deb,ui: tear the live view down through the interrupt core

The ephemeral guard registers its chroot removal as an interrupt
cleanup hook and, once interrupted, stands down from its own teardown
so the two cannot race umount/rm; bootstrap bails out of tarball
extraction and the lockfile wait, keeping the hook registered on the
bootstrap error path so the watchdog can remove the partial tree. The
live view registers an interrupt reporter that suspends the widget and
returns the log-file hint, silences the tty rendering of the ^C
keypress (the echoed "^C" can wrap near the right edge and shift the
teardown erase by a row, leaving the first widget line on screen) and
kills the shared draw target so late log records cannot repaint the
cleared bars. Failure summaries stay quiet when interrupted: the
captured errors are just the killed children's death throes, and the
dose-builddebcheck diagnosis is skipped for a dependency failure the
user interrupted themselves.

src/deb/local.rs

@@ -725,8 +725,17 @@ fn install_build_dependencies(
         let status = cap(&mut cmd, sink).status()?;
         if !status.success() {
             view.suspend();
-            if let Err(e) =
-                dose3_explain_dependencies(package, version, arch, build_root, cross, ctx.clone())
+            // Diagnosing a dependency failure the user interrupted themselves
+            // is wasted work
+            if !crate::interrupt::interrupted()
+                && let Err(e) = dose3_explain_dependencies(
+                    package,
+                    version,
+                    arch,
+                    build_root,
+                    cross,
+                    ctx.clone(),
+                )
             {
                 log::debug!("dose-builddebcheck diagnosis failed: {e}");
             }