fix: keep slot IN_FLIGHT during execution so evaluator sees busy and drops instead of queuing

src/events.c

@@ -238,13 +238,15 @@ void *event_executor_thread(void *arg) {
         /* Fast path: check slot state without poll */
         if (atomic_load_explicit(&slot->state, memory_order_acquire) == EXECUTOR_SLOT_READY) {
             signal_entry_t sig = slot->signal;
-            atomic_store_explicit(&slot->state, EXECUTOR_SLOT_FREE, memory_order_release);
+            atomic_store_explicit(&slot->state, EXECUTOR_SLOT_IN_FLIGHT, memory_order_release);
             /* Drain eventfd so poll can block next time */
             uint64_t val;
             if (read(slot->eventfd, &val, sizeof(val)) < 0) {}
 
             executor_execute_triangle(exec, &sig);
 
+            atomic_store_explicit(&slot->state, EXECUTOR_SLOT_FREE, memory_order_release);
+
             int64_t now = now_mono_ms();
             if (last_keepalive_ms == 0 || now - last_keepalive_ms >= 30000) {
                 executor_keepalive(exec);

src/slot.h

@@ -8,6 +8,7 @@
 #define EXECUTOR_SLOT_FREE       0
 #define EXECUTOR_SLOT_CLAIMED    1
 #define EXECUTOR_SLOT_READY      2
+#define EXECUTOR_SLOT_IN_FLIGHT  3
 
 typedef struct {
     _Atomic int       state;