refactor(api): separate business logic into game, tournament, session packages

Extract business logic from api/handler.go into dedicated service packages:
- session: context helpers (resolves admin → api import dependency)
- game: game state, code submission, ranking, watch logic
- tournament: bracket construction and seed ordering
- api/convert.go: domain → API type conversion functions

api/handler.go is now a thin adapter that delegates to services and
maps domain errors to HTTP status codes.

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

16 files changed, 1478 insertions, 1249 deletions

diff --git a/backend/admin/handler.go b/backend/admin/handler.go
index 8eac425..09303ac 100644
--- a/backend/admin/handler.go
+++ b/backend/admin/handler.go
@@ -14,9 +14,9 @@ import (
 	"github.com/labstack/echo/v4"
 
 	"albatross-2026-backend/account"
-	"albatross-2026-backend/api"
 	"albatross-2026-backend/config"
 	"albatross-2026-backend/db"
+	"albatross-2026-backend/session"
 )
 
 var jst = time.FixedZone("Asia/Tokyo", 9*60*60)
@@ -39,7 +39,7 @@ func NewHandler(q db.Querier, txm db.TxManager, hub GameHub, conf *config.Config
 func (h *Handler) newAdminMiddleware() echo.MiddlewareFunc {
 	return func(next echo.HandlerFunc) echo.HandlerFunc {
 		return func(c echo.Context) error {
-			user, ok := api.GetUserFromContext(c.Request().Context())
+			user, ok := session.GetUserFromContext(c.Request().Context())
 			if !ok {
 				return c.Redirect(http.StatusSeeOther, h.conf.BasePath+"login")
 			}
diff --git a/backend/admin/handler_test.go b/backend/admin/handler_test.go
index 9de9a0b..20f5775 100644
--- a/backend/admin/handler_test.go
+++ b/backend/admin/handler_test.go
@@ -14,9 +14,9 @@ import (
 	"github.com/jackc/pgx/v5/pgtype"
 	"github.com/labstack/echo/v4"
 
-	"albatross-2026-backend/api"
 	"albatross-2026-backend/config"
 	"albatross-2026-backend/db"
+	"albatross-2026-backend/session"
 )
 
 // mockQuerier implements db.Querier for admin handler testing.
@@ -395,7 +395,7 @@ func newEchoContextWithForm(path string, params map[string]string, form url.Valu
 // --- Admin middleware tests ---
 
 func setUserInContext(c echo.Context, user *db.User) {
-	ctx := api.SetUserInContext(c.Request().Context(), user)
+	ctx := session.SetUserInContext(c.Request().Context(), user)
 	c.SetRequest(c.Request().WithContext(ctx))
 }
 
diff --git a/backend/api/auth_middleware.go b/backend/api/auth_middleware.go
index f2a3987..a588185 100644
--- a/backend/api/auth_middleware.go
+++ b/backend/api/auth_middleware.go
@@ -1,17 +1,13 @@
 package api
 
 import (
-	"context"
-
 	"github.com/labstack/echo/v4"
 
 	"albatross-2026-backend/auth"
 	"albatross-2026-backend/db"
+	"albatross-2026-backend/session"
 )
 
-type sessionIDContextKey struct{}
-type userContextKey struct{}
-
 func SessionCookieMiddleware(q db.Querier) echo.MiddlewareFunc {
 	return func(next echo.HandlerFunc) echo.HandlerFunc {
 		return func(c echo.Context) error {
@@ -25,31 +21,14 @@ func SessionCookieMiddleware(q db.Querier) echo.MiddlewareFunc {
 				return next(c)
 			}
 			ctx := c.Request().Context()
-			ctx = context.WithValue(ctx, sessionIDContextKey{}, hashedID)
-			ctx = context.WithValue(ctx, userContextKey{}, &user)
+			ctx = session.SetSessionIDInContext(ctx, hashedID)
+			ctx = session.SetUserInContext(ctx, &user)
 			c.SetRequest(c.Request().WithContext(ctx))
 			return next(c)
 		}
 	}
 }
 
-func GetSessionIDFromContext(ctx context.Context) (string, bool) {
-	sessionID, ok := ctx.Value(sessionIDContextKey{}).(string)
-	return sessionID, ok
-}
-
-func GetUserFromContext(ctx context.Context) (*db.User, bool) {
-	user, ok := ctx.Value(userContextKey{}).(*db.User)
-	return user, ok
-}
-
-// SetUserInContext sets a user in the context. Intended for testing.
-func SetUserInContext(ctx context.Context, user *db.User) context.Context {
-	return context.WithValue(ctx, userContextKey{}, user)
-}
-
-type clientIPContextKey struct{}
-
 // ClientIPMiddleware extracts the client IP from echo.Context.RealIP()
 // and stores it in the request's context.Context so that handlers
 // receiving only context.Context (via generated code) can access it.
@@ -57,14 +36,9 @@ func ClientIPMiddleware() echo.MiddlewareFunc {
 	return func(next echo.HandlerFunc) echo.HandlerFunc {
 		return func(c echo.Context) error {
 			ip := c.RealIP()
-			ctx := context.WithValue(c.Request().Context(), clientIPContextKey{}, ip)
+			ctx := session.SetClientIPInContext(c.Request().Context(), ip)
 			c.SetRequest(c.Request().WithContext(ctx))
 			return next(c)
 		}
 	}
 }
-
-func GetClientIPFromContext(ctx context.Context) string {
-	ip, _ := ctx.Value(clientIPContextKey{}).(string)
-	return ip
-}
diff --git a/backend/api/auth_middleware_test.go b/backend/api/auth_middleware_test.go
index d84eef7..9fc20af 100644
--- a/backend/api/auth_middleware_test.go
+++ b/backend/api/auth_middleware_test.go
@@ -9,62 +9,9 @@ import (
 	"github.com/labstack/echo/v4"
 
 	"albatross-2026-backend/db"
+	"albatross-2026-backend/session"
 )
 
-func TestGetSessionIDFromContext_NotSet(t *testing.T) {
-	ctx := context.Background()
-	_, ok := GetSessionIDFromContext(ctx)
-	if ok {
-		t.Error("expected ok=false when session ID is not set")
-	}
-}
-
-func TestGetSessionIDFromContext_Set(t *testing.T) {
-	ctx := context.WithValue(context.Background(), sessionIDContextKey{}, "abc123")
-	id, ok := GetSessionIDFromContext(ctx)
-	if !ok {
-		t.Fatal("expected ok=true when session ID is set")
-	}
-	if id != "abc123" {
-		t.Errorf("expected session ID 'abc123', got %q", id)
-	}
-}
-
-func TestGetUserFromContext_NotSet(t *testing.T) {
-	ctx := context.Background()
-	_, ok := GetUserFromContext(ctx)
-	if ok {
-		t.Error("expected ok=false when user is not set")
-	}
-}
-
-func TestGetUserFromContext_Set(t *testing.T) {
-	user := &db.User{UserID: 42, Username: "testuser"}
-	ctx := context.WithValue(context.Background(), userContextKey{}, user)
-	u, ok := GetUserFromContext(ctx)
-	if !ok {
-		t.Fatal("expected ok=true when user is set")
-	}
-	if u.UserID != 42 {
-		t.Errorf("expected user ID 42, got %d", u.UserID)
-	}
-	if u.Username != "testuser" {
-		t.Errorf("expected username 'testuser', got %q", u.Username)
-	}
-}
-
-func TestSetUserInContext(t *testing.T) {
-	user := &db.User{UserID: 7, Username: "admin"}
-	ctx := SetUserInContext(context.Background(), user)
-	u, ok := GetUserFromContext(ctx)
-	if !ok {
-		t.Fatal("expected ok=true after SetUserInContext")
-	}
-	if u.UserID != 7 {
-		t.Errorf("expected user ID 7, got %d", u.UserID)
-	}
-}
-
 // mockSessionQuerier implements the subset of db.Querier needed by SessionCookieMiddleware.
 type mockSessionQuerier struct {
 	db.Querier
@@ -89,7 +36,7 @@ func TestSessionCookieMiddleware_NoCookie(t *testing.T) {
 	handler := mw(func(c echo.Context) error {
 		called = true
 		// User should not be set
-		_, ok := GetUserFromContext(c.Request().Context())
+		_, ok := session.GetUserFromContext(c.Request().Context())
 		if ok {
 			t.Error("expected no user in context when no cookie is present")
 		}
@@ -122,14 +69,14 @@ func TestSessionCookieMiddleware_ValidSession(t *testing.T) {
 	var called bool
 	handler := mw(func(c echo.Context) error {
 		called = true
-		user, ok := GetUserFromContext(c.Request().Context())
+		user, ok := session.GetUserFromContext(c.Request().Context())
 		if !ok {
 			t.Fatal("expected user in context")
 		}
 		if user.UserID != 10 {
 			t.Errorf("expected user ID 10, got %d", user.UserID)
 		}
-		sid, ok := GetSessionIDFromContext(c.Request().Context())
+		sid, ok := session.GetSessionIDFromContext(c.Request().Context())
 		if !ok {
 			t.Fatal("expected session ID in context")
 		}
@@ -164,7 +111,7 @@ func TestSessionCookieMiddleware_InvalidSession(t *testing.T) {
 	var called bool
 	handler := mw(func(c echo.Context) error {
 		called = true
-		_, ok := GetUserFromContext(c.Request().Context())
+		_, ok := session.GetUserFromContext(c.Request().Context())
 		if ok {
 			t.Error("expected no user in context for invalid session")
 		}
diff --git a/backend/api/convert.go b/backend/api/convert.go
new file mode 100644
index 0000000..f05f3bf
--- /dev/null
+++ b/backend/api/convert.go
@@ -0,0 +1,160 @@
+package api
+
+import (
+	"github.com/oapi-codegen/nullable"
+
+	"albatross-2026-backend/game"
+	"albatross-2026-backend/tournament"
+)
+
+func toAPIUser(p game.Player) User {
+	return User{
+		UserID:      p.UserID,
+		Username:    p.Username,
+		DisplayName: p.DisplayName,
+		IconPath:    p.IconPath,
+		IsAdmin:     p.IsAdmin,
+		Label:       toNullable(p.Label),
+	}
+}
+
+func toAPIGame(g game.GameDetail) Game {
+	var startedAt *int64
+	if g.StartedAt != nil {
+		ts := g.StartedAt.Unix()
+		startedAt = &ts
+	}
+	mainPlayers := make([]User, len(g.MainPlayers))
+	for i, p := range g.MainPlayers {
+		mainPlayers[i] = toAPIUser(p)
+	}
+	return Game{
+		GameID:          g.GameID,
+		GameType:        GameType(g.GameType),
+		IsPublic:        g.IsPublic,
+		DisplayName:     g.DisplayName,
+		DurationSeconds: g.DurationSeconds,
+		StartedAt:       startedAt,
+		Problem: Problem{
+			ProblemID:   g.Problem.ProblemID,
+			Title:       g.Problem.Title,
+			Description: g.Problem.Description,
+			Language:    ProblemLanguage(g.Problem.Language),
+			SampleCode:  g.Problem.SampleCode,
+		},
+		MainPlayers: mainPlayers,
+	}
+}
+
+func toAPILatestState(s game.LatestState) LatestGameState {
+	var score nullable.Nullable[int]
+	if s.Score != nil {
+		score = nullable.NewNullableWithValue(*s.Score)
+	} else {
+		score = nullable.NewNullNullable[int]()
+	}
+	var submittedAt nullable.Nullable[int64]
+	if s.BestScoreSubmittedAt != nil {
+		submittedAt = nullable.NewNullableWithValue(*s.BestScoreSubmittedAt)
+	} else {
+		submittedAt = nullable.NewNullNullable[int64]()
+	}
+	return LatestGameState{
+		Code:                 s.Code,
+		Score:                score,
+		BestScoreSubmittedAt: submittedAt,
+		Status:               ExecutionStatus(s.Status),
+	}
+}
+
+func toAPIRankingEntry(r game.RankingEntry) RankingEntry {
+	var code nullable.Nullable[string]
+	if r.Code != nil {
+		code = nullable.NewNullableWithValue(*r.Code)
+	} else {
+		code = nullable.NewNullNullable[string]()
+	}
+	return RankingEntry{
+		Player: toAPIUser(r.Player),
+		Score:  r.Score,
+		SubmittedAt: r.SubmittedAt,
+		Code:   code,
+	}
+}
+
+func toAPISubmission(s game.SubmissionDetail) Submission {
+	return Submission{
+		SubmissionID: s.SubmissionID,
+		GameID:       s.GameID,
+		Code:         s.Code,
+		CodeSize:     s.CodeSize,
+		Status:       ExecutionStatus(s.Status),
+		CreatedAt:    s.CreatedAt,
+	}
+}
+
+func toAPITournamentUser(p tournament.Player) User {
+	return User{
+		UserID:      p.UserID,
+		Username:    p.Username,
+		DisplayName: p.DisplayName,
+		IconPath:    p.IconPath,
+		IsAdmin:     p.IsAdmin,
+		Label:       toNullable(p.Label),
+	}
+}
+
+func toAPITournamentPlayerPtr(p *tournament.Player) *User {
+	if p == nil {
+		return nil
+	}
+	u := toAPITournamentUser(*p)
+	return &u
+}
+
+func toAPITournament(t tournament.TournamentBracket) Tournament {
+	entries := make([]TournamentEntry, len(t.Entries))
+	for i, e := range t.Entries {
+		entries[i] = TournamentEntry{
+			User: toAPITournamentUser(e.User),
+			Seed: e.Seed,
+		}
+	}
+	matches := make([]TournamentMatch, len(t.Matches))
+	for i, m := range t.Matches {
+		matches[i] = TournamentMatch{
+			TournamentMatchID: m.TournamentMatchID,
+			Round:             m.Round,
+			Position:          m.Position,
+			GameID:            m.GameID,
+			Player1:           toAPITournamentPlayerPtr(m.Player1),
+			Player2:           toAPITournamentPlayerPtr(m.Player2),
+			Player1Score:      m.Player1Score,
+			Player2Score:      m.Player2Score,
+			WinnerUserID:      m.WinnerUserID,
+			IsBye:             m.IsBye,
+		}
+	}
+	return Tournament{
+		TournamentID: t.TournamentID,
+		DisplayName:  t.DisplayName,
+		BracketSize:  t.BracketSize,
+		NumRounds:    t.NumRounds,
+		Entries:      entries,
+		Matches:      matches,
+	}
+}
+
+func toNullable[T any](p *T) nullable.Nullable[T] {
+	if p == nil {
+		return nullable.NewNullNullable[T]()
+	}
+	return nullable.NewNullableWithValue(*p)
+}
+
+func toNullableWith[T, U any](p *T, f func(T) U) nullable.Nullable[U] {
+	if p == nil {
+		return nullable.NewNullNullable[U]()
+	}
+	return nullable.NewNullableWithValue(f(*p))
+}
diff --git a/backend/api/handler.go b/backend/api/handler.go
index dcebfa1..4d729f1 100644
--- a/backend/api/handler.go
+++ b/backend/api/handler.go
@@ -9,14 +9,15 @@ import (
 	"strconv"
 	"time"
 
