The editor registry resolved buffer paths with a string join that
passed absolute paths through verbatim and never normalized `..` —
an unconfined read and write primitive over IPC while files.read was
carefully guarded. Buffer paths now resolve through
resolveUnderRootFollowingSymlinks: traversal, absolute escapes, and
symlinks-out are rejected at open, and re-checked at save so a
symlink swapped in under an open buffer's path can't redirect the
write. D-80's extra read roots deliberately do not apply — a buffer
is a write surface. Handlers map PathOutsideRoot to the same error
files.read uses. Also merges a duplicate Added heading that had crept
into the Unreleased changelog section.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>