Fix MPSC force-stop hangs after the consumer thread exits.

Clear consumer_thread_id when a pool worker leaves run() so ~Pool() does not
wait on a dead consumer, and stop pools outside pools_mutex so a blocking
MPSC drain cannot deadlock with get_pool() during live shutdown.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: TrentHouliston

src/threading/scheduler/Pool.cpp

@@ -267,6 +267,7 @@ namespace threading {
             }
             catch (const ShutdownThreadException&) {
                 Pool::current_pool = nullptr;
+                consumer_thread_id = std::thread::id{};
                 return;
             }
         }

src/threading/scheduler/Scheduler.cpp

@@ -103,9 +103,20 @@ namespace threading {
 
         void Scheduler::stop(bool force) {
             running.store(false, std::memory_order_release);
-            const std::lock_guard<std::mutex> lock(pools_mutex);
-            for (const auto& pool : pools) {
-                pool.second->stop(force ? Pool::StopType::FORCE : Pool::StopType::NORMAL);
+
+            // Copy pool pointers under the mutex, then stop outside it. Pool::stop(FORCE) on
+            // single-consumer (MPSC) pools may block until that pool's worker drains the queue;
+            // workers can call get_pool() during that drain, which needs pools_mutex.
+            std::vector<std::shared_ptr<Pool>> pools_to_stop;
+            {
+                const std::lock_guard<std::mutex> lock(pools_mutex);
+                pools_to_stop.reserve(pools.size());
+                for (const auto& pool : pools) {
+                    pools_to_stop.push_back(pool.second);
+                }
+            }
+            for (const auto& pool : pools_to_stop) {
+                pool->stop(force ? Pool::StopType::FORCE : Pool::StopType::NORMAL);
             }
         }