feat: add holiday hours conflict detection with shared scheduling core

Extract computeAvailableHours as shared core between GetAvailableHours and GetPreviewAvailableHours, eliminating ~320 lines of duplication. Add GetConflictingBookingsForExceptionHandler (POST) for holiday hours conflict detection with batch service loading, int-based time comparison, and ActiveBookingStatuses constant. Add RESERVATION:placeholder cleanup (24h TTL). Fix scan error propagation in all scheduling row iterations. Add rows.Err() checks.

backend/handlers/scheduling/contact-availability.go

@@ -79,10 +79,16 @@ func GetContactAvailability(w http.ResponseWriter, r *http.Request) {
 		var b bookingInfo
 		if err := rows.Scan(&b.StartTime, &b.DurationMinutes, &b.Status); err != nil {
 			log.Printf("Failed to scan booking for contact-availability: %v", err)
-			continue
+			http.Error(w, "Internal server error", http.StatusInternalServerError)
+			return
 		}
 		bookings = append(bookings, b)
 	}
+	if err := rows.Err(); err != nil {
+		log.Printf("Error iterating bookings for contact-availability: %v", err)
+		http.Error(w, "Internal server error", http.StatusInternalServerError)
+		return
+	}
 
 	for _, b := range bookings {
 		if b.Status != "in_progress" {

backend/handlers/scheduling/default-hours.go

@@ -1,6 +1,7 @@
 package scheduling
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -21,6 +22,12 @@ import (
 
 var londonLocation = clock.London
 
+// ActiveBookingStatuses is the SQL filter used by all scheduling handlers to
+// exclude inactive booking statuses. Must stay in sync with the bookings
+// package's overlapping endpoints. Includes pending_release so clients who
+// owe deposits are also contacted before schedule changes.
+const ActiveBookingStatuses = `status NOT IN ('completed', 'client_cancelled', 'we_cancelled', 'no_show', 'deposit_lapsed')`
+
 // --- Types ---
 type DefaultHours struct {
 	Weekday   int    `json:"weekday" validate:"gte=0,lte=6"`
@@ -59,6 +66,10 @@ func GetDefaultHours(w http.ResponseWriter, r *http.Request) {
 		}
 		hours = append(hours, h)
 	}
+	if err := rows.Err(); err != nil {
+		http.Error(w, "error iterating default hours", http.StatusInternalServerError)
+		return
+	}
 
 	w.Header().Set("Content-Type", "application/json")
 	if err := json.NewEncoder(w).Encode(hours); err != nil {
@@ -178,17 +189,31 @@ func GetWorkingHours(w http.ResponseWriter, r *http.Request) {
 
 	// Load default hours
 	defaultMap := map[int]DefaultHours{}
-	defRows, _ := db.Conn.Query(r.Context(), `
+	defRows, err := db.Conn.Query(r.Context(), `
 		SELECT weekday, start_time::text, end_time, is_open
 		FROM working_hours
 	`)
+	if err != nil {
+		log.Printf("Failed to load default hours: %v", err)
+		http.Error(w, "Failed to load default hours", http.StatusInternalServerError)
+		return
+	}
 	for defRows.Next() {
 		var d DefaultHours
-		if err := defRows.Scan(&d.Weekday, &d.StartTime, &d.EndTime, &d.IsOpen); err == nil {
-			defaultMap[d.Weekday] = d
+		if err := defRows.Scan(&d.Weekday, &d.StartTime, &d.EndTime, &d.IsOpen); err != nil {
+			defRows.Close()
+			log.Printf("Failed to scan default hours row: %v", err)
+			http.Error(w, "Failed to read default hours", http.StatusInternalServerError)
+			return
 		}
+		defaultMap[d.Weekday] = d
 	}
 	defRows.Close()
+	if err := defRows.Err(); err != nil {
+		log.Printf("Error iterating default hours: %v", err)
+		http.Error(w, "Failed to read default hours", http.StatusInternalServerError)
+		return
+	}
 
 	// Load exceptional applications for Mondays in range
 	// Expand start to the Monday of its week so single-day queries still find the correct application
@@ -199,11 +224,16 @@ func GetWorkingHours(w http.ResponseWriter, r *http.Request) {
 	}
 	queryStart := start.AddDate(0, 0, -daysSinceMonday)
 
