fix(aw-sync): use atomic counter in test tmp_db to fix parallel-test path collision

aw-sync/tests/sync_roundtrip.rs

@@ -10,21 +10,32 @@
 ///
 /// Both copies then render in /timeline, so every event is shown twice.
 use std::path::PathBuf;
+use std::sync::atomic::{AtomicU64, Ordering};
 
 use aw_datastore::Datastore;
 use aw_models::{Bucket, BucketMetadata};
 use aw_sync::{sync_datastores, AccessMethod, SyncSpec};
 
+// Tests in this binary run in parallel. Use a monotonic counter to guarantee
+// each datastore gets a unique path even when two tests start within the same
+// clock tick (seen on macOS where SystemTime resolution can be coarser than
+// nanoseconds, causing path collisions and SQLite migration races).
+static DB_COUNTER: AtomicU64 = AtomicU64::new(0);
+
 fn tmp_db(name: &str) -> PathBuf {
     let mut p = std::env::temp_dir();
+    // Combine a per-process counter (within-run uniqueness) with a timestamp
+    // (cross-run uniqueness when the PID is reused and the counter resets to 0).
+    let ts = std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .unwrap()
+        .as_nanos();
     p.push(format!(
-        "aw-sync-roundtrip-{}-{}-{}.db",
+        "aw-sync-roundtrip-{}-{}-{}-{}.db",
         std::process::id(),
         name,
-        std::time::SystemTime::now()
-            .duration_since(std::time::UNIX_EPOCH)
-            .unwrap()
-            .as_nanos()
+        DB_COUNTER.fetch_add(1, Ordering::Relaxed),
+        ts,
     ));
     p
 }