A plain Save that the location refuses (read-only filesystem or permission denied) now opens Save As with the name filled in, instead of ending in an error dialog. The refusal travels as a typed engine error (READ_ONLY_LOCATION), so the control protocol and MCP still return an error and never open a panel. Recovery failures, explicit destinations, a busy picker and Close/Quit keep their existing flow.
Closes#6146
File › Scripts › Other Script… picks a .js or .jsx file, shows a warning
that can be turned off in Preferences › General, and runs the script
against the open documents through the `vc` object. The new
`script.run` and `script.stop` commands run and stop a script over MCP.
- A run is one transaction. Each document it changed gets one undo step
named Run Script. An uncaught error, a limit or a stop puts every
document, the paint, the clipboard, menu state and preferences back.
- A command that fails inside a run, or whose result is too large to
reach the script, is undone and throws an error the script can catch.
- Files a command wrote stay on disk and the report names them, also
when the run is stopped from the quit question.
- While a script runs, other commands that change anything fail with a
busy error; MCP reports it as JSON-RPC error -32003.
- In the app the run advances one slice per frame with a Stop button in
the status bar. A run that adds a great many objects asks whether to
continue; Stop and Escape end it.
- Commands that change state outside the documents, such as prefs.*,
plugin.* and file.place.queue, are refused to scripts.
Docs: docs/mcp.md, docs/gaps.md, docs/roadmap.md,
docs/target-app-parity.md.
Ahmed Gomaa