diff --git a/backend/README.md b/backend/README.md
index a27452e..f9181f1 100644
--- a/backend/README.md
+++ b/backend/README.md
@@ -257,7 +257,10 @@ introduce its own request/response types.
 
 Endpoints used:
 
-- `POST /api/v1/admin/init`
+- `POST /api/v1/admin/init` — the runtime worker passes the canonical
+  `game_id` (the same UUID that names the engine container and the
+  host bind-mount directory) in the request body so the engine's
+  `state.json` shares identity with the backend's `games.game_id`.
 - `GET  /api/v1/admin/status`
 - `PUT  /api/v1/admin/turn`
 - `POST /api/v1/admin/race/banish`
diff --git a/backend/docs/flows.md b/backend/docs/flows.md
index 6ae5aba..c6b91ef 100644
--- a/backend/docs/flows.md
+++ b/backend/docs/flows.md
@@ -234,8 +234,8 @@ sequenceDiagram
 
     Workers->>Docker: pull / create / start engine container
     Docker-->>Workers: container id
-    Workers->>Engine: POST /api/v1/admin/init
-    Engine-->>Workers: ok / error
+    Workers->>Engine: POST /api/v1/admin/init {gameId, races}
+    Engine-->>Workers: StateResponse{id == gameId} / error
     Workers->>Runtime: write runtime_records (running or start_failed)
     Workers->>Lobby: OnRuntimeJobResult
 
diff --git a/backend/docs/runtime.md b/backend/docs/runtime.md
index 0969019..bd500f4 100644
--- a/backend/docs/runtime.md
+++ b/backend/docs/runtime.md
@@ -141,7 +141,10 @@ boot).
   polls the engine `/healthz` until the listener is bound (Docker
   marks a container running as soon as the entrypoint starts; the
   Go binary inside takes a moment to bind its TCP port). Only after
-  `/healthz` succeeds does the worker call `/admin/init`.
+  `/healthz` succeeds does the worker call `/admin/init`, passing the
+  same `game_id` the backend uses to mount the engine's storage
+  directory; the engine echoes it back in `StateResponse.id`. The
+  engine rejects a mismatched gameId with `409 Conflict`.
 - **Runtime scheduler** (`internal/runtime.SchedulerComponent`) —
   `pkg/cronutil` schedule per running game; each tick invokes the
   engine `admin/turn`. Force-next-turn flips a one-shot skip flag in
diff --git a/backend/internal/engineclient/client_test.go b/backend/internal/engineclient/client_test.go
index 6819f2f..f6f3c10 100644
--- a/backend/internal/engineclient/client_test.go
+++ b/backend/internal/engineclient/client_test.go
@@ -26,6 +26,7 @@ func newTestClient(t *testing.T, srv *httptest.Server) *Client {
 
 func TestClientInitSuccess(t *testing.T) {
 	wantID := uuid.New()
+	var gotReq rest.InitRequest
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.URL.Path != pathAdminInit {
 			t.Fatalf("unexpected path: %s", r.URL.Path)
@@ -33,13 +34,16 @@ func TestClientInitSuccess(t *testing.T) {
 		if r.Method != http.MethodPost {
 			t.Fatalf("unexpected method: %s", r.Method)
 		}
+		if err := json.NewDecoder(r.Body).Decode(&gotReq); err != nil {
+			t.Fatalf("decode request: %v", err)
+		}
 		w.Header().Set("Content-Type", "application/json")
 		_ = json.NewEncoder(w).Encode(rest.StateResponse{ID: wantID, Turn: 1, Players: []rest.PlayerState{{ID: uuid.New(), RaceName: "alpha"}}})
 	}))
 	t.Cleanup(srv.Close)
 
 	cli := newTestClient(t, srv)
-	got, err := cli.Init(context.Background(), srv.URL, rest.InitRequest{Races: []rest.InitRace{{RaceName: "alpha"}}})
+	got, err := cli.Init(context.Background(), srv.URL, rest.InitRequest{GameID: wantID, Races: []rest.InitRace{{RaceName: "alpha"}}})
 	if err != nil {
 		t.Fatalf("Init returned error: %v", err)
 	}
@@ -49,6 +53,9 @@ func TestClientInitSuccess(t *testing.T) {
 	if got.Turn != 1 {
 		t.Fatalf("Turn = %d, want 1", got.Turn)
 	}
+	if gotReq.GameID != wantID {
+		t.Fatalf("request gameId = %s, want %s", gotReq.GameID, wantID)
+	}
 }
 
 func TestClientInitValidationError(t *testing.T) {
diff --git a/backend/internal/runtime/service.go b/backend/internal/runtime/service.go
index a7d13e8..c39099b 100644
--- a/backend/internal/runtime/service.go
+++ b/backend/internal/runtime/service.go
@@ -607,7 +607,7 @@ func (s *Service) runStart(ctx context.Context, op OperationLog) error {
 		return err
 	}
 
