Address production-readiness review: clearer errors, safer votes, and ops hardening.

Distinguish auth/lookup failures, make votes idempotent on visible questions, bound shutdown, page admin users, LRU throttle, trusted-proxy CIDRs, avatar cleanup, versioned migrations, and session cleanup logging.

internal/store/sqlc/votes.sql.go

@@ -42,20 +42,41 @@ func (q *Queries) GetVote(ctx context.Context, arg GetVoteParams) (int32, error)
 	return value, err
 }
 
-const upsertVote = `-- name: UpsertVote :exec
-INSERT INTO votes (user_id, question_id, value)
-VALUES ($1, $2, $3)
-ON CONFLICT (user_id, question_id) DO UPDATE
-SET value = excluded.value
+const questionIsVisible = `-- name: QuestionIsVisible :one
+SELECT EXISTS(
+  SELECT 1 FROM questions WHERE id = $1 AND hidden = 0
+)::bool
 `
 
-type UpsertVoteParams struct {
+func (q *Queries) QuestionIsVisible(ctx context.Context, id string) (bool, error) {
+	row := q.db.QueryRowContext(ctx, questionIsVisible, id)
+	var column_1 bool
+	err := row.Scan(&column_1)
+	return column_1, err
+}
+
+const upsertVoteOnVisible = `-- name: UpsertVoteOnVisible :execrows
+INSERT INTO votes (user_id, question_id, value)
+SELECT $1, $2, $3
+FROM questions q
+WHERE q.id = $2 AND q.hidden = 0
+ON CONFLICT (user_id, question_id) DO UPDATE
+SET value = excluded.value
+WHERE EXISTS (
+  SELECT 1 FROM questions q2 WHERE q2.id = excluded.question_id AND q2.hidden = 0
+)
+`
+
+type UpsertVoteOnVisibleParams struct {
 	UserID     string
 	QuestionID string
 	Value      int32
 }
 
-func (q *Queries) UpsertVote(ctx context.Context, arg UpsertVoteParams) error {
-	_, err := q.db.ExecContext(ctx, upsertVote, arg.UserID, arg.QuestionID, arg.Value)
-	return err
+func (q *Queries) UpsertVoteOnVisible(ctx context.Context, arg UpsertVoteOnVisibleParams) (int64, error) {
+	result, err := q.db.ExecContext(ctx, upsertVoteOnVisible, arg.UserID, arg.QuestionID, arg.Value)
+	if err != nil {
+		return 0, err
+	}
+	return result.RowsAffected()
 }