-	appRows, _ := db.Conn.Query(r.Context(), `
+	appRows, err := db.Conn.Query(r.Context(), `
 		SELECT group_id, week_start
 		FROM exceptional_group_applications
 		WHERE week_start BETWEEN $1 AND $2
 	`, queryStart, end)
+	if err != nil {
+		log.Printf("Failed to load exceptional applications: %v", err)
+		http.Error(w, "Failed to load exceptional applications", http.StatusInternalServerError)
+		return
+	}
 	type appEntry struct {
 		GroupID   int
 		WeekStart time.Time
@@ -212,28 +242,51 @@ func GetWorkingHours(w http.ResponseWriter, r *http.Request) {
 	groupIDs := []int{}
 	for appRows.Next() {
 		var a appEntry
-		if err := appRows.Scan(&a.GroupID, &a.WeekStart); err == nil {
-			a.WeekStart = time.Date(a.WeekStart.Year(), a.WeekStart.Month(), a.WeekStart.Day(), 0, 0, 0, 0, time.UTC)
-			apps = append(apps, a)
-			groupIDs = append(groupIDs, a.GroupID)
+		if err := appRows.Scan(&a.GroupID, &a.WeekStart); err != nil {
+			appRows.Close()
+			log.Printf("Failed to scan exceptional application row: %v", err)
+			http.Error(w, "Failed to read exceptional applications", http.StatusInternalServerError)
+			return
 		}
+		a.WeekStart = time.Date(a.WeekStart.Year(), a.WeekStart.Month(), a.WeekStart.Day(), 0, 0, 0, 0, time.UTC)
+		apps = append(apps, a)
+		groupIDs = append(groupIDs, a.GroupID)
 	}
 	appRows.Close()
+	if err := appRows.Err(); err != nil {
+		log.Printf("Error iterating exceptional applications: %v", err)
+		http.Error(w, "Failed to read exceptional applications", http.StatusInternalServerError)
+		return
+	}
 
 	exHoursMap := map[int]map[int]ExceptionalHours{}
 	if len(groupIDs) > 0 {
-		query, args, _ := sqlIn("SELECT group_id, weekday, start_time::text, end_time, is_open FROM exceptional_working_hours WHERE group_id IN (%s)", groupIDs)
-		rows, _ := db.Conn.Query(r.Context(), query, args...)
+		query, args := sqlIn("SELECT group_id, weekday, start_time::text, end_time, is_open FROM exceptional_working_hours WHERE group_id IN (%s)", groupIDs)
+		rows, err := db.Conn.Query(r.Context(), query, args...)
+		if err != nil {
+			log.Printf("Failed to load exceptional hours: %v", err)
+			http.Error(w, "Failed to load exceptional hours", http.StatusInternalServerError)
+			return
+		}
 		for rows.Next() {
 			var h ExceptionalHours
-			if err := rows.Scan(&h.GroupID, &h.Weekday, &h.StartTime, &h.EndTime, &h.IsOpen); err == nil {
-				if _, ok := exHoursMap[h.GroupID]; !ok {
-					exHoursMap[h.GroupID] = map[int]ExceptionalHours{}
-				}
-				exHoursMap[h.GroupID][h.Weekday] = h
+			if err := rows.Scan(&h.GroupID, &h.Weekday, &h.StartTime, &h.EndTime, &h.IsOpen); err != nil {
+				rows.Close()
+				log.Printf("Failed to scan exceptional hours row: %v", err)
+				http.Error(w, "Failed to read exceptional hours", http.StatusInternalServerError)
+				return
 			}
+			if _, ok := exHoursMap[h.GroupID]; !ok {
+				exHoursMap[h.GroupID] = map[int]ExceptionalHours{}
+			}
+			exHoursMap[h.GroupID][h.Weekday] = h
 		}
 		rows.Close()
+		if err := rows.Err(); err != nil {
+			log.Printf("Error iterating exceptional hours: %v", err)
+			http.Error(w, "Failed to read exceptional hours", http.StatusInternalServerError)
+			return
+		}
 	}
 
 	// Generate final result per day
@@ -321,7 +374,7 @@ func isValidTime15Min(t string) bool {
 }
 
 // --- helper: sqlIn generates IN queries dynamically for Postgres ---
-func sqlIn(query string, args []int) (string, []any, error) {
+func sqlIn(query string, args []int) (string, []any) {
 	inArgs := []any{}
 	var placeholders strings.Builder
 	for i, arg := range args {
@@ -332,7 +385,7 @@ func sqlIn(query string, args []int) (string, []any, error) {
 		inArgs = append(inArgs, arg)
 	}
 	query = fmt.Sprintf(query, placeholders.String())
-	return query, inArgs, nil
+	return query, inArgs
 }
 
 // --- Types for Available Hours ---
@@ -350,6 +403,17 @@ type DayAvailableHours struct {
 	Blockers []TimeSlot `json:"blockers,omitempty"`
 }
 
+// availableHoursParams holds parameters for computeAvailableHours.
+type availableHoursParams struct {
+	Start             time.Time
+	End               time.Time
+	OutOfHours        bool
+	IsAdmin           bool
+	ExcludeUserID     *string
+	ProposedHours     []ExceptionalHours // nil for normal mode
+	ProposedWeekStarts []string          // nil for normal mode
+}
+
 // --- GetAvailableHours (with bookings, UK-local) ---
 func GetAvailableHours(w http.ResponseWriter, r *http.Request) {
 	startStr := r.URL.Query().Get("start")
@@ -358,41 +422,95 @@ func GetAvailableHours(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "start and end query params required", http.StatusBadRequest)
 		return
 	}
-	start, _ := time.Parse("2006-01-02", startStr)
-	end, _ := time.Parse("2006-01-02", endStr)
+	start, err := time.Parse("2006-01-02", startStr)
+	if err != nil {
+		http.Error(w, "invalid start date", http.StatusBadRequest)
+		return
+	}
+	end, err := time.Parse("2006-01-02", endStr)
+	if err != nil {
+		http.Error(w, "invalid end date", http.StatusBadRequest)
+		return
+	}
 
-	// Parse out_of_hours toggle (admin-only extended hours)
 	outOfHours := r.URL.Query().Get("out_of_hours") == "true"
 
