refactor(auth): wrap JWT operations in transactions and migrate to clock.Now()

Wrap JTI revocation, cleanup, refresh token generation, and verification in explicit DB transactions with Begin/defer Rollback/Commit. Replace time.Now() with clock.Now() for testability.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/auth/jwt.go

@@ -5,9 +5,11 @@ import (
 	"crypto/rand"
 	"errors"
 	"fmt"
+	"log"
 	"time"
 
 	"crussell/db"
+	"crussell/clock"
 	"github.com/jackc/pgx/v5"
 
 	"github.com/go-chi/jwtauth/v5"
@@ -39,13 +41,25 @@ func RevokeJTI(ctx context.Context, jti string, expiresAt time.Time) {
 	if db.Conn == nil {
 		return
 	}
-	_, err := db.Conn.Exec(ctx,
+	tx, err := db.Conn.Begin(ctx)
+	if err != nil {
+		fmt.Printf("WARN: Failed to begin transaction for JTI revocation: %v\n", err)
+		return
+	}
+	defer tx.Rollback(ctx)
+
+	_, err = tx.Exec(ctx,
 		`INSERT INTO revoked_jtis (jti, expires_at) VALUES ($1, $2)
 		 ON CONFLICT (jti) DO NOTHING`,
 		jti, expiresAt)
 	if err != nil {
 		// Log but don't fail - this is best effort
 		fmt.Printf("WARN: Failed to revoke JTI %s: %v\n", jti, err)
+		return
+	}
+
+	if err := tx.Commit(ctx); err != nil {
+		fmt.Printf("WARN: Failed to commit transaction for JTI revocation: %v\n", err)
 	}
 }
 
@@ -72,10 +86,22 @@ func CleanupRevokedJTIs(ctx context.Context) {
 	if db.Conn == nil {
 		return
 	}
-	_, err := db.Conn.Exec(ctx,
+	tx, err := db.Conn.Begin(ctx)
+	if err != nil {
+		fmt.Printf("WARN: Failed to begin transaction for JTI cleanup: %v\n", err)
+		return
+	}
+	defer tx.Rollback(ctx)
+
+	_, err = tx.Exec(ctx,
 		`DELETE FROM revoked_jtis WHERE expires_at < NOW()`)
 	if err != nil {
 		fmt.Printf("WARN: Failed to cleanup revoked JTIs: %v\n", err)
+		return
+	}
+
+	if err := tx.Commit(ctx); err != nil {
+		fmt.Printf("WARN: Failed to commit transaction for JTI cleanup: %v\n", err)
 	}
 }
 
@@ -85,7 +111,14 @@ func StartJTICleanup() {
 		ticker := time.NewTicker(30 * time.Minute)
 		defer ticker.Stop()
 		for range ticker.C {
-			CleanupRevokedJTIs(context.Background())
+			func() {
+				defer func() {
+					if r := recover(); r != nil {
+						log.Printf("Panic recovered in JWT cleanup ticker: %v", r)
+					}
+				}()
+				CleanupRevokedJTIs(context.Background())
+			}()
 		}
 	}()
 }
@@ -106,7 +139,7 @@ func GenerateToken(userID string, role string) (string, string, error) {
 		"user_id": userID,
 		"role":    role,
 		"jti":     jti,
-		"exp":     time.Now().Add(1 * time.Hour).Unix(), // 1 hour
+		"exp":     clock.Now().Add(1 * time.Hour).Unix(), // 1 hour
 	})
 	return tokenString, jti, err
 }
@@ -175,12 +208,22 @@ func GenerateRefreshToken(ctx context.Context, userID string, role string) (stri
 		VALUES ($1, encode(sha256($2::bytea), 'hex'), $3, NOW() + INTERVAL '90 days')
 		RETURNING id`
 
+	tx, err := db.Conn.Begin(ctx)
+	if err != nil {
+		return "", fmt.Errorf("failed to begin transaction: %w", err)
+	}
+	defer tx.Rollback(ctx)
+
 	var tokenID int64
-	err = db.Conn.QueryRow(ctx, query, userID, token, role).Scan(&tokenID)
+	err = tx.QueryRow(ctx, query, userID, token, role).Scan(&tokenID)
 	if err != nil {
 		return "", fmt.Errorf("failed to store refresh token: %w", err)
 	}
 
+	if err := tx.Commit(ctx); err != nil {
+		return "", fmt.Errorf("failed to commit transaction: %w", err)
+	}
+
 	return token, nil
 }
 
@@ -194,7 +237,13 @@ func VerifyRefreshToken(ctx context.Context, tokenString string) (userID string,
 		AND NOT revoked
 		RETURNING user_id, role`
 
-	err = db.Conn.QueryRow(ctx, query, tokenString).Scan(&userID, &role)
+	tx, err := db.Conn.Begin(ctx)
+	if err != nil {
+		return "", "", fmt.Errorf("failed to begin transaction: %w", err)
+	}
+	defer tx.Rollback(ctx)
+
+	err = tx.QueryRow(ctx, query, tokenString).Scan(&userID, &role)
 	if err != nil {
 		if errors.Is(err, pgx.ErrNoRows) {
 			return "", "", fmt.Errorf("invalid or expired refresh token")
@@ -202,6 +251,10 @@ func VerifyRefreshToken(ctx context.Context, tokenString string) (userID string,
 		return "", "", fmt.Errorf("failed to verify refresh token: %w", err)
 	}
 
+	if err := tx.Commit(ctx); err != nil {
+		return "", "", fmt.Errorf("failed to commit transaction: %w", err)
+	}
+
 	// Token was consumed (DELETE returned it) — this is rotation
 	// If a token is used twice, the second DELETE returns no rows = invalid
 	return userID, role, nil