-	initResp, err := s.deps.Engine.Init(ctx, runResult.EngineEndpoint, rest.InitRequest{Races: races})
+	initResp, err := s.deps.Engine.Init(ctx, runResult.EngineEndpoint, rest.InitRequest{GameID: gameID, Races: races})
 	if err != nil {
 		s.deps.Logger.Warn("engine init failed",
 			zap.String("game_id", gameID.String()),
diff --git a/backend/internal/runtime/service_e2e_test.go b/backend/internal/runtime/service_e2e_test.go
index 78362c6..e441609 100644
--- a/backend/internal/runtime/service_e2e_test.go
+++ b/backend/internal/runtime/service_e2e_test.go
@@ -203,6 +203,13 @@ func TestServiceStartGameEndToEnd(t *testing.T) {
 		case "/healthz":
 			w.WriteHeader(http.StatusOK)
 		case "/api/v1/admin/init":
+			var got rest.InitRequest
+			if err := json.NewDecoder(r.Body).Decode(&got); err != nil {
+				t.Errorf("decode init request: %v", err)
+			}
+			if got.GameID != gameID {
+				t.Errorf("init request gameId = %s, want %s", got.GameID, gameID)
+			}
 			_ = json.NewEncoder(w).Encode(rest.StateResponse{ID: gameID, Turn: 0, Players: []rest.PlayerState{{RaceName: "Alpha", Planets: 3, Population: 10}}})
 		case "/api/v1/admin/status":
 			_ = json.NewEncoder(w).Encode(rest.StateResponse{ID: gameID, Turn: 1, Players: []rest.PlayerState{{RaceName: "Alpha", Planets: 5, Population: 12}}})
diff --git a/docs/ARCHITECTURE.md b/docs/ARCHITECTURE.md
index ecbed78..748ad81 100644
--- a/docs/ARCHITECTURE.md
+++ b/docs/ARCHITECTURE.md
@@ -402,6 +402,14 @@ Container state is owned by `backend/internal/runtime`:
   always `http://galaxy-game-{game_id}:8080`.
 - Engine probes (`/healthz`) feed `runtime` health observations and turn
   generation status.
+- Canonical game identity is owned by backend. The `game_id` allocated
+  at game-create time is reused everywhere downstream: it names the
+  container, the host bind-mount directory, and is passed verbatim to
+  the engine in `POST /api/v1/admin/init`'s `gameId` field. The engine
+  persists this value into `state.json` and echoes it in every
+  `StateResponse`; the engine never mints its own game UUID. A zero
+  UUID or a conflict with an existing `state.json` is rejected by the
+  engine (`400` / `409` respectively).
 
 ## 10. Geo Profile (reduced)
 
diff --git a/game/README.md b/game/README.md
index bf3baa7..e30ace4 100644
--- a/game/README.md
+++ b/game/README.md
@@ -43,7 +43,7 @@ described below. Endpoints split into two route classes:
 
 | Class | Path | Caller | Purpose |
 | --- | --- | --- | --- |
-| Admin (GM-only) | `POST /api/v1/admin/init` | `Game Master` | Initialise the engine with the race roster. |
+| Admin (GM-only) | `POST /api/v1/admin/init` | `Game Master` | Initialise the engine with a canonical `gameId` and the race roster. |
 | Admin (GM-only) | `GET /api/v1/admin/status` | `Game Master` | Read the full game state. |
 | Admin (GM-only) | `PUT /api/v1/admin/turn` | `Game Master` | Generate the next turn. |
 | Admin (GM-only) | `POST /api/v1/admin/race/banish` | `Game Master` | Deactivate a race after a permanent platform removal. |
@@ -65,6 +65,24 @@ Documented in [`openapi.yaml`](openapi.yaml). When the engine has not been
 initialised through `POST /api/v1/admin/init`, game endpoints respond
 `501 Not Implemented` to make the uninitialised state unambiguous.
 