-	// set start/end of day in Europe/London (see comment above)
-	start = time.Date(start.Year(), start.Month(), start.Day(), 0, 0, 0, 0, londonLocation)
-	end = time.Date(end.Year(), end.Month(), end.Day(), 23, 59, 59, 999999999, londonLocation)
+	isAdmin := false
+	if userRole, ok := r.Context().Value(mw.UserRoleKey).(string); ok {
+		isAdmin = userRole == "admin"
+	}
+
+	var excludeUserID *string
+	if uid, ok := r.Context().Value(mw.UserIDKey).(string); ok && uid != "" {
+		excludeUserID = &uid
+	}
+
+	startLondon := time.Date(start.Year(), start.Month(), start.Day(), 0, 0, 0, 0, londonLocation)
+	endLondon := time.Date(end.Year(), end.Month(), end.Day(), 23, 59, 59, 999999999, londonLocation)
+
+	results, err := computeAvailableHours(r.Context(), availableHoursParams{
+		Start:         startLondon,
+		End:           endLondon,
+		OutOfHours:    outOfHours,
+		IsAdmin:       isAdmin,
+		ExcludeUserID: excludeUserID,
+	})
+	if err != nil {
+		log.Printf("Failed to compute available hours: %v", err)
+		http.Error(w, "Internal server error", http.StatusInternalServerError)
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	if err := json.NewEncoder(w).Encode(results); err != nil {
+		log.Printf("Failed to encode JSON response: %v", err)
+	}
+}
+
+// computeAvailableHours is the shared core for both GetAvailableHours and
+// GetPreviewAvailableHours. It loads default hours, exceptional applications,
+// bookings, and time blockers, then generates per-day available slot lists.
+// When params.ProposedHours is non-nil, those hours override exceptional
+// applications for the specified weeks (what-if simulation).
+func computeAvailableHours(ctx context.Context, params availableHoursParams) ([]DayAvailableHours, error) {
+	start := params.Start
+	end := params.End
 
 	// Load default hours
 	defaultMap := map[int]DefaultHours{}
-	defRows, _ := db.Conn.Query(r.Context(), `SELECT weekday, start_time::text, end_time, is_open FROM working_hours`)
+	defRows, err := db.Conn.Query(ctx, `SELECT weekday, start_time::text, end_time, is_open FROM working_hours`)
+	if err != nil {
+		return nil, fmt.Errorf("failed to load default hours: %w", err)
+	}
 	for defRows.Next() {
 		var d DefaultHours
-		if err := defRows.Scan(&d.Weekday, &d.StartTime, &d.EndTime, &d.IsOpen); err == nil {
-			defaultMap[d.Weekday] = d
+		if err := defRows.Scan(&d.Weekday, &d.StartTime, &d.EndTime, &d.IsOpen); err != nil {
+			defRows.Close()
+			return nil, fmt.Errorf("failed to scan default hours row: %w", err)
 		}
+		defaultMap[d.Weekday] = d
 	}
 	defRows.Close()
+	if err := defRows.Err(); err != nil {
+		return nil, fmt.Errorf("error iterating default hours: %w", err)
+	}
 
 	// Load exceptional applications for Mondays in range
-	// Expand start to the Monday of its week so single-day queries still find the correct application
 	startWeekday := int(start.Weekday())
 	daysSinceMonday := startWeekday - 1
 	if daysSinceMonday < 0 {
-		daysSinceMonday = 6 // Sunday
+		daysSinceMonday = 6
 	}
 	queryStart := start.AddDate(0, 0, -daysSinceMonday)
 
-	appRows, _ := db.Conn.Query(r.Context(), `
+	appRows, err := db.Conn.Query(ctx, `
 		SELECT group_id, week_start
 		FROM exceptional_group_applications
 		WHERE week_start BETWEEN $1 AND $2
 	`, queryStart, end)
+	if err != nil {
+		return nil, fmt.Errorf("failed to load exceptional applications: %w", err)
+	}
 	type appEntry struct {
 		GroupID   int
 		WeekStart time.Time
@@ -401,83 +519,100 @@ func GetAvailableHours(w http.ResponseWriter, r *http.Request) {
 	groupIDs := []int{}
 	for appRows.Next() {
 		var a appEntry
-		if err := appRows.Scan(&a.GroupID, &a.WeekStart); err == nil {
-			a.WeekStart = time.Date(a.WeekStart.Year(), a.WeekStart.Month(), a.WeekStart.Day(), 0, 0, 0, 0, time.UTC)
-			apps = append(apps, a)
-			groupIDs = append(groupIDs, a.GroupID)
+		if err := appRows.Scan(&a.GroupID, &a.WeekStart); err != nil {
+			appRows.Close()
+			return nil, fmt.Errorf("failed to scan exceptional application row: %w", err)
 		}
+		a.WeekStart = time.Date(a.WeekStart.Year(), a.WeekStart.Month(), a.WeekStart.Day(), 0, 0, 0, 0, time.UTC)
+		apps = append(apps, a)
+		groupIDs = append(groupIDs, a.GroupID)
 	}
 	appRows.Close()
+	if err := appRows.Err(); err != nil {
+		return nil, fmt.Errorf("error iterating exceptional applications: %w", err)
+	}
 