-	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgtype"
 	"github.com/labstack/echo/v4"
-	"github.com/oapi-codegen/nullable"
 
 	"albatross-2026-backend/auth"
 	"albatross-2026-backend/config"
 	"albatross-2026-backend/db"
+	"albatross-2026-backend/game"
+	"albatross-2026-backend/session"
+	"albatross-2026-backend/tournament"
 )
 
 type AuthenticatorInterface interface {
@@ -24,16 +25,11 @@ type AuthenticatorInterface interface {
 }
 
 type Handler struct {
-	q    db.Querier
-	txm  db.TxManager
-	hub  GameHubInterface
-	auth AuthenticatorInterface
-	conf *config.Config
-}
-
-type GameHubInterface interface {
-	CalcCodeSize(code string, language string) int
-	EnqueueTestTasks(ctx context.Context, submissionID, gameID, userID int, language, code string) error
+	gameSvc       *game.Service
+	tournamentSvc *tournament.Service
+	auth          AuthenticatorInterface
+	conf          *config.Config
+	q             db.Querier // for session management (login/logout)
 }
 
 type postLoginCookieResponse struct {
@@ -51,7 +47,7 @@ func (r postLoginCookieResponse) VisitPostLoginResponse(w http.ResponseWriter) e
 func (h *Handler) PostLogin(ctx context.Context, request PostLoginRequestObject) (PostLoginResponseObject, error) {
 	username := request.Body.Username
 	password := request.Body.Password
-	ip := GetClientIPFromContext(ctx)
+	ip := session.GetClientIPFromContext(ctx)
 
 	userID, err := h.auth.Login(ctx, username, password)
 	if err != nil {
@@ -138,7 +134,7 @@ func (r postLogoutCookieResponse) VisitPostLogoutResponse(w http.ResponseWriter)
 }
 
 func (h *Handler) PostLogout(ctx context.Context, _ PostLogoutRequestObject, _ *db.User) (PostLogoutResponseObject, error) {
-	if sessionID, ok := GetSessionIDFromContext(ctx); ok {
+	if sessionID, ok := session.GetSessionIDFromContext(ctx); ok {
 		_ = h.q.DeleteSession(ctx, sessionID)
 	}
 	return postLogoutCookieResponse{
@@ -155,631 +151,125 @@ func (h *Handler) PostLogout(ctx context.Context, _ PostLogoutRequestObject, _ *
 }
 
 func (h *Handler) GetGames(ctx context.Context, _ GetGamesRequestObject, _ *db.User) (GetGamesResponseObject, error) {
-	gameRows, err := h.q.ListPublicGames(ctx)
-	if err != nil {
-		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
-	}
-	games := make([]Game, len(gameRows))
-	gameIDs := make([]int32, len(gameRows))
-	gameID2Index := make(map[int32]int, len(gameRows))
-	for i, row := range gameRows {
-		var startedAt *int64
-		if row.StartedAt.Valid {
-			startedAtTimestamp := row.StartedAt.Time.Unix()
-			startedAt = &startedAtTimestamp
-		}
-		games[i] = Game{
-			GameID:          int(row.GameID),
-			GameType:        GameType(row.GameType),
-			IsPublic:        row.IsPublic,
-			DisplayName:     row.DisplayName,
-			DurationSeconds: int(row.DurationSeconds),
-			StartedAt:       startedAt,
-			Problem: Problem{
-				ProblemID:   int(row.ProblemID),
-				Title:       row.Title,
-				Description: row.Description,
-				Language:    ProblemLanguage(row.Language),
-				SampleCode:  row.SampleCode,
-			},
-		}
-		gameIDs[i] = row.GameID
-		gameID2Index[row.GameID] = i
-	}
-	mainPlayerRows, err := h.q.ListMainPlayers(ctx, gameIDs)
+	games, err := h.gameSvc.ListPublicGames(ctx)
 	if err != nil {
 		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
 	}
-	for _, row := range mainPlayerRows {
-		idx := gameID2Index[row.GameID]
-		game := &games[idx]
-		game.MainPlayers = append(game.MainPlayers, User{
-			UserID:      int(row.UserID),
-			Username:    row.Username,
-			DisplayName: row.DisplayName,
-			IconPath:    row.IconPath,
-			IsAdmin:     row.IsAdmin,
-			Label:       toNullable(row.Label),
-		})
+	apiGames := make([]Game, len(games))
+	for i, g := range games {
+		apiGames[i] = toAPIGame(g)
 	}
-	return GetGames200JSONResponse{
-		Games: games,
-	}, nil
+	return GetGames200JSONResponse{Games: apiGames}, nil
 }
 
 func (h *Handler) GetGame(ctx context.Context, request GetGameRequestObject, user *db.User) (GetGameResponseObject, error) {
-	gameID := request.GameID
-	row, err := h.q.GetGameByID(ctx, int32(gameID))
+	isAdmin := user != nil && user.IsAdmin
+	g, err := h.gameSvc.GetGameByID(ctx, request.GameID, isAdmin)
 	if err != nil {
-		if errors.Is(err, pgx.ErrNoRows) {
-			return GetGame404JSONResponse{
-				Message: "Game not found",
-			}, nil
+		if errors.Is(err, game.ErrNotFound) {
+			return GetGame404JSONResponse{Message: "Game not found"}, nil
 		}
 		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
 	}
-	if !row.IsPublic && (user == nil || !user.IsAdmin) {
-		return GetGame404JSONResponse{
-			Message: "Game not found",
-		}, nil
-	}
-	var startedAt *int64
-	if row.StartedAt.Valid {
-		startedAtTimestamp := row.StartedAt.Time.Unix()
-		startedAt = &startedAtTimestamp
-	}
-	mainPlayerRows, err := h.q.ListMainPlayers(ctx, []int32{int32(gameID)})
-	if err != nil {
-		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
-	}
-	mainPlayers := make([]User, len(mainPlayerRows))
-	for i, playerRow := range mainPlayerRows {
-		mainPlayers[i] = User{
-			UserID:      int(playerRow.UserID),
-			Username:    playerRow.Username,
-			DisplayName: playerRow.DisplayName,
-			IconPath:    playerRow.IconPath,
-			IsAdmin:     playerRow.IsAdmin,
-			Label:       toNullable(playerRow.Label),
-		}
-	}
-	game := Game{
-		GameID:          int(row.GameID),
-		GameType:        GameType(row.GameType),
-		IsPublic:        row.IsPublic,
-		DisplayName:     row.DisplayName,
-		DurationSeconds: int(row.DurationSeconds),
-		StartedAt:       startedAt,
-		Problem: Problem{
-			ProblemID:   int(row.ProblemID),
-			Title:       row.Title,
-			Description: row.Description,
-			Language:    ProblemLanguage(row.Language),
-			SampleCode:  row.SampleCode,
-		},
-		MainPlayers: mainPlayers,
-	}
-	return GetGame200JSONResponse{
-		Game: game,
-	}, nil
+	return GetGame200JSONResponse{Game: toAPIGame(g)}, nil
 }
 
 func (h *Handler) GetGamePlayLatestState(ctx context.Context, request GetGamePlayLatestStateRequestObject, user *db.User) (GetGamePlayLatestStateResponseObject, error) {
-	gameID := request.GameID
-	row, err := h.q.GetLatestState(ctx, db.GetLatestStateParams{
-		GameID: int32(gameID),
-		UserID: user.UserID,
-	})
+	state, err := h.gameSvc.GetLatestState(ctx, request.GameID, user.UserID)
 	if err != nil {
-		if errors.Is(err, pgx.ErrNoRows) {
-			return GetGamePlayLatestState200JSONResponse{
-				State: LatestGameState{
-					Code:                 "",
-					Score:                nullable.NewNullNullable[int](),
-					BestScoreSubmittedAt: nullable.NewNullNullable[int64](),
-					Status:               None,
-				},
-			}, nil
-		}
 		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
 	}
-	return GetGamePlayLatestState200JSONResponse{
-		State: LatestGameState{
-			Code:                 row.Code,
-			Score:                toNullableWith(row.CodeSize, func(x int32) int { return int(x) }),
-			BestScoreSubmittedAt: nullable.NewNullableWithValue(row.CreatedAt.Time.Unix()),
-			Status:               ExecutionStatus(row.Status),
-		},
-	}, nil
+	return GetGamePlayLatestState200JSONResponse{State: toAPILatestState(state)}, nil
 }
 
 func (h *Handler) GetGameWatchLatestStates(ctx context.Context, request GetGameWatchLatestStatesRequestObject, user *db.User) (GetGameWatchLatestStatesResponseObject, error) {
-	gameID := request.GameID
-	rows, err := h.q.GetLatestStatesOfMainPlayers(ctx, int32(gameID))
-	if err != nil {
-		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
+	var userID *int32
+	var isAdmin bool
+	if user != nil {
+		userID = &user.UserID
+		isAdmin = user.IsAdmin
 	}
-	states := make(map[string]LatestGameState, len(rows))
-	for _, row := range rows {
-		var code string
-		if row.Code != nil {
-			code = *row.Code
-		}
-		var status ExecutionStatus
-		if row.Status != nil {
-			status = ExecutionStatus(*row.Status)
-		} else {
-			status = None
-		}
-		states[strconv.Itoa(int(row.UserID))] = LatestGameState{
-			Code:                 code,
-			Score:                toNullableWith(row.CodeSize, func(x int32) int { return int(x) }),
-			BestScoreSubmittedAt: nullable.NewNullableWithValue(row.CreatedAt.Time.Unix()),
-			Status:               status,
-		}
-
-		if user != nil && row.UserID == user.UserID && !user.IsAdmin {
+	stateMap, err := h.gameSvc.GetWatchLatestStates(ctx, request.GameID, userID, isAdmin)
+	if err != nil {
+		if errors.Is(err, game.ErrForbidden) {
 			return GetGameWatchLatestStates403JSONResponse{
 				Message: "You are one of the main players of this game",
 			}, nil
 		}
+		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
 	}
-	return GetGameWatchLatestStates200JSONResponse{
-		States: states,
-	}, nil
+	states := make(map[string]LatestGameState, len(stateMap))
+	for uid, s := range stateMap {
+		states[strconv.Itoa(uid)] = toAPILatestState(s)
+	}
+	return GetGameWatchLatestStates200JSONResponse{States: states}, nil
 }
 
 func (h *Handler) GetGameWatchRanking(ctx context.Context, request GetGameWatchRankingRequestObject, _ *db.User) (GetGameWatchRankingResponseObject, error) {
-	gameID := request.GameID
-
-	gameRow, err := h.q.GetGameByID(ctx, int32(gameID))
+	ranking, _, err := h.gameSvc.GetRanking(ctx, request.GameID)
 	if err != nil {
-		if errors.Is(err, pgx.ErrNoRows) {
-			return GetGameWatchRanking404JSONResponse{
-				Message: "Game not found",
-			}, nil
+		if errors.Is(err, game.ErrNotFound) {
+			return GetGameWatchRanking404JSONResponse{Message: "Game not found"}, nil
 		}
 		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
 	}
-	gameFinished := isGameFinished(gameRow)
-
-	rows, err := h.q.GetRanking(ctx, int32(gameID))
-	if err != nil {
-		if errors.Is(err, pgx.ErrNoRows) {
-			return GetGameWatchRanking200JSONResponse{}, nil
-		}
-	}
-	ranking := make([]RankingEntry, len(rows))
-	for i, row := range rows {
-		var code nullable.Nullable[string]
-		if gameFinished {
-			code = nullable.NewNullableWithValue(row.Submission.Code)
-		} else {
-			code = nullable.NewNullNullable[string]()
-		}
-		ranking[i] = RankingEntry{
-			Player: User{
-				UserID:      int(row.User.UserID),
-				Username:    row.User.Username,
-				DisplayName: row.User.DisplayName,
-				IconPath:    row.User.IconPath,
-				IsAdmin:     row.User.IsAdmin,
-				Label:       toNullable(row.User.Label),
-			},
-			Score:       int(row.Submission.CodeSize),
-			SubmittedAt: row.Submission.CreatedAt.Time.Unix(),
-			Code:        code,
-		}
+	apiRanking := make([]RankingEntry, len(ranking))
+	for i, r := range ranking {
+		apiRanking[i] = toAPIRankingEntry(r)
 	}
-	return GetGameWatchRanking200JSONResponse{
-		Ranking: ranking,
-	}, nil
+	return GetGameWatchRanking200JSONResponse{Ranking: apiRanking}, nil
 }
 
 func (h *Handler) GetGamePlaySubmissions(ctx context.Context, request GetGamePlaySubmissionsRequestObject, user *db.User) (GetGamePlaySubmissionsResponseObject, error) {
-	gameID := request.GameID
-
-	_, err := h.q.GetGameByID(ctx, int32(gameID))
+	submissions, err := h.gameSvc.GetSubmissions(ctx, request.GameID, user.UserID)
 	if err != nil {
-		if errors.Is(err, pgx.ErrNoRows) {
-			return GetGamePlaySubmissions404JSONResponse{
-				Message: "Game not found",
-			}, nil
+		if errors.Is(err, game.ErrNotFound) {
+			return GetGamePlaySubmissions404JSONResponse{Message: "Game not found"}, nil
 		}
 		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
 	}
-
-	rows, err := h.q.GetSubmissionsByGameIDAndUserID(ctx, db.GetSubmissionsByGameIDAndUserIDParams{
-		GameID: int32(gameID),
-		UserID: user.UserID,
-	})
-	if err != nil {
-		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
-	}
-
-	submissions := make([]Submission, len(rows))
-	for i, row := range rows {
-		submissions[i] = Submission{
-			SubmissionID: int(row.SubmissionID),
-			GameID:       int(row.GameID),
-			Code:         row.Code,
-			CodeSize:     int(row.CodeSize),
-			Status:       ExecutionStatus(row.Status),
-			CreatedAt:    row.CreatedAt.Time.Unix(),
-		}
+	apiSubmissions := make([]Submission, len(submissions))
+	for i, s := range submissions {
+		apiSubmissions[i] = toAPISubmission(s)
 	}
-
-	return GetGamePlaySubmissions200JSONResponse{
-		Submissions: submissions,
-	}, nil
+	return GetGamePlaySubmissions200JSONResponse{Submissions: apiSubmissions}, nil
 }
 