+### `POST /api/v1/admin/init`
+
+The canonical game identity is owned by the orchestrator (`Game Master`),
+not by the engine. The request body is `{ "gameId": "<uuid>", "races": [...] }`
+where:
+
+- `gameId` is a non-zero UUID generated by the orchestrator before the
+  engine container is launched. The same value names the engine's host
+  storage directory and is persisted into `state.json`. The engine
+  rejects the zero UUID with `400 Bad Request` and any value that
+  conflicts with an existing `state.json` on disk with
+  `409 Conflict`. A second `init` on the same `gameId` is also
+  rejected with `409`; idempotency is not part of the contract.
+- `races` is the race roster; minimum 10 entries.
+
+On success the engine responds `201 Created` with a `StateResponse`
+whose `id` echoes the supplied `gameId`.
+
 ### `StateResponse.finished`
 
 `StateResponse` (returned by `GET /api/v1/admin/status` and
diff --git a/game/internal/controller/controller.go b/game/internal/controller/controller.go
index 542ba59..72b8f98 100644
--- a/game/internal/controller/controller.go
+++ b/game/internal/controller/controller.go
@@ -2,8 +2,10 @@ package controller
 
 import (
 	"errors"
+	"fmt"
 	"time"
 
+	e "galaxy/error"
 	"galaxy/game/internal/model/game"
 
 	"github.com/google/uuid"
@@ -87,7 +89,16 @@ type Ctrl interface {
 	PlanetRouteRemove(actor, loadType string, origin uint) error
 }
 
-func GenerateGame(configure func(*Param), races []string) (s game.State, err error) {
+// GenerateGame initialises a fresh game in storage under the supplied
+// canonical gameID. The orchestrator must allocate gameID before the
+// engine container is started and pass it here as the request body of
+// POST /api/v1/admin/init. A zero UUID is rejected with
+// ErrGameInitNilUUID; an attempt to init on top of an existing
+// state.json is rejected with ErrGameAlreadyInit.
+func GenerateGame(configure func(*Param), gameID uuid.UUID, races []string) (s game.State, err error) {
+	if gameID == uuid.Nil {
+		return game.State{}, ErrGameInitNilUUID
+	}
 	ec, err := NewRepoController(configure)
 	if err != nil {
 		return game.State{}, err
@@ -102,10 +113,26 @@ func GenerateGame(configure func(*Param), races []string) (s game.State, err err
 		}
 	}()
 
-	_, err = NewGame(ec.Repo, races)
+	if existing, loadErr := ec.Repo.LoadState(); loadErr == nil {
+		err = fmt.Errorf("%w: stored gameId=%s, requested=%s", ErrGameAlreadyInit, existing.ID, gameID)
+		return
+	} else if !isGameNotInitialized(loadErr) {
+		err = fmt.Errorf("check existing state: %w", loadErr)
+		return
+	}
+
+	_, err = NewGame(ec.Repo, gameID, races)
 	return
 }
 
+// isGameNotInitialized reports whether err is the engine's canonical
+// "no state.json on disk" signal returned by Repo.LoadState on a
+// fresh storage directory.
+func isGameNotInitialized(err error) bool {
+	var ge *e.GenericError
+	return errors.As(err, &ge) && ge.Code == e.ErrGameNotInitialized
+}
+
 func GenerateTurn(configure func(*Param)) (err error) {
 	ec, err := NewRepoController(configure)
 	if err != nil {
diff --git a/game/internal/controller/generate_game.go b/game/internal/controller/generate_game.go
index a564308..2be6528 100644
--- a/game/internal/controller/generate_game.go
+++ b/game/internal/controller/generate_game.go
@@ -11,18 +11,21 @@ import (
 	"github.com/google/uuid"
 )
 
-func NewGame(r Repo, races []string) (uuid.UUID, error) {
+// NewGame initialises a fresh game in storage under the supplied
+// gameID. The caller is expected to have validated gameID against
+// uuid.Nil and to have ruled out collisions with existing state.
+func NewGame(r Repo, gameID uuid.UUID, races []string) (uuid.UUID, error) {
 	m, err := generator.Generate(func(ms *generator.MapSetting) {
 		ms.Players = uint32(len(races))
 	})
 	if err != nil {
 		return uuid.Nil, fmt.Errorf("generate map: %s", err)
 	}
-	return newGameOnMap(r, races, m)
+	return newGameOnMap(r, gameID, races, m)
 }
 
