fix(sqlite): concurrent migrate retries

crates/adapters/sqlite/tests/migration_ledger_test.rs

@@ -56,3 +56,47 @@ async fn a_database_migrated_by_the_old_layout_migrates_again_cleanly() {
 
     assert_eq!(ledger(&pool).await, LEDGER);
 }
+
+async fn wal_pool(path: &Path, create: bool) -> SqlitePool {
+    let opts = SqliteConnectOptions::new()
+        .filename(path)
+        .create_if_missing(create)
+        .journal_mode(sqlx::sqlite::SqliteJournalMode::Wal)
+        .busy_timeout(std::time::Duration::from_secs(5));
+    SqlitePoolOptions::new()
+        .max_connections(2)
+        .connect_with(opts)
+        .await
+        .unwrap()
+}
+
+async fn race_two_migrators(start: Option<&Path>) {
+    for _ in 0..10 {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("race.db");
+        if let Some(src) = start {
+            std::fs::copy(src, &path).unwrap();
+        }
+        let a = wal_pool(&path, start.is_none()).await;
+        let b = wal_pool(&path, false).await;
+
+        let (ra, rb) = tokio::join!(sqlite::migrate(&a), sqlite::migrate(&b));
+
+        ra.unwrap();
+        rb.unwrap();
+        assert_eq!(ledger(&a).await, LEDGER);
+    }
+}
+
+#[tokio::test]
+async fn two_processes_migrating_the_same_fresh_database_both_succeed() {
+    race_two_migrators(None).await;
+}
+
+#[tokio::test]
+async fn two_processes_migrating_a_database_at_the_old_version_both_succeed() {
+    race_two_migrators(Some(
+        &Path::new(env!("CARGO_MANIFEST_DIR")).join(PRE_MERGE_DB),
+    ))
+    .await;
+}