Stage 17 round 6 (#18, PR D): admin Messages moderation section

A new /_gm/messages console page lists posted chat messages (nudges
excluded) newest-first — time, source (guest/robot/oldest identity kind),
sender (linked to the user card), IP, body, game (linked to the game card)
— searchable by sender name / external-id glob masks and pinnable to one
game (?game=) or sender (?user=), linked from the game and user cards.

The list query lives in social (raw SQL, kind='message', source via a SQL
CASE), reusing the now-exported account.LikePattern. Server-rendered
adminconsole MessagesView + messages.gohtml, 50/page via the shared pager.

Tests: adminconsole render case; backend integration AdminListMessages
(real Postgres) — nudge exclusion, game/sender pins, glob masks, source.
Docs: ARCHITECTURE section 8 chat moderation, PLAN round-6.

backend/internal/social/adminchat.go

@@ -0,0 +1,113 @@
+package social
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/google/uuid"
+
+	"scrabble/backend/internal/account"
+)
+
+// AdminMessage is one chat message in the admin moderation list (Stage 17): the message
+// plus its sender's resolved display name and source, for the operator console.
+type AdminMessage struct {
+	ID         uuid.UUID
+	GameID     uuid.UUID
+	SenderID   uuid.UUID
+	SenderName string
+	// Source is the sender's account kind: "guest", "robot", or its oldest identity kind
+	// (e.g. "email", "telegram"); "—" when it has none.
+	Source    string
+	Body      string
+	SenderIP  string
+	CreatedAt time.Time
+}
+
+// AdminMessageFilter narrows the admin message list. A nil GameID/SenderID leaves that
+// field unfiltered; NameMask/ExtMask are glob masks (account.LikePattern) matched
+// case-insensitively against the sender's display name / any identity's external id.
+type AdminMessageFilter struct {
+	GameID   uuid.UUID
+	SenderID uuid.UUID
+	NameMask string
+	ExtMask  string
+}
+
+// AdminListMessages returns the filtered chat messages — real messages only, nudges
+// excluded — newest first, paginated, for the admin moderation console.
+func (svc *Service) AdminListMessages(ctx context.Context, f AdminMessageFilter, limit, offset int) ([]AdminMessage, error) {
+	return svc.store.adminListMessages(ctx, f, limit, offset)
+}
+
+// AdminCountMessages counts the filtered chat messages, for the admin list pager.
+func (svc *Service) AdminCountMessages(ctx context.Context, f AdminMessageFilter) (int, error) {
+	return svc.store.adminCountMessages(ctx, f)
+}
+
+// adminMessageSource is the SQL CASE projecting a sender's source: guest, robot, or its
+// oldest identity kind ("—" when it has none).
+const adminMessageSource = `CASE
+	WHEN a.is_guest THEN 'guest'
+	WHEN EXISTS (SELECT 1 FROM backend.identities i WHERE i.account_id = a.account_id AND i.kind = 'robot') THEN 'robot'
+	ELSE COALESCE((SELECT i2.kind FROM backend.identities i2 WHERE i2.account_id = a.account_id ORDER BY i2.created_at ASC LIMIT 1), '—')
+END`
+
+// adminMessageWhere builds the shared WHERE clause and its positional args (from $1).
+// Only real messages are listed; nudges are excluded.
+func adminMessageWhere(f AdminMessageFilter) (string, []any) {
+	where := `m.kind = 'message'`
+	var args []any
+	if f.GameID != uuid.Nil {
+		args = append(args, f.GameID)
+		where += fmt.Sprintf(` AND m.game_id = $%d`, len(args))
+	}
+	if f.SenderID != uuid.Nil {
+		args = append(args, f.SenderID)
+		where += fmt.Sprintf(` AND m.sender_id = $%d`, len(args))
+	}
+	if name := account.LikePattern(f.NameMask); name != "" {
+		args = append(args, name)
+		where += fmt.Sprintf(` AND a.display_name ILIKE $%d ESCAPE '\'`, len(args))
+	}
+	if ext := account.LikePattern(f.ExtMask); ext != "" {
+		args = append(args, ext)
+		where += fmt.Sprintf(` AND EXISTS (SELECT 1 FROM backend.identities ie WHERE ie.account_id = a.account_id AND ie.external_id ILIKE $%d ESCAPE '\')`, len(args))
+	}
+	return where, args
+}
+
+func (s *Store) adminListMessages(ctx context.Context, f AdminMessageFilter, limit, offset int) ([]AdminMessage, error) {
+	where, args := adminMessageWhere(f)
+	q := `SELECT m.message_id, m.game_id, m.sender_id, a.display_name, ` + adminMessageSource + ` AS source, m.body, COALESCE(m.sender_ip, ''), m.created_at
+FROM backend.chat_messages m
+JOIN backend.accounts a ON a.account_id = m.sender_id
+WHERE ` + where +
+		fmt.Sprintf(` ORDER BY m.created_at DESC LIMIT $%d OFFSET $%d`, len(args)+1, len(args)+2)
+	args = append(args, limit, offset)
+	rows, err := s.db.QueryContext(ctx, q, args...)
+	if err != nil {
+		return nil, fmt.Errorf("social: admin list messages: %w", err)
+	}
+	defer rows.Close()
+	var out []AdminMessage
+	for rows.Next() {
+		var m AdminMessage
+		if err := rows.Scan(&m.ID, &m.GameID, &m.SenderID, &m.SenderName, &m.Source, &m.Body, &m.SenderIP, &m.CreatedAt); err != nil {
+			return nil, fmt.Errorf("social: scan admin message: %w", err)
+		}
+		out = append(out, m)
+	}
+	return out, rows.Err()
+}
+
+func (s *Store) adminCountMessages(ctx context.Context, f AdminMessageFilter) (int, error) {
+	where, args := adminMessageWhere(f)
+	var n int
+	q := `SELECT COUNT(*) FROM backend.chat_messages m JOIN backend.accounts a ON a.account_id = m.sender_id WHERE ` + where
+	if err := s.db.QueryRowContext(ctx, q, args...).Scan(&n); err != nil {
+		return 0, fmt.Errorf("social: admin count messages: %w", err)
+	}
+	return n, nil
+}