
 		log.Printf("create event: %v", err)
@@ -154,6 +176,10 @@ type EventPageData struct {
 	DescriptionHTML template.HTML
 	User            *db.User
 	AuthEnabled     bool
+	Capped          bool
+	SpotsLeft       int64
+	CapFull         bool
+	PlusOneMax      int64
 }
 
 func (s *Server) loadEventPage(r *http.Request, slug string, isAdmin bool) (*EventPageData, error) {
@@ -217,6 +243,22 @@ func (s *Server) loadEventPage(r *http.Request, slug string, isAdmin bool) (*Eve
 		descHTML = RenderMarkdown(event.Description)
 	}
 
+	capped := s.features.Auth && event.AttendeeCap > 0
+	var spotsLeft int64
+	plusOneMax := int64(maxPlusOne)
+	if capped {
+		spotsLeft = event.AttendeeCap - totalGoing
+		if spotsLeft < 0 {
+			spotsLeft = 0
+		}
+		if spotsLeft-1 < plusOneMax {
+			plusOneMax = spotsLeft - 1
+		}
+		if plusOneMax < 0 {
+			plusOneMax = 0
+		}
+	}
+
 	return &EventPageData{
 		Event:           event,
 		Slots:           slotViews,
@@ -228,6 +270,10 @@ func (s *Server) loadEventPage(r *http.Request, slug string, isAdmin bool) (*Eve
 		DescriptionHTML: descHTML,
 		User:            s.currentUser(r),
 		AuthEnabled:     s.features.Auth,
+		Capped:          capped,
+		SpotsLeft:       spotsLeft,
+		CapFull:         capped && totalGoing >= event.AttendeeCap,
+		PlusOneMax:      plusOneMax,
 	}, nil
 }
 
@@ -324,6 +370,38 @@ func (s *Server) handleRsvp(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Capped events require login and enforce the cap on total people going.
+	capped := s.features.Auth && event.AttendeeCap > 0
+	user := s.currentUser(r)
+	alreadyRsvped := false
+	if capped {
+		if user == nil {
+			http.Error(w, "You must be logged in to RSVP", http.StatusUnauthorized)
+			return
+		}
+		_, err := s.q.GetRsvpByUser(r.Context(), db.GetRsvpByUserParams{
+			EventID: event.ID,
+			UserID:  sql.NullInt64{Int64: user.ID, Valid: true},
+		})
+		alreadyRsvped = err == nil
+		if !alreadyRsvped {
+			going, err := s.q.CountGoing(r.Context(), event.ID)
+			if err != nil {
+				http.Error(w, "error", http.StatusInternalServerError)
+				return
+			}
+			if going+1+plusOne > event.AttendeeCap {
+				left := event.AttendeeCap - going
+				if left <= 0 {
+					http.Error(w, "Event is full", http.StatusConflict)
+				} else {
+					http.Error(w, fmt.Sprintf("Only %d spot%s left", left, plural(left)), http.StatusConflict)
+				}
+				return
+			}
+		}
+	}
+
 	// Optional slot claim
 	if slotIDStr := r.FormValue("slot_id"); slotIDStr != "" {
 		slotID, err := strconv.ParseInt(slotIDStr, 10, 64)
@@ -363,27 +441,33 @@ func (s *Server) handleRsvp(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Create RSVP (deduped — skip if already on the list)
-	_, err = s.q.GetRsvpByName(r.Context(), db.GetRsvpByNameParams{
+	if !alreadyRsvped {
-		EventID: event.ID, Name: name,
+		var userID sql.NullInt64
-	})
+		if user != nil {
-	if err == sql.ErrNoRows {
+			userID = sql.NullInt64{Int64: user.ID, Valid: true}
-		count, err := s.q.CountRsvps(r.Context(), event.ID)
-		if err != nil {
-			http.Error(w, "error", http.StatusInternalServerError)
-			return
 		}
-		if count >= maxRsvps {
+		_, err = s.q.GetRsvpByName(r.Context(), db.GetRsvpByNameParams{
-			http.Error(w, "RSVP list is full", http.StatusConflict)
+			EventID: event.ID, Name: name,
-			return
-		}
-
-		_, err = s.q.CreateRsvp(r.Context(), db.CreateRsvpParams{
-			EventID: event.ID, Name: name, Note: note, PlusOne: plusOne,
 		})
-		if err != nil {
+		if err == sql.ErrNoRows {
-			log.Printf("create rsvp: %v", err)
+			count, err := s.q.CountRsvps(r.Context(), event.ID)
-			http.Error(w, "Failed", http.StatusInternalServerError)
+			if err != nil {
-			return
+				http.Error(w, "error", http.StatusInternalServerError)
+				return
+			}
+			if count >= maxRsvps {
+				http.Error(w, "RSVP list is full", http.StatusConflict)
+				return
+			}
+
+			_, err = s.q.CreateRsvp(r.Context(), db.CreateRsvpParams{
+				EventID: event.ID, Name: name, Note: note, PlusOne: plusOne, UserID: userID,
+			})
+			if err != nil {
+				log.Printf("create rsvp: %v", err)
+				http.Error(w, "Failed", http.StatusInternalServerError)
+				return
+			}
 		}
 	}
 
