CVE-2026-53789: stop a malicious sender expanding --delete scope by
reclassifying implied parent directories as content dirs; the receiver now
re-derives implied-parent status from its own implied_filter_list and
rejects a non-directory encoding of the synthetic "." transfer root
Also guard the p[-1] read in the vendor-rewritten add_implied_include()
when the normalized transfer argument is empty; the new implied-parent
check depends on the root rule's exact spelling, and the unguarded read
was an out-of-bounds read on an ordinary module-root transfer