diff --git a/docs/skill/references/docs/guides/notebook-runtime.md b/docs/skill/references/docs/guides/notebook-runtime.md
index 44f22d2..96d35c9 100644
--- a/docs/skill/references/docs/guides/notebook-runtime.md
+++ b/docs/skill/references/docs/guides/notebook-runtime.md
@@ -167,7 +167,11 @@ sca ls [DIR]                 # the notebooks under DIR: id, part or assembly, th
 ```
 
 A **workspace** is any directory tree: its models are the notebooks whose
-header has `[tool.simplecadapi]`, wherever they are. There is no manifest.
+header has `[tool.simplecadapi]`, at any depth. There is no manifest. Skipped
+everywhere: names starting with `.` or `_`, and `node_modules`, `venv`,
+`site-packages`, `build`, `dist` — a notebook in such a place is not listed
+by `sca ls` or the editor's workspace tab, so keep notebooks in normally
+named paths.
 
 `sca edit [WORKSPACE]` (needs `pip install "simplecadapi[editor]"`) opens a
 code-first editor on a workspace. The notebooks run in a marimo kernel with
diff --git a/docs/skill/references/domains/editor-collaboration.md b/docs/skill/references/domains/editor-collaboration.md
index 3ad24e1..ab65bcd 100644
--- a/docs/skill/references/domains/editor-collaboration.md
+++ b/docs/skill/references/domains/editor-collaboration.md
@@ -35,9 +35,14 @@ sca edit <workspace> --no-browser --port 7180
 
 - Needs the `editor` extra (`pip install "simplecadapi[editor]"`); without it
   the command says so and stops.
-- The workspace is any directory tree. Models are the notebooks whose header has
-  `[tool.simplecadapi]`; assemblies list the parts they `use(...)`. Open the
-  assembly to see the product, a part to edit that part.
+- The workspace is any directory tree, scanned to any depth. Models are the
+  notebooks whose header has `[tool.simplecadapi]`; assemblies list the parts
+  they `use(...)`. Open the assembly to see the product, a part to edit that
+  part. Working in a subfolder is fine; what hides a file from the workspace
+  tab is its name: directories and files starting with `.` or `_`, and
+  anything under `node_modules`, `venv`, `site-packages`, `build` or `dist`,
+  are not listed and are never a candidate at boot. Keep notebooks and the
+  modules they import in normally named paths.
 - The URL is printed (default `http://127.0.0.1:7180`). Give it to the person.
 - To try it: `sca example u_link` copies a motor-mount workspace (two parts and
   the assembly that fixes them together) to `./u_link_motor_mount`, then
diff --git a/editor-web/src/App.tsx b/editor-web/src/App.tsx
index b92747a..9425eae 100644
--- a/editor-web/src/App.tsx
+++ b/editor-web/src/App.tsx
@@ -48,7 +48,6 @@ export function App() {
   // kernel is up, and a late answer of the workspace list cannot undo it.
   const [currentPath, setCurrentPath] = useState<string | null>(null);
   const [kernelAlive, setKernelAlive] = useState(false);
-  const [marimoUrl, setMarimoUrl] = useState<string | null>(null);
   const [status, setStatus] = useState("Connecting…");
 
   const [params, setParams] = useState<ParamMeta[]>([]);
@@ -126,7 +125,6 @@ export function App() {
       const stage = envelope["notebook"] ? (envelope["kernel"] ? "building the model" : "starting the kernel") : null;
       setLoading(stage);
       setStatus(stage ? `${stage[0].toUpperCase()}${stage.slice(1)}…` : "No notebook yet: create one in the workspace tab");
-      setMarimoUrl((envelope["marimo_url"] as string) ?? null);
       refreshWorkspace();
     });
 
@@ -335,7 +333,6 @@ export function App() {
         kind={kind}
         kernelAlive={kernelAlive}
         status={status}
-        marimoUrl={marimoUrl}
         themePreference={theme.preference}
         onTheme={theme.cycle}
         running={running}
diff --git a/editor-web/src/components/Header.tsx b/editor-web/src/components/Header.tsx
index 37a3936..4ca168c 100644
--- a/editor-web/src/components/Header.tsx
+++ b/editor-web/src/components/Header.tsx
@@ -1,4 +1,4 @@
-import { ExternalLink, Monitor, Moon, Play, Square, Sun } from "lucide-react";
+import { Monitor, Moon, Play, Square, Sun } from "lucide-react";
 
 import type { ThemePreference } from "@/lib/theme";
 
@@ -15,7 +15,6 @@ export function Header({
   onRunAll,
   running,
   onStop,
-  marimoUrl,
   themePreference,
   onTheme,
 }: {
@@ -27,7 +26,6 @@ export function Header({
   /** The kernel is running cells: the button stops them instead. */
   running: boolean;
   onStop: () => void;
-  marimoUrl: string | null;
   themePreference: ThemePreference;
   onTheme: () => void;
 }) {
@@ -63,13 +61,6 @@ export function Header({
           <Play /> run all
         </Button>
       )}
-      {marimoUrl && (
-        <Button size="sm" variant="ghost" asChild>
