fix(crawler): don't hold browser mutex across Chromium close()

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/crawler/browser_manager.rs

@@ -234,12 +234,20 @@ impl BrowserManager {
         await_drain(&self.active, drain_deadline).await;
 
         self.set_phase(RestartPhase::Restarting);
-        let relaunch = {
+        // Take the dead handle out under the lock, release the lock, THEN run
+        // the (slow) Chromium teardown — so a worker that raced past the drain
+        // can't block on `acquire()` behind one dead browser's close(). Mirrors
+        // the idle reaper's take-drop-close ordering. Re-acquire to relaunch.
+        let dead = {
             let mut guard = self.inner.lock().await;
             guard.shared = None;
-            if let Some(handle) = guard.handle.take() {
-                let _ = handle.close().await;
-            }
+            guard.handle.take()
+        };
+        if let Some(handle) = dead {
+            let _ = handle.close().await;
+        }
+        let relaunch = {
+            let mut guard = self.inner.lock().await;
             self.launch_into(&mut guard).await
         };
 
@@ -257,9 +265,14 @@ impl BrowserManager {
     /// Used on daemon shutdown. After this returns the next acquire will
     /// re-launch from scratch.
     pub async fn shutdown(&self) {
-        let mut guard = self.inner.lock().await;
-        guard.shared = None;
-        if let Some(handle) = guard.handle.take() {
+        // Take-then-drop-then-close: don't hold the lock across Chromium
+        // teardown (see `invalidate` / the idle reaper).
+        let handle = {
+            let mut guard = self.inner.lock().await;
+            guard.shared = None;
+            guard.handle.take()
+        };
+        if let Some(handle) = handle {
             let _ = handle.close().await;
         }
     }
@@ -278,9 +291,16 @@ impl BrowserManager {
     /// Idempotent: calling on an already-invalidated manager is a
     /// no-op.
     pub async fn invalidate(&self) {
-        let mut guard = self.inner.lock().await;
-        guard.shared = None;
-        if let Some(handle) = guard.handle.take() {
+        // Take the handle out under the lock, then release the lock BEFORE the
+        // slow Chromium close() — otherwise every other worker's `acquire()`
+        // serializes behind one dead browser's teardown. Matches the idle
+        // reaper's ordering at the bottom of this file.
+        let handle = {
+            let mut guard = self.inner.lock().await;
+            guard.shared = None;
+            guard.handle.take()
+        };
+        if let Some(handle) = handle {
             let _ = handle.close().await;
             tracing::warn!("BrowserManager: handle invalidated — next acquire will relaunch");
         }