context: add ContextDriver::is_dir

list_files returns context-relative paths (rooted inside the chroot
for an unshare context, on the remote for ssh): whether an entry is
a directory can only be decided through the context, never with a
host-side stat. Give every driver a proper is_dir rather than
approximating it with exists, so callers can keep directories and
files apart — the deb package-directory search lists directories
only.

src/context/api.rs

@@ -70,6 +70,12 @@ pub trait ContextDriver {
     fn read_file(&self, path: &Path) -> io::Result<String>;
     fn write_file(&self, path: &Path, content: &str) -> io::Result<()>;
     fn exists(&self, path: &Path) -> io::Result<bool>;
+    /// Check if a path is a directory inside the context
+    ///
+    /// Distinct from [`ContextDriver::exists`] because paths returned by
+    /// [`ContextDriver::list_files`] are context-relative and can only be
+    /// classified through the context, never with a host-side stat.
+    fn is_dir(&self, path: &Path) -> io::Result<bool>;
 
     /// Clean up any resources held by the driver (e.g. unmount overlay filesystems).
     /// Called before the chroot directory is removed.
@@ -313,6 +319,15 @@ impl Context {
         self.driver().as_ref().unwrap().exists(path)
     }
 
+    /// Check if a path is a directory inside context
+    ///
+    /// Paths returned by [`Context::list_files`] are context-relative
+    /// (e.g. rooted inside the chroot for an unshare context): whether they
+    /// are directories can only be decided through the context.
+    pub fn is_dir(&self, path: &Path) -> io::Result<bool> {
+        self.driver().as_ref().unwrap().is_dir(path)
+    }
+
     /// Clean up any resources held by the driver (e.g. unmount overlay filesystems).
     /// Called before the chroot directory is removed.
     pub fn cleanup(&self) -> io::Result<()> {

src/context/local.rs

@@ -155,6 +155,10 @@ impl ContextDriver for LocalDriver {
     fn exists(&self, path: &Path) -> io::Result<bool> {
         Ok(path.exists())
     }
+
+    fn is_dir(&self, path: &Path) -> io::Result<bool> {
+        Ok(path.is_dir())
+    }
 }
 
 fn copy_dir_recursive(src: &Path, dest: &Path) -> io::Result<()> {

src/context/mod.rs

@@ -385,6 +385,40 @@ mod tests {
         assert!(!dest.join("src/.svn").exists());
     }
 
+    /// The unshare driver maps context-relative paths onto the chroot root
+    /// on the host: `is_dir` must answer through that mapping (a host-side
+    /// stat of the unmapped path sees nothing), which is what lets the deb
+    /// package-directory search classify staged entries.
+    #[test]
+    fn test_unshare_is_dir_maps_through_the_chroot_root() {
+        let chroot = tempfile::tempdir().unwrap();
+        fs::create_dir_all(chroot.path().join("tmp/work/tree/debian")).unwrap();
+        fs::write(chroot.path().join("tmp/work/orig.tar.xz"), "tar").unwrap();
+
+        let base = Context::new(ContextConfig::Local).unwrap();
+        let ctx = Context::with_parent(
+            ContextConfig::Unshare {
+                path: chroot.path().to_string_lossy().to_string(),
+                parent: None,
+            },
+            Arc::new(base),
+        );
+
+        assert!(ctx.is_dir(std::path::Path::new("/tmp/work/tree")).unwrap());
+        assert!(
+            ctx.exists(std::path::Path::new("/tmp/work/tree/debian"))
+                .unwrap()
+        );
+        assert!(
+            !ctx.is_dir(std::path::Path::new("/tmp/work/orig.tar.xz"))
+                .unwrap()
+        );
+        assert!(
+            !ctx.exists(std::path::Path::new("/tmp/work/missing"))
+                .unwrap()
+        );
+    }
+
     /// The overlay-mount path exposes the tree verbatim, so pruning happens
     /// after the fact: nested VCS metadata must be removed recursively.
     #[test]

src/context/schroot.rs

@@ -296,6 +296,16 @@ impl ContextDriver for SchrootDriver {
         )?;
         Ok(status.success())
     }
+
+    fn is_dir(&self, path: &Path) -> io::Result<bool> {
+        let status = self.run(
+            "test",
+            &["-d".to_string(), path.to_string_lossy().to_string()],
+            &[],
+            None,
+        )?;
+        Ok(status.success())
+    }
 }
 
 #[cfg(test)]

src/context/ssh.rs

@@ -306,6 +306,14 @@ impl ContextDriver for SshDriver {
             Err(_) => Ok(false),
         }
     }
+
+    fn is_dir(&self, path: &Path) -> io::Result<bool> {
+        let sess = connect_ssh(&self.host, self.user.as_deref(), self.port)?;
+        let sftp = sess.sftp().map_err(io::Error::other)?;
+        // Same error tolerance as `exists`: an unreachable path is not a
+        // directory, and the caller decides what absence means.
+        Ok(sftp.stat(path).map(|stat| stat.is_dir()).unwrap_or(false))
+    }
 }
 
 impl SshDriver {

src/context/unshare.rs

@@ -356,6 +356,11 @@ impl ContextDriver for UnshareDriver {
         let host_path = Path::new(&self.path).join(path.to_string_lossy().trim_start_matches('/'));
         self.parent().exists(&host_path)
     }
+
+    fn is_dir(&self, path: &Path) -> io::Result<bool> {
+        let host_path = Path::new(&self.path).join(path.to_string_lossy().trim_start_matches('/'));
+        Ok(host_path.is_dir())
+    }
 }
 
 impl UnshareDriver {

src/test_support.rs

@@ -445,6 +445,10 @@ mod imp {
             self.inner.exists(path)
         }
 
+        fn is_dir(&self, path: &Path) -> io::Result<bool> {
+            self.inner.is_dir(path)
+        }
+
         fn cleanup(&self) -> io::Result<()> {
             self.inner.cleanup()
         }