-func newGameOnMap(r Repo, races []string, m generator.Map) (uuid.UUID, error) {
-	g, err := buildGameOnMap(races, m)
+func newGameOnMap(r Repo, gameID uuid.UUID, races []string, m generator.Map) (uuid.UUID, error) {
+	g, err := buildGameOnMap(gameID, races, m)
 	if err != nil {
 		return uuid.Nil, err
 	}
@@ -38,14 +41,10 @@ func newGameOnMap(r Repo, races []string, m generator.Map) (uuid.UUID, error) {
 	return g.ID, nil
 }
 
-func buildGameOnMap(races []string, m generator.Map) (*game.Game, error) {
+func buildGameOnMap(gameID uuid.UUID, races []string, m generator.Map) (*game.Game, error) {
 	if len(races) != len(m.HomePlanets) {
 		return nil, fmt.Errorf("generate map: wrong number of home planets: %d, expected: %d ", len(m.HomePlanets), len(races))
 	}
-	gameID, err := uuid.NewRandom()
-	if err != nil {
-		return nil, fmt.Errorf("generate game uuid: %s", err)
-	}
 	g := &game.Game{
 		ID:   gameID,
 		Turn: 0,
diff --git a/game/internal/controller/generate_game_test.go b/game/internal/controller/generate_game_test.go
index aded8d0..d6fa684 100644
--- a/game/internal/controller/generate_game_test.go
+++ b/game/internal/controller/generate_game_test.go
@@ -28,16 +28,18 @@ func TestNewGame(t *testing.T) {
 	for i := range players {
 		races[i] = fmt.Sprintf("race_%02d", i)
 	}
+	requestedID := uuid.New()
 	assert.NoError(t, r.Lock())
-	gameID, err := controller.NewGame(r, races)
+	gameID, err := controller.NewGame(r, requestedID, races)
 	assert.NoError(t, err)
+	assert.Equal(t, requestedID, gameID, "NewGame must echo the supplied gameID")
 
 	assert.FileExists(t, filepath.Join(root, "state.json"))
 	assert.FileExists(t, filepath.Join(root, "0000/state.json"))
 
 	g, err := r.LoadState()
 	assert.NoError(t, err)
-	assert.Equal(t, gameID, g.ID)
+	assert.Equal(t, requestedID, g.ID, "persisted game.ID must match the supplied gameID")
 	assert.Equal(t, uint(0), g.Turn)
 	assert.Equal(t, players, len(g.Race))
 
@@ -68,3 +70,34 @@ func TestNewGame(t *testing.T) {
 
 	assert.NoError(t, r.Release())
 }
+
+func TestGenerateGameRejectsExistingState(t *testing.T) {
+	root, cleanup := util.CreateWorkDir(t)
+	defer cleanup()
+
+	races := make([]string, 10)
+	for i := range races {
+		races[i] = fmt.Sprintf("race_%02d", i)
+	}
+	configure := func(p *controller.Param) { p.StoragePath = root }
+
+	firstID := uuid.New()
+	_, err := controller.GenerateGame(configure, firstID, races)
+	assert.NoError(t, err)
+
+	_, err = controller.GenerateGame(configure, uuid.New(), races)
+	assert.ErrorIs(t, err, controller.ErrGameAlreadyInit)
+}
+
+func TestGenerateGameRejectsNilUUID(t *testing.T) {
+	root, cleanup := util.CreateWorkDir(t)
+	defer cleanup()
+
+	races := make([]string, 10)
+	for i := range races {
+		races[i] = fmt.Sprintf("race_%02d", i)
+	}
+
+	_, err := controller.GenerateGame(func(p *controller.Param) { p.StoragePath = root }, uuid.Nil, races)
+	assert.ErrorIs(t, err, controller.ErrGameInitNilUUID)
+}
diff --git a/game/internal/controller/init_errors.go b/game/internal/controller/init_errors.go
new file mode 100644
index 0000000..bdc8216
--- /dev/null
+++ b/game/internal/controller/init_errors.go
@@ -0,0 +1,14 @@
+package controller
+
+import "errors"
+
+// ErrGameInitNilUUID is returned by GenerateGame when the supplied
+// game UUID is the zero value. The HTTP layer maps it to 400.
+var ErrGameInitNilUUID = errors.New("game init: gameId must not be the zero UUID")
+
+// ErrGameAlreadyInit is returned by GenerateGame when the engine
+// storage directory already contains a state.json. The HTTP layer
+// maps it to 409. Repeated init on the same gameId is intentionally
+// rejected rather than treated as a no-op; full idempotency is not
+// part of the contract.
+var ErrGameAlreadyInit = errors.New("game init: game already initialized")
diff --git a/game/internal/router/handler/handler.go b/game/internal/router/handler/handler.go
index 62ccfdc..bd04ea5 100644
--- a/game/internal/router/handler/handler.go
+++ b/game/internal/router/handler/handler.go
@@ -21,7 +21,7 @@ import (
 )
 