@@ -442,6 +526,29 @@ func (s *Server) handleUpdateRsvp(w http.ResponseWriter, r *http.Request) {
 		plusOne = 10
 	}
 
+	event, err := s.q.GetEventBySlug(r.Context(), slug)
+	if err != nil {
+		http.Error(w, "Event not found", http.StatusNotFound)
+		return
+	}
+	// Raising plus_one can't exceed the attendee cap.
+	if s.features.Auth && event.AttendeeCap > 0 {
+		old, err := s.q.GetRsvp(r.Context(), rsvpID)
+		if err != nil {
+			http.Error(w, "RSVP not found", http.StatusNotFound)
+			return
+		}
+		going, err := s.q.CountGoing(r.Context(), event.ID)
+		if err != nil {
+			http.Error(w, "error", http.StatusInternalServerError)
+			return
+		}
+		if going-old.PlusOne+plusOne > event.AttendeeCap {
+			http.Error(w, "Not enough spots left", http.StatusConflict)
+			return
+		}
+	}
+
 	err = s.q.UpdateRsvp(r.Context(), db.UpdateRsvpParams{
 		Name: name, Note: note, PlusOne: plusOne, ID: rsvpID,
 	})

handlers_test.go

@@ -215,6 +215,91 @@ func TestUpdateRsvp(t *testing.T) {
 	}
 }
 
+func TestCountGoing(t *testing.T) {
+	_, q := setupTestDB(t)
+	ctx := context.Background()
+	event := createTestEvent(t, q)
+
+	going, err := q.CountGoing(ctx, event.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if going != 0 {
+		t.Fatalf("expected 0 going on empty event, got %d", going)
+	}
+
+	q.CreateRsvp(ctx, db.CreateRsvpParams{EventID: event.ID, Name: "Alice", PlusOne: 0})
+	q.CreateRsvp(ctx, db.CreateRsvpParams{EventID: event.ID, Name: "Bob", PlusOne: 2})
+
+	going, err = q.CountGoing(ctx, event.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if going != 4 {
+		t.Fatalf("expected 4 going (2 RSVPs + 2 plus-ones), got %d", going)
+	}
+}
+
+func TestGetRsvpByUser(t *testing.T) {
+	_, q := setupTestDB(t)
+	ctx := context.Background()
+	event := createTestEvent(t, q)
+
+	user, err := q.CreateUserByEmail(ctx, sql.NullString{String: "alice@example.com", Valid: true})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = q.GetRsvpByUser(ctx, db.GetRsvpByUserParams{
+		EventID: event.ID, UserID: sql.NullInt64{Int64: user.ID, Valid: true},
+	})
+	if err != sql.ErrNoRows {
+		t.Fatalf("expected ErrNoRows before RSVP, got %v", err)
+	}
+
+	q.CreateRsvp(ctx, db.CreateRsvpParams{
+		EventID: event.ID, Name: "Alice", PlusOne: 1,
+		UserID: sql.NullInt64{Int64: user.ID, Valid: true},
+	})
+
+	rsvp, err := q.GetRsvpByUser(ctx, db.GetRsvpByUserParams{
+		EventID: event.ID, UserID: sql.NullInt64{Int64: user.ID, Valid: true},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if rsvp.Name != "Alice" {
+		t.Fatalf("expected RSVP name Alice, got %s", rsvp.Name)
+	}
+}
+
+func TestAttendeeCapArithmetic(t *testing.T) {
