Fix known-hosts trust deadlock, host key stat, and optional nozstd build

- stdout logger: release mutex while waiting on pause resume so prompt
  callbacks can log (fixes hang after trusting new hosts; known_hosts
  was written but Resume never ran).
- known hosts callback: stop borrowing the SSH dial throttle channel
  (could block or interact badly with parallel handshakes).
- host key path: use errors.Is(..., fs.ErrNotExist) for RootedPath.Stat
  wrapped errors; stat errors now fail fast instead of mis-read.
- public key path: same ErrNotExist check for authorized_keys miss.
- Build: optional DTAIL_NO_ZSTD=yes / nozstd tag for CGO-free builds;
  split zstd readers into tagged files.
- Docs/examples: firewalld note for port 2222, log prune timer+script,
  SSHBindAddress note, dserver unit disabled-by-default comment;
  firewalld helper script example.
- Regression test for stdout pause/mutex behavior.

Made-with: Cursor

1 files changed, 9 insertions, 0 deletions

diff --git a/examples/dserver-prune-logs.timer.example b/examples/dserver-prune-logs.timer.example
new file mode 100644
index 0000000..2ec13b6
--- /dev/null
+++ b/examples/dserver-prune-logs.timer.example
@@ -0,0 +1,9 @@
+[Unit]
+Description=Daily cleanup of dserver logs older than 7 days
+
+[Timer]
+OnCalendar=daily
+RandomizedDelaySec=1800
+
+[Install]
+WantedBy=timers.target