harden(gateway): constrain service-account role/identity_mode at API boundary (Stage 1 PR4)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/gateway/routers/service_accounts.py

@@ -7,6 +7,8 @@ cross-workspace targets return 404 (existence hidden).
 
 from __future__ import annotations
 
+from typing import Literal
+
 from fastapi import APIRouter, Depends, HTTPException, Request
 from pydantic import BaseModel, Field
 
@@ -19,8 +21,11 @@ router = APIRouter(prefix="/api/v1/service-accounts", tags=["service-accounts"])
 
 class CreateServiceAccountRequest(BaseModel):
     name: str = Field(..., min_length=1, max_length=64)
-    role: str = Field(default="member")
-    identity_mode: str = Field(default="collapsed")
+    # Constrained to Stage-1-supported values; widen these Literals in
+    # future stages alongside the behavior (Stage 2 RBAC opens role
+    # admin/viewer; the passthrough PR opens identity_mode).
+    role: Literal["member"] = "member"
+    identity_mode: Literal["collapsed"] = "collapsed"
 
 
 class UpdateServiceAccountRequest(BaseModel):

backend/tests/test_service_accounts_router.py

@@ -121,3 +121,26 @@ async def test_patch_other_workspace_sa_404(tmp_path):
         assert r.status_code == 404
     finally:
         await _cleanup()
+
+
+async def test_list_is_scoped_to_current_workspace(tmp_path):
+    await _init_db(tmp_path)
+    try:
+        w1 = TestClient(_make_app(role="owner", workspace_id="w-1"))
+        w1.post("/api/v1/service-accounts", json={"name": "bot-w1"})
+        # A caller in w-2 must NOT see w-1's service accounts.
+        w2 = TestClient(_make_app(role="owner", workspace_id="w-2"))
+        rows = w2.get("/api/v1/service-accounts").json()
+        assert rows == []
+    finally:
+        await _cleanup()
+
+
+async def test_create_rejects_unknown_role(tmp_path):
+    await _init_db(tmp_path)
+    try:
+        client = TestClient(_make_app(role="owner"))
+        r = client.post("/api/v1/service-accounts", json={"name": "x", "role": "superadmin"})
+        assert r.status_code == 422
+    finally:
+        await _cleanup()