diff --git a/client/public/version.js b/client/public/version.js
index 9fd78f2..cffa6dc 100644
--- a/client/public/version.js
+++ b/client/public/version.js
@@ -1,6 +1,6 @@
 // Maintainer-controlled web client version metadata.
 window.CHGRID_RELEASE_VERSION = "0.1.0";
-window.CHGRID_BUILD_REVISION = "R342";
+window.CHGRID_BUILD_REVISION = "R343";
 window.CHGRID_WEB_VERSION = `${window.CHGRID_RELEASE_VERSION} ${window.CHGRID_BUILD_REVISION}`;
 // Optional display timezone for timestamps. Falls back to America/Detroit if unset/invalid.
 window.CHGRID_TIME_ZONE = "America/Detroit";
diff --git a/docs/protocol-notes.md b/docs/protocol-notes.md
index 022e3e0..1d260bc 100644
--- a/docs/protocol-notes.md
+++ b/docs/protocol-notes.md
@@ -96,7 +96,7 @@ This is a behavior guide for packet semantics beyond raw schemas.
   - `policy` (`usernameMinLength`, `usernameMaxLength`, `passwordMinLength`, `passwordMaxLength`)
 - `auth_required.authPolicy`: server auth limits advertised before login/register submit.
 - `auth_result.authPolicy`: server auth limits echoed on auth success/failure responses.
-- `auth_result.sessionToken` is used by the client to call the instance-scoped HTTP endpoint `GET <base_path>auth/session/set` (`Authorization: Bearer <sessionToken>`, `X-Chgrid-Auth-Client: 1`) so the server can issue `Set-Cookie: chgrid_session_token=...; HttpOnly`.
+- `auth_result.sessionToken` is used by the client to call the instance-scoped HTTP endpoint `GET <base_path>auth/session/set` (`Authorization: Bearer <sessionToken>`, `X-Chgrid-Auth-Client: 1`) so the server can issue an instance-scoped `HttpOnly` session cookie.
 - `welcome.worldConfig.gridSize`: server-authoritative grid size used by clients for bounds/drawing.
 - `welcome.worldConfig.movementTickMs`: server movement-rate window used for client movement pacing.
 - `welcome.worldConfig.movementMaxStepsPerTick`: max allowed grid steps per movement window.
@@ -127,7 +127,7 @@ This is a behavior guide for packet semantics beyond raw schemas.
 - Server also supports websocket handshake cookie resume:
   - accepts browser sockets only when websocket `Origin` matches `CHGRID_HOST_ORIGIN`
   - websocket and auth helper routes are scoped under the configured `server.base_path`
-  - reads `chgrid_session_token` from websocket `Cookie` header
+  - reads the instance-scoped session cookie from the websocket `Cookie` header
   - attempts resume before sending `auth_required`
   - exposes `GET <base_path>auth/session/clear` to expire the `HttpOnly` cookie (`X-Chgrid-Auth-Client: 1` and matching `Origin` required)
 - Server applies auth hardening before accepting login/register/resume:
diff --git a/docs/runtime-flow.md b/docs/runtime-flow.md
index 891e47d..9fa6c0b 100644
--- a/docs/runtime-flow.md
+++ b/docs/runtime-flow.md
@@ -5,7 +5,7 @@
 1. User clicks connect.
 2. Client validates auth form and sets up local media.
 3. Client connects signaling websocket from the configured app origin.
-4. Server accepts the socket only on the configured instance websocket path and when the browser `Origin` matches `CHGRID_HOST_ORIGIN`, then attempts cookie-based session resume from websocket handshake cookie (`chgrid_session_token`).
+4. Server accepts the socket only on the configured instance websocket path and when the browser `Origin` matches `CHGRID_HOST_ORIGIN`, then attempts cookie-based session resume from the instance-scoped websocket handshake cookie.
 5. If resume does not authenticate, server sends `auth_required`.
    - includes `authPolicy` limits for username/password.
 6. Client sends `auth_login` or `auth_register` (or explicit `auth_resume` if provided by caller).
diff --git a/server/app/server.py b/server/app/server.py
index 3cc8a69..281d85a 100644
--- a/server/app/server.py
+++ b/server/app/server.py
@@ -193,6 +193,7 @@ class SignalingServer:
         self.server_version = self._resolve_server_version()
         self.host_origin = normalize_origin(host_origin, field_name="host origin") if host_origin else None
         self.base_path = self._normalize_base_path(base_path)
+        self.auth_session_cookie_name = self._session_cookie_name_for_base_path(self.base_path)
         self.websocket_path = self._base_path_join(WEBSOCKET_PATH)
         self.auth_session_cookie_set_path = self._base_path_join(AUTH_SESSION_COOKIE_SET_PATH)
         self.auth_session_cookie_clear_path = self._base_path_join(AUTH_SESSION_COOKIE_CLEAR_PATH)
@@ -287,6 +288,17 @@ class SignalingServer:
             return f"/{token}"
         return f"{self.base_path}{token}"
 
+    @staticmethod
+    def _session_cookie_name_for_base_path(base_path: str) -> str:
+        """Return one deterministic session cookie name for the configured instance path."""
+
+        if base_path == "/":
+            return AUTH_SESSION_COOKIE_NAME
+        suffix = re.sub(r"[^a-z0-9]+", "_", base_path.strip("/").casefold()).strip("_")
+        if not suffix:
+            return AUTH_SESSION_COOKIE_NAME
+        return f"chgrid_session_{suffix}"
+
     def _session_cookie_secure(self, request: HttpRequest | None = None) -> bool:
         """Return True when session cookies should be marked Secure."""
 
