* Fix ssh-relay install on hosts with split shell/SFTP namespaces
On Synology DSM and similar hosts, the SSH shell and SFTP subsystem expose
different absolute paths for the same directory (e.g., /var/services/homes/alice
vs /homes/alice). The relay installer silently picked the wrong path and failed
discovery. This fix implements SFTP namespace detection: each install creates an
unguessable ownership marker and probes both namespaces to detect divergence.
When paths differ, SFTP writes redirect to the candidate namespace while shell
commands keep the canonical path. Markers are random tokens redacted from logs.
* Fix ssh-relay install on hosts with split shell/SFTP namespaces
Strengthen path validation to catch traversal and empty segments in
absolute POSIX paths, preventing security issues. Improve split-namespace
handling with comprehensive wire tests for uploads and file writes.
Ensure system SSH connections bypass namespace mapping entirely rather
than attempting incorrect retargeting.
Jinjing
