fix(scripts): correct autotag rule direction in legacy migration

The old autotags worked child -> parent (adding child_id pulled in parent_id,
per tfm__add_file_to_tag_recursive). The new tag_rules model is "when_tag
applied -> then_tag follows", so child must map to when_tag and parent to
then_tag. The transform had it reversed, so migrated rules never fired —
adding a tag added only itself.

Map child_id -> when_tag_id, parent_id -> then_tag_id. Verified on a scratch DB.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/migrate-legacy/README.md

@@ -56,7 +56,7 @@ psql "$NEW_DSN" -v ON_ERROR_STOP=1 -f transform.sql
 | `mime`                | `core.mime_types`       | id **uuid → smallint** (remapped by `name`); types not already seeded are added |
 | `categories`          | `data.categories`       | id kept; `is_private` → **`is_public`** (inverted) |
 | `tags`                | `data.tags`             | id + `category_id` kept; inverted privacy |
-| `autotags`            | `data.tag_rules`        | `parent_id` → `when_tag_id`, `child_id` → `then_tag_id` |
+| `autotags`            | `data.tag_rules`        | `child_id` → `when_tag_id`, `parent_id` → `then_tag_id` (old: adding the child pulled in the parent) |
 | `files`               | `data.files`            | id kept; `datetime` → `content_datetime`; `orig_name` → `original_name`; **EXIF** lifted from `metadata->'exif'` into the `exif` column, the rest stays as user `metadata` |
 | `file_tag`            | `data.file_tag`         | orphan rows skipped |
 | `pools`               | `data.pools`            | id kept; `parent_id` + `created` preserved under `metadata` (see below) |

scripts/migrate-legacy/transform.sql

@@ -92,14 +92,17 @@ JOIN user_id_map um ON um.old_id = t.creator_id
 ON CONFLICT (id) DO NOTHING;
 
 -- ---------------------------------------------------------------------------
--- 5. Tag rules (old `autotags`): parent -> when_tag, child -> then_tag.
+-- 5. Tag rules (old `autotags`).  In the old schema adding the child tag pulled
+--    in its parent (tfm__add_file_to_tag_recursive: for child_id = t_id it adds
+--    parent_id). The new model is "when_tag applied -> then_tag follows", so the
+--    trigger child becomes when_tag and the auto-applied parent becomes then_tag.
 --    Skip rules whose tags didn't migrate.
 -- ---------------------------------------------------------------------------
 INSERT INTO data.tag_rules (when_tag_id, then_tag_id, is_active)
-SELECT a.parent_id, a.child_id, a.is_active
+SELECT a.child_id, a.parent_id, a.is_active
 FROM legacy.autotags a
-WHERE EXISTS (SELECT 1 FROM data.tags t WHERE t.id = a.parent_id)
+WHERE EXISTS (SELECT 1 FROM data.tags t WHERE t.id = a.child_id)
-  AND EXISTS (SELECT 1 FROM data.tags t WHERE t.id = a.child_id)
+  AND EXISTS (SELECT 1 FROM data.tags t WHERE t.id = a.parent_id)
 ON CONFLICT (when_tag_id, then_tag_id) DO NOTHING;
 
 -- ---------------------------------------------------------------------------