+	_, q := setupTestDB(t)
+	ctx := context.Background()
+	event, err := q.CreateEvent(ctx, db.CreateEventParams{
+		Slug: "capped", Title: "Capped Event", Date: "June 1", Time: "2pm",
+		Location: "Park", AdminToken: "tok456", AttendeeCap: 3,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if event.AttendeeCap != 3 {
+		t.Fatalf("expected AttendeeCap=3, got %d", event.AttendeeCap)
+	}
+
+	q.CreateRsvp(ctx, db.CreateRsvpParams{EventID: event.ID, Name: "Alice", PlusOne: 1})
+
+	going, _ := q.CountGoing(ctx, event.ID)
+	// Same check as handleRsvp: a new RSVP with plus_one=1 would exceed the cap.
+	if going+1+1 <= event.AttendeeCap {
+		t.Fatalf("expected RSVP +1 to exceed cap (going=%d, cap=%d)", going, event.AttendeeCap)
+	}
+	// A solo RSVP still fits.
+	if going+1+0 > event.AttendeeCap {
+		t.Fatalf("expected solo RSVP to fit (going=%d, cap=%d)", going, event.AttendeeCap)
+	}
+}
+
 func TestRsvpPlusOne(t *testing.T) {
 	_, q := setupTestDB(t)
 	ctx := context.Background()

migrate.go

@@ -33,6 +33,9 @@ func runMigrations(database *sql.DB) {
 			user_agent TEXT    NOT NULL DEFAULT '',
 			created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
 		)`,
+		// Attendee cap (0 = uncapped); capped events require login to RSVP.
+		`ALTER TABLE events ADD COLUMN attendee_cap INTEGER NOT NULL DEFAULT 0`,
+		`ALTER TABLE rsvps ADD COLUMN user_id INTEGER REFERENCES users(id)`,
 	}
 	for _, m := range migrations {
 		_, err := database.Exec(m)

schema.sql

@@ -7,6 +7,7 @@ CREATE TABLE IF NOT EXISTS events (
     location   TEXT    NOT NULL,
     admin_token TEXT   NOT NULL UNIQUE,
     description TEXT    NOT NULL DEFAULT '',
+    attendee_cap INTEGER NOT NULL DEFAULT 0, -- 0 = uncapped; capped events require login to RSVP
     user_id    INTEGER REFERENCES users(id),
     created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
 );
@@ -34,6 +35,7 @@ CREATE TABLE IF NOT EXISTS rsvps (
     name       TEXT    NOT NULL,
     note       TEXT    NOT NULL DEFAULT '',
     plus_one   INTEGER NOT NULL DEFAULT 0,
+    user_id    INTEGER REFERENCES users(id),
     created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
 );
 

templates/event.html

@@ -19,7 +19,7 @@
 
 {{define "content"}}
 <div class="event-header">
-  <div class="event-tag">Open · {{.TotalGoing}} going</div>
+  <div class="event-tag">Open · {{.TotalGoing}} going{{if .Capped}} · {{if .CapFull}}FULL{{else}}{{.SpotsLeft}} spot{{if ne .SpotsLeft 1}}s{{end}} left{{end}}{{end}}</div>
   <h1 class="event-title">{{.Event.Title}}</h1>
   <div class="event-meta">
     {{if .Event.Date}}<span>&#128197; {{.Event.Date}}</span>{{end}}
@@ -41,6 +41,23 @@
 