-          <a href={marimoUrl} target="_blank" rel="noreferrer" title="Open the raw marimo editor">
-            <ExternalLink /> marimo
-          </a>
-        </Button>
-      )}
       <Button
         size="sm"
         variant="ghost"
diff --git a/src/simplecadapi/editor/server.py b/src/simplecadapi/editor/server.py
index 3dfa5ca..02e4650 100644
--- a/src/simplecadapi/editor/server.py
+++ b/src/simplecadapi/editor/server.py
@@ -642,6 +642,7 @@ def cell_command(self, op: str, body: dict) -> dict:
         kernel = self.kernel
         if kernel is None:
             return {"error": "the editor has no kernel yet; wait for it to start"}
+        self._begin_run()
         self.push_cells()
         touched: list[str] = []
         try:
@@ -691,6 +692,7 @@ def cell_command(self, op: str, body: dict) -> dict:
         return report
 
     def _rerun_changed(self, kernel: MarimoKernel, changed: list[str]) -> None:
+        self._begin_run()
         kernel.run_until_settled(changed)
         self.schedule_settle()
 
@@ -758,6 +760,7 @@ def _propagate(self) -> None:
                     if not uses:
                         continue
                     kernel.run_until_settled(uses)
+                self._begin_run()
                 self.schedule_settle()
         except Exception as exc:
             with self._module_lock:
@@ -881,6 +884,17 @@ def hello(self) -> dict:
             "marimo_url": self.kernel.marimo_url if self.kernel else None,
         }
 
+    def settled_error(self) -> dict | None:
+        """The publish error of the last settle, for a page that connects late.
+
+        ``status`` envelopes are momentary and not replayed, but a page that
+        refreshes after a failed publish must still learn why no model is
+        coming — its veil only lifts on a ``preview`` or an error.
+        """
+        if not self._last_publish_error:
+            return None
+        return {"type": "status", "error": self._last_publish_error[-300:]}
+
     # -- settling: the cells ran; publish what they made -----------------------
 
     def schedule_settle(self) -> None:
@@ -931,6 +945,18 @@ def settle(self) -> None:
                 self._last_publish_error = message
                 self.hub.broadcast({"type": "status", "error": message[-300:]})
 
+    def _begin_run(self) -> None:
+        """Cells are about to run because someone asked for it: report afresh.
+
+        The dedup above is for the parameter burst, where a product-less
+        notebook would repeat the same line on every slider tick.  A discrete
+        run (a page command, an agent edit, a file change) is a new question:
+        its failure must be told even if it repeats the last error word for
+        word, or the page waits out its whole veil for an answer that never
+        comes.
+        """
+        self._last_publish_error = ""
+
     @property
     def preview_url(self) -> str:
         return f"http://127.0.0.1:{self.port}/api/runtime/preview"
@@ -1111,6 +1137,7 @@ def save() -> None:
             return {"type": "error", "message": f"unknown command: {kind}"}
 
         def run() -> None:
+            self._begin_run()
             result = action()
             if result.get("success") is False:
                 self.hub.broadcast(
@@ -1265,6 +1292,7 @@ def _commit(self, kernel: MarimoKernel, names: list[str], *, revert: bool) -> No
         write_saved_params(config, saved)
         if revert:
             kernel.run_until_settled([self.specs[name].cell for name in names if name in self.specs])
+        self._begin_run()
         self.schedule_settle()
 
     # -- selection and the agent snapshot ----------------------------------------
@@ -1801,6 +1829,9 @@ async def ws_endpoint(websocket) -> None:
         await websocket.send_json(state.hello())
         for envelope in state.replay():
             await websocket.send_json(envelope)
+        settled = state.settled_error()
+        if settled is not None:
+            await websocket.send_json(settled)
         try:
             while True:
                 message = await websocket.receive_json()
diff --git a/test/test_editor.py b/test/test_editor.py
index e14be88..f704cfa 100644
--- a/test/test_editor.py
+++ b/test/test_editor.py
@@ -976,3 +976,128 @@ def test_an_edit_of_the_file_is_taken_in_and_not_written_over(self) -> None:
             finally:
                 if state.kernel is not None:
                     state.kernel.stop()
+
+
+class PublishErrorReportingTest(unittest.TestCase):
+    """A page's veil lifts on a preview or an error: a failed publish is told
+    once per identical state, told again on every run someone asked for, and
+    told to a page that connects after it happened."""
