fix(cli,fuse): keep answering the systemd watchdog while the daemon retries

The watchdog is armed when the process starts, but only the mount's supervisor
pinged it. A daemon waiting for a login or backing off after a failed mount
(#26: key unlock failing) was aborted after WatchdogSec and left a coredump
instead of its error. Sleep through idle_sleep in those stretches; the mounted
ping still has to pass the control-socket probe.

crates/pdfs-cli/src/main.rs

@@ -2027,7 +2027,7 @@ fn cmd_daemon(mountpoint: Option<PathBuf>) -> Result<()> {
     loop {
         // Wait until a session is stored. The GUI enables this service on login,
         // but the service may also start at boot before the user has logged in.
-        wait_for_session(|| auth::load().map(|_| ()), std::thread::sleep)?;
+        wait_for_session(|| auth::load().map(|_| ()), pdfs_fuse::idle_sleep)?;
 
         match mount_once(mountpoint.clone()) {
             Ok(pdfs_fuse::MountOutcome::Shutdown) => {
@@ -2036,13 +2036,13 @@ fn cmd_daemon(mountpoint: Option<PathBuf>) -> Result<()> {
             }
             Ok(pdfs_fuse::MountOutcome::Unmounted) => {
                 tracing::warn!("mount ended externally; remounting in 2s");
-                std::thread::sleep(std::time::Duration::from_secs(2));
+                pdfs_fuse::idle_sleep(std::time::Duration::from_secs(2));
             }
             Err(e) => {
                 // `{:#}` so the whole anyhow chain lands in the log — the top
                 // context alone ("mount failed") never says *why*.
                 tracing::error!(error = format!("{e:#}"), "mount failed; retrying in 5s");
-                std::thread::sleep(std::time::Duration::from_secs(5));
+                pdfs_fuse::idle_sleep(std::time::Duration::from_secs(5));
             }
         }
     }

crates/pdfs-fuse/src/lib.rs

@@ -123,6 +123,7 @@ use mount::{
 };
 use reads::{BlockFlight, BlockRing, PREFETCH_BUDGET, Prefetch, ReaderSlot, STREAM_BYPASS_MIN};
 use state::{Entry, Intervals, PendingRevision, State, StateGuard, WriteHandle};
+pub use systemd::idle_sleep;
 use tracing::{debug, error, info, warn};
 use transfers::{CountingWriter, JobGuard, OwnedCountingReader, TransferRegistry};
 use r#virtual::{

crates/pdfs-fuse/src/systemd.rs

@@ -74,6 +74,26 @@ pub(crate) fn watchdog_ping() {
     let _ = notify("WATCHDOG=1\n");
 }
 
+/// Sleep for `duration`, pinging the watchdog on the way.
+///
+/// For the stretches where the daemon is alive but has no mount, and so no
+/// supervisor: waiting for a login, or backing off after a failed mount. The
+/// manager arms the watchdog when the process starts, so without these pings a
+/// daemon that is merely retrying is aborted after `WatchdogSec` and leaves a
+/// coredump instead of the error it was logging. Never use this while mounted:
+/// there the ping must prove the control socket answers.
+pub fn idle_sleep(duration: Duration) {
+    const CHUNK: Duration = Duration::from_secs(10);
+    let mut left = duration;
+    watchdog_ping();
+    while !left.is_zero() {
+        let step = left.min(CHUNK);
+        std::thread::sleep(step);
+        left -= step;
+        watchdog_ping();
+    }
+}
+
 /// Tell the manager the daemon is stopping, so a slow teardown is not mistaken
 /// for a hang by the watchdog it is racing.
 pub(crate) fn stopping() {