feat(db): backfill prefix snapshots and switch read path

Backfill миграция; чтение префиксов через snapshot; запись без дублирования rows.

Co-authored-by: Cursor <[email protected]>

migrations/postgres/000017_prefix_snapshot_backfill.down.sql

@@ -0,0 +1,3 @@
+DELETE FROM prefix_snapshot_row;
+UPDATE config_revision SET prefix_snapshot_id = NULL WHERE prefix_snapshot_id IS NOT NULL;
+DELETE FROM prefix_snapshot;

migrations/postgres/000017_prefix_snapshot_backfill.up.sql

@@ -0,0 +1,31 @@
+-- Backfill prefix snapshots from revision_materialized_prefix.
+
+WITH new_snaps AS (
+    INSERT INTO prefix_snapshot (id, content_hash)
+    SELECT gen_random_uuid(),
+        substr(replace(cr.id::text, '-', '') || replace(cr.id::text, '-', ''), 1, 64)
+    FROM config_revision cr
+    WHERE cr.prefix_snapshot_id IS NULL
+      AND EXISTS (
+          SELECT 1 FROM revision_materialized_prefix rmp WHERE rmp.revision_id = cr.id
+      )
+    RETURNING id, content_hash
+)
+UPDATE config_revision cr
+SET prefix_snapshot_id = ns.id
+FROM new_snaps ns
+WHERE cr.prefix_snapshot_id IS NULL
+  AND ns.content_hash = substr(replace(cr.id::text, '-', '') || replace(cr.id::text, '-', ''), 1, 64);
+
+INSERT INTO prefix_snapshot_row (snapshot_id, ord, prefix, community_id, source)
+SELECT cr.prefix_snapshot_id,
+    (row_number() OVER (PARTITION BY cr.id ORDER BY rmp.id) - 1)::int,
+    rmp.prefix,
+    rmp.community_id,
+    rmp.source
+FROM config_revision cr
+JOIN revision_materialized_prefix rmp ON rmp.revision_id = cr.id
+WHERE cr.prefix_snapshot_id IS NOT NULL
+  AND NOT EXISTS (
+      SELECT 1 FROM prefix_snapshot_row psr WHERE psr.snapshot_id = cr.prefix_snapshot_id
+  );