 <div class="section-label" style="margin-top:40px">Sign up</div>
 
+{{if and .Capped .CapFull}}
+<div class="claim-form-wrapper">
+  <div class="form-title">Event is full</div>
+  <p style="font-family:'DM Mono',monospace;font-size:0.8rem;color:#555;">
+    All {{.Event.AttendeeCap}} spots are taken.
+  </p>
+</div>
+{{else if and .Capped (not .User)}}
+<div class="claim-form-wrapper">
+  <div class="form-title">Log in to RSVP</div>
+  <p style="font-family:'DM Mono',monospace;font-size:0.8rem;color:#555;margin-bottom:16px;">
+    This event has limited spots ({{.SpotsLeft}} left), so RSVPs require an account.
+  </p>
+  <a class="btn-submit" style="display:inline-block;text-decoration:none;text-align:center;"
+     href="/login?next=/e/{{.Event.Slug}}">Log in to RSVP &#8599;</a>
+</div>
+{{else}}
 <div class="claim-form-wrapper">
   <div class="form-title">I'm coming &#8594;</div>
   <form hx-post="/e/{{.Event.Slug}}/rsvp"
@@ -64,7 +81,7 @@
     {{end}}
     <div class="form-row">
       <label>Bringing anyone?</label>
-      <input type="number" name="plus_one" value="0" min="0" max="10">
+      <input type="number" name="plus_one" value="0" min="0" max="{{if .Capped}}{{.PlusOneMax}}{{else}}10{{end}}">
     </div>
     <div class="form-row" id="claim-note">
       <label>Note (optional)</label>
@@ -73,6 +90,7 @@
     <button class="btn-submit" type="submit">Count me in &#8599;</button>
   </form>
 </div>
+{{end}}
 
 {{if .IsAdmin}}
 <div class="section-label" style="margin-top:40px">Admin: Location</div>

templates/home.html

@@ -33,6 +33,12 @@
       <label>Description (optional, markdown supported)</label>
       <textarea name="description" rows="4" placeholder="e.g. Bring your own blanket! We'll have a grill set up near the big oak tree." style="border:var(--border-w) solid var(--border);background:var(--cream);padding:10px 14px;font-family:'Bricolage Grotesque',sans-serif;font-size:0.95rem;resize:vertical;outline:none;"></textarea>
     </div>
+    {{if .AuthEnabled}}
+    <div class="form-row">
+      <label>Attendee cap (optional — guests must log in to RSVP)</label>
+      <input type="number" name="attendee_cap" min="0" max="1000" placeholder="e.g. 30 — leave blank for unlimited">
+    </div>
+    {{end}}
 
     <div class="section-label" style="margin:24px 0 16px">Slots</div>
 

templates/login.html

@@ -14,6 +14,7 @@
 <div class="claim-form-wrapper">
   {{if eq .Step "identify"}}
   <form method="POST" action="/login">
+    {{if .Next}}<input type="hidden" name="next" value="{{.Next}}">{{end}}
     <div class="form-row">
       <label>Email</label>
       <input type="email" name="identifier" placeholder="you@example.com" required autofocus>
@@ -23,6 +24,7 @@
   {{else}}
   <form method="POST" action="/login/verify">
     <input type="hidden" name="identifier" value="{{.Identifier}}">
+    {{if .Next}}<input type="hidden" name="next" value="{{.Next}}">{{end}}
     <p style="font-family:'DM Mono',monospace;font-size:0.78rem;color:#555;margin-bottom:16px;">
       Code sent to <strong>{{.Identifier}}</strong>
     </p>

templates/name.html

@@ -13,6 +13,7 @@
 
 <div class="claim-form-wrapper">
   <form method="POST" action="/account/name">
+    {{if .Next}}<input type="hidden" name="next" value="{{.Next}}">{{end}}
     <div class="form-row">
       <label>Name</label>
       <input type="text" name="name" placeholder="Your name" required autofocus

templates/slots.html

@@ -32,7 +32,7 @@
 {{end}}
 </div>
 
-<div class="section-label">Going ({{.TotalGoing}})</div>
+<div class="section-label">Going ({{.TotalGoing}}{{if .Capped}} / {{.Event.AttendeeCap}}{{end}})</div>
 <div class="rsvp-list">
   {{if .GoingList}}
     {{range .GoingList}}