 func (h *Handler) PostGamePlayCode(ctx context.Context, request PostGamePlayCodeRequestObject, user *db.User) (PostGamePlayCodeResponseObject, error) {
-	gameID := request.GameID
-
-	gameRow, err := h.q.GetGameByID(ctx, int32(gameID))
+	err := h.gameSvc.SaveCode(ctx, request.GameID, user.UserID, request.Body.Code)
 	if err != nil {
-		if errors.Is(err, pgx.ErrNoRows) {
-			return PostGamePlayCode404JSONResponse{
-				Message: "Game not found",
-			}, nil
+		if errors.Is(err, game.ErrNotFound) {
+			return PostGamePlayCode404JSONResponse{Message: "Game not found"}, nil
+		}
+		if errors.Is(err, game.ErrGameNotRunning) {
+			return PostGamePlayCode403JSONResponse{Message: "Game is not running"}, nil
 		}
-		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
-	}
-	if !isGameRunning(gameRow) {
-		return PostGamePlayCode403JSONResponse{
-			Message: "Game is not running",
-		}, nil
-	}
-
-	err = h.q.UpdateCode(ctx, db.UpdateCodeParams{
-		GameID: int32(gameID),
-		UserID: user.UserID,
-		Code:   request.Body.Code,
-		Status: "none",
-	})
-	if err != nil {
 		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
 	}
 	return PostGamePlayCode200Response{}, nil
 }
 
 func (h *Handler) PostGamePlaySubmit(ctx context.Context, request PostGamePlaySubmitRequestObject, user *db.User) (PostGamePlaySubmitResponseObject, error) {
-	gameID := request.GameID
-	code := request.Body.Code
-
-	gameRow, err := h.q.GetGameByID(ctx, int32(gameID))
+	err := h.gameSvc.SubmitCode(ctx, request.GameID, user.UserID, request.Body.Code)
 	if err != nil {
-		if errors.Is(err, pgx.ErrNoRows) {
+		if errors.Is(err, game.ErrNotFound) {
 			return PostGamePlaySubmit404JSONResponse{}, nil
 		}
-		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
-	}
-
-	language := gameRow.Language
-	codeSize := h.hub.CalcCodeSize(code, language)
-
-	if !isGameRunning(gameRow) {
-		return PostGamePlaySubmit403JSONResponse{
-			Message: "Game is not running",
-		}, nil
-	}
-
-	var submissionID int32
-	err = h.txm.RunInTx(ctx, func(qtx db.Querier) error {
-		if err := qtx.UpdateCodeAndStatus(ctx, db.UpdateCodeAndStatusParams{
-			GameID: int32(gameID),
-			UserID: user.UserID,
-			Code:   code,
-			Status: "running",
-		}); err != nil {
-			return err
+		if errors.Is(err, game.ErrGameNotRunning) {
+			return PostGamePlaySubmit403JSONResponse{Message: "Game is not running"}, nil
 		}
-		var err error
-		submissionID, err = qtx.CreateSubmission(ctx, db.CreateSubmissionParams{
-			GameID:   int32(gameID),
-			UserID:   user.UserID,
-			Code:     code,
-			CodeSize: int32(codeSize),
-		})
-		return err
-	})
-	if err != nil {
-		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
-	}
-
-	err = h.hub.EnqueueTestTasks(ctx, int(submissionID), gameID, int(user.UserID), language, code)
-	if err != nil {
 		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
 	}
 	return PostGamePlaySubmit200Response{}, nil
 }
 
 func (h *Handler) GetTournament(ctx context.Context, request GetTournamentRequestObject, _ *db.User) (GetTournamentResponseObject, error) {
-	tournamentID := int32(request.TournamentID)
-
-	tournament, err := h.q.GetTournamentByID(ctx, tournamentID)
+	t, err := h.tournamentSvc.GetTournament(ctx, request.TournamentID)
 	if err != nil {
-		if errors.Is(err, pgx.ErrNoRows) {
+		if errors.Is(err, game.ErrNotFound) {
 			return GetTournament404JSONResponse{Message: "Tournament not found"}, nil
 		}
 		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
 	}
-
-	entryRows, err := h.q.ListTournamentEntries(ctx, tournamentID)
-	if err != nil {
-		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
-	}
-
-	seedToUser := make(map[int]User)
-	entries := make([]TournamentEntry, len(entryRows))
-	for i, e := range entryRows {
-		u := User{
-			UserID:      int(e.UserID),
-			Username:    e.Username,
-			DisplayName: e.DisplayName,
-			IconPath:    e.IconPath,
-			IsAdmin:     e.IsAdmin,
-			Label:       toNullable(e.Label),
-		}
-		seedToUser[int(e.Seed)] = u
-		entries[i] = TournamentEntry{
-			User: u,
-			Seed: int(e.Seed),
-		}
-	}
-
-	matchRows, err := h.q.ListTournamentMatches(ctx, tournamentID)
-	if err != nil {
-		return nil, echo.NewHTTPError(http.StatusInternalServerError, err.Error())
-	}
-
-	bracketSize := int(tournament.BracketSize)
-	numRounds := int(tournament.NumRounds)
-	bracketSeeds := standardBracketSeeds(bracketSize)
-
-	// Index matches by (round, position)
-	type matchKey struct{ round, position int }
-	matchByKey := make(map[matchKey]db.TournamentMatch)
-	for _, m := range matchRows {
-		matchByKey[matchKey{int(m.Round), int(m.Position)}] = m
-	}
-
-	// Collect game IDs for batch fetching
-	gameIDs := make(map[int32]bool)
-	for _, m := range matchRows {
-		if m.GameID != nil {
-			gameIDs[*m.GameID] = true
-		}
-	}
-
-	// Fetch rankings for all games that have started
-	type rankingResult struct {
-		scores   map[int]int // userID -> score
-		winnerID int
-	}
-	gameRankings := make(map[int32]*rankingResult)
-	for gid := range gameIDs {
-		gameRow, err := h.q.GetGameByID(ctx, gid)
-		if err != nil {
-			continue
-		}
-		if !gameRow.StartedAt.Valid {
-			continue
-		}
-		rankingRows, err := h.q.GetRanking(ctx, gid)
-		if err != nil || len(rankingRows) == 0 {
-			continue
-		}
-		rr := &rankingResult{scores: make(map[int]int)}
-		for i, r := range rankingRows {
-			rr.scores[int(r.User.UserID)] = int(r.Submission.CodeSize)
-			if i == 0 {
-				rr.winnerID = int(r.User.UserID)
-			}
-		}
-		gameRankings[gid] = rr
-	}
-
-	// Build match results bottom-up
-	type matchResult struct {
-		player1   *User
-		player2   *User
-		p1Score   *int
-		p2Score   *int
-		winnerUID *int
-		isBye     bool
-	}
-	resultByKey := make(map[matchKey]*matchResult)
-
-	for round := range numRounds {
-		numPositions := bracketSize / (1 << (round + 1))
-		for pos := range numPositions {
-			m, exists := matchByKey[matchKey{round, pos}]
-			mr := &matchResult{}
-
-			if round == 0 {
-				// First round: resolve players from bracket seeds
-				slot1 := pos * 2
-				slot2 := pos*2 + 1
-				seed1 := bracketSeeds[slot1]
-				seed2 := bracketSeeds[slot2]
-
-				if u, ok := seedToUser[seed1]; ok {
-					mr.player1 = &u
-				}
-				if u, ok := seedToUser[seed2]; ok {
-					mr.player2 = &u
-				}
-			} else {
-				// Later rounds: resolve from child match winners
-				child1 := resultByKey[matchKey{round - 1, pos * 2}]
-				child2 := resultByKey[matchKey{round - 1, pos*2 + 1}]
-
-				if child1 != nil && child1.winnerUID != nil {
-					if u, ok := seedToUser[findSeedByUserID(entries, *child1.winnerUID)]; ok {
-						mr.player1 = &u
-					}
-				}
-				if child2 != nil && child2.winnerUID != nil {
-					if u, ok := seedToUser[findSeedByUserID(entries, *child2.winnerUID)]; ok {
-						mr.player2 = &u
-					}
-				}
-			}
-
-			// Check for bye
-			if mr.player1 == nil && mr.player2 != nil {
-				mr.isBye = true
-				uid := mr.player2.UserID
-				mr.winnerUID = &uid
-			} else if mr.player1 != nil && mr.player2 == nil {
-				mr.isBye = true
-				uid := mr.player1.UserID
-				mr.winnerUID = &uid
-			}
-
-			// Resolve scores from game
-			if exists && m.GameID != nil && !mr.isBye {
-				if rr, ok := gameRankings[*m.GameID]; ok {
-					if mr.player1 != nil {
-						if s, ok := rr.scores[mr.player1.UserID]; ok {
-							score := s
-							mr.p1Score = &score
-						}
-					}
-					if mr.player2 != nil {
-						if s, ok := rr.scores[mr.player2.UserID]; ok {
-							score := s
-							mr.p2Score = &score
-						}
-					}
-					// Winner is the one with the best (lowest) score in the ranking
-					if mr.player1 != nil && mr.player2 != nil {
-						if rr.winnerID == mr.player1.UserID || rr.winnerID == mr.player2.UserID {
-							w := rr.winnerID
-							mr.winnerUID = &w
-						} else {
-							// Both players have scores; pick the one with lower score
-							if mr.p1Score != nil && mr.p2Score != nil {
-								if *mr.p1Score <= *mr.p2Score {
-									w := mr.player1.UserID
-									mr.winnerUID = &w
-								} else {
-									w := mr.player2.UserID
-									mr.winnerUID = &w
-								}
-							}
-						}
-					}
-				}
-			}
-
-			resultByKey[matchKey{round, pos}] = mr
-		}
-	}
-
-	// Build API response matches
-	apiMatches := make([]TournamentMatch, 0, len(matchRows))
-	for round := 0; round < numRounds; round++ {
-		numPositions := bracketSize / (1 << (round + 1))
-		for pos := 0; pos < numPositions; pos++ {
-			m, exists := matchByKey[matchKey{round, pos}]
-			mr := resultByKey[matchKey{round, pos}]
-
-			matchID := 0
-			var gameID *int
-			if exists {
-				matchID = int(m.TournamentMatchID)
-				if m.GameID != nil {
-					gid := int(*m.GameID)
-					gameID = &gid
-				}
-			}
-
-			apiMatches = append(apiMatches, TournamentMatch{
-				TournamentMatchID: matchID,
-				Round:             round,
-				Position:          pos,
-				GameID:            gameID,
-				Player1:           mr.player1,
-				Player2:           mr.player2,
-				Player1Score:      mr.p1Score,
-				Player2Score:      mr.p2Score,
-				WinnerUserID:      mr.winnerUID,
-				IsBye:             mr.isBye,
-			})
-		}
-	}
-
-	return GetTournament200JSONResponse{
-		Tournament: Tournament{
-			TournamentID: int(tournament.TournamentID),
-			DisplayName:  tournament.DisplayName,
-			BracketSize:  bracketSize,
-			NumRounds:    numRounds,
-			Entries:      entries,
-			Matches:      apiMatches,
-		},
-	}, nil
-}
-
-func findSeedByUserID(entries []TournamentEntry, userID int) int {
-	for _, e := range entries {
-		if e.User.UserID == userID {
-			return e.Seed
-		}
-	}
-	return 0
-}
-
-// standardBracketSeeds returns the seed assignments for each slot in a standard
-// single-elimination bracket. For bracket_size=8:
-// Position: [0]=1, [1]=8, [2]=5, [3]=4, [4]=3, [5]=6, [6]=7, [7]=2
-// This ensures Seed 1 vs Seed 2 are on opposite sides, and higher seeds face lower seeds.
-func standardBracketSeeds(bracketSize int) []int {
-	seeds := make([]int, bracketSize)
-	seeds[0] = 1
-	// Build the bracket by repeatedly splitting
-	for size := 2; size <= bracketSize; size *= 2 {
-		// For each pair in the current level, the new opponent for seed[i]
-		// is (size + 1 - seed[i])
-		temp := make([]int, size)
-		for i := 0; i < size/2; i++ {
-			temp[i*2] = seeds[i]
-			temp[i*2+1] = size + 1 - seeds[i]
-		}
-		copy(seeds, temp)
-	}
-	return seeds
-}
-
-func isGameRunning(game db.GetGameByIDRow) bool {
-	if !game.StartedAt.Valid {
-		return false
-	}
-	endTime := game.StartedAt.Time.Add(time.Duration(game.DurationSeconds) * time.Second)
-	return time.Now().Before(endTime)
-}
-
-func isGameFinished(game db.GetGameByIDRow) bool {
-	if !game.StartedAt.Valid {
-		return false
-	}
-	endTime := game.StartedAt.Time.Add(time.Duration(game.DurationSeconds) * time.Second)
-	return !time.Now().Before(endTime)
-}
-
-func toNullable[T any](p *T) nullable.Nullable[T] {
-	if p == nil {
-		return nullable.NewNullNullable[T]()
-	}
-	return nullable.NewNullableWithValue(*p)
-}
-
-func toNullableWith[T, U any](p *T, f func(T) U) nullable.Nullable[U] {
-	if p == nil {
-		return nullable.NewNullNullable[U]()
-	}
-	return nullable.NewNullableWithValue(f(*p))
+	return GetTournament200JSONResponse{Tournament: toAPITournament(t)}, nil
 }
diff --git a/backend/api/handler_test.go b/backend/api/handler_test.go
index a28d605..2b8c06a 100644
--- a/backend/api/handler_test.go
+++ b/backend/api/handler_test.go
@@ -11,6 +11,9 @@ import (
 
 	"albatross-2026-backend/config"
 	"albatross-2026-backend/db"
+	"albatross-2026-backend/game"
+	"albatross-2026-backend/session"
+	"albatross-2026-backend/tournament"
 )
 
 // mockQuerier implements db.Querier for testing.
@@ -28,6 +31,7 @@ type mockQuerier struct {
 	listTournamentEntriesFunc           func(ctx context.Context, tournamentID int32) ([]db.ListTournamentEntriesRow, error)
 	listTournamentMatchesFunc           func(ctx context.Context, tournamentID int32) ([]db.TournamentMatch, error)
 	getSubmissionsByGameIDAndUserIDFunc func(ctx context.Context, arg db.GetSubmissionsByGameIDAndUserIDParams) ([]db.Submission, error)
+	getUserByIDFunc                     func(ctx context.Context, userID int32) (db.User, error)
 }
 
 func (m *mockQuerier) GetGameByID(ctx context.Context, gameID int32) (db.GetGameByIDRow, error) {
@@ -114,6 +118,13 @@ func (m *mockQuerier) ListTournamentMatches(ctx context.Context, tournamentID in
 	return nil, nil
 }
 
+func (m *mockQuerier) GetUserByID(ctx context.Context, userID int32) (db.User, error) {
+	if m.getUserByIDFunc != nil {
+		return m.getUserByIDFunc(ctx, userID)
+	}
+	return db.User{}, pgx.ErrNoRows
+}
+
 // mockTxManager implements db.TxManager for testing.
 type mockTxManager struct{}
 
@@ -121,7 +132,7 @@ func (m *mockTxManager) RunInTx(_ context.Context, fn func(q db.Querier) error)
 	return fn(&mockQuerier{})
 }
 
-// mockGameHub implements GameHubInterface for testing.
+// mockGameHub implements game.GameHubInterface for testing.
 type mockGameHub struct {
 	calcCodeSizeResult int
 	enqueueErr         error
@@ -145,14 +156,29 @@ func (m *mockAuthenticator) Login(_ context.Context, _, _ string) (int, error) {
 	return m.loginResult, m.loginErr
 }
 