 	exHoursMap := map[int]map[int]ExceptionalHours{}
 	if len(groupIDs) > 0 {
-		query, args, _ := sqlIn("SELECT group_id, weekday, start_time::text, end_time, is_open FROM exceptional_working_hours WHERE group_id IN (%s)", groupIDs)
-		rows, _ := db.Conn.Query(r.Context(), query, args...)
+		query, args := sqlIn("SELECT group_id, weekday, start_time::text, end_time, is_open FROM exceptional_working_hours WHERE group_id IN (%s)", groupIDs)
+		rows, err := db.Conn.Query(ctx, query, args...)
+		if err != nil {
+			return nil, fmt.Errorf("failed to load exceptional hours: %w", err)
+		}
 		for rows.Next() {
 			var h ExceptionalHours
-			if err := rows.Scan(&h.GroupID, &h.Weekday, &h.StartTime, &h.EndTime, &h.IsOpen); err == nil {
-				if _, ok := exHoursMap[h.GroupID]; !ok {
-					exHoursMap[h.GroupID] = map[int]ExceptionalHours{}
-				}
-				exHoursMap[h.GroupID][h.Weekday] = h
+			if err := rows.Scan(&h.GroupID, &h.Weekday, &h.StartTime, &h.EndTime, &h.IsOpen); err != nil {
+				rows.Close()
+				return nil, fmt.Errorf("failed to scan exceptional hours row: %w", err)
 			}
+			if _, ok := exHoursMap[h.GroupID]; !ok {
+				exHoursMap[h.GroupID] = map[int]ExceptionalHours{}
+			}
+			exHoursMap[h.GroupID][h.Weekday] = h
 		}
 		rows.Close()
+		if err := rows.Err(); err != nil {
+			return nil, fmt.Errorf("error iterating exceptional hours: %w", err)
+		}
+	}
+
+	// Build proposed hours lookup maps
+	proposedByWeekday := map[int]ExceptionalHours{}
+	for _, ph := range params.ProposedHours {
+		proposedByWeekday[ph.Weekday] = ph
+	}
+	proposedWeekSet := map[string]bool{}
+	for _, ws := range params.ProposedWeekStarts {
+		proposedWeekSet[ws] = true
 	}
 
 	// Load bookings that overlap the query range.
-	// Must catch bookings that STARTED before the range but EXTEND INTO it
-	// (e.g. a booking at 23:00 the previous day lasting 120min crosses midnight).
-	// Use the same overlap condition as the booking creation handlers.
-	bookingRows, _ := db.Conn.Query(r.Context(), `
+	bookingRows, err := db.Conn.Query(ctx, `
 		SELECT
 			b.start_time,
 			b.total_duration_minutes AS total_duration
 		FROM bookings b
 		WHERE b.start_time < $2
 		  AND b.end_time > $1
-		  AND b.status NOT IN ('client_cancelled', 'we_cancelled', 'no_show', 'pending_release', 'deposit_lapsed')
+		  AND `+ActiveBookingStatuses+`
 		ORDER BY b.start_time
 	`, start, end)
+	if err != nil {
+		return nil, fmt.Errorf("failed to load bookings: %w", err)
+	}
 
 	bookings := map[string][]TimeSlot{}
 	for bookingRows.Next() {
 		var t time.Time
 		var dur int
-		if err := bookingRows.Scan(&t, &dur); err == nil {
-			tLondon := t.In(londonLocation)
-			dateStr := tLondon.Format("2006-01-02")
-			endTime := t.Add(time.Duration(dur) * time.Minute)
-			bookings[dateStr] = append(bookings[dateStr], TimeSlot{
-				StartTime: tLondon.Format("15:04"),
-				EndTime:   endTime.In(londonLocation).Format("15:04"),
-			})
+		if err := bookingRows.Scan(&t, &dur); err != nil {
+			bookingRows.Close()
+			return nil, fmt.Errorf("failed to scan booking row: %w", err)
 		}
+		tLondon := t.In(londonLocation)
+		dateStr := tLondon.Format("2006-01-02")
+		endTime := t.Add(time.Duration(dur) * time.Minute)
+		bookings[dateStr] = append(bookings[dateStr], TimeSlot{
+			StartTime: tLondon.Format("15:04"),
+			EndTime:   endTime.In(londonLocation).Format("15:04"),
+		})
 	}
 	bookingRows.Close()
+	if err := bookingRows.Err(); err != nil {
+		return nil, fmt.Errorf("error iterating bookings: %w", err)
+	}
 
-	// Load time blockers, excluding the current user's own RESERVATION entries
-	// so their existing reservation doesn't hide the slot from them
-	var excludeUserID *string
-	if uid, ok := r.Context().Value(mw.UserIDKey).(string); ok && uid != "" {
-		excludeUserID = &uid
-	}
-	blockers, err := GetTimeBlockersInRange(r.Context(), start, end, excludeUserID)
+	// Load time blockers
+	blockers, err := GetTimeBlockersInRange(ctx, start, end, params.ExcludeUserID)
 	if err != nil {
-		log.Printf("Failed to load time blockers: %v", err)
+		return nil, fmt.Errorf("failed to load time blockers: %w", err)
 	}
-	// Convert blockers to map by date for easier lookup
 
 	blockerMap := make(map[string][]TimeSlot)
-
 	for _, blocker := range blockers {
 		blockStart := blocker.StartTime
 		blockEnd := blockStart.Add(time.Duration(blocker.DurationMinutes) * time.Minute)
 
