diff --git a/backend/fluksio/mcp/server.py b/backend/fluksio/mcp/server.py
index 94432ce..5c7b5a8 100644
--- a/backend/fluksio/mcp/server.py
+++ b/backend/fluksio/mcp/server.py
@@ -15,12 +15,13 @@ from __future__ import annotations
 import logging
 from contextvars import ContextVar
 from typing import Any
-from urllib.parse import quote
 
 import httpx
 from mcp.server.fastmcp import FastMCP
 from mcp.server.lowlevel.server import request_ctx
 
+from fluksio.sdk.client import seg as _seg
+
 logger = logging.getLogger(__name__)
 
 mcp = FastMCP("fluksio")
@@ -86,17 +87,6 @@ async def forward_caller_auth(request: httpx.Request) -> None:
         request.headers["authorization"] = authorization
 
 
-def _seg(value: str) -> str:
-    """*value* as one path segment, and nothing more.
-
-    httpx resolves ``..`` before sending, so a name put into a path as written
-    could climb out of the route it was meant for: ``save_flow("../ai/config")``
-    was ``PUT /ai/config``. ``quote`` covers the slashes but leaves dots alone,
-    hence encoding those too; the server decodes both.
-    """
-    return quote(value, safe="").replace(".", "%2E")
-
-
 async def _call(method: str, path: str, **kwargs: Any) -> Any:
     """One REST call, with failures handed back as data rather than raised.
 
diff --git a/backend/fluksio/sdk/client.py b/backend/fluksio/sdk/client.py
index db7ad9d..0ef0ded 100644
--- a/backend/fluksio/sdk/client.py
+++ b/backend/fluksio/sdk/client.py
@@ -15,6 +15,7 @@ import uuid
 from collections.abc import Iterable
 from pathlib import Path
 from typing import Any
+from urllib.parse import quote
 
 from fluksio.sdk import MARKER, Flow, SyncError
 
@@ -27,6 +28,7 @@ __all__ = [
     "find_data_dir",
     "ignore_self",
     "login",
+    "seg",
     "sync",
     "write_config",
 ]
@@ -126,6 +128,17 @@ def _stored() -> dict[str, str]:
     return {}
 
 
+def seg(value: str) -> str:
+    """*value* as one path segment, and nothing more.
+
+    httpx resolves ``..`` before sending, so a name put into a path as written
+    could climb out of the route it was meant for: ``get_flow("../ai/config")``
+    was ``GET /ai/config``. ``quote`` covers the slashes but leaves dots alone,
+    hence encoding those too; the server decodes both.
+    """
+    return quote(value, safe="").replace(".", "%2E")
+
+
 class ApiError(Exception):
     """The engine refused, with what it said."""
 
@@ -226,7 +239,7 @@ class Client:
     def get_flow(self, name: str) -> dict[str, Any] | None:
         """The stored flow, draft included, or ``None`` if there is none."""
         try:
-            result: dict[str, Any] = self._call("GET", f"/flows/{name}")
+            result: dict[str, Any] = self._call("GET", f"/flows/{seg(name)}")
         except ApiError as exc:
             if exc.status == 404:
                 return None
@@ -235,7 +248,7 @@ class Client:
 
     def put_flow(self, document: dict[str, Any]) -> dict[str, Any]:
         result: dict[str, Any] = self._call(
-            "PUT", f"/flows/{document['name']}", json=document
+            "PUT", f"/flows/{seg(document['name'])}", json=document
         )
         return result
 
@@ -249,18 +262,20 @@ class Client:
         somebody edited: the engine answers a new-node template for both, and
         only one of them is work worth refusing to overwrite.
         """
-        result: dict[str, Any] = self._call("GET", f"/flows/{flow}/nodes/{node}/source")
+        result: dict[str, Any] = self._call(
+            "GET", f"/flows/{seg(flow)}/nodes/{seg(node)}/source"
+        )
         return result or {}
 
     def put_source(self, flow: str, node: str, code: str) -> dict[str, Any]:
         result: dict[str, Any] = self._call(
-            "PUT", f"/flows/{flow}/nodes/{node}/source", json={"code": code}
+            "PUT", f"/flows/{seg(flow)}/nodes/{seg(node)}/source", json={"code": code}
         )
         return result
 
     def publish(self, name: str, version: int) -> dict[str, Any]:
         result: dict[str, Any] = self._call(
-            "POST", f"/flows/{name}/publish", json={"version": version}
+            "POST", f"/flows/{seg(name)}/publish", json={"version": version}
         )
         return result
 
