diff --git a/crates/harness-store/src/lib.rs b/crates/harness-store/src/lib.rs
index d418dfa..1d78956 100644
--- a/crates/harness-store/src/lib.rs
+++ b/crates/harness-store/src/lib.rs
@@ -140,6 +140,21 @@ pub struct StoreBundle {
     pub channel_instances: Arc<dyn ChannelInstanceStore>,
 }
 
+/// In-memory `TenantStore` fallback for the SQL backends.
+///
+/// There's no SQL `TenantStore` impl yet (only JSON-file and SQLite),
+/// so the Postgres / MySQL arms fall back to in-memory — tenant rows
+/// won't survive restarts under those deployments until a SQL impl
+/// lands. Mirrors the channel-store fallback used in the same arms.
+#[cfg(any(feature = "postgres", feature = "mysql"))]
+fn ephemeral_tenants(backend: &str) -> Arc<dyn TenantStore> {
+    tracing::warn!(
+        backend,
+        "no SQL TenantStore impl yet; tenants fall back to in-memory and won't survive restarts"
+    );
+    Arc::new(MemoryTenantStore::new()) as Arc<dyn TenantStore>
+}
+
 /// Open both stores for a given database URL. The scheme selects the
 /// backend (see [module docs](crate)).
 ///
diff --git a/crates/harness-store/src/mysql.rs b/crates/harness-store/src/mysql.rs
index 3962759..25dbf2d 100644
--- a/crates/harness-store/src/mysql.rs
+++ b/crates/harness-store/src/mysql.rs
@@ -118,15 +118,22 @@ async fn migrate(pool: &MySqlPool) -> Result<(), StoreError> {
     .await?
         > 0;
     if !has_workspaces {
-        sqlx::query("ALTER TABLE projects ADD COLUMN workspaces TEXT NOT NULL")
+        // Add the column nullable first: under strict SQL mode (MySQL 8
+        // default STRICT_TRANS_TABLES) an `ADD COLUMN ... TEXT NOT NULL`
+        // with no default aborts on a populated table because TEXT has no
+        // implicit default. So add it nullable, backfill, then tighten to
+        // NOT NULL — this works across MySQL 5.7/8.x regardless of sql_mode.
+        sqlx::query("ALTER TABLE projects ADD COLUMN workspaces TEXT")
             .execute(pool)
             .await?;
-        // Backfill so the NOT NULL constraint is satisfied for legacy rows.
         sqlx::query(
             "UPDATE projects SET workspaces = '[]' WHERE workspaces IS NULL OR workspaces = ''",
         )
         .execute(pool)
         .await?;
+        sqlx::query("ALTER TABLE projects MODIFY COLUMN workspaces TEXT NOT NULL")
+            .execute(pool)
+            .await?;
     }
     let has_columns: bool = sqlx::query_scalar::<_, i64>(
         "SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS