Wait for browser shutdown before cleaning private profiles (#827)

Thanks @Agapenordev! Supervised browser hand-off now waits for process-group/Job Object shutdown, and private-profile removal retries transient locks for up to five seconds. Missing profiles count as already cleaned.

Reviewed source head 6e3398d28b. Hosted Ubuntu CI is green. On AnayPC, the applicable engine/platform tests, clippy, layers, locks, secrets and wasm checks pass. Two Windows UI-automation tests also fail on pristine main because the SSH session cannot create interactive WinForms windows; their baseline and candidate failures are preserved.

Related #810 remains open: this follow-up does not establish that the broader live macOS/Brave issue is fully resolved.

crates/engine/src/tools/web_common.rs

@@ -58,11 +58,21 @@ pub struct Browser {
 
 struct BrowserProfile(std::path::PathBuf);
 
+fn remove_profile_with(mut remove: impl FnMut() -> std::io::Result<()>) -> std::io::Result<()> {
+    let started = std::time::Instant::now();
+    loop {
+        match remove() {
+            Ok(()) => return Ok(()),
+            Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(()),
+            Err(e) if started.elapsed() >= Duration::from_secs(5) => return Err(e),
+            Err(_) => std::thread::sleep(Duration::from_millis(50)),
+        }
+    }
+}
+
 impl Drop for BrowserProfile {
     fn drop(&mut self) {
-        if let Err(e) = std::fs::remove_dir_all(&self.0)
-            && e.kind() != std::io::ErrorKind::NotFound
-        {
+        if let Err(e) = remove_profile_with(|| std::fs::remove_dir_all(&self.0)) {
             log::warn!("couldn't remove the private browser profile {}: {e}", self.0.display());
         }
     }
@@ -1081,6 +1091,21 @@ mod tests {
         assert!(!profile.exists(), "the private browser profile survived its owner");
     }
 
+    #[test]
+    fn profile_cleanup_retries_while_the_browser_releases_files() {
+        let root = tempfile::tempdir().unwrap();
+        let profile = root.path().join("private-profile");
+        std::fs::create_dir(&profile).unwrap();
+        let mut attempts = 0;
+        super::remove_profile_with(|| {
+            attempts += 1;
+            if attempts < 3 { Err(std::io::Error::new(std::io::ErrorKind::PermissionDenied, "still locked")) } else { std::fs::remove_dir_all(&profile) }
+        })
+        .unwrap();
+        assert_eq!(attempts, 3);
+        assert!(!profile.exists());
+    }
+
     /// #747: a Flatpak or Snap browser keeps its profile where its sandbox can reach it and we can
     /// read its port; any other browser uses the temp folder.
     #[test]

crates/platform/src/process.rs

@@ -758,7 +758,7 @@ impl Supervisor {
             let _ = self.child.kill();
         } else {
             // The leader exited; take any leftover group members with it so they can't hold the pipes.
-            let _ = self.child.start_kill();
+            let _ = self.child.kill();
         }
         self.drain();
         let duration = self.start.elapsed();