Index: src/config/database.js
===================================================================
--- src/config/database.js	(revision 55bc7f95d6ee2d94bdaba55d6ca87265e217dbc4)
+++ src/config/database.js	(revision 7c44c1227391a3e62327e785d8a67b661aaae489)
@@ -328,4 +328,5 @@
       content TEXT,                         -- sanitized HTML (reply)
       published TEXT,
+      parent_uri TEXT,                      -- the note this reply replies to (for nesting)
       created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
       UNIQUE(kind, post_id, actor_uri, object_uri)
@@ -345,4 +346,5 @@
     CREATE INDEX IF NOT EXISTS idx_ap_outbox_post ON ap_outbox(post_id);
   `);
+  ensureColumn('ap_interactions', 'parent_uri', 'TEXT'); // nesting (existing DBs)
 }