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/sqlite/000017_prefix_snapshot_backfill.down.sql

@@ -0,0 +1,3 @@
+DELETE FROM prefix_snapshot_row;
+UPDATE config_revision SET prefix_snapshot_id = NULL;
+DELETE FROM prefix_snapshot;

migrations/sqlite/000017_prefix_snapshot_backfill.up.sql

@@ -0,0 +1,30 @@
+-- SQLite backfill: one snapshot per revision with materialized prefixes.
+
+INSERT INTO prefix_snapshot (id, content_hash)
+SELECT lower(hex(randomblob(16))),
+    substr(replace(cr.id, '-', '') || replace(cr.id, '-', ''), 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);
+
+UPDATE config_revision
+SET prefix_snapshot_id = (
+    SELECT ps.id FROM prefix_snapshot ps
+    WHERE ps.content_hash = substr(replace(config_revision.id, '-', '') || replace(config_revision.id, '-', ''), 1, 64)
+)
+WHERE prefix_snapshot_id IS NULL
+  AND EXISTS (SELECT 1 FROM revision_materialized_prefix rmp WHERE rmp.revision_id = config_revision.id);
+
+INSERT INTO prefix_snapshot_row (snapshot_id, ord, prefix, community_id, source)
+SELECT cr.prefix_snapshot_id,
+    (SELECT COUNT(*) FROM revision_materialized_prefix r2
+     WHERE r2.revision_id = cr.id AND r2.id <= rmp.id) - 1,
+    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
+  );