 type CommandExecutor interface {
-	GenerateGame([]string) (rest.StateResponse, error)
+	GenerateGame(gameID uuid.UUID, races []string) (rest.StateResponse, error)
 	GenerateTurn() (rest.StateResponse, error)
 	GameState() (rest.StateResponse, error)
 	BanishRace(string) error
@@ -92,8 +92,8 @@ func (e *executor) FetchBattle(turn uint, ID uuid.UUID) (*report.BattleReport, b
 	return controller.FetchBattle(e.cfg, turn, ID)
 }
 
-func (e *executor) GenerateGame(races []string) (rest.StateResponse, error) {
-	s, err := controller.GenerateGame(e.cfg, races)
+func (e *executor) GenerateGame(gameID uuid.UUID, races []string) (rest.StateResponse, error) {
+	s, err := controller.GenerateGame(e.cfg, gameID, races)
 	if err != nil {
 		return rest.StateResponse{}, err
 	}
diff --git a/game/internal/router/handler/init.go b/game/internal/router/handler/init.go
index 7abfe78..08db7d3 100644
--- a/game/internal/router/handler/init.go
+++ b/game/internal/router/handler/init.go
@@ -1,11 +1,14 @@
 package handler
 
 import (
+	"errors"
 	"net/http"
 
+	"galaxy/game/internal/controller"
 	"galaxy/model/rest"
 
 	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
 )
 
 func InitHandler(c *gin.Context, executor CommandExecutor) {
@@ -13,15 +16,25 @@ func InitHandler(c *gin.Context, executor CommandExecutor) {
 	if errorResponse(c, c.ShouldBindJSON(&init)) {
 		return
 	}
+	if init.GameID == uuid.Nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": controller.ErrGameInitNilUUID.Error()})
+		return
+	}
 
 	races := make([]string, len(init.Races))
 	for i := range init.Races {
 		races[i] = init.Races[i].RaceName
 	}
 
-	s, err := executor.GenerateGame(races)
-	if errorResponse(c, err) {
-		return
+	s, err := executor.GenerateGame(init.GameID, races)
+	if err != nil {
+		if errors.Is(err, controller.ErrGameAlreadyInit) {
+			c.JSON(http.StatusConflict, gin.H{"error": err.Error()})
+			return
+		}
+		if errorResponse(c, err) {
+			return
+		}
 	}
 
 	c.JSON(http.StatusCreated, s)
diff --git a/game/internal/router/init_test.go b/game/internal/router/init_test.go
index 8341ccb..addc680 100644
--- a/game/internal/router/init_test.go
+++ b/game/internal/router/init_test.go
@@ -33,8 +33,7 @@ func TestInit(t *testing.T) {
 	assert.Equal(t, http.StatusCreated, w.Code, w.Body)
 	var initResponse rest.StateResponse
 	assert.NoError(t, json.Unmarshal(w.Body.Bytes(), &initResponse))
-	assert.NoError(t, uuid.Validate(initResponse.ID.String()))
-	assert.NotEqual(t, uuid.Nil, uuid.MustParse(initResponse.ID.String()))
+	assert.Equal(t, payload.GameID, initResponse.ID, "engine must echo the orchestrator-supplied gameId")
 }
 
 func TestInitValidators(t *testing.T) {
@@ -47,3 +46,39 @@ func TestInitValidators(t *testing.T) {
 