-func TestGetGamePlaySubmissions_GameNotFound(t *testing.T) {
-	h := Handler{
-		q:    &mockQuerier{},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
+func newTestHandler(q *mockQuerier) Handler {
+	hub := &mockGameHub{}
+	return Handler{
+		gameSvc:       game.NewService(q, &mockTxManager{}, hub),
+		tournamentSvc: tournament.NewService(q),
+		auth:          &mockAuthenticator{},
+		conf:          &config.Config{},
+		q:             q,
 	}
+}
+
+func newTestHandlerWithHub(q *mockQuerier, hub *mockGameHub) Handler {
+	return Handler{
+		gameSvc:       game.NewService(q, &mockTxManager{}, hub),
+		tournamentSvc: tournament.NewService(q),
+		auth:          &mockAuthenticator{},
+		conf:          &config.Config{},
+		q:             q,
+	}
+}
+
+func TestGetGamePlaySubmissions_GameNotFound(t *testing.T) {
+	h := newTestHandler(&mockQuerier{})
 	user := &db.User{UserID: 1}
 	resp, err := h.GetGamePlaySubmissions(context.Background(), GetGamePlaySubmissionsRequestObject{
 		GameID: 999,
@@ -166,20 +192,14 @@ func TestGetGamePlaySubmissions_GameNotFound(t *testing.T) {
 }
 
 func TestGetGamePlaySubmissions_Empty(t *testing.T) {
-	h := Handler{
-		q: &mockQuerier{
-			getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
-				return db.GetGameByIDRow{
-					GameID:   1,
-					Language: "php",
-				}, nil
-			},
+	h := newTestHandler(&mockQuerier{
+		getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
+			return db.GetGameByIDRow{
+				GameID:   1,
+				Language: "php",
+			}, nil
 		},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+	})
 	user := &db.User{UserID: 1}
 	resp, err := h.GetGamePlaySubmissions(context.Background(), GetGamePlaySubmissionsRequestObject{
 		GameID: 1,
@@ -198,45 +218,39 @@ func TestGetGamePlaySubmissions_Empty(t *testing.T) {
 
 func TestGetGamePlaySubmissions_WithSubmissions(t *testing.T) {
 	now := time.Now()
-	h := Handler{
-		q: &mockQuerier{
-			getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
-				return db.GetGameByIDRow{
-					GameID:   1,
-					Language: "php",
-				}, nil
-			},
-			getSubmissionsByGameIDAndUserIDFunc: func(_ context.Context, arg db.GetSubmissionsByGameIDAndUserIDParams) ([]db.Submission, error) {
-				if arg.GameID != 1 || arg.UserID != 42 {
-					t.Errorf("unexpected query params: game_id=%d, user_id=%d", arg.GameID, arg.UserID)
-				}
-				return []db.Submission{
-					{
-						SubmissionID: 10,
-						GameID:       1,
-						UserID:       42,
-						Code:         "<?php echo 1;",
-						CodeSize:     14,
-						Status:       "success",
-						CreatedAt:    pgtype.Timestamp{Time: now, Valid: true},
-					},
-					{
-						SubmissionID: 9,
-						GameID:       1,
-						UserID:       42,
-						Code:         "<?php echo 'hello';",
-						CodeSize:     20,
-						Status:       "wrong_answer",
-						CreatedAt:    pgtype.Timestamp{Time: now.Add(-5 * time.Minute), Valid: true},
-					},
-				}, nil
-			},
+	h := newTestHandler(&mockQuerier{
+		getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
+			return db.GetGameByIDRow{
+				GameID:   1,
+				Language: "php",
+			}, nil
 		},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+		getSubmissionsByGameIDAndUserIDFunc: func(_ context.Context, arg db.GetSubmissionsByGameIDAndUserIDParams) ([]db.Submission, error) {
+			if arg.GameID != 1 || arg.UserID != 42 {
+				t.Errorf("unexpected query params: game_id=%d, user_id=%d", arg.GameID, arg.UserID)
+			}
+			return []db.Submission{
+				{
+					SubmissionID: 10,
+					GameID:       1,
+					UserID:       42,
+					Code:         "<?php echo 1;",
+					CodeSize:     14,
+					Status:       "success",
+					CreatedAt:    pgtype.Timestamp{Time: now, Valid: true},
+				},
+				{
+					SubmissionID: 9,
+					GameID:       1,
+					UserID:       42,
+					Code:         "<?php echo 'hello';",
+					CodeSize:     20,
+					Status:       "wrong_answer",
+					CreatedAt:    pgtype.Timestamp{Time: now.Add(-5 * time.Minute), Valid: true},
+				},
+			}, nil
+		},
+	})
 	user := &db.User{UserID: 42}
 	resp, err := h.GetGamePlaySubmissions(context.Background(), GetGamePlaySubmissionsRequestObject{
 		GameID: 1,
@@ -282,13 +296,7 @@ func TestGetGamePlaySubmissions_WithSubmissions(t *testing.T) {
 }
 
 func TestPostGamePlaySubmit_GameNotFound(t *testing.T) {
-	h := Handler{
-		q:    &mockQuerier{},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+	h := newTestHandler(&mockQuerier{})
 	user := &db.User{UserID: 1}
 	resp, err := h.PostGamePlaySubmit(context.Background(), PostGamePlaySubmitRequestObject{
 		GameID: 999,
@@ -303,23 +311,17 @@ func TestPostGamePlaySubmit_GameNotFound(t *testing.T) {
 }
 
 func TestPostGamePlaySubmit_GameNotRunning(t *testing.T) {
-	h := Handler{
-		q: &mockQuerier{
-			getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
-				return db.GetGameByIDRow{
-					GameID:   1,
-					Language: "php",
-					StartedAt: pgtype.Timestamp{
-						Valid: false,
-					},
-				}, nil
-			},
+	h := newTestHandlerWithHub(&mockQuerier{
+		getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
+			return db.GetGameByIDRow{
+				GameID:   1,
+				Language: "php",
+				StartedAt: pgtype.Timestamp{
+					Valid: false,
+				},
+			}, nil
 		},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{calcCodeSizeResult: 10},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+	}, &mockGameHub{calcCodeSizeResult: 10})
 	user := &db.User{UserID: 1}
 	resp, err := h.PostGamePlaySubmit(context.Background(), PostGamePlaySubmitRequestObject{
 		GameID: 1,
@@ -335,121 +337,8 @@ func TestPostGamePlaySubmit_GameNotRunning(t *testing.T) {
 	}
 }
 
-func TestIsGameRunning(t *testing.T) {
-	now := time.Now()
-	tests := []struct {
-		name string
-		game db.GetGameByIDRow
-		want bool
-	}{
-		{
-			name: "not started",
-			game: db.GetGameByIDRow{
-				StartedAt:       pgtype.Timestamp{Valid: false},
-				DurationSeconds: 300,
-			},
-			want: false,
-		},
-		{
-			name: "running",
-			game: db.GetGameByIDRow{
-				StartedAt:       pgtype.Timestamp{Time: now.Add(-1 * time.Minute), Valid: true},
-				DurationSeconds: 300,
-			},
-			want: true,
-		},
-		{
-			name: "finished",
-			game: db.GetGameByIDRow{
-				StartedAt:       pgtype.Timestamp{Time: now.Add(-10 * time.Minute), Valid: true},
-				DurationSeconds: 300,
-			},
-			want: false,
-		},
-	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			got := isGameRunning(tt.game)
-			if got != tt.want {
-				t.Errorf("isGameRunning() = %v, want %v", got, tt.want)
-			}
-		})
-	}
-}
-
-func TestIsGameFinished(t *testing.T) {
-	now := time.Now()
-	tests := []struct {
-		name string
-		game db.GetGameByIDRow
-		want bool
-	}{
-		{
-			name: "not started",
-			game: db.GetGameByIDRow{
-				StartedAt:       pgtype.Timestamp{Valid: false},
-				DurationSeconds: 300,
-			},
-			want: false,
-		},
-		{
-			name: "still running",
-			game: db.GetGameByIDRow{
-				StartedAt:       pgtype.Timestamp{Time: now.Add(-1 * time.Minute), Valid: true},
-				DurationSeconds: 300,
-			},
-			want: false,
-		},
-		{
-			name: "finished",
-			game: db.GetGameByIDRow{
-				StartedAt:       pgtype.Timestamp{Time: now.Add(-10 * time.Minute), Valid: true},
-				DurationSeconds: 300,
-			},
-			want: true,
-		},
-	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			got := isGameFinished(tt.game)
-			if got != tt.want {
-				t.Errorf("isGameFinished() = %v, want %v", got, tt.want)
-			}
-		})
-	}
-}
-
-func TestToNullable(t *testing.T) {
-	t.Run("nil value", func(t *testing.T) {
-		result := toNullable[string](nil)
-		if !result.IsNull() {
-			t.Error("expected null for nil input")
-		}
-	})
-	t.Run("non-nil value", func(t *testing.T) {
-		s := "hello"
-		result := toNullable(&s)
-		if result.IsNull() {
-			t.Error("expected non-null for non-nil input")
-		}
-		v, err := result.Get()
-		if err != nil {
-			t.Fatalf("unexpected error: %v", err)
-		}
-		if v != "hello" {
-			t.Errorf("expected 'hello', got %q", v)
-		}
-	})
-}
-
 func TestGetMe(t *testing.T) {
-	h := Handler{
-		q:    &mockQuerier{},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+	h := newTestHandler(&mockQuerier{})
 	user := &db.User{
 		UserID:      1,
 		Username:    "testuser",
@@ -476,13 +365,7 @@ func TestGetMe(t *testing.T) {
 }
 
 func TestGetGame_NotFound(t *testing.T) {
-	h := Handler{
-		q:    &mockQuerier{},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+	h := newTestHandler(&mockQuerier{})
 	user := &db.User{UserID: 1}
 	resp, err := h.GetGame(context.Background(), GetGameRequestObject{GameID: 999}, user)
 	if err != nil {
@@ -494,21 +377,15 @@ func TestGetGame_NotFound(t *testing.T) {
 }
 
 func TestGetGame_NonPublicAsNonAdmin(t *testing.T) {
-	h := Handler{
-		q: &mockQuerier{
-			getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
-				return db.GetGameByIDRow{
-					GameID:   1,
-					IsPublic: false,
-					Language: "php",
-				}, nil
-			},
+	h := newTestHandler(&mockQuerier{
+		getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
+			return db.GetGameByIDRow{
+				GameID:   1,
+				IsPublic: false,
+				Language: "php",
+			}, nil
 		},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+	})
 	user := &db.User{UserID: 1, IsAdmin: false}
 	resp, err := h.GetGame(context.Background(), GetGameRequestObject{GameID: 1}, user)
 	if err != nil {
@@ -521,34 +398,28 @@ func TestGetGame_NonPublicAsNonAdmin(t *testing.T) {
 
 func TestGetGame_PublicGameSuccess(t *testing.T) {
 	now := time.Now()
-	h := Handler{
-		q: &mockQuerier{
-			getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
-				return db.GetGameByIDRow{
-					GameID:          1,
-					IsPublic:        true,
-					Language:        "php",
-					DisplayName:     "Test Game",
-					DurationSeconds: 300,
-					StartedAt:       pgtype.Timestamp{Time: now, Valid: true},
-					GameType:        "golf",
-					ProblemID:       10,
-					Title:           "Test Problem",
-					Description:     "desc",
-					SampleCode:      "<?php",
-				}, nil
-			},
-			listMainPlayersFunc: func(_ context.Context, _ []int32) ([]db.ListMainPlayersRow, error) {
-				return []db.ListMainPlayersRow{
-					{UserID: 1, Username: "player1", DisplayName: "Player 1", IsAdmin: false},
-				}, nil
-			},
+	h := newTestHandler(&mockQuerier{
+		getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
+			return db.GetGameByIDRow{
+				GameID:          1,
+				IsPublic:        true,
+				Language:        "php",
+				DisplayName:     "Test Game",
+				DurationSeconds: 300,
+				StartedAt:       pgtype.Timestamp{Time: now, Valid: true},
+				GameType:        "golf",
+				ProblemID:       10,
+				Title:           "Test Problem",
+				Description:     "desc",
+				SampleCode:      "<?php",
+			}, nil
 		},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+		listMainPlayersFunc: func(_ context.Context, _ []int32) ([]db.ListMainPlayersRow, error) {
+			return []db.ListMainPlayersRow{
+				{UserID: 1, Username: "player1", DisplayName: "Player 1", IsAdmin: false},
+			}, nil
+		},
+	})
 	user := &db.User{UserID: 1, IsAdmin: false}
 	resp, err := h.GetGame(context.Background(), GetGameRequestObject{GameID: 1}, user)
 	if err != nil {
@@ -571,11 +442,11 @@ func TestGetGame_PublicGameSuccess(t *testing.T) {
 
 func TestPostLogin_AuthFailure(t *testing.T) {
 	h := Handler{
-		q:    &mockQuerier{},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{loginErr: errors.New("invalid credentials")},
-		conf: &config.Config{},
+		gameSvc:       game.NewService(&mockQuerier{}, &mockTxManager{}, &mockGameHub{}),
+		tournamentSvc: tournament.NewService(&mockQuerier{}),
+		auth:          &mockAuthenticator{loginErr: errors.New("invalid credentials")},
+		conf:          &config.Config{},
+		q:             &mockQuerier{},
 	}
 	resp, err := h.PostLogin(context.Background(), PostLoginRequestObject{
 		Body: &PostLoginJSONRequestBody{Username: "user", Password: "wrong"},
@@ -590,15 +461,14 @@ func TestPostLogin_AuthFailure(t *testing.T) {
 
 func TestPostLogout(t *testing.T) {
 	h := Handler{
-		q:    &mockQuerier{},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{BasePath: "/"},
+		gameSvc:       game.NewService(&mockQuerier{}, &mockTxManager{}, &mockGameHub{}),
+		tournamentSvc: tournament.NewService(&mockQuerier{}),
+		auth:          &mockAuthenticator{},
+		conf:          &config.Config{BasePath: "/"},
+		q:             &mockQuerier{},
 	}
 	user := &db.User{UserID: 1}
-	// Set session ID in context
-	ctx := context.WithValue(context.Background(), sessionIDContextKey{}, "hashed-session")
+	ctx := session.SetSessionIDInContext(context.Background(), "hashed-session")
 	resp, err := h.PostLogout(ctx, PostLogoutRequestObject{}, user)
 	if err != nil {
 		t.Fatalf("unexpected error: %v", err)
@@ -609,13 +479,7 @@ func TestPostLogout(t *testing.T) {
 }
 
 func TestGetGames_Empty(t *testing.T) {
-	h := Handler{
-		q:    &mockQuerier{},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+	h := newTestHandler(&mockQuerier{})
 	user := &db.User{UserID: 1}
 	resp, err := h.GetGames(context.Background(), GetGamesRequestObject{}, user)
 	if err != nil {
@@ -632,34 +496,28 @@ func TestGetGames_Empty(t *testing.T) {
 
