fix(host,client): stream bounded listings, declare schemastery, guard Choose again

The browse level now streams through opendir into a name-sorted window of
maxEntries + 1 candidates (boundedInsert), so memory stays O(maxEntries)
no matter how many children a directory holds and enterability probing
touches only windowed candidates; a windowed broken symlink is not
backfilled since the eviction already marks the level truncated.
schemastery joins the package's runtime dependencies (the source launcher
and isolated installs failed to resolve the value import). The
folder-error dialog's Choose again goes inert while the flow hole is
empty, and the withdrawal effect also keys on the open transition, so a
flow can never open over a hole nobody serves.

packages/client/ui-workspace/src/client/WorkspacePicker.tsx

@@ -98,9 +98,12 @@ export function WorkspaceCreateFlow({
   const flowAvailable = useDirectoryFlow(occupied => occupied)
   // An occupant that unloads mid-interaction leaves nobody to cancel: an
   // open flow over an empty hole withdraws so the menu actions come back.
+  // flowOpen is a dependency because the flow can also OPEN over an already
+  // empty hole (Choose again after the occupant unloaded with the error
+  // dialog up) — that transition must snap back too, not just occupancy loss.
   useEffect(() => {
-    if (!flowAvailable) setFlowOpen(false)
-  }, [flowAvailable])
+    if (flowOpen && !flowAvailable) setFlowOpen(false)
+  }, [flowOpen, flowAvailable])
   const createEntries: MenuEntry[] = [
     ...(flowAvailable
       ? [{ id: OPEN_LOCAL_FOLDER, label: 'Open local folder…', icon: <IconFolderClose16 size={16} />, disabled: flowBusy }]
@@ -224,7 +227,9 @@ export function WorkspaceCreateFlow({
         footer={(
           <>
             <Button variant="outline" className={css.modalAction} onClick={closeModal}>Cancel</Button>
-            <Button variant="primary" className={css.modalAction} onClick={openLocalFolder}>Choose again</Button>
+            {/* Retrying needs an occupant to serve the flow; without one the
+              * button would open a flow nobody can answer or cancel. */}
+            <Button variant="primary" className={css.modalAction} disabled={!flowAvailable} onClick={openLocalFolder}>Choose again</Button>
           </>
         )}
       >