 	assert.Equal(t, http.StatusBadRequest, w.Code, w.Body)
 }
+
+func TestInitRejectsNilUUID(t *testing.T) {
+	root, cleanup := util.CreateWorkDir(t)
+	defer cleanup()
+
+	r := router.SetupRouter(handler.NewDefaultConfigExecutor(func(p *controller.Param) { p.StoragePath = root }))
+
+	payload := generateInitRequest(10)
+	payload.GameID = uuid.Nil
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("POST", "/api/v1/admin/init", asBody(payload))
+	r.ServeHTTP(w, req)
+
+	assert.Equal(t, http.StatusBadRequest, w.Code, w.Body)
+}
+
+func TestInitRejectsExistingGameWithDifferentID(t *testing.T) {
+	root, cleanup := util.CreateWorkDir(t)
+	defer cleanup()
+
+	r := router.SetupRouter(handler.NewDefaultConfigExecutor(func(p *controller.Param) { p.StoragePath = root }))
+
+	first := generateInitRequest(10)
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("POST", "/api/v1/admin/init", asBody(first))
+	r.ServeHTTP(w, req)
+	assert.Equal(t, http.StatusCreated, w.Code, w.Body)
+
+	second := generateInitRequest(10)
+	second.GameID = uuid.New()
+	w = httptest.NewRecorder()
+	req, _ = http.NewRequest("POST", "/api/v1/admin/init", asBody(second))
+	r.ServeHTTP(w, req)
+	assert.Equal(t, http.StatusConflict, w.Code, w.Body)
+}
diff --git a/game/internal/router/router_helper_test.go b/game/internal/router/router_helper_test.go
index 8b87936..e7aa8b3 100644
--- a/game/internal/router/router_helper_test.go
+++ b/game/internal/router/router_helper_test.go
@@ -86,8 +86,8 @@ func (e *dummyExecutor) Execute(command ...handler.Command) error {
 	return nil
 }
 
-func (e *dummyExecutor) GenerateGame(races []string) (rest.StateResponse, error) {
-	return rest.StateResponse{}, nil
+func (e *dummyExecutor) GenerateGame(gameID uuid.UUID, races []string) (rest.StateResponse, error) {
+	return rest.StateResponse{ID: gameID}, nil
 }
 
 func (e *dummyExecutor) GenerateTurn() (rest.StateResponse, error) {
diff --git a/game/internal/router/router_test.go b/game/internal/router/router_test.go
index 4fac54c..a8dda9a 100644
--- a/game/internal/router/router_test.go
+++ b/game/internal/router/router_test.go
@@ -15,6 +15,7 @@ import (
 	"galaxy/game/internal/router"
 
 	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -70,7 +71,8 @@ func limitTestingRouter() *gin.Engine {
 