 func TestGetGames_WithGames(t *testing.T) {
 	now := time.Now()
-	h := Handler{
-		q: &mockQuerier{
-			listPublicGamesFunc: func(_ context.Context) ([]db.ListPublicGamesRow, error) {
-				return []db.ListPublicGamesRow{
-					{
-						GameID:          1,
-						GameType:        "golf",
-						IsPublic:        true,
-						DisplayName:     "Game 1",
-						DurationSeconds: 300,
-						StartedAt:       pgtype.Timestamp{Time: now, Valid: true},
-						ProblemID:       10,
-						Title:           "Problem 1",
-						Description:     "desc",
-						Language:        "php",
-						SampleCode:      "<?php",
-					},
-				}, nil
-			},
-			listMainPlayersFunc: func(_ context.Context, _ []int32) ([]db.ListMainPlayersRow, error) {
-				return nil, nil
-			},
+	h := newTestHandler(&mockQuerier{
+		listPublicGamesFunc: func(_ context.Context) ([]db.ListPublicGamesRow, error) {
+			return []db.ListPublicGamesRow{
+				{
+					GameID:          1,
+					GameType:        "golf",
+					IsPublic:        true,
+					DisplayName:     "Game 1",
+					DurationSeconds: 300,
+					StartedAt:       pgtype.Timestamp{Time: now, Valid: true},
+					ProblemID:       10,
+					Title:           "Problem 1",
+					Description:     "desc",
+					Language:        "php",
+					SampleCode:      "<?php",
+				},
+			}, nil
 		},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+		listMainPlayersFunc: func(_ context.Context, _ []int32) ([]db.ListMainPlayersRow, error) {
+			return nil, nil
+		},
+	})
 	user := &db.User{UserID: 1}
 	resp, err := h.GetGames(context.Background(), GetGamesRequestObject{}, user)
 	if err != nil {
@@ -681,13 +539,7 @@ func TestGetGames_WithGames(t *testing.T) {
 }
 
 func TestGetGamePlayLatestState_NoState(t *testing.T) {
-	h := Handler{
-		q:    &mockQuerier{},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+	h := newTestHandler(&mockQuerier{})
 	user := &db.User{UserID: 1}
 	resp, err := h.GetGamePlayLatestState(context.Background(), GetGamePlayLatestStateRequestObject{GameID: 1}, user)
 	if err != nil {
@@ -706,13 +558,7 @@ func TestGetGamePlayLatestState_NoState(t *testing.T) {
 }
 
 func TestPostGamePlayCode_GameNotFound(t *testing.T) {
-	h := Handler{
-		q:    &mockQuerier{},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+	h := newTestHandler(&mockQuerier{})
 	user := &db.User{UserID: 1}
 	resp, err := h.PostGamePlayCode(context.Background(), PostGamePlayCodeRequestObject{
 		GameID: 999,
@@ -727,23 +573,17 @@ func TestPostGamePlayCode_GameNotFound(t *testing.T) {
 }
 
 func TestPostGamePlayCode_GameNotRunning(t *testing.T) {
-	h := Handler{
-		q: &mockQuerier{
-			getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
-				return db.GetGameByIDRow{
-					GameID:   1,
-					Language: "php",
-					StartedAt: pgtype.Timestamp{
-						Valid: false,
-					},
-				}, nil
-			},
+	h := newTestHandler(&mockQuerier{
+		getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
+			return db.GetGameByIDRow{
+				GameID:   1,
+				Language: "php",
+				StartedAt: pgtype.Timestamp{
+					Valid: false,
+				},
+			}, nil
 		},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+	})
 	user := &db.User{UserID: 1}
 	resp, err := h.PostGamePlayCode(context.Background(), PostGamePlayCodeRequestObject{
 		GameID: 1,
@@ -760,26 +600,20 @@ func TestPostGamePlayCode_GameNotRunning(t *testing.T) {
 func TestPostGamePlayCode_Success(t *testing.T) {
 	now := time.Now()
 	var updatedCode string
-	h := Handler{
-		q: &mockQuerier{
-			getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
-				return db.GetGameByIDRow{
-					GameID:          1,
-					Language:        "php",
-					StartedAt:       pgtype.Timestamp{Time: now, Valid: true},
-					DurationSeconds: 600,
-				}, nil
-			},
-			updateCodeFunc: func(_ context.Context, arg db.UpdateCodeParams) error {
-				updatedCode = arg.Code
-				return nil
-			},
+	h := newTestHandler(&mockQuerier{
+		getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
+			return db.GetGameByIDRow{
+				GameID:          1,
+				Language:        "php",
+				StartedAt:       pgtype.Timestamp{Time: now, Valid: true},
+				DurationSeconds: 600,
+			}, nil
 		},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+		updateCodeFunc: func(_ context.Context, arg db.UpdateCodeParams) error {
+			updatedCode = arg.Code
+			return nil
+		},
+	})
 	user := &db.User{UserID: 1}
 	resp, err := h.PostGamePlayCode(context.Background(), PostGamePlayCodeRequestObject{
 		GameID: 1,
@@ -797,13 +631,7 @@ func TestPostGamePlayCode_Success(t *testing.T) {
 }
 
 func TestGetGameWatchRanking_NotFound(t *testing.T) {
-	h := Handler{
-		q:    &mockQuerier{},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+	h := newTestHandler(&mockQuerier{})
 	user := &db.User{UserID: 1}
 	resp, err := h.GetGameWatchRanking(context.Background(), GetGameWatchRankingRequestObject{GameID: 999}, user)
 	if err != nil {
@@ -816,25 +644,19 @@ func TestGetGameWatchRanking_NotFound(t *testing.T) {
 
 func TestGetGameWatchRanking_EmptyRanking(t *testing.T) {
 	now := time.Now()
-	h := Handler{
-		q: &mockQuerier{
-			getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
-				return db.GetGameByIDRow{
-					GameID:          1,
-					Language:        "php",
-					StartedAt:       pgtype.Timestamp{Time: now.Add(-10 * time.Minute), Valid: true},
-					DurationSeconds: 300,
-				}, nil
-			},
-			getRankingFunc: func(_ context.Context, _ int32) ([]db.GetRankingRow, error) {
-				return nil, nil
-			},
+	h := newTestHandler(&mockQuerier{
+		getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
+			return db.GetGameByIDRow{
+				GameID:          1,
+				Language:        "php",
+				StartedAt:       pgtype.Timestamp{Time: now.Add(-10 * time.Minute), Valid: true},
+				DurationSeconds: 300,
+			}, nil
 		},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+		getRankingFunc: func(_ context.Context, _ int32) ([]db.GetRankingRow, error) {
+			return nil, nil
+		},
+	})
 	user := &db.User{UserID: 1}
 	resp, err := h.GetGameWatchRanking(context.Background(), GetGameWatchRankingRequestObject{GameID: 1}, user)
 	if err != nil {
@@ -850,13 +672,7 @@ func TestGetGameWatchRanking_EmptyRanking(t *testing.T) {
 }
 
 func TestGetGameWatchLatestStates_Empty(t *testing.T) {
-	h := Handler{
-		q:    &mockQuerier{},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+	h := newTestHandler(&mockQuerier{})
 	user := &db.User{UserID: 1}
 	resp, err := h.GetGameWatchLatestStates(context.Background(), GetGameWatchLatestStatesRequestObject{GameID: 1}, user)
 	if err != nil {
@@ -871,16 +687,16 @@ func TestGetGameWatchLatestStates_Empty(t *testing.T) {
 	}
 }
 
-func TestToNullableWith(t *testing.T) {
+func TestToNullable(t *testing.T) {
 	t.Run("nil value", func(t *testing.T) {
-		result := toNullableWith(nil, func(_ int) string { return "x" })
+		result := toNullable[string](nil)
 		if !result.IsNull() {
 			t.Error("expected null for nil input")
 		}
 	})
 	t.Run("non-nil value", func(t *testing.T) {
-		x := 42
-		result := toNullableWith(&x, func(_ int) string { return "hello" })
+		s := "hello"
+		result := toNullable(&s)
 		if result.IsNull() {
 			t.Error("expected non-null for non-nil input")
 		}
@@ -894,111 +710,33 @@ func TestToNullableWith(t *testing.T) {
 	})
 }
 
-// --- Tournament tests ---
-
-func TestStandardBracketSeeds(t *testing.T) {
-	tests := []struct {
-		name        string
-		bracketSize int
-		expected    []int
-	}{
-		{
-			name:        "bracket_size=2",
-			bracketSize: 2,
-			expected:    []int{1, 2},
-		},
-		{
-			name:        "bracket_size=4",
-			bracketSize: 4,
-			expected:    []int{1, 4, 2, 3},
-		},
-		{
-			name:        "bracket_size=8",
-			bracketSize: 8,
-			expected:    []int{1, 8, 4, 5, 2, 7, 3, 6},
-		},
-	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			got := standardBracketSeeds(tt.bracketSize)
-			if len(got) != len(tt.expected) {
-				t.Fatalf("expected length %d, got %d", len(tt.expected), len(got))
-			}
-			for i, v := range tt.expected {
-				if got[i] != v {
-					t.Errorf("position %d: expected seed %d, got %d", i, v, got[i])
-				}
-			}
-		})
-	}
-}
-
-func TestStandardBracketSeeds_Seed1And2OppositeSides(t *testing.T) {
-	seeds := standardBracketSeeds(8)
-	// Seed 1 should be in the first half, Seed 2 in the second half
-	seed1Pos := -1
-	seed2Pos := -1
-	for i, s := range seeds {
-		if s == 1 {
-			seed1Pos = i
+func TestToNullableWith(t *testing.T) {
+	t.Run("nil value", func(t *testing.T) {
+		result := toNullableWith(nil, func(_ int) string { return "x" })
+		if !result.IsNull() {
+			t.Error("expected null for nil input")
 		}
-		if s == 2 {
-			seed2Pos = i
+	})
+	t.Run("non-nil value", func(t *testing.T) {
+		x := 42
+		result := toNullableWith(&x, func(_ int) string { return "hello" })
+		if result.IsNull() {
+			t.Error("expected non-null for non-nil input")
 		}
-	}
-	if seed1Pos >= 4 {
-		t.Errorf("Seed 1 should be in first half, but at position %d", seed1Pos)
-	}
-	if seed2Pos < 4 {
-		t.Errorf("Seed 2 should be in second half, but at position %d", seed2Pos)
-	}
-}
-
-func TestStandardBracketSeeds_AllSeedsPresent(t *testing.T) {
-	for _, size := range []int{2, 4, 8, 16} {
-		seeds := standardBracketSeeds(size)
-		seen := make(map[int]bool)
-		for _, s := range seeds {
-			if s < 1 || s > size {
-				t.Errorf("bracket_size=%d: seed %d out of range", size, s)
-			}
-			if seen[s] {
-				t.Errorf("bracket_size=%d: duplicate seed %d", size, s)
-			}
-			seen[s] = true
+		v, err := result.Get()
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
 		}
-		if len(seen) != size {
-			t.Errorf("bracket_size=%d: expected %d unique seeds, got %d", size, size, len(seen))
+		if v != "hello" {
+			t.Errorf("expected 'hello', got %q", v)
 		}
-	}
+	})
 }
 
-func TestFindSeedByUserID(t *testing.T) {
-	entries := []TournamentEntry{
-		{User: User{UserID: 10}, Seed: 1},
-		{User: User{UserID: 20}, Seed: 2},
-		{User: User{UserID: 30}, Seed: 3},
-	}
-
-	if got := findSeedByUserID(entries, 10); got != 1 {
-		t.Errorf("expected seed 1 for user 10, got %d", got)
-	}
-	if got := findSeedByUserID(entries, 20); got != 2 {
-		t.Errorf("expected seed 2 for user 20, got %d", got)
-	}
-	if got := findSeedByUserID(entries, 999); got != 0 {
-		t.Errorf("expected seed 0 for unknown user, got %d", got)
-	}
-}
+// --- Tournament tests ---
 
 func TestGetTournament_NotFound(t *testing.T) {
-	h := Handler{
-		q:    &mockQuerier{},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+	h := newTestHandler(&mockQuerier{})
 	user := &db.User{UserID: 1}
 	resp, err := h.GetTournament(context.Background(), GetTournamentRequestObject{TournamentID: 999}, user)
 	if err != nil {
@@ -1010,22 +748,16 @@ func TestGetTournament_NotFound(t *testing.T) {
 }
 
 func TestGetTournament_Success_NoEntries(t *testing.T) {
-	h := Handler{
-		q: &mockQuerier{
-			getTournamentByIDFunc: func(_ context.Context, _ int32) (db.Tournament, error) {
-				return db.Tournament{
-					TournamentID: 1,
-					DisplayName:  "Test Tournament",
-					BracketSize:  4,
-					NumRounds:    2,
-				}, nil
-			},
+	h := newTestHandler(&mockQuerier{
+		getTournamentByIDFunc: func(_ context.Context, _ int32) (db.Tournament, error) {
+			return db.Tournament{
+				TournamentID: 1,
+				DisplayName:  "Test Tournament",
+				BracketSize:  4,
+				NumRounds:    2,
+			}, nil
 		},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+	})
 	user := &db.User{UserID: 1}
 	resp, err := h.GetTournament(context.Background(), GetTournamentRequestObject{TournamentID: 1}, user)
 	if err != nil {
@@ -1051,42 +783,36 @@ func TestGetTournament_Success_NoEntries(t *testing.T) {
 
 func TestGetTournament_WithEntriesAndMatches(t *testing.T) {
 	gameID := int32(10)
-	h := Handler{
-		q: &mockQuerier{
-			getTournamentByIDFunc: func(_ context.Context, _ int32) (db.Tournament, error) {
-				return db.Tournament{
-					TournamentID: 1,
-					DisplayName:  "Test",
-					BracketSize:  4,
-					NumRounds:    2,
-				}, nil
-			},
-			listTournamentEntriesFunc: func(_ context.Context, _ int32) ([]db.ListTournamentEntriesRow, error) {
-				return []db.ListTournamentEntriesRow{
-					{Seed: 1, UserID: 100, Username: "alice", DisplayName: "Alice", IsAdmin: false},
-					{Seed: 2, UserID: 200, Username: "bob", DisplayName: "Bob", IsAdmin: false},
-					{Seed: 3, UserID: 300, Username: "carol", DisplayName: "Carol", IsAdmin: false},
-				}, nil
-			},
-			listTournamentMatchesFunc: func(_ context.Context, _ int32) ([]db.TournamentMatch, error) {
-				return []db.TournamentMatch{
-					{TournamentMatchID: 1, TournamentID: 1, Round: 0, Position: 0, GameID: &gameID},
-					{TournamentMatchID: 2, TournamentID: 1, Round: 0, Position: 1, GameID: nil},
-					{TournamentMatchID: 3, TournamentID: 1, Round: 1, Position: 0, GameID: nil},
-				}, nil
-			},
-			getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
-				return db.GetGameByIDRow{
-					GameID:    10,
-					StartedAt: pgtype.Timestamp{Valid: false},
-				}, nil
-			},
+	h := newTestHandler(&mockQuerier{
+		getTournamentByIDFunc: func(_ context.Context, _ int32) (db.Tournament, error) {
+			return db.Tournament{
+				TournamentID: 1,
+				DisplayName:  "Test",
+				BracketSize:  4,
+				NumRounds:    2,
+			}, nil
 		},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+		listTournamentEntriesFunc: func(_ context.Context, _ int32) ([]db.ListTournamentEntriesRow, error) {
+			return []db.ListTournamentEntriesRow{
+				{Seed: 1, UserID: 100, Username: "alice", DisplayName: "Alice", IsAdmin: false},
+				{Seed: 2, UserID: 200, Username: "bob", DisplayName: "Bob", IsAdmin: false},
+				{Seed: 3, UserID: 300, Username: "carol", DisplayName: "Carol", IsAdmin: false},
+			}, nil
+		},
+		listTournamentMatchesFunc: func(_ context.Context, _ int32) ([]db.TournamentMatch, error) {
+			return []db.TournamentMatch{
+				{TournamentMatchID: 1, TournamentID: 1, Round: 0, Position: 0, GameID: &gameID},
+				{TournamentMatchID: 2, TournamentID: 1, Round: 0, Position: 1, GameID: nil},
+				{TournamentMatchID: 3, TournamentID: 1, Round: 1, Position: 0, GameID: nil},
+			}, nil
+		},
+		getGameByIDFunc: func(_ context.Context, _ int32) (db.GetGameByIDRow, error) {
+			return db.GetGameByIDRow{
+				GameID:    10,
+				StartedAt: pgtype.Timestamp{Valid: false},
+			}, nil
+		},
+	})
 	user := &db.User{UserID: 1}
 	resp, err := h.GetTournament(context.Background(), GetTournamentRequestObject{TournamentID: 1}, user)
 	if err != nil {
@@ -1097,17 +823,14 @@ func TestGetTournament_WithEntriesAndMatches(t *testing.T) {
 		t.Fatalf("expected 200 response, got %T", resp)
 	}
 
