pane.spawn (via PtyException.errno) and editor.open (via
FileSystemException.osError.errorCode) now route ENOENT to
not_found, EACCES/EPERM to user_error with a permissions hint,
EISDIR/ENOTDIR/EEXIST to distinct user-error/conflict, and
EMFILE/ENFILE to tool_error with a "fd limit hit" hint. The
mapping lives in lib/src/ipc/errno_mapping.dart so other handlers
can adopt the same surface as they pick up errno-bearing failures.
Co-Authored-By: Claude <noreply@anthropic.com>