-		// Split multi-day blockers into per-day segments so subtractTimeSlots
-		// only compares times within the same calendar day. Each segment's end
-		// time uses "24:00" for day boundaries (midnight of the next day) since
-		// "00:00" as an end time would incorrectly appear before all slot times.
 		cur := blockStart
 		for cur.Before(blockEnd) {
 			dayEnd := time.Date(cur.Year(), cur.Month(), cur.Day(), 0, 0, 0, 0, londonLocation).AddDate(0, 0, 1)
@@ -487,8 +622,6 @@ func GetAvailableHours(w http.ResponseWriter, r *http.Request) {
 			}
 
 			dateStr := cur.Format("2006-01-02")
-			// Format times in Europe/London so that blocker time strings use
-			// wall-clock hours matching working_hours and booking slots.
 			londonStart := cur.In(londonLocation)
 			londonEnd := segEnd.In(londonLocation)
 			endStr := londonEnd.Format("15:04")
@@ -504,12 +637,6 @@ func GetAvailableHours(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	// Check if user is admin
-	isAdmin := false
-	if userRole, ok := r.Context().Value(mw.UserRoleKey).(string); ok {
-		isAdmin = userRole == "admin"
-	}
-
 	// Generate available slots per day
 	var results []DayAvailableHours
 	for d := start; !d.After(end); d = d.AddDate(0, 0, 1) {
@@ -523,7 +650,7 @@ func GetAvailableHours(w http.ResponseWriter, r *http.Request) {
 		// Calculate the Monday of this week
 		daysSinceMonday := int(d.Weekday()) - 1
 		if daysSinceMonday < 0 {
-			daysSinceMonday = 6 // Sunday
+			daysSinceMonday = 6
 		}
 		weekStart := d.AddDate(0, 0, -daysSinceMonday)
 		weekStart = time.Date(weekStart.Year(), weekStart.Month(), weekStart.Day(), 0, 0, 0, 0, time.UTC)
@@ -546,7 +673,31 @@ func GetAvailableHours(w http.ResponseWriter, r *http.Request) {
 
 		var baseStart, baseEnd string
 		var isOpen bool
-		if applied != nil {
+
+		// Proposed hours override (what-if simulation for preview)
+		if proposedWeekSet[weekStartStr] {
+			if ph, ok := proposedByWeekday[weekday]; ok {
+				baseStart = ph.StartTime
+				baseEnd = ph.EndTime
+				isOpen = ph.IsOpen
+				day.Source = "proposed"
+			} else if applied != nil {
+				baseStart = applied.StartTime
+				baseEnd = applied.EndTime
+				isOpen = applied.IsOpen
+				day.Source = "exceptional"
+			} else if def, ok := defaultMap[weekday]; ok {
+				baseStart = def.StartTime
+				baseEnd = def.EndTime
+				isOpen = def.IsOpen
+				day.Source = "default"
+			} else {
+				baseStart = "00:00"
+				baseEnd = "00:00"
+				isOpen = false
+				day.Source = "default"
+			}
+		} else if applied != nil {
 			baseStart = applied.StartTime
 			baseEnd = applied.EndTime
 			isOpen = applied.IsOpen
@@ -564,7 +715,7 @@ func GetAvailableHours(w http.ResponseWriter, r *http.Request) {
 		}
 
 		// Out-of-hours override for admin
-		if outOfHours && isAdmin {
+		if params.OutOfHours && params.IsAdmin {
 			baseStart = "06:00"
 			baseEnd = "22:00"
 			isOpen = true
@@ -573,7 +724,6 @@ func GetAvailableHours(w http.ResponseWriter, r *http.Request) {
 
 		day.IsOpen = isOpen
 		if isOpen {
-			// Normalize to HH:MM to match blocker and booking time formats
 			baseStart = normalizeTime(baseStart)
 			baseEnd = normalizeTime(baseEnd)
 			slots := []TimeSlot{{StartTime: baseStart, EndTime: baseEnd}}
@@ -581,26 +731,21 @@ func GetAvailableHours(w http.ResponseWriter, r *http.Request) {
 				slots = subtractTimeSlots(slots, booked)
 			}
 			day.Slots = slots
-			// Subtract time blockers from available slots for ALL users
-			// (prevents showing blocked slots that would fail on reserve)
 			if dayBlockers, ok := blockerMap[day.Date]; ok {
 				day.Slots = subtractTimeSlots(day.Slots, dayBlockers)
-				// Store blockers separately for admin warning display
-				if isAdmin {
+				if params.IsAdmin {
 					day.Blockers = dayBlockers
 				}
 			}
 
