deb: retry the interrupt chroot removal while children die off

dpkg defers SIGINT until it reaches a safe state, so it can still be
writing into the chroot when the watchdog's rm -rf starts racing
through it, failing with "directory not empty" and leaving the tree
half-removed. Retry the removal for a few seconds while the
interrupted children finish dying off; a genuinely stuck tree still
ends in the pkh prune message.

src/deb/ephemeral.rs

@@ -60,31 +60,48 @@ fn sigint_cleanup_chroot(chroot_path: &Path) {
         }
     }
 
-    // Remove the chroot tree itself (tolerates a missing directory)
-    let status = privileged_command("rm", is_root)
-        .arg("-rf")
-        .arg(chroot_path)
-        .status();
-    match status {
-        Ok(status) if status.success() => {
+    // Remove the chroot tree itself (tolerates a missing directory). A
+    // child the Ctrl+C interrupted may still be finishing its writeout —
+    // dpkg defers SIGINT until it reaches a safe state — so retry while rm
+    // reports the tree non-empty instead of leaving it half-removed.
+    const RETRIES: usize = 10;
+    const RETRY_DELAY: std::time::Duration = std::time::Duration::from_millis(300);
+    let mut last = None;
+    for attempt in 0..=RETRIES {
+        if attempt > 0 {
+            std::thread::sleep(RETRY_DELAY);
+        }
+        last = Some(
+            privileged_command("rm", is_root)
+                .arg("-rf")
+                .arg(chroot_path)
+                .status(),
+        );
+        if matches!(&last, Some(Ok(status)) if status.success()) {
+            break;
+        }
+    }
+    match last {
+        Some(Ok(status)) if status.success() => {
             log::debug!(
                 "Removed chroot {} during interrupt cleanup",
                 chroot_path.display()
             );
         }
-        Ok(status) => {
+        Some(Ok(status)) => {
             log::error!(
                 "Failed to remove chroot {} during interrupt cleanup \
                  (rm exited with {status}); run `pkh prune`",
                 chroot_path.display()
             );
         }
-        Err(e) => {
+        Some(Err(e)) => {
             log::error!(
                 "Failed to run rm for chroot {} during interrupt cleanup: {e}; run `pkh prune`",
                 chroot_path.display()
             );
         }
+        None => unreachable!("at least one rm attempt ran"),
     }
 }