+
+    ERROR = "ProductNotFoundError: no top-level Part or Assembly has the notebook id"
+
+    def setUp(self) -> None:
+        tmp = tempfile.TemporaryDirectory()
+        self.addCleanup(tmp.cleanup)
+        self.root = Path(tmp.name).resolve()
+
+    def state(self) -> tuple[WorkspaceState, list[dict]]:
+        path = create_notebook(self.root, "bracket", "part")
+        state = WorkspaceState(self.root, path)
+        sent: list[dict] = []
+        state.hub.broadcast = sent.append  # type: ignore[method-assign]
+        state.push_cells = lambda: None  # type: ignore[method-assign]
+        state._signature = lambda notebook: None  # type: ignore[method-assign]
+        self.fail_kernel(state)
+        return state, sent
+
+    def fail_kernel(self, state: WorkspaceState) -> None:
+        state_error = self.ERROR
+        state.kernel = type(  # type: ignore[assignment]
+            "K",
+            (),
+            {
+                "publish_preview": lambda self, url, step="": {"ok": False, "error": state_error},
+                "setup_errors": [],
+            },
+        )()
+
+    @staticmethod
+    def told(sent: list[dict]) -> int:
+        return len([message for message in sent if message.get("type") == "status" and message.get("error")])
+
+    def test_a_failure_is_told_once_and_an_identical_repeat_is_not(self) -> None:
+        state, sent = self.state()
+        state.settle()
+        state.settle()
+        self.assertEqual(self.told(sent), 1)
+
+    def test_a_rerun_asked_for_on_the_page_reports_afresh(self) -> None:
+        import threading
+
+        state, sent = self.state()
+        state_error = self.ERROR
+        state.kernel = type(  # type: ignore[assignment]
+            "K",
+            (),
+            {
+                "run_cells": lambda self, ids: {},
+                "wait_idle": lambda self: True,
+                "publish_preview": lambda self, url, step="": {"ok": False, "error": state_error},
+                "setup_errors": [],
+            },
+        )()
+        state.cells = [{"id": "c1", "code": "x = 1"}]
+        settled = threading.Event()
+        state.schedule_settle = lambda: settled.set()  # type: ignore[method-assign]
+        state.settle()
+        state.settle()
+        self.assertEqual(self.told(sent), 1)
+        state.dispatch_command({"type": "rerun.request"})
+        self.assertTrue(settled.wait(5))
+        state.settle()
+        self.assertEqual(self.told(sent), 2)
+
+    def test_an_agent_cell_run_reports_afresh(self) -> None:
+        state, sent = self.state()
+        state_error = self.ERROR
+        state.kernel = type(  # type: ignore[assignment]
+            "K",
+            (),
+            {
+                "run_until_settled": lambda self, ids: {},
+                "wait_idle": lambda self: True,
+                "publish_preview": lambda self, url, step="": {"ok": False, "error": state_error},
+                "setup_errors": [],
+            },
+        )()
+        state.cells = [{"id": "c1", "code": "x = 1"}]
+        state.schedule_settle = lambda: None  # type: ignore[method-assign]
+        state.settle()
+        state.settle()
+        state.cell_command("run", {"cells": ["c1"]})
+        state.settle()
+        self.assertEqual(self.told(sent), 2)
+
+    def test_a_page_that_connects_late_is_told_the_last_error_until_it_clears(self) -> None:
+        state, _ = self.state()
+        self.assertIsNone(state.settled_error())
+        state.settle()
+        self.assertEqual(state.settled_error(), {"type": "status", "error": self.ERROR})
+        state.kernel = type(  # type: ignore[assignment]
+            "K",
+            (),
+            {"publish_preview": lambda self, url, step="": {"ok": True}, "setup_errors": []},
+        )()
+        state.settle()
+        self.assertIsNone(state.settled_error())
+
+    def test_the_ws_handshake_ends_with_the_last_error(self) -> None:
+        from starlette.testclient import TestClient
+
+        from simplecadapi.editor.server import create_app
+
+        state, _ = self.state()
+        state.settle()
+        state.kernel = type(  # type: ignore[assignment]
+            "K",
+            (),
+            {
+                "publish_preview": lambda self, url, step="": {"ok": False, "error": self.ERROR},
+                "setup_errors": [],
+                "alive": False,
+                "marimo_url": None,
+            },
+        )()
+        with TestClient(create_app(state)) as client, client.websocket_connect("/ws") as ws:
+            self.assertEqual(ws.receive_json()["type"], "hello")
+            self.assertEqual(ws.receive_json(), {"type": "status", "error": self.ERROR})