 func generateInitRequest(races int) rest.InitRequest {
 	request := rest.InitRequest{
-		Races: make([]rest.InitRace, races),
+		GameID: uuid.New(),
+		Races:  make([]rest.InitRace, races),
 	}
 	for i := range request.Races {
 		request.Races[i] = rest.InitRace{RaceName: raceName(i)}
diff --git a/game/openapi.yaml b/game/openapi.yaml
index 42bfd75..b2208a9 100644
--- a/game/openapi.yaml
+++ b/game/openapi.yaml
@@ -69,8 +69,10 @@ paths:
       operationId: adminInitGame
       summary: Initialize a new game
       description: |
-        Generates a new game instance with the supplied list of races.
-        Requires at least 10 race entries. Routed only from the trusted
+        Generates a new game instance with the supplied canonical
+        `gameId` and list of races. Requires at least 10 race entries.
+        The engine refuses to overwrite an already-initialised storage
+        directory (responds with 409). Routed only from the trusted
         network segment that connects `Game Master` to the engine
         container.
       requestBody:
@@ -88,6 +90,8 @@ paths:
                 $ref: "#/components/schemas/StateResponse"
         "400":
           $ref: "#/components/responses/ValidationError"
+        "409":
+          $ref: "#/components/responses/ConflictError"
         "500":
           $ref: "#/components/responses/InternalError"
   /api/v1/admin/race/banish:
@@ -410,10 +414,23 @@ components:
           description: True when the race has been eliminated or voluntarily quit.
     InitRequest:
       type: object
-      description: Initialization request specifying the race list for a new game.
+      description: |
+        Initialization request specifying the canonical game identity
+        and the race list for a new game. `gameId` is generated by the
+        orchestrator (the platform's backend) before the engine
+        container is launched; the engine rejects the zero UUID and
+        any value that conflicts with an existing `state.json` on
+        disk.
       required:
+        - gameId
         - races
       properties:
+        gameId:
+          type: string
+          format: uuid
+          description: |
+            Canonical game identity supplied by the orchestrator. Must
+            be a non-zero UUID.
         races:
           type: array
           description: List of participating races. Minimum 10 entries required.
@@ -1299,6 +1316,19 @@ components:
         error:
           type: string
           description: Human-readable validation error message from the binding layer.
+    ConflictErrorResponse:
+      type: object
+      description: |
+        Conflict error returned when the engine refuses an operation
+        that would clash with persisted state. Today the only producer
+        is `POST /api/v1/admin/init` when the storage directory
+        already contains a game state.
+      required:
+        - error
+      properties:
+        error:
+          type: string
+          description: Human-readable conflict description.
     InternalErrorResponse:
       type: object
       description: |
@@ -1326,6 +1356,17 @@ components:
             validationError:
               value:
                 error: "Key: 'InitRequest.Races' Error:Field validation for 'Races' failed on the 'gte' tag"
+    ConflictError:
+      description: |
+        The requested operation conflicts with persisted engine state.
+      content:
+        application/json:
+          schema:
+            $ref: "#/components/schemas/ConflictErrorResponse"
+          examples:
+            alreadyInitialized:
+              value:
+                error: "game init: game already initialized"
     InternalError:
       description: Internal Game Service error.
       content:
diff --git a/game/openapi_contract_test.go b/game/openapi_contract_test.go
index 9f1cfac..0b12728 100644
--- a/game/openapi_contract_test.go
+++ b/game/openapi_contract_test.go
@@ -187,11 +187,23 @@ func TestGameOpenAPISpecFreezesInitRequest(t *testing.T) {
 	assertSchemaRef(t, requestSchemaRef(t, operation), "#/components/schemas/InitRequest", "init request schema")
 
 	schema := componentSchemaRef(t, doc, "InitRequest")
-	assertRequiredFields(t, schema, "races")
+	assertRequiredFields(t, schema, "gameId", "races")
+
+	gameIDSchema := schema.Value.Properties["gameId"]
+	require.NotNil(t, gameIDSchema, "InitRequest.gameId schema must exist")
+	require.True(t, gameIDSchema.Value.Type.Is("string"), "InitRequest.gameId must be string")
+	require.Equal(t, "uuid", gameIDSchema.Value.Format, "InitRequest.gameId format must be uuid")
 
 	racesSchema := schema.Value.Properties["races"]
 	require.NotNil(t, racesSchema, "InitRequest.races schema must exist")
 	require.Equal(t, uint64(10), racesSchema.Value.MinItems, "InitRequest.races minItems must be 10")
+
+	if operation.Responses == nil {
+		require.FailNow(t, "init operation is missing responses")
+	}
+	conflict := operation.Responses.Status(http.StatusConflict)
+	require.NotNil(t, conflict, "init operation must declare 409 response")
+	require.NotNil(t, conflict.Value, "init 409 response must have a value")
 }
 
 func TestGameOpenAPISpecFreezesAdminOperationIDs(t *testing.T) {
diff --git a/pkg/model/rest/init.go b/pkg/model/rest/init.go
index 1bbcf8e..d9d11ca 100644
--- a/pkg/model/rest/init.go
+++ b/pkg/model/rest/init.go
@@ -1,11 +1,22 @@
 package rest
 
+import "github.com/google/uuid"
+
+// InitRequest is the body of POST /api/v1/admin/init. The orchestrator
+// (game backend) generates GameID before launching the engine container
+// and creating the per-game storage directory, then passes the same
+// value here so the engine state and the orchestrator's persisted
+// identity stay aligned.
 type InitRequest struct {
-	// List of the Races in the Game
+	// GameID is the canonical identity of the new game. The engine
+	// rejects requests with the zero UUID and requests that conflict
+	// with an existing state.json on disk.
+	GameID uuid.UUID `json:"gameId" binding:"required"`
+	// Races lists the participating races. Minimum 10 entries.
 	Races []InitRace `json:"races" binding:"required,gte=10"`
 }
 
 type InitRace struct {
-	// Name of the Race
+	// RaceName is the human-readable name of the race.
 	RaceName string `json:"raceName" binding:"required,notblank"`
 }