@@ -302,7 +314,7 @@ class SignalingServer:
 
         secure = "; Secure" if self._session_cookie_secure(request) else ""
         return (
-            f"{AUTH_SESSION_COOKIE_NAME}={token}; Path={self.base_path}; HttpOnly; SameSite=Lax; "
+            f"{self.auth_session_cookie_name}={token}; Path={self.base_path}; HttpOnly; SameSite=Lax; "
             f"Max-Age={AUTH_SESSION_COOKIE_MAX_AGE_SECONDS}{secure}"
         )
 
@@ -310,7 +322,7 @@ class SignalingServer:
         """Build Set-Cookie header value that expires the session cookie."""
 
         secure = "; Secure" if self._session_cookie_secure(request) else ""
-        return f"{AUTH_SESSION_COOKIE_NAME}=; Path={self.base_path}; HttpOnly; SameSite=Lax; Max-Age=0{secure}"
+        return f"{self.auth_session_cookie_name}=; Path={self.base_path}; HttpOnly; SameSite=Lax; Max-Age=0{secure}"
 
     def _origin_allowed(self, request: HttpRequest) -> bool:
         """Return whether one auth helper HTTP request comes from the configured app origin."""
@@ -364,7 +376,7 @@ class SignalingServer:
 
         if path == self.auth_session_cookie_check_path:
             cookie_header = str(request.headers.get("Cookie", "")).strip()
-            token = self._cookie_value(cookie_header, AUTH_SESSION_COOKIE_NAME)
+            token = self._cookie_value(cookie_header, self.auth_session_cookie_name)
             if not token:
                 return HttpResponse(401, "Unauthorized", headers, b"missing session")
             try:
@@ -400,7 +412,7 @@ class SignalingServer:
         cookie_header = str(headers.get("Cookie", "")).strip()
         if not cookie_header:
             return ""
-        return self._cookie_value(cookie_header, AUTH_SESSION_COOKIE_NAME)
+        return self._cookie_value(cookie_header, self.auth_session_cookie_name)
 
     def _build_admin_menu_actions_for_client(self, client: ClientConnection | None) -> list[dict[str, str]]:
         """Build server-authored admin menu actions allowed for one client."""
diff --git a/server/tests/test_http_session_cookie.py b/server/tests/test_http_session_cookie.py
index bbe89f4..f1fc8f0 100644
--- a/server/tests/test_http_session_cookie.py
+++ b/server/tests/test_http_session_cookie.py
@@ -11,7 +11,6 @@ from app.server import (
     AUTH_SESSION_COOKIE_CLIENT_HEADER,
     AUTH_SESSION_COOKIE_CHECK_PATH,
     AUTH_SESSION_COOKIE_CLEAR_PATH,
-    AUTH_SESSION_COOKIE_NAME,
     AUTH_SESSION_COOKIE_SET_PATH,
     SignalingServer,
 )
@@ -47,7 +46,7 @@ async def test_session_cookie_set_endpoint_sets_httponly_cookie() -> None:
     assert response is not None
     assert response.status_code == 200
     set_cookie = response.headers.get("Set-Cookie", "")
-    assert f"{AUTH_SESSION_COOKIE_NAME}=" in set_cookie
+    assert f"{server.auth_session_cookie_name}=" in set_cookie
     assert "Path=/chgrid/" in set_cookie
     assert "HttpOnly" in set_cookie
     assert "SameSite=Lax" in set_cookie
@@ -66,7 +65,7 @@ async def test_session_cookie_clear_endpoint_expires_cookie() -> None:
     assert response is not None
     assert response.status_code == 200
     set_cookie = response.headers.get("Set-Cookie", "")
-    assert f"{AUTH_SESSION_COOKIE_NAME}=" in set_cookie
+    assert f"{server.auth_session_cookie_name}=" in set_cookie
     assert "Max-Age=0" in set_cookie
     assert "HttpOnly" in set_cookie
 
@@ -80,7 +79,7 @@ async def test_session_cookie_check_endpoint_accepts_valid_cookie() -> None:
         server.auth_session_cookie_check_path,
         headers={
             AUTH_SESSION_COOKIE_CLIENT_HEADER: "1",
-            "Cookie": f"{AUTH_SESSION_COOKIE_NAME}={session.token}",
+            "Cookie": f"{server.auth_session_cookie_name}={session.token}",
             "Origin": "https://example.com",
         },
     )
@@ -120,13 +119,21 @@ async def test_session_cookie_helpers_reject_wrong_origin() -> None:
 
 
 def test_session_token_from_websocket_cookie_reads_named_cookie() -> None:
-    server = SignalingServer("127.0.0.1", 8765, None, None)
+    server = SignalingServer("127.0.0.1", 8765, None, None, base_path="/chgrid/")
     websocket = SimpleNamespace(
         request=SimpleNamespace(
-            headers=Headers({"Cookie": f"foo=bar; {AUTH_SESSION_COOKIE_NAME}=abc123; hello=world"})
+            headers=Headers({"Cookie": f"foo=bar; {server.auth_session_cookie_name}=abc123; hello=world"})
         )
     )
 
     token = server._session_token_from_websocket_cookie(websocket)
 
     assert token == "abc123"
+
+
+def test_session_cookie_name_scopes_to_base_path() -> None:
+    root_server = SignalingServer("127.0.0.1", 8765, None, None, base_path="/")
+    nested_server = SignalingServer("127.0.0.1", 8765, None, None, base_path="/ttgrid/")
+
+    assert root_server.auth_session_cookie_name == "chgrid_session_token"
+    assert nested_server.auth_session_cookie_name == "chgrid_session_ttgrid"