 			// Late night lock: after 22:00, block next morning 00:00-11:00 for non-admin users
-			if !isAdmin {
+			if !params.IsAdmin {
 				now := clock.Now()
 				londonNow := now.In(londonLocation)
 				if londonNow.Hour() >= 22 {
-					// Check if this is tomorrow's date
 					tomorrow := now.AddDate(0, 0, 1)
 					tomorrowStr := tomorrow.Format("2006-01-02")
 					if day.Date == tomorrowStr {
-						// Add a fake blocker for 00:00-11:00
 						lateNightBlock := TimeSlot{
 							StartTime: "00:00",
 							EndTime:   "11:00",
@@ -616,10 +761,7 @@ func GetAvailableHours(w http.ResponseWriter, r *http.Request) {
 		results = append(results, day)
 	}
 
-	w.Header().Set("Content-Type", "application/json")
-	if err := json.NewEncoder(w).Encode(results); err != nil {
-		log.Printf("Failed to encode JSON response: %v", err)
-	}
+	return results, nil
 }
 
 // normalizeTime strips seconds from HH:MM:SS to HH:MM for consistent string
@@ -688,3 +830,74 @@ func subtractTimeSlots(available []TimeSlot, gaps []TimeSlot) []TimeSlot {
 
 	return result
 }
+
+// --- GetPreviewAvailableHours (with proposed hours what-if simulation) ---
+func GetPreviewAvailableHours(w http.ResponseWriter, r *http.Request) {
+	startStr := r.URL.Query().Get("start")
+	endStr := r.URL.Query().Get("end")
+	if startStr == "" || endStr == "" {
+		http.Error(w, "start and end query params required", http.StatusBadRequest)
+		return
+	}
+	startDate, err := time.Parse("2006-01-02", startStr)
+	if err != nil {
+		http.Error(w, "invalid start date", http.StatusBadRequest)
+		return
+	}
+	endDate, err := time.Parse("2006-01-02", endStr)
+	if err != nil {
+		http.Error(w, "invalid end date", http.StatusBadRequest)
+		return
+	}
+
+	outOfHours := r.URL.Query().Get("out_of_hours") == "true"
+
+	// Parse proposed hours and weeks (what-if simulation)
+	var proposedHours []ExceptionalHours
+	if phStr := r.URL.Query().Get("proposed_hours"); phStr != "" {
+		if err := json.Unmarshal([]byte(phStr), &proposedHours); err != nil {
+			http.Error(w, "invalid proposed_hours JSON", http.StatusBadRequest)
+			return
+		}
+	}
+	var proposedWeekStarts []string
+	if pwStr := r.URL.Query().Get("proposed_weeks"); pwStr != "" {
+		if err := json.Unmarshal([]byte(pwStr), &proposedWeekStarts); err != nil {
+			http.Error(w, "invalid proposed_weeks JSON", http.StatusBadRequest)
+			return
+		}
+	}
+
+	isAdmin := false
+	if userRole, ok := r.Context().Value(mw.UserRoleKey).(string); ok {
+		isAdmin = userRole == "admin"
+	}
+
+	var excludeUserID *string
+	if uid, ok := r.Context().Value(mw.UserIDKey).(string); ok && uid != "" {
+		excludeUserID = &uid
+	}
+
+	startLondon := time.Date(startDate.Year(), startDate.Month(), startDate.Day(), 0, 0, 0, 0, londonLocation)
+	endLondon := time.Date(endDate.Year(), endDate.Month(), endDate.Day(), 23, 59, 59, 999999999, londonLocation)
+
+	results, err := computeAvailableHours(r.Context(), availableHoursParams{
+		Start:              startLondon,
+		End:                endLondon,
+		OutOfHours:         outOfHours,
+		IsAdmin:            isAdmin,
+		ExcludeUserID:      excludeUserID,
+		ProposedHours:      proposedHours,
+		ProposedWeekStarts: proposedWeekStarts,
+	})
+	if err != nil {
+		log.Printf("Failed to compute preview available hours: %v", err)
+		http.Error(w, "Internal server error", http.StatusInternalServerError)
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	if err := json.NewEncoder(w).Encode(results); err != nil {
+		log.Printf("Failed to encode JSON response: %v", err)
+	}
+}

backend/handlers/scheduling/exceptional-hours.go

@@ -7,6 +7,7 @@ import (
 	"log/slog"
 	"net/http"
 	"strconv"
+	"strings"
 	"time"
 
 	"crussell/db"
@@ -29,7 +30,7 @@ type ExceptionalGroup struct {
 	Name        string             `json:"name" validate:"required"`
 	Description string             `json:"description" validate:"required"`
 	Hours       []ExceptionalHours `json:"hours,omitempty" validate:"required,min=7,max=7,dive"`
-	WeekStarts  []string           `json:"weekStarts,omitempty" validate:"required,min=1,dive,required"`
+		WeekStarts  []string           `json:"weekStarts,omitempty" validate:"required,min=1,max=52,dive,required"`
 }
 
 // --- List Groups with Hours and Applications ---
@@ -300,7 +301,7 @@ func DeleteExceptionalGroup(w http.ResponseWriter, r *http.Request) {
 func UpdateExceptionalApplications(w http.ResponseWriter, r *http.Request) {
 	var req struct {
 		GroupID    int      `json:"groupId" validate:"required"`
-		WeekStarts []string `json:"weekStarts" validate:"required,min=1,dive,required"`
+		WeekStarts []string `json:"weekStarts" validate:"required,min=1,max=52,dive,required"`
 	}
 
