feat(auth): AuthMiddleware injects workspace ContextVar from JWT wid/role

deps.get_current_user_from_request now stashes the decoded payload on
request.state.auth_payload so AuthMiddleware can populate the
workspace_context ContextVar without a second decode. Reset is paired
in the same try/finally as user_context to keep teardown atomic.

Also adds:
- auth.models.ActiveWorkspace — minimal proxy that satisfies the
  CurrentWorkspace protocol (id + role only).
- auth.models.User.default_workspace_id — surfaces the DB column added
  in T4.4 so the eventual /auth/me payload can reference it.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/gateway/auth/models.py

@@ -31,6 +31,12 @@ class User(BaseModel):
     needs_setup: bool = Field(default=False, description="True for auto-created admin until setup completes")
     token_version: int = Field(default=0, description="Incremented on password change to invalidate old JWTs")
 
+    # Workspace linkage (Stage 0 PR4)
+    default_workspace_id: str | None = Field(
+        default=None,
+        description="The workspace the user lands in by default after login. NULL → /select-workspace.",
+    )
+
 
 class UserResponse(BaseModel):
     """Response model for user info endpoint."""
@@ -39,3 +45,18 @@ class UserResponse(BaseModel):
     email: str
     system_role: Literal["admin", "user"]
     needs_setup: bool = False
+
+
+class ActiveWorkspace(BaseModel):
+    """Lightweight workspace proxy injected into the request-scoped contextvar.
+
+    Implements the structural ``CurrentWorkspace`` protocol expected by
+    ``deerflow.runtime.workspace_context``: only ``.id`` (str) and
+    ``.role`` (str) are required. We intentionally do *not* embed the
+    full ``WorkspaceRow`` here — the middleware needs to set the
+    contextvar on every request and an extra DB lookup just to populate
+    a name/slug we don't use yet would be wasted work.
+    """
+
+    id: str
+    role: str

backend/app/gateway/auth_middleware.py

@@ -17,9 +17,11 @@ from starlette.responses import JSONResponse
 from starlette.types import ASGIApp
 
 from app.gateway.auth.errors import AuthErrorCode, AuthErrorResponse
+from app.gateway.auth.models import ActiveWorkspace
 from app.gateway.authz import _ALL_PERMISSIONS, AuthContext
 from app.gateway.internal_auth import INTERNAL_AUTH_HEADER_NAME, get_internal_user, is_valid_internal_auth_token
 from deerflow.runtime.user_context import reset_current_user, set_current_user
+from deerflow.runtime.workspace_context import reset_current_workspace, set_current_workspace
 
 # Paths that never require authentication.
 _PUBLIC_PATH_PREFIXES: tuple[str, ...] = (
@@ -119,8 +121,22 @@ class AuthMiddleware(BaseHTTPMiddleware):
         # JWT-decode + DB-lookup pipeline a second time per request).
         request.state.user = user
         request.state.auth = AuthContext(user=user, permissions=_ALL_PERMISSIONS)
-        token = set_current_user(user)
+        user_token = set_current_user(user)
+
+        # Inject workspace contextvar from the JWT's wid/role claims.
+        # decode_token has already rejected legacy no-wid tokens upstream,
+        # so by the time we get here payload.wid is guaranteed non-None
+        # for cookie-authenticated requests. Internal-auth requests skip
+        # the workspace contextvar (they don't have a workspace scope —
+        # the internal user is a system actor).
+        ws_token = None
+        payload = getattr(request.state, "auth_payload", None)
+        if payload is not None and payload.wid is not None:
+            ws_token = set_current_workspace(ActiveWorkspace(id=payload.wid, role=payload.role or "owner"))
+
         try:
             return await call_next(request)
         finally:
-            reset_current_user(token)
+            if ws_token is not None:
+                reset_current_workspace(ws_token)
+            reset_current_user(user_token)

backend/app/gateway/deps.py

@@ -220,6 +220,10 @@ async def get_current_user_from_request(request: Request):
             detail=AuthErrorResponse(code=AuthErrorCode.TOKEN_INVALID, message="Token revoked (password changed)").model_dump(),
         )
 
+    # Stash decoded payload on request.state so AuthMiddleware can read
+    # wid/role for the workspace contextvar without a second decode.
+    request.state.auth_payload = payload
+
     return user