Automation: a confined renderQueue.add without output needs a saved project (#2479)

On a project that was never saved, renderQueue.add without output queued
an item whose default output was the home folder, outside every
automation root (rendering it was refused, but the queue held a path the
agent may not write). While file access is confined, such an add is now
refused with a hint to give output inside a write root; a saved
project's default output (beside it) is checked when the queue renders,
as before.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/mcp.md

@@ -11,7 +11,9 @@ written only under a write root; with no write root nothing is written. Every en
 (`execute_command`, `command_run`, each `batch` step) is checked before it runs: its file
 parameters must be absolute paths inside the roots (symbolic links resolved, no `..`), and so must
 any other absolute path in its parameters. Save, Increment and Save and rendering the Render
-Queue are checked against the files they write (the open project's, the queued outputs). Scripts
+Queue are checked against the files they write (the open project's, the queued outputs);
+`renderQueue.add` without `output` needs a saved project, since an unsaved one's default output
+would go to the home folder (#2479). Scripts
 (`run_script`, `file.runScript`…), Execute File, Reveal in Finder, `$N` references to file paths
 in a batch, and the bridge's UI-driving tools (`ui_click`, `ui_key`, `ui_type`, `ui_drag`,
 `ui_set`, `script_ui`, `control`) are refused while confined. Without the flags nothing changes.