fix: make attachment path-containment guard separator-aware

Attachment::saveTo()'s escape guard compared paths with a bare
QString::startsWith(), which is not a path-boundary test: "/tmp/safe-evil"
textually starts with "/tmp/safe", so a sibling directory whose name merely
extends the target's name would incorrectly pass as contained within it.

Extract the check into Attachment::isPathInsideDirectory(), comparing
QDir::cleanPath()'d absolute paths and requiring an exact match or a prefix
ending at a '/' boundary. Not exploitable today since safeFilename() always
reduces the name to a bare basename before saveTo() builds the target, so
the guard is unreachable via saveTo()'s public interface; comments on both
now say so plainly instead of implying it is currently load-bearing.

Add pathInsideDirectoryRejectsSiblingPrefix, testing the guard directly
(independent of safeFilename(), which would mask a broken guard by never
producing an escaping path), and safeFilenameStripsPathComponents, testing
the sanitiser that actually stops traversal today.

0 files changed, 0 insertions, 0 deletions