Closing gaps and cleaning house

internal/topdata/FAMILY_EXPANSION_CONTRACT.md

@@ -45,6 +45,7 @@ Canonical generated families declare:
   "name_prefix": "Weapon Focus",
   "label_prefix": "FEAT_WEAPON_FOCUS",
   "constant_prefix": "FEAT_WEAPON_FOCUS",
+  "legacy_family_keys": ["epic_weapon_focus"],
   "default_fields": {
     "DESCRIPTION": {
       "tlk": {
@@ -86,6 +87,8 @@ Rules:
   `REQSKILL`
 - `identity_source: "child_source_value"` tells the builder to reuse IDs/keys from the
   source column when that column already carries feat identity
+- `legacy_family_keys` declares previous generated-family prefixes that should donate
+  existing locked row IDs to the current family when a family is renamed
 - `auto_prereq_fields` binds prerequisite fields to other authored families by
   `family_key`, without code changes
 - `allow_existing_only` limits expansion to already-authored child rows when a family is