H-337: restore Web widget reply visibility (#64)

* H-337: restore widget reply delivery

* H-337: harden widget conversation ownership

---------

Co-authored-by: Rogee <rogee@ipao.vip>

backend/migrations/000082_backfill_widget_conversation_contact_inboxes.down.sql

@@ -0,0 +1,10 @@
+UPDATE conversations
+SET contact_inbox_id = NULL
+WHERE EXISTS (
+  SELECT 1
+  FROM widget_conversation_contact_inbox_backfills AS backfills
+  WHERE backfills.conversation_id = conversations.id
+    AND backfills.contact_inbox_id = conversations.contact_inbox_id
+);
+
+DROP TABLE widget_conversation_contact_inbox_backfills;

backend/migrations/000082_backfill_widget_conversation_contact_inboxes.up.sql

@@ -0,0 +1,24 @@
+CREATE TABLE widget_conversation_contact_inbox_backfills (
+  conversation_id BIGINT PRIMARY KEY,
+  contact_inbox_id BIGINT NOT NULL
+);
+
+INSERT INTO widget_conversation_contact_inbox_backfills (conversation_id, contact_inbox_id)
+SELECT conversations.id, MIN(contact_inboxes.id)
+FROM conversations
+JOIN inboxes ON inboxes.id = conversations.inbox_id
+JOIN contact_inboxes
+  ON contact_inboxes.contact_id = conversations.contact_id
+ AND contact_inboxes.inbox_id = conversations.inbox_id
+WHERE conversations.contact_inbox_id IS NULL
+  AND inboxes.channel_type IN ('web_widget', 'Channel::WebWidget')
+GROUP BY conversations.id
+HAVING COUNT(contact_inboxes.id) = 1;
+
+UPDATE conversations
+SET contact_inbox_id = (
+  SELECT backfills.contact_inbox_id
+  FROM widget_conversation_contact_inbox_backfills AS backfills
+  WHERE backfills.conversation_id = conversations.id
+)
+WHERE id IN (SELECT conversation_id FROM widget_conversation_contact_inbox_backfills);