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>

1 files changed, 4 insertions, 30 deletions

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
-}