refactor(backend): introduce DI interfaces for testability

Replace concrete *db.Queries and *pgxpool.Pool dependencies with
db.Querier and db.TxManager interfaces across all handlers, game hub,
and auth. This enables unit testing with mocks.

- Enable sqlc emit_interface to generate Querier interface
- Add TxManager abstraction to encapsulate transactions
- Convert auth package-level functions to Authenticator struct
- Add TaskQueueInterface/TaskWorkerInterface for game.Hub
- Add initial unit tests for game logic and API handlers

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 29 insertions, 47 deletions

diff --git a/backend/auth/auth.go b/backend/auth/auth.go
index 7d9a4c2..a1fcb64 100644
--- a/backend/auth/auth.go
+++ b/backend/auth/auth.go
@@ -7,7 +7,6 @@ import (
 	"time"
 
 	"github.com/jackc/pgx/v5"
-	"github.com/jackc/pgx/v5/pgxpool"
 	"golang.org/x/crypto/bcrypt"
 
 	"albatross-2026-backend/account"
@@ -15,28 +14,32 @@ import (
 	"albatross-2026-backend/fortee"
 )
 
-var (
-	ErrForteeLoginTimeout = errors.New("fortee login timeout")
-)
+var ErrForteeLoginTimeout = errors.New("fortee login timeout")
 
 const (
 	forteeAPITimeout = 3 * time.Second
 )
 
-func Login(
+type Authenticator struct {
+	q   db.Querier
+	txm db.TxManager
+}
+
+func NewAuthenticator(q db.Querier, txm db.TxManager) *Authenticator {
+	return &Authenticator{q: q, txm: txm}
+}
+
+func (a *Authenticator) Login(
 	ctx context.Context,
-	queries *db.Queries,
-	pool *pgxpool.Pool,
 	username string,
 	password string,
 ) (int, error) {
-	userAuth, err := queries.GetUserAuthByUsername(ctx, username)
+	userAuth, err := a.q.GetUserAuthByUsername(ctx, username)
 	if err != nil && !errors.Is(err, pgx.ErrNoRows) {
 		return 0, err
 	}
 
 	if userAuth.AuthType == "password" {
-		// Authenticate with password.
 		passwordHash := userAuth.PasswordHash
 		if passwordHash == nil {
 			return 0, errors.New("inconsistent data: password auth type but no password hash")
@@ -48,14 +51,11 @@ func Login(
 		return int(userAuth.UserID), nil
 	}
 
-	// Authenticate with fortee.
-	return verifyForteeAccountOrSignup(ctx, queries, pool, username, password)
+	return a.verifyForteeAccountOrSignup(ctx, username, password)
 }
 
-func verifyForteeAccountOrSignup(
+func (a *Authenticator) verifyForteeAccountOrSignup(
 	ctx context.Context,
-	queries *db.Queries,
-	pool *pgxpool.Pool,
 	username string,
 	password string,
 ) (int, error) {
@@ -63,58 +63,40 @@ func verifyForteeAccountOrSignup(
 	if err != nil {
 		return 0, err
 	}
-	userID, err := queries.GetUserIDByUsername(ctx, canonicalizedUsername)
+	userID, err := a.q.GetUserIDByUsername(ctx, canonicalizedUsername)
 	if err != nil {
 		if errors.Is(err, pgx.ErrNoRows) {
-			return signup(
-				ctx,
-				queries,
-				pool,
-				canonicalizedUsername,
-			)
+			return a.signup(ctx, canonicalizedUsername)
 		}
 		return 0, err
 	}
 	return int(userID), nil
 }
 
-func signup(
+func (a *Authenticator) signup(
 	ctx context.Context,
-	queries *db.Queries,
-	pool *pgxpool.Pool,
 	username string,
 ) (int, error) {
-	tx, err := pool.Begin(ctx)
-	if err != nil {
-		return 0, err
-	}
-	defer func() {
-		if err := tx.Rollback(ctx); err != nil && err != pgx.ErrTxClosed {
-			slog.Error("failed to rollback transaction", "error", err)
+	var userID int32
+	err := a.txm.RunInTx(ctx, func(qtx db.Querier) error {
+		var err error
+		userID, err = qtx.CreateUser(ctx, username)
+		if err != nil {
+			return err
 		}
-	}()
-
-	qtx := queries.WithTx(tx)
-	userID, err := qtx.CreateUser(ctx, username)
+		return qtx.CreateUserAuth(ctx, db.CreateUserAuthParams{
+			UserID:   userID,
+			AuthType: "fortee",
+		})
+	})
 	if err != nil {
 		return 0, err
 	}
-	if err := qtx.CreateUserAuth(ctx, db.CreateUserAuthParams{
-		UserID:   userID,
-		AuthType: "fortee",
-	}); err != nil {
-		return 0, err
-	}
-
-	if err := tx.Commit(ctx); err != nil {
-		return 0, err
-	}
 
 	go func() {
-		err := account.FetchIcon(context.Background(), queries, int(userID))
+		err := account.FetchIcon(context.Background(), a.q, int(userID))
 		if err != nil {
 			slog.Error("failed to fetch icon", "error", err)
-			// The failure is intentionally ignored. Retry manually if needed.
 		}
 	}()
 	return int(userID), nil