@@ -345,7 +360,7 @@ class Client:
         """
         row = self._call(
             "POST",
-            f"/runs/flows/{flow}",
+            f"/runs/flows/{seg(flow)}",
             idempotent=True,
             json={
                 "params": params or {},
@@ -371,7 +386,7 @@ class Client:
         keyed = [{**entry, "idempotency_key": uuid.uuid4().hex} for entry in entries]
         rows = self._call(
             "POST",
-            f"/runs/flows/{flow}/sweep",
+            f"/runs/flows/{seg(flow)}/sweep",
             idempotent=True,
             json={"runs": keyed, "no_cache": no_cache},
         )
@@ -397,7 +412,7 @@ class Client:
         return answers
 
     def run(self, run_id: str) -> dict[str, Any]:
-        result: dict[str, Any] = self._call("GET", f"/runs/{run_id}")
+        result: dict[str, Any] = self._call("GET", f"/runs/{seg(run_id)}")
         return result
 
     def runs(self, flow: str = "", limit: int = 20, **filters: Any) -> Any:
@@ -410,7 +425,7 @@ class Client:
         query: dict[str, Any] = {"stride": stride}
         if name:
             query["name"] = name
-        return self._call("GET", f"/runs/{run_id}/metrics", params=query)
+        return self._call("GET", f"/runs/{seg(run_id)}/metrics", params=query)
 
     def metric_names(
         self, ids: Iterable[str] = (), flow: str = "", **filters: Any
@@ -512,14 +527,14 @@ class Client:
 
     def cancel(self, run_id: str) -> Any:
         # Cancelling a cancelled run is cancelled.
-        return self._call("POST", f"/runs/{run_id}/cancel", idempotent=True)
+        return self._call("POST", f"/runs/{seg(run_id)}/cancel", idempotent=True)
 
     def retry(self, run_id: str) -> Any:
         """Submit the same run again. Not idempotent: it makes a run."""
-        return self._call("POST", f"/runs/{run_id}/retry")
+        return self._call("POST", f"/runs/{seg(run_id)}/retry")
 
     def download(self, digest: str) -> bytes:
-        response = self._request("GET", f"/artifacts/{digest}", idempotent=True)
+        response = self._request("GET", f"/artifacts/{seg(digest)}", idempotent=True)
         if response.status_code >= 400:
             raise ApiError(response.status_code, _detail(response))
         return bytes(response.content)
diff --git a/backend/tests/sdk/test_client.py b/backend/tests/sdk/test_client.py
index bab6c18..8092f7b 100644
--- a/backend/tests/sdk/test_client.py
+++ b/backend/tests/sdk/test_client.py
@@ -181,3 +181,23 @@ def test_a_history_is_imported_a_page_at_a_time(monkeypatch):
     assert [one["external_id"] for one in answers] == [
         e["external_id"] for e in entries
     ]
+
+
+def test_a_name_cannot_climb_out_of_its_route(monkeypatch):
+    """httpx resolves ``..``, so ``get_flow("../x")`` was ``GET /api/v1/x``."""
+    seen = []
+
+    def handler(request):
+        seen.append(request.url.raw_path.decode())
+        return httpx.Response(200, json={})
+
+    client = a_client(handler, monkeypatch)
+    client.get_flow("../x")
+    client.put_source("..", "../x", "code")
+    client.run("..")
+
+    assert seen == [
+        "/api/v1/flows/%2E%2E%2Fx",
+        "/api/v1/flows/%2E%2E/nodes/%2E%2E%2Fx/source",
+        "/api/v1/runs/%2E%2E",
+    ]