-	// Check entries
 	if len(okResp.Tournament.Entries) != 3 {
 		t.Fatalf("expected 3 entries, got %d", len(okResp.Tournament.Entries))
 	}
 
-	// Check matches: bracket_size=4, num_rounds=2 → round 0: 2 matches, round 1: 1 match
 	if len(okResp.Tournament.Matches) != 3 {
 		t.Fatalf("expected 3 matches, got %d", len(okResp.Tournament.Matches))
 	}
 
-	// Round 0, Position 0: Seed 1 (Alice) vs Seed 4 (bye)
 	m0 := okResp.Tournament.Matches[0]
 	if m0.Round != 0 || m0.Position != 0 {
 		t.Errorf("match 0: expected round=0, pos=0, got round=%d, pos=%d", m0.Round, m0.Position)
@@ -1125,7 +848,6 @@ func TestGetTournament_WithEntriesAndMatches(t *testing.T) {
 		t.Error("match 0: expected winner to be Alice (user_id=100)")
 	}
 
-	// Round 0, Position 1: Seed 2 (Bob) vs Seed 3 (Carol)
 	m1 := okResp.Tournament.Matches[1]
 	if m1.Round != 0 || m1.Position != 1 {
 		t.Errorf("match 1: expected round=0, pos=1, got round=%d, pos=%d", m1.Round, m1.Position)
@@ -1142,38 +864,30 @@ func TestGetTournament_WithEntriesAndMatches(t *testing.T) {
 }
 
 func TestGetTournament_ByeAutoWinner(t *testing.T) {
-	// 3 players in bracket_size=4: seed 4 is empty → round 0, pos 0 is a bye
-	// The bye winner should propagate to round 1
-	h := Handler{
-		q: &mockQuerier{
-			getTournamentByIDFunc: func(_ context.Context, _ int32) (db.Tournament, error) {
-				return db.Tournament{
-					TournamentID: 1,
-					DisplayName:  "Bye Test",
-					BracketSize:  4,
-					NumRounds:    2,
-				}, nil
-			},
-			listTournamentEntriesFunc: func(_ context.Context, _ int32) ([]db.ListTournamentEntriesRow, error) {
-				return []db.ListTournamentEntriesRow{
-					{Seed: 1, UserID: 100, Username: "alice", DisplayName: "Alice"},
-					{Seed: 2, UserID: 200, Username: "bob", DisplayName: "Bob"},
-					{Seed: 3, UserID: 300, Username: "carol", DisplayName: "Carol"},
-				}, nil
-			},
-			listTournamentMatchesFunc: func(_ context.Context, _ int32) ([]db.TournamentMatch, error) {
-				return []db.TournamentMatch{
-					{TournamentMatchID: 1, Round: 0, Position: 0},
-					{TournamentMatchID: 2, Round: 0, Position: 1},
-					{TournamentMatchID: 3, Round: 1, Position: 0},
-				}, nil
-			},
+	h := newTestHandler(&mockQuerier{
+		getTournamentByIDFunc: func(_ context.Context, _ int32) (db.Tournament, error) {
+			return db.Tournament{
+				TournamentID: 1,
+				DisplayName:  "Bye Test",
+				BracketSize:  4,
+				NumRounds:    2,
+			}, nil
 		},
-		txm:  &mockTxManager{},
-		hub:  &mockGameHub{},
-		auth: &mockAuthenticator{},
-		conf: &config.Config{},
-	}
+		listTournamentEntriesFunc: func(_ context.Context, _ int32) ([]db.ListTournamentEntriesRow, error) {
+			return []db.ListTournamentEntriesRow{
+				{Seed: 1, UserID: 100, Username: "alice", DisplayName: "Alice"},
+				{Seed: 2, UserID: 200, Username: "bob", DisplayName: "Bob"},
+				{Seed: 3, UserID: 300, Username: "carol", DisplayName: "Carol"},
+			}, nil
+		},
+		listTournamentMatchesFunc: func(_ context.Context, _ int32) ([]db.TournamentMatch, error) {
+			return []db.TournamentMatch{
+				{TournamentMatchID: 1, Round: 0, Position: 0},
+				{TournamentMatchID: 2, Round: 0, Position: 1},
+				{TournamentMatchID: 3, Round: 1, Position: 0},
+			}, nil
+		},
+	})
 	user := &db.User{UserID: 1}
 	resp, err := h.GetTournament(context.Background(), GetTournamentRequestObject{TournamentID: 1}, user)
 	if err != nil {
@@ -1181,7 +895,6 @@ func TestGetTournament_ByeAutoWinner(t *testing.T) {
 	}
 	okResp := resp.(GetTournament200JSONResponse)
 
-	// Round 1, Position 0 (final): player1 should be Alice (bye winner from round 0 pos 0)
 	final := okResp.Tournament.Matches[2]
 	if final.Round != 1 || final.Position != 0 {
 		t.Fatalf("expected final at round=1, pos=0")
diff --git a/backend/api/handler_wrapper.go b/backend/api/handler_wrapper.go
index 1c8bc83..6a6c724 100644
--- a/backend/api/handler_wrapper.go
+++ b/backend/api/handler_wrapper.go
@@ -7,6 +7,9 @@ import (
 
 	"albatross-2026-backend/config"
 	"albatross-2026-backend/db"
+	"albatross-2026-backend/game"
+	"albatross-2026-backend/session"
+	"albatross-2026-backend/tournament"
 )
 
 var _ StrictServerInterface = (*HandlerWrapper)(nil)
@@ -15,25 +18,25 @@ type HandlerWrapper struct {
 	impl Handler
 }
 
-func NewHandler(queries db.Querier, txm db.TxManager, hub GameHubInterface, auth AuthenticatorInterface, conf *config.Config) *HandlerWrapper {
+func NewHandler(gameSvc *game.Service, tournamentSvc *tournament.Service, auth AuthenticatorInterface, queries db.Querier, conf *config.Config) *HandlerWrapper {
 	return &HandlerWrapper{
 		impl: Handler{
-			q:    queries,
-			txm:  txm,
-			hub:  hub,
-			auth: auth,
-			conf: conf,
+			gameSvc:       gameSvc,
+			tournamentSvc: tournamentSvc,
+			auth:          auth,
+			conf:          conf,
+			q:             queries,
 		},
 	}
 }
 
 func (h *HandlerWrapper) GetGame(ctx context.Context, request GetGameRequestObject) (GetGameResponseObject, error) {
-	user, _ := GetUserFromContext(ctx)
+	user, _ := session.GetUserFromContext(ctx)
 	return h.impl.GetGame(ctx, request, user)
 }
 
 func (h *HandlerWrapper) GetGamePlayLatestState(ctx context.Context, request GetGamePlayLatestStateRequestObject) (GetGamePlayLatestStateResponseObject, error) {
-	user, ok := GetUserFromContext(ctx)
+	user, ok := session.GetUserFromContext(ctx)
 	if !ok {
 		return GetGamePlayLatestState401JSONResponse{
 			Message: "Unauthorized",
@@ -43,7 +46,7 @@ func (h *HandlerWrapper) GetGamePlayLatestState(ctx context.Context, request Get
 }
 
 func (h *HandlerWrapper) GetGamePlaySubmissions(ctx context.Context, request GetGamePlaySubmissionsRequestObject) (GetGamePlaySubmissionsResponseObject, error) {
-	user, ok := GetUserFromContext(ctx)
+	user, ok := session.GetUserFromContext(ctx)
 	if !ok {
 		return GetGamePlaySubmissions401JSONResponse{
 			Message: "Unauthorized",
@@ -53,22 +56,22 @@ func (h *HandlerWrapper) GetGamePlaySubmissions(ctx context.Context, request Get
 }
 
 func (h *HandlerWrapper) GetGameWatchLatestStates(ctx context.Context, request GetGameWatchLatestStatesRequestObject) (GetGameWatchLatestStatesResponseObject, error) {
-	user, _ := GetUserFromContext(ctx)
+	user, _ := session.GetUserFromContext(ctx)
 	return h.impl.GetGameWatchLatestStates(ctx, request, user)
 }
 
 func (h *HandlerWrapper) GetGameWatchRanking(ctx context.Context, request GetGameWatchRankingRequestObject) (GetGameWatchRankingResponseObject, error) {
-	user, _ := GetUserFromContext(ctx)
+	user, _ := session.GetUserFromContext(ctx)
 	return h.impl.GetGameWatchRanking(ctx, request, user)
 }
 
 func (h *HandlerWrapper) GetGames(ctx context.Context, request GetGamesRequestObject) (GetGamesResponseObject, error) {
-	user, _ := GetUserFromContext(ctx)
+	user, _ := session.GetUserFromContext(ctx)
 	return h.impl.GetGames(ctx, request, user)
 }
 
 func (h *HandlerWrapper) GetMe(ctx context.Context, request GetMeRequestObject) (GetMeResponseObject, error) {
-	user, ok := GetUserFromContext(ctx)
+	user, ok := session.GetUserFromContext(ctx)
 	if !ok {
 		return GetMe401JSONResponse{
 			Message: "Unauthorized",
@@ -78,12 +81,12 @@ func (h *HandlerWrapper) GetMe(ctx context.Context, request GetMeRequestObject)
 }
 
 func (h *HandlerWrapper) GetTournament(ctx context.Context, request GetTournamentRequestObject) (GetTournamentResponseObject, error) {
-	user, _ := GetUserFromContext(ctx)
+	user, _ := session.GetUserFromContext(ctx)
 	return h.impl.GetTournament(ctx, request, user)
 }
 
 func (h *HandlerWrapper) PostGamePlayCode(ctx context.Context, request PostGamePlayCodeRequestObject) (PostGamePlayCodeResponseObject, error) {
-	user, ok := GetUserFromContext(ctx)
+	user, ok := session.GetUserFromContext(ctx)
 	if !ok {
 		return PostGamePlayCode401JSONResponse{
 			Message: "Unauthorized",
@@ -93,7 +96,7 @@ func (h *HandlerWrapper) PostGamePlayCode(ctx context.Context, request PostGameP
 }
 
 func (h *HandlerWrapper) PostGamePlaySubmit(ctx context.Context, request PostGamePlaySubmitRequestObject) (PostGamePlaySubmitResponseObject, error) {
-	user, ok := GetUserFromContext(ctx)
+	user, ok := session.GetUserFromContext(ctx)
 	if !ok {
 		return PostGamePlaySubmit401JSONResponse{
 			Message: "Unauthorized",
@@ -107,7 +110,7 @@ func (h *HandlerWrapper) PostLogin(ctx context.Context, request PostLoginRequest
 }
 