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
@@ -368,3 +369,224 @@ func UpdateExceptionalApplications(w http.ResponseWriter, r *http.Request) {
 
 	w.WriteHeader(http.StatusNoContent)
 }
+
+// Response types mirroring bookings.OverlappingBooking, bookings.OverlappingBookingsResponse, and bookings.UserSummary
+// (defined locally to avoid circular import: bookings → scheduling → bookings)
+type (
+	UserSummary struct {
+		ID                string  `json:"id"`
+		FullName          string  `json:"full_name"`
+		Email             *string `json:"email,omitempty"`
+		Phone             *string `json:"phone,omitempty"`
+		PreviousFirstName *string `json:"previous_first_name,omitempty"`
+		PreviousLastName  *string `json:"previous_last_name,omitempty"`
+	}
+
+	OverlappingBooking struct {
+		ID        string           `json:"id"`
+		StartTime time.Time        `json:"start_time"`
+		Duration  int              `json:"duration_minutes"`
+		Status    string           `json:"status"`
+		CreatedAt time.Time        `json:"created_at"`
+		User      *UserSummary     `json:"user,omitempty"`
+		Services  []string         `json:"services,omitempty"`
+	}
+
+	OverlappingBookingsResponse struct {
+		Bookings []OverlappingBooking `json:"bookings"`
+	}
+
+	ConflictingBookingsRequest struct {
+		WeekStarts     []string           `json:"weekStarts" validate:"required,max=52,dive,required"`
+		ProposedHours []ExceptionalHours `json:"proposedHours" validate:"required,len=7,dive"`
+	}
+)
+
+// GetConflictingBookingsForExceptionHandler accepts POST with proposed exceptional hours
+// and week starts, queries active bookings that would conflict (bookings that overlap
+// with the affected weeks but fall OUTSIDE the proposed open hours), and returns them
+// in the existing OverlappingBookingsResponse format.
+func GetConflictingBookingsForExceptionHandler(w http.ResponseWriter, r *http.Request) {
+	var req ConflictingBookingsRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		http.Error(w, "invalid payload", http.StatusBadRequest)
+		return
+	}
+
+	if err := validators.Validate.Struct(&req); err != nil {
+		log.Printf("Failed to process request: %v", err)
+		http.Error(w, "Invalid request", http.StatusBadRequest)
+		return
+	}
+
+	if len(req.ProposedHours) != 7 {
+		http.Error(w, "must provide exactly 7 weekday entries (0-6)", http.StatusBadRequest)
+		return
+	}
+
+	var allConflicts []OverlappingBooking
+
+	// Build weekday map for robust lookup (not relying on array index = weekday)
+	proposedByWeekday := map[int]ExceptionalHours{}
+	for _, h := range req.ProposedHours {
+		proposedByWeekday[h.Weekday] = h
+	}
+
+	for _, weekStart := range req.WeekStarts {
+		ws, err := time.Parse("2006-01-02", weekStart)
+		if err != nil {
+			log.Printf("Invalid week_start format: %v", err)
+			http.Error(w, "invalid week_start format, expected YYYY-MM-DD", http.StatusBadRequest)
+			return
+		}
+
+		wsLondon := ws.In(londonLocation)
+		rangeStart := time.Date(wsLondon.Year(), wsLondon.Month(), wsLondon.Day(), 0, 0, 0, 0, londonLocation)
+		rangeEnd := rangeStart.AddDate(0, 0, 7).Add(-time.Nanosecond) // Sun 23:59:59.999999999
+
+		rows, err := db.Conn.Query(r.Context(), `
+			SELECT
+				b.id,
+				b.start_time,
+				b.status,
+				b.created_at,
+				b.total_duration_minutes as duration,
+				u.id as user_id,
+				u.fn,
+				u.email,
+				u.phone
+			FROM bookings b
+			LEFT JOIN users u ON b.user_id = u.id
+			WHERE `+ActiveBookingStatuses+`
+				AND b.start_time < $2
+				AND b.end_time > $1
+			ORDER BY b.start_time ASC
+		`, rangeStart, rangeEnd)
+		if err != nil {
+			log.Printf("Failed to query conflicting bookings: %v", err)
+			http.Error(w, "Internal server error", http.StatusInternalServerError)
+			return
+		}
+
+		for rows.Next() {
+			var ob OverlappingBooking
+			ob.User = &UserSummary{}
+			if err := rows.Scan(&ob.ID, &ob.StartTime, &ob.Status, &ob.CreatedAt, &ob.Duration, &ob.User.ID, &ob.User.FullName, &ob.User.Email, &ob.User.Phone); err != nil {
+				log.Printf("Failed to scan conflicting booking row: %v", err)
+				rows.Close()
+				http.Error(w, "Internal server error", http.StatusInternalServerError)
+				return
+			}
+
+			// Determine which weekday this booking falls on (London wall-clock time)
+			bookingLondon := ob.StartTime.In(londonLocation)
+			// Go: Sun=0,Mon=1,...,Sat=6 → Our convention: Mon=0,...,Sun=6
+			ourWeekday := int((bookingLondon.Weekday() + 6) % 7)
+
+			proposed, _ := proposedByWeekday[ourWeekday]
+
+			isConflict := false
+			if !proposed.IsOpen {
+				// Salon is closed on this day — any active booking conflicts
+				isConflict = true
+			} else {
+				startMinutes := bookingLondon.Hour()*60 + bookingLondon.Minute()
+				endLondon := ob.StartTime.Add(time.Duration(ob.Duration) * time.Minute).In(londonLocation)
+				endMinutes := endLondon.Hour()*60 + endLondon.Minute()
+
+				propStartMinutes := parseTimeToMinutes(proposed.StartTime)
+				propEndMinutes := parseTimeToMinutes(proposed.EndTime)
+
+				// Check if booking starts before opening or ends after closing.
+				// For midnight-crossing bookings (endMinutes < startMinutes), the booking
+				// extends past midnight and always conflicts with daily hours since the
+				// day's open window cannot span past midnight.
+				if startMinutes < 0 || endMinutes < 0 {
+					// parse error — treat as conflict
+					isConflict = true
+				} else if endMinutes < startMinutes {
+					// Booking crosses midnight — always a conflict with daily hours
+					isConflict = true
+				} else if startMinutes < propStartMinutes || endMinutes > propEndMinutes {
+					isConflict = true
+				}
+			}
+
+			if isConflict {
+				allConflicts = append(allConflicts, ob)
+			}
+		}
+		rows.Close()
+
+		if err := rows.Err(); err != nil {
+			log.Printf("Error iterating conflicting bookings: %v", err)
+			http.Error(w, "Internal server error", http.StatusInternalServerError)
+			return
+		}
+	}
+
+	if len(allConflicts) > 0 {
+		ids := make([]string, len(allConflicts))
+		for i, ob := range allConflicts {
+			ids[i] = ob.ID
+		}
+		serviceRows, err := db.Conn.Query(r.Context(), `
+			SELECT booking_id, name FROM (
+				SELECT bs.booking_id, s.name
+				FROM booking_services bs
+				JOIN services s ON bs.service_id = s.id
+				WHERE bs.booking_id = ANY($1)
+				UNION ALL
+				SELECT bcs.booking_id, cs.name
+				FROM booking_custom_services bcs
+				JOIN custom_services cs ON bcs.custom_service_id = cs.id
+				WHERE bcs.booking_id = ANY($1)
+			) sub ORDER BY booking_id, name
+		`, ids)
+		if err != nil {
+			log.Printf("Failed to batch-load services for conflicting bookings: %v", err)
+		} else {
+			serviceMap := map[string][]string{}
+			for serviceRows.Next() {
+				var bookingID, name string
+				if err := serviceRows.Scan(&bookingID, &name); err != nil {
+					log.Printf("Failed to scan service row: %v", err)
+					continue
+				}
+				serviceMap[bookingID] = append(serviceMap[bookingID], name)
+			}
+			serviceRows.Close()
+			if err := serviceRows.Err(); err != nil {
+				log.Printf("Error iterating services for conflicting bookings: %v", err)
+			}
+			for i, ob := range allConflicts {
+				allConflicts[i].Services = serviceMap[ob.ID]
+			}
+		}
+	}
+
+	if allConflicts == nil {
+		allConflicts = []OverlappingBooking{}
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	if err := json.NewEncoder(w).Encode(OverlappingBookingsResponse{Bookings: allConflicts}); err != nil {
+		log.Printf("Failed to encode conflicting bookings response: %v", err)
+		http.Error(w, "Internal server error", http.StatusInternalServerError)
+	}
+}
+
+// parseTimeToMinutes converts a "HH:MM" string to minutes since midnight.
+// Returns -1 on parse failure.
+func parseTimeToMinutes(t string) int {
+	parts := strings.Split(t, ":")
+	if len(parts) < 2 {
+		return -1
+	}
+	h, err1 := strconv.Atoi(parts[0])
+	m, err2 := strconv.Atoi(parts[1])
+	if err1 != nil || err2 != nil || h < 0 || h > 23 || m < 0 || m > 59 {
+		return -1
+	}
+	return h*60 + m
+}

