test(ha-commit-durability): end-to-end durable-majority commit + liveness integration tests (task 5.1)

src/controller/persist.c

@@ -302,6 +302,16 @@ static uint64_t flusher_flush_once(persist_t* p)
     if (tip > dur)
         atomic_store_explicit(&p->durable_lsn, tip, memory_order_release);
 
+#ifdef XCE_TESTING
+    /* Record which thread ran this successful fdatasync (task 5.1 / Req 1.6):
+     * a liveness test asserts this is the dedicated flusher thread, never the
+     * caller/iomgr/heartbeat thread. Written under p->lock; read after the
+     * flusher has caught up, so no extra synchronization is needed. */
+    p->test_last_fdatasync_thread = pthread_self();
+    atomic_store_explicit(&p->test_last_fdatasync_thread_set, 1,
+                          memory_order_release);
+#endif
+
     pthread_mutex_unlock(&p->lock);
     return tip;
 }
@@ -841,6 +851,18 @@ unsigned persist_test_replicated_fdatasync_count(persist_t* p)
                                 memory_order_relaxed);
 }
 
+pthread_t persist_test_last_fdatasync_thread(persist_t* p)
+{
+    /* If no flusher fdatasync has advanced durable_lsn yet, return the
+     * caller's own id so an unprimed read never spuriously looks off-thread.
+     * After a flush, return the recorded flusher thread id (Req 1.6). */
+    if (!p ||
+        atomic_load_explicit(&p->test_last_fdatasync_thread_set,
+                             memory_order_acquire) == 0)
+        return pthread_self();
+    return p->test_last_fdatasync_thread;
+}
+
 /* ------------------------------------------------------------------ *
  * Durability-verification test seam (ha-commit-durability Req 3.2/3.3)*
  *                                                                     *