 func (h *HandlerWrapper) PostLogout(ctx context.Context, request PostLogoutRequestObject) (PostLogoutResponseObject, error) {
-	user, ok := GetUserFromContext(ctx)
+	user, ok := session.GetUserFromContext(ctx)
 	if !ok {
 		return PostLogout401JSONResponse{
 			Message: "Unauthorized",
diff --git a/backend/game/errors.go b/backend/game/errors.go
new file mode 100644
index 0000000..9f7505a
--- /dev/null
+++ b/backend/game/errors.go
@@ -0,0 +1,9 @@
+package game
+
+import "errors"
+
+var (
+	ErrNotFound       = errors.New("not found")
+	ErrGameNotRunning = errors.New("game is not running")
+	ErrForbidden      = errors.New("forbidden")
+)
diff --git a/backend/game/service.go b/backend/game/service.go
new file mode 100644
index 0000000..86e0eb3
--- /dev/null
+++ b/backend/game/service.go
@@ -0,0 +1,406 @@
+package game
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgtype"
+
+	"albatross-2026-backend/db"
+)
+
+type GameHubInterface interface {
+	CalcCodeSize(code string, language string) int
+	EnqueueTestTasks(ctx context.Context, submissionID, gameID, userID int, language, code string) error
+}
+
+type Service struct {
+	q   db.Querier
+	txm db.TxManager
+	hub GameHubInterface
+}
+
+func NewService(q db.Querier, txm db.TxManager, hub GameHubInterface) *Service {
+	return &Service{q: q, txm: txm, hub: hub}
+}
+
+// Domain types
+
+type Player struct {
+	UserID      int
+	Username    string
+	DisplayName string
+	IconPath    *string
+	IsAdmin     bool
+	Label       *string
+}
+
+type ProblemDetail struct {
+	ProblemID   int
+	Title       string
+	Description string
+	Language    string
+	SampleCode  string
+}
+
+type GameDetail struct {
+	GameID          int
+	GameType        string
+	IsPublic        bool
+	DisplayName     string
+	DurationSeconds int
+	StartedAt       *time.Time
+	Problem         ProblemDetail
+	MainPlayers     []Player
+}
+
+type LatestState struct {
+	Code                 string
+	Score                *int
+	BestScoreSubmittedAt *int64
+	Status               string
+}
+
+type RankingEntry struct {
+	Player      Player
+	Score       int
+	SubmittedAt int64
+	Code        *string
+}
+
+type SubmissionDetail struct {
+	SubmissionID int
+	GameID       int
+	Code         string
+	CodeSize     int
+	Status       string
+	CreatedAt    int64
+}
+
+// Helper functions
+
+func IsGameRunning(startedAt pgtype.Timestamp, durationSeconds int32) bool {
+	if !startedAt.Valid {
+		return false
+	}
+	endTime := startedAt.Time.Add(time.Duration(durationSeconds) * time.Second)
+	return time.Now().Before(endTime)
+}
+
+func IsGameFinished(startedAt pgtype.Timestamp, durationSeconds int32) bool {
+	if !startedAt.Valid {
+		return false
+	}
+	endTime := startedAt.Time.Add(time.Duration(durationSeconds) * time.Second)
+	return !time.Now().Before(endTime)
+}
+
+func playerFromMainPlayerRow(row db.ListMainPlayersRow) Player {
+	return Player{
+		UserID:      int(row.UserID),
+		Username:    row.Username,
+		DisplayName: row.DisplayName,
+		IconPath:    row.IconPath,
+		IsAdmin:     row.IsAdmin,
+		Label:       row.Label,
+	}
+}
+
+func gameDetailFromPublicRow(row db.ListPublicGamesRow) GameDetail {
+	var startedAt *time.Time
+	if row.StartedAt.Valid {
+		t := row.StartedAt.Time
+		startedAt = &t
+	}
+	return GameDetail{
+		GameID:          int(row.GameID),
+		GameType:        row.GameType,
+		IsPublic:        row.IsPublic,
+		DisplayName:     row.DisplayName,
+		DurationSeconds: int(row.DurationSeconds),
+		StartedAt:       startedAt,
+		Problem: ProblemDetail{
+			ProblemID:   int(row.ProblemID),
+			Title:       row.Title,
+			Description: row.Description,
+			Language:    row.Language,
+			SampleCode:  row.SampleCode,
+		},
+	}
+}
+
+func gameDetailFromGetRow(row db.GetGameByIDRow) GameDetail {
+	var startedAt *time.Time
+	if row.StartedAt.Valid {
+		t := row.StartedAt.Time
+		startedAt = &t
+	}
+	return GameDetail{
+		GameID:          int(row.GameID),
+		GameType:        row.GameType,
+		IsPublic:        row.IsPublic,
+		DisplayName:     row.DisplayName,
+		DurationSeconds: int(row.DurationSeconds),
+		StartedAt:       startedAt,
+		Problem: ProblemDetail{
+			ProblemID:   int(row.ProblemID),
+			Title:       row.Title,
+			Description: row.Description,
+			Language:    row.Language,
+			SampleCode:  row.SampleCode,
+		},
+	}
+}
+
+// Service methods
+
+func (s *Service) ListPublicGames(ctx context.Context) ([]GameDetail, error) {
+	gameRows, err := s.q.ListPublicGames(ctx)
+	if err != nil {
+		return nil, err
+	}
+	games := make([]GameDetail, len(gameRows))
+	gameIDs := make([]int32, len(gameRows))
+	gameID2Index := make(map[int32]int, len(gameRows))
+	for i, row := range gameRows {
+		games[i] = gameDetailFromPublicRow(row)
+		gameIDs[i] = row.GameID
+		gameID2Index[row.GameID] = i
+	}
+	mainPlayerRows, err := s.q.ListMainPlayers(ctx, gameIDs)
+	if err != nil {
+		return nil, err
+	}
+	for _, row := range mainPlayerRows {
+		idx := gameID2Index[row.GameID]
+		games[idx].MainPlayers = append(games[idx].MainPlayers, playerFromMainPlayerRow(row))
+	}
+	return games, nil
+}
+
+func (s *Service) GetGameByID(ctx context.Context, gameID int, isAdmin bool) (GameDetail, error) {
+	row, err := s.q.GetGameByID(ctx, int32(gameID))
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return GameDetail{}, ErrNotFound
+		}
+		return GameDetail{}, err
+	}
+	if !row.IsPublic && !isAdmin {
+		return GameDetail{}, ErrNotFound
+	}
+	game := gameDetailFromGetRow(row)
+	mainPlayerRows, err := s.q.ListMainPlayers(ctx, []int32{int32(gameID)})
+	if err != nil {
+		return GameDetail{}, err
+	}
+	for _, playerRow := range mainPlayerRows {
+		game.MainPlayers = append(game.MainPlayers, playerFromMainPlayerRow(playerRow))
+	}
+	return game, nil
+}
+
+func (s *Service) SaveCode(ctx context.Context, gameID int, userID int32, code string) error {
+	gameRow, err := s.q.GetGameByID(ctx, int32(gameID))
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return ErrNotFound
+		}
+		return err
+	}
+	if !IsGameRunning(gameRow.StartedAt, gameRow.DurationSeconds) {
+		return ErrGameNotRunning
+	}
+	return s.q.UpdateCode(ctx, db.UpdateCodeParams{
+		GameID: int32(gameID),
+		UserID: userID,
+		Code:   code,
+		Status: "none",
+	})
+}
+
+func (s *Service) SubmitCode(ctx context.Context, gameID int, userID int32, code string) error {
+	gameRow, err := s.q.GetGameByID(ctx, int32(gameID))
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return ErrNotFound
+		}
+		return err
+	}
+
+	language := gameRow.Language
+	codeSize := s.hub.CalcCodeSize(code, language)
+
+	if !IsGameRunning(gameRow.StartedAt, gameRow.DurationSeconds) {
+		return ErrGameNotRunning
+	}
+
+	var submissionID int32
+	err = s.txm.RunInTx(ctx, func(qtx db.Querier) error {
+		if err := qtx.UpdateCodeAndStatus(ctx, db.UpdateCodeAndStatusParams{
+			GameID: int32(gameID),
+			UserID: userID,
+			Code:   code,
+			Status: "running",
+		}); err != nil {
+			return err
+		}
+		var err error
+		submissionID, err = qtx.CreateSubmission(ctx, db.CreateSubmissionParams{
+			GameID:   int32(gameID),
+			UserID:   userID,
+			Code:     code,
+			CodeSize: int32(codeSize),
+		})
+		return err
+	})
+	if err != nil {
+		return err
+	}
+
+	return s.hub.EnqueueTestTasks(ctx, int(submissionID), gameID, int(userID), language, code)
+}
+
+func (s *Service) GetLatestState(ctx context.Context, gameID int, userID int32) (LatestState, error) {
+	row, err := s.q.GetLatestState(ctx, db.GetLatestStateParams{
+		GameID: int32(gameID),
+		UserID: userID,
+	})
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return LatestState{Status: "none"}, nil
+		}
+		return LatestState{}, err
+	}
+	var score *int
+	if row.CodeSize != nil {
+		s := int(*row.CodeSize)
+		score = &s
+	}
+	var submittedAt *int64
+	if row.CreatedAt.Valid {
+		ts := row.CreatedAt.Time.Unix()
+		submittedAt = &ts
+	}
+	return LatestState{
+		Code:                 row.Code,
+		Score:                score,
+		BestScoreSubmittedAt: submittedAt,
+		Status:               row.Status,
+	}, nil
+}
+
+func (s *Service) GetWatchLatestStates(ctx context.Context, gameID int, userID *int32, isAdmin bool) (map[int]LatestState, error) {
+	rows, err := s.q.GetLatestStatesOfMainPlayers(ctx, int32(gameID))
+	if err != nil {
+		return nil, err
+	}
+	states := make(map[int]LatestState, len(rows))
+	for _, row := range rows {
+		var code string
+		if row.Code != nil {
+			code = *row.Code
+		}
+		var status string
+		if row.Status != nil {
+			status = *row.Status
+		} else {
+			status = "none"
+		}
+		var score *int
+		if row.CodeSize != nil {
+			s := int(*row.CodeSize)
+			score = &s
+		}
+		var submittedAt *int64
+		if row.CreatedAt.Valid {
+			ts := row.CreatedAt.Time.Unix()
+			submittedAt = &ts
+		}
+
+		if userID != nil && row.UserID == *userID && !isAdmin {
+			return nil, ErrForbidden
+		}
+
+		states[int(row.UserID)] = LatestState{
+			Code:                 code,
+			Score:                score,
+			BestScoreSubmittedAt: submittedAt,
+			Status:               status,
+		}
+	}
+	return states, nil
+}
+
+func (s *Service) GetRanking(ctx context.Context, gameID int) ([]RankingEntry, bool, error) {
+	gameRow, err := s.q.GetGameByID(ctx, int32(gameID))
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, false, ErrNotFound
+		}
+		return nil, false, err
+	}
+	finished := IsGameFinished(gameRow.StartedAt, gameRow.DurationSeconds)
+
+	rows, err := s.q.GetRanking(ctx, int32(gameID))
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, finished, nil
+		}
+		return nil, false, err
+	}
+	ranking := make([]RankingEntry, len(rows))
+	for i, row := range rows {
+		var code *string
+		if finished {
+			code = &row.Submission.Code
+		}
+		ranking[i] = RankingEntry{
+			Player: Player{
+				UserID:      int(row.User.UserID),
+				Username:    row.User.Username,
+				DisplayName: row.User.DisplayName,
+				IconPath:    row.User.IconPath,
+				IsAdmin:     row.User.IsAdmin,
+				Label:       row.User.Label,
+			},
+			Score:       int(row.Submission.CodeSize),
+			SubmittedAt: row.Submission.CreatedAt.Time.Unix(),
+			Code:        code,
+		}
+	}
+	return ranking, finished, nil
+}
+
+func (s *Service) GetSubmissions(ctx context.Context, gameID int, userID int32) ([]SubmissionDetail, error) {
+	_, err := s.q.GetGameByID(ctx, int32(gameID))
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, ErrNotFound
+		}
+		return nil, err
+	}
+
+	rows, err := s.q.GetSubmissionsByGameIDAndUserID(ctx, db.GetSubmissionsByGameIDAndUserIDParams{
+		GameID: int32(gameID),
+		UserID: userID,
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	submissions := make([]SubmissionDetail, len(rows))
+	for i, row := range rows {
+		submissions[i] = SubmissionDetail{
+			SubmissionID: int(row.SubmissionID),
+			GameID:       int(row.GameID),
+			Code:         row.Code,
+			CodeSize:     int(row.CodeSize),
+			Status:       row.Status,
+			CreatedAt:    row.CreatedAt.Time.Unix(),
+		}
+	}
+	return submissions, nil
+}
diff --git a/backend/game/service_test.go b/backend/game/service_test.go
new file mode 100644
index 0000000..95ceef6
--- /dev/null
+++ b/backend/game/service_test.go
@@ -0,0 +1,82 @@
+package game
+
+import (
+	"testing"
+	"time"
+
+	"github.com/jackc/pgx/v5/pgtype"
+)
+
+func TestIsGameRunning(t *testing.T) {
+	now := time.Now()
+	tests := []struct {
+		name            string
+		startedAt       pgtype.Timestamp
+		durationSeconds int32
+		want            bool
+	}{
+		{
+			name:            "not started",
+			startedAt:       pgtype.Timestamp{Valid: false},
+			durationSeconds: 300,
+			want:            false,
+		},
+		{
+			name:            "running",
+			startedAt:       pgtype.Timestamp{Time: now.Add(-1 * time.Minute), Valid: true},
+			durationSeconds: 300,
+			want:            true,
+		},
+		{
+			name:            "finished",
+			startedAt:       pgtype.Timestamp{Time: now.Add(-10 * time.Minute), Valid: true},
+			durationSeconds: 300,
+			want:            false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := IsGameRunning(tt.startedAt, tt.durationSeconds)
+			if got != tt.want {
+				t.Errorf("IsGameRunning() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestIsGameFinished(t *testing.T) {
+	now := time.Now()
+	tests := []struct {
+		name            string
+		startedAt       pgtype.Timestamp
+		durationSeconds int32
+		want            bool
+	}{
+		{
+			name:            "not started",
+			startedAt:       pgtype.Timestamp{Valid: false},
+			durationSeconds: 300,
+			want:            false,
+		},
+		{
+			name:            "still running",
+			startedAt:       pgtype.Timestamp{Time: now.Add(-1 * time.Minute), Valid: true},
+			durationSeconds: 300,
+			want:            false,
+		},
+		{
+			name:            "finished",
+			startedAt:       pgtype.Timestamp{Time: now.Add(-10 * time.Minute), Valid: true},
+			durationSeconds: 300,
+			want:            true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := IsGameFinished(tt.startedAt, tt.durationSeconds)
+			if got != tt.want {
+				t.Errorf("IsGameFinished() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
diff --git a/backend/gen/api/handler_wrapper_gen.go b/backend/gen/api/handler_wrapper_gen.go
index 88f55c6..ef2baa1 100644
--- a/backend/gen/api/handler_wrapper_gen.go
+++ b/backend/gen/api/handler_wrapper_gen.go
@@ -117,6 +117,9 @@ import (
 
 	"albatross-2026-backend/config"
 	"albatross-2026-backend/db"
+	"albatross-2026-backend/game"
+	"albatross-2026-backend/session"
+	"albatross-2026-backend/tournament"
 )
 
 var _ StrictServerInterface = (*HandlerWrapper)(nil)
@@ -125,14 +128,14 @@ type HandlerWrapper struct {
 	impl Handler
 }
 