backend/handlers/scheduling/time-blockers.go

@@ -124,7 +124,7 @@ func ListTimeBlockers(w http.ResponseWriter, r *http.Request) {
 func CreateTimeBlocker(w http.ResponseWriter, r *http.Request) {
 	var req CreateTimeBlockerRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		http.Error(w, "invalid JSON: "+err.Error(), http.StatusBadRequest)
+		http.Error(w, "invalid request body", http.StatusBadRequest)
 		return
 	}
 
@@ -398,6 +398,8 @@ func CleanupOldReservations(ctx context.Context) (int, error) {
 		   OR (description LIKE 'RESERVATION:admin:callin:%' AND created_at < $3)
 		   OR (description LIKE 'RESERVATION:edit_request:%' AND created_at < $4)
 		   OR (description LIKE 'PAYMENT_IN_FLIGHT:%' AND start_time + (duration_minutes * INTERVAL '1 minute') < NOW())
+		   OR (description LIKE 'RESERVATION:placeholder:%' AND created_at < $4)
+		   OR (description LIKE 'RESERVATION:holiday_placeholder:%' AND created_at < $4)
 	`, oneHourAgo, tenMinutesAgo, fifteenMinutesAgo, twentyFourHoursAgo)
 	if err != nil {
 		return 0, err