-func NewHandler(queries db.Querier, txm db.TxManager, hub GameHubInterface, auth AuthenticatorInterface, conf *config.Config) *HandlerWrapper {
+func NewHandler(gameSvc *game.Service, tournamentSvc *tournament.Service, auth AuthenticatorInterface, queries db.Querier, conf *config.Config) *HandlerWrapper {
 	return &HandlerWrapper{
 		impl: Handler{
-			q:    queries,
-			txm:  txm,
-			hub:  hub,
-			auth: auth,
-			conf: conf,
+			gameSvc:       gameSvc,
+			tournamentSvc: tournamentSvc,
+			auth:          auth,
+			conf:          conf,
+			q:             queries,
 		},
 	}
 }
@@ -140,7 +143,7 @@ func NewHandler(queries db.Querier, txm db.TxManager, hub GameHubInterface, auth
 {{ range . }}
 	func (h *HandlerWrapper) {{ .Name }}(ctx context.Context, request {{ .Name }}RequestObject) ({{ .Name }}ResponseObject, error) {
 		{{ if .RequiresLogin -}}
-			user, ok := GetUserFromContext(ctx)
+			user, ok := session.GetUserFromContext(ctx)
 			if !ok {
 				return {{ .Name }}401JSONResponse{
 					Message: "Unauthorized",
@@ -155,7 +158,7 @@ func NewHandler(queries db.Querier, txm db.TxManager, hub GameHubInterface, auth
 			{{ end -}}
 			return h.impl.{{ .Name }}(ctx, request, user)
 		{{ else if .LoginOptional -}}
-			user, _ := GetUserFromContext(ctx)
+			user, _ := session.GetUserFromContext(ctx)
 			return h.impl.{{ .Name }}(ctx, request, user)
 		{{ else -}}
 			return h.impl.{{ .Name }}(ctx, request)
diff --git a/backend/main.go b/backend/main.go
index 2825b84..7220ca6 100644
--- a/backend/main.go
+++ b/backend/main.go
@@ -24,6 +24,7 @@ import (
 	"albatross-2026-backend/game"
 	"albatross-2026-backend/ratelimit"
 	"albatross-2026-backend/taskqueue"
+	"albatross-2026-backend/tournament"
 )
 
 func connectDB(ctx context.Context, dsn string) (*pgxpool.Pool, error) {
@@ -105,7 +106,9 @@ func main() {
 	apiGroup.Use(ratelimit.LoginRateLimitMiddleware(loginRL))
 	apiGroup.Use(api.SessionCookieMiddleware(queries))
 	apiGroup.Use(oapimiddleware.OapiRequestValidator(openAPISpec))
-	apiHandler := api.NewHandler(queries, txm, gameHub, authenticator, conf)
+	gameSvc := game.NewService(queries, txm, gameHub)
+	tournamentSvc := tournament.NewService(queries)
+	apiHandler := api.NewHandler(gameSvc, tournamentSvc, authenticator, queries, conf)
 	api.RegisterHandlers(apiGroup, api.NewStrictHandler(apiHandler, nil))
 
 	adminHandler := admin.NewHandler(queries, txm, gameHub, conf)
diff --git a/backend/session/context.go b/backend/session/context.go
new file mode 100644
index 0000000..60f88b4
--- /dev/null
+++ b/backend/session/context.go
@@ -0,0 +1,39 @@
+package session
+
+import (
+	"context"
+
+	"albatross-2026-backend/db"
+)
+
+type sessionIDContextKey struct{}
+type userContextKey struct{}
+type clientIPContextKey struct{}
+
+func GetSessionIDFromContext(ctx context.Context) (string, bool) {
+	sessionID, ok := ctx.Value(sessionIDContextKey{}).(string)
+	return sessionID, ok
+}
+
+func SetSessionIDInContext(ctx context.Context, sessionID string) context.Context {
+	return context.WithValue(ctx, sessionIDContextKey{}, sessionID)
+}
+
+func GetUserFromContext(ctx context.Context) (*db.User, bool) {
+	user, ok := ctx.Value(userContextKey{}).(*db.User)
+	return user, ok
+}
+
+// SetUserInContext sets a user in the context. Intended for testing.
+func SetUserInContext(ctx context.Context, user *db.User) context.Context {
+	return context.WithValue(ctx, userContextKey{}, user)
+}
+
+func GetClientIPFromContext(ctx context.Context) string {
+	ip, _ := ctx.Value(clientIPContextKey{}).(string)
+	return ip
+}
+
+func SetClientIPInContext(ctx context.Context, ip string) context.Context {
+	return context.WithValue(ctx, clientIPContextKey{}, ip)
+}
diff --git a/backend/tournament/service.go b/backend/tournament/service.go
new file mode 100644
index 0000000..1bc8aeb
--- /dev/null
+++ b/backend/tournament/service.go
@@ -0,0 +1,303 @@
+package tournament
+
+import (
+	"context"
+	"errors"
+
+	"github.com/jackc/pgx/v5"
+
+	"albatross-2026-backend/db"
+	"albatross-2026-backend/game"
+)
+
+type Service struct {
+	q db.Querier
+}
+
+func NewService(q db.Querier) *Service {
+	return &Service{q: q}
+}
+
+// Domain types
+
+type Player struct {
+	UserID      int
+	Username    string
+	DisplayName string
+	IconPath    *string
+	IsAdmin     bool
+	Label       *string
+}
+
+type TournamentEntry struct {
+	User Player
+	Seed int
+}
+
+type TournamentMatch struct {
+	TournamentMatchID int
+	Round             int
+	Position          int
+	GameID            *int
+	Player1           *Player
+	Player2           *Player
+	Player1Score      *int
+	Player2Score      *int
+	WinnerUserID      *int
+	IsBye             bool
+}
+
+type TournamentBracket struct {
+	TournamentID int
+	DisplayName  string
+	BracketSize  int
+	NumRounds    int
+	Entries      []TournamentEntry
+	Matches      []TournamentMatch
+}
+
+// StandardBracketSeeds returns the seed assignments for each slot in a standard
+// single-elimination bracket.
+func StandardBracketSeeds(bracketSize int) []int {
+	seeds := make([]int, bracketSize)
+	seeds[0] = 1
+	for size := 2; size <= bracketSize; size *= 2 {
+		temp := make([]int, size)
+		for i := 0; i < size/2; i++ {
+			temp[i*2] = seeds[i]
+			temp[i*2+1] = size + 1 - seeds[i]
+		}
+		copy(seeds, temp)
+	}
+	return seeds
+}
+
+func findSeedByUserID(entries []TournamentEntry, userID int) int {
+	for _, e := range entries {
+		if e.User.UserID == userID {
+			return e.Seed
+		}
+	}
+	return 0
+}
+
+func (s *Service) GetTournament(ctx context.Context, tournamentID int) (TournamentBracket, error) {
+	t, err := s.q.GetTournamentByID(ctx, int32(tournamentID))
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return TournamentBracket{}, game.ErrNotFound
+		}
+		return TournamentBracket{}, err
+	}
+
+	entryRows, err := s.q.ListTournamentEntries(ctx, int32(tournamentID))
+	if err != nil {
+		return TournamentBracket{}, err
+	}
+
+	seedToUser := make(map[int]Player)
+	entries := make([]TournamentEntry, len(entryRows))
+	for i, e := range entryRows {
+		u := Player{
+			UserID:      int(e.UserID),
+			Username:    e.Username,
+			DisplayName: e.DisplayName,
+			IconPath:    e.IconPath,
+			IsAdmin:     e.IsAdmin,
+			Label:       e.Label,
+		}
+		seedToUser[int(e.Seed)] = u
+		entries[i] = TournamentEntry{
+			User: u,
+			Seed: int(e.Seed),
+		}
+	}
+
+	matchRows, err := s.q.ListTournamentMatches(ctx, int32(tournamentID))
+	if err != nil {
+		return TournamentBracket{}, err
+	}
+
+	bracketSize := int(t.BracketSize)
+	numRounds := int(t.NumRounds)
+	bracketSeeds := StandardBracketSeeds(bracketSize)
+
+	// Index matches by (round, position)
+	type matchKey struct{ round, position int }
+	matchByKey := make(map[matchKey]db.TournamentMatch)
+	for _, m := range matchRows {
+		matchByKey[matchKey{int(m.Round), int(m.Position)}] = m
+	}
+
+	// Collect game IDs for batch fetching
+	gameIDs := make(map[int32]bool)
+	for _, m := range matchRows {
+		if m.GameID != nil {
+			gameIDs[*m.GameID] = true
+		}
+	}
+
+	// Fetch rankings for all games that have started
+	type rankingResult struct {
+		scores   map[int]int // userID -> score
+		winnerID int
+	}
+	gameRankings := make(map[int32]*rankingResult)
+	for gid := range gameIDs {
+		gameRow, err := s.q.GetGameByID(ctx, gid)
+		if err != nil {
+			continue
+		}
+		if !gameRow.StartedAt.Valid {
+			continue
+		}
+		rankingRows, err := s.q.GetRanking(ctx, gid)
+		if err != nil || len(rankingRows) == 0 {
+			continue
+		}
+		rr := &rankingResult{scores: make(map[int]int)}
+		for i, r := range rankingRows {
+			rr.scores[int(r.User.UserID)] = int(r.Submission.CodeSize)
+			if i == 0 {
+				rr.winnerID = int(r.User.UserID)
+			}
+		}
+		gameRankings[gid] = rr
+	}
+
+	// Build match results bottom-up
+	type matchResult struct {
+		player1   *Player
+		player2   *Player
+		p1Score   *int
+		p2Score   *int
+		winnerUID *int
+		isBye     bool
+	}
+	resultByKey := make(map[matchKey]*matchResult)
+
+	for round := range numRounds {
+		numPositions := bracketSize / (1 << (round + 1))
+		for pos := range numPositions {
+			m, exists := matchByKey[matchKey{round, pos}]
+			mr := &matchResult{}
+
+			if round == 0 {
+				slot1 := pos * 2
+				slot2 := pos*2 + 1
+				seed1 := bracketSeeds[slot1]
+				seed2 := bracketSeeds[slot2]
+
+				if u, ok := seedToUser[seed1]; ok {
+					mr.player1 = &u
+				}
+				if u, ok := seedToUser[seed2]; ok {
+					mr.player2 = &u
+				}
+			} else {
+				child1 := resultByKey[matchKey{round - 1, pos * 2}]
+				child2 := resultByKey[matchKey{round - 1, pos*2 + 1}]
+
+				if child1 != nil && child1.winnerUID != nil {
+					if u, ok := seedToUser[findSeedByUserID(entries, *child1.winnerUID)]; ok {
+						mr.player1 = &u
+					}
+				}
+				if child2 != nil && child2.winnerUID != nil {
+					if u, ok := seedToUser[findSeedByUserID(entries, *child2.winnerUID)]; ok {
+						mr.player2 = &u
+					}
+				}
+			}
+
+			// Check for bye
+			if mr.player1 == nil && mr.player2 != nil {
+				mr.isBye = true
+				uid := mr.player2.UserID
+				mr.winnerUID = &uid
+			} else if mr.player1 != nil && mr.player2 == nil {
+				mr.isBye = true
+				uid := mr.player1.UserID
+				mr.winnerUID = &uid
+			}
+
+			// Resolve scores from game
+			if exists && m.GameID != nil && !mr.isBye {
+				if rr, ok := gameRankings[*m.GameID]; ok {
+					if mr.player1 != nil {
+						if s, ok := rr.scores[mr.player1.UserID]; ok {
+							score := s
+							mr.p1Score = &score
+						}
+					}
+					if mr.player2 != nil {
+						if s, ok := rr.scores[mr.player2.UserID]; ok {
+							score := s
+							mr.p2Score = &score
+						}
+					}
+					if mr.player1 != nil && mr.player2 != nil {
+						if rr.winnerID == mr.player1.UserID || rr.winnerID == mr.player2.UserID {
+							w := rr.winnerID
+							mr.winnerUID = &w
+						} else {
+							if mr.p1Score != nil && mr.p2Score != nil {
+								if *mr.p1Score <= *mr.p2Score {
+									w := mr.player1.UserID
+									mr.winnerUID = &w
+								} else {
+									w := mr.player2.UserID
+									mr.winnerUID = &w
+								}
+							}
+						}
+					}
+				}
+			}
+
+			resultByKey[matchKey{round, pos}] = mr
+		}
+	}
+
+	// Build response matches
+	apiMatches := make([]TournamentMatch, 0, len(matchRows))
+	for round := 0; round < numRounds; round++ {
+		numPositions := bracketSize / (1 << (round + 1))
+		for pos := 0; pos < numPositions; pos++ {
+			m, exists := matchByKey[matchKey{round, pos}]
+			mr := resultByKey[matchKey{round, pos}]
+
+			matchID := 0
+			var gameID *int
+			if exists {
+				matchID = int(m.TournamentMatchID)
+				if m.GameID != nil {
+					gid := int(*m.GameID)
+					gameID = &gid
+				}
+			}
+
+			apiMatches = append(apiMatches, TournamentMatch{
+				TournamentMatchID: matchID,
+				Round:             round,
+				Position:          pos,
+				GameID:            gameID,
+				Player1:           mr.player1,
+				Player2:           mr.player2,
+				Player1Score:      mr.p1Score,
+				Player2Score:      mr.p2Score,
+				WinnerUserID:      mr.winnerUID,
+				IsBye:             mr.isBye,
+			})
+		}
+	}
+
+	return TournamentBracket{
+		TournamentID: int(t.TournamentID),
+		DisplayName:  t.DisplayName,
+		BracketSize:  bracketSize,
+		NumRounds:    numRounds,
+		Entries:      entries,
+		Matches:      apiMatches,
+	}, nil
+}
diff --git a/backend/tournament/service_test.go b/backend/tournament/service_test.go
new file mode 100644
index 0000000..d1ca78c
--- /dev/null
+++ b/backend/tournament/service_test.go
@@ -0,0 +1,97 @@
+package tournament
+
+import "testing"
+
+func TestStandardBracketSeeds(t *testing.T) {
+	tests := []struct {
+		name        string
+		bracketSize int
+		expected    []int
+	}{
+		{
+			name:        "bracket_size=2",
+			bracketSize: 2,
+			expected:    []int{1, 2},
+		},
+		{
+			name:        "bracket_size=4",
+			bracketSize: 4,
+			expected:    []int{1, 4, 2, 3},
+		},
+		{
+			name:        "bracket_size=8",
+			bracketSize: 8,
+			expected:    []int{1, 8, 4, 5, 2, 7, 3, 6},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := StandardBracketSeeds(tt.bracketSize)
+			if len(got) != len(tt.expected) {
+				t.Fatalf("expected length %d, got %d", len(tt.expected), len(got))
+			}
+			for i, v := range tt.expected {
+				if got[i] != v {
+					t.Errorf("position %d: expected seed %d, got %d", i, v, got[i])
+				}
+			}
+		})
+	}
+}
+
+func TestStandardBracketSeeds_Seed1And2OppositeSides(t *testing.T) {
+	seeds := StandardBracketSeeds(8)
+	seed1Pos := -1
+	seed2Pos := -1
+	for i, s := range seeds {
+		if s == 1 {
+			seed1Pos = i
+		}
+		if s == 2 {
+			seed2Pos = i
+		}
+	}
+	if seed1Pos >= 4 {
+		t.Errorf("Seed 1 should be in first half, but at position %d", seed1Pos)
+	}
+	if seed2Pos < 4 {
+		t.Errorf("Seed 2 should be in second half, but at position %d", seed2Pos)
+	}
+}
+
+func TestStandardBracketSeeds_AllSeedsPresent(t *testing.T) {
+	for _, size := range []int{2, 4, 8, 16} {
+		seeds := StandardBracketSeeds(size)
+		seen := make(map[int]bool)
+		for _, s := range seeds {
+			if s < 1 || s > size {
+				t.Errorf("bracket_size=%d: seed %d out of range", size, s)
+			}
+			if seen[s] {
+				t.Errorf("bracket_size=%d: duplicate seed %d", size, s)
+			}
+			seen[s] = true
+		}
+		if len(seen) != size {
+			t.Errorf("bracket_size=%d: expected %d unique seeds, got %d", size, size, len(seen))
+		}
+	}
+}
+
+func TestFindSeedByUserID(t *testing.T) {
+	entries := []TournamentEntry{
+		{User: Player{UserID: 10}, Seed: 1},
+		{User: Player{UserID: 20}, Seed: 2},
+		{User: Player{UserID: 30}, Seed: 3},
+	}
+
+	if got := findSeedByUserID(entries, 10); got != 1 {
+		t.Errorf("expected seed 1 for user 10, got %d", got)
+	}
+	if got := findSeedByUserID(entries, 20); got != 2 {
+		t.Errorf("expected seed 2 for user 20, got %d", got)
+	}
+	if got := findSeedByUserID(entries, 999); got != 0 {
+		t.Errorf("expected seed 0 for unknown user, got %d", got)
+	}
+}