diff --git a/migrations/04_fk_policies.sql b/migrations/04_fk_policies.sql
new file mode 100644
index 0000000..e1144f1
--- /dev/null
+++ b/migrations/04_fk_policies.sql
@@ -0,0 +1,190 @@
+-- ==========================================================
+-- 04_fk_policies.sql : normalisation des politiques ON DELETE
+-- A exécuter après 01_init.sql et 03_checks.sql
+-- ==========================================================
+
+-- Helper: Drop FK d'une table/colonne si elle existe (par son/leurs noms de colonne)
+-- puis recrée la contrainte avec la clause fournie
+-- Utilise information_schema pour retrouver le nom de contrainte auto-généré
+-- NB: schema = public
+
+-- ========== messages.id_expediteur -> utilisateurs.id : SET NULL (au lieu de CASCADE)
+DO $$
+DECLARE
+  conname text;
+BEGIN
+  SELECT tc.constraint_name INTO conname
+  FROM information_schema.table_constraints tc
+  JOIN information_schema.key_column_usage kcu
+    ON tc.constraint_name = kcu.constraint_name AND tc.table_schema = kcu.table_schema
+  WHERE tc.table_schema='public'
+    AND tc.table_name='messages'
+    AND tc.constraint_type='FOREIGN KEY'
+    AND kcu.column_name='id_expediteur';
+  IF conname IS NOT NULL THEN
+    EXECUTE format('ALTER TABLE public.messages DROP CONSTRAINT %I', conname);
+  END IF;
+  EXECUTE $sql$
+    ALTER TABLE public.messages
+    ADD CONSTRAINT fk_messages_id_expediteur
+    FOREIGN KEY (id_expediteur) REFERENCES public.utilisateurs(id) ON DELETE SET NULL
+  $sql$;
+END $$;
+
+-- ========== parents.id_co_parent -> utilisateurs.id : SET NULL
+DO $$
+DECLARE conname text;
+BEGIN
+  SELECT tc.constraint_name INTO conname
+  FROM information_schema.table_constraints tc
+  JOIN information_schema.key_column_usage kcu
+    ON tc.constraint_name = kcu.constraint_name AND tc.table_schema = kcu.table_schema
+  WHERE tc.table_schema='public'
+    AND tc.table_name='parents'
+    AND tc.constraint_type='FOREIGN KEY'
+    AND kcu.column_name='id_co_parent';
+  IF conname IS NOT NULL THEN
+    EXECUTE format('ALTER TABLE public.parents DROP CONSTRAINT %I', conname);
+  END IF;
+  EXECUTE $sql$
+    ALTER TABLE public.parents
+    ADD CONSTRAINT fk_parents_id_co_parent
+    FOREIGN KEY (id_co_parent) REFERENCES public.utilisateurs(id) ON DELETE SET NULL
+  $sql$;
+END $$;
+
+-- ========== avenants_contrats.initie_par -> utilisateurs.id : SET NULL
+DO $$
+DECLARE conname text;
+BEGIN
+  SELECT tc.constraint_name INTO conname
+  FROM information_schema.table_constraints tc
+  JOIN information_schema.key_column_usage kcu
+    ON tc.constraint_name = kcu.constraint_name AND tc.table_schema = kcu.table_schema
+  WHERE tc.table_schema='public'
+    AND tc.table_name='avenants_contrats'
+    AND tc.constraint_type='FOREIGN KEY'
+    AND kcu.column_name='initie_par';
+  IF conname IS NOT NULL THEN
+    EXECUTE format('ALTER TABLE public.avenants_contrats DROP CONSTRAINT %I', conname);
+  END IF;
+  EXECUTE $sql$
+    ALTER TABLE public.avenants_contrats
+    ADD CONSTRAINT fk_avenants_contrats_initie_par
+    FOREIGN KEY (initie_par) REFERENCES public.utilisateurs(id) ON DELETE SET NULL
+  $sql$;
+END $$;
+
+-- ========== evenements.id_am -> utilisateurs.id : SET NULL
+DO $$
+DECLARE conname text;
+BEGIN
+  SELECT tc.constraint_name INTO conname
+  FROM information_schema.table_constraints tc
+  JOIN information_schema.key_column_usage kcu
+    ON tc.constraint_name = kcu.constraint_name AND tc.table_schema = kcu.table_schema
+  WHERE tc.table_schema='public'
+    AND tc.table_name='evenements'
+    AND tc.constraint_type='FOREIGN KEY'
+    AND kcu.column_name='id_am';
+  IF conname IS NOT NULL THEN
+    EXECUTE format('ALTER TABLE public.evenements DROP CONSTRAINT %I', conname);
+  END IF;
+  EXECUTE $sql$
+    ALTER TABLE public.evenements
+    ADD CONSTRAINT fk_evenements_id_am
+    FOREIGN KEY (id_am) REFERENCES public.utilisateurs(id) ON DELETE SET NULL
+  $sql$;
+END $$;
+
+-- ========== evenements.id_parent -> parents.id_utilisateur : SET NULL
+DO $$
+DECLARE conname text;
+BEGIN
+  SELECT tc.constraint_name INTO conname
+  FROM information_schema.table_constraints tc
+  JOIN information_schema.key_column_usage kcu
+    ON tc.constraint_name = kcu.constraint_name AND tc.table_schema = kcu.table_schema
+  WHERE tc.table_schema='public'
+    AND tc.table_name='evenements'
+    AND tc.constraint_type='FOREIGN KEY'
+    AND kcu.column_name='id_parent';
+  IF conname IS NOT NULL THEN
+    EXECUTE format('ALTER TABLE public.evenements DROP CONSTRAINT %I', conname);
+  END IF;
+  EXECUTE $sql$
+    ALTER TABLE public.evenements
+    ADD CONSTRAINT fk_evenements_id_parent
+    FOREIGN KEY (id_parent) REFERENCES public.parents(id_utilisateur) ON DELETE SET NULL
+  $sql$;
+END $$;
+
+-- ========== evenements.cree_par -> utilisateurs.id : SET NULL
+DO $$
+DECLARE conname text;
+BEGIN
+  SELECT tc.constraint_name INTO conname
+  FROM information_schema.table_constraints tc
+  JOIN information_schema.key_column_usage kcu
+    ON tc.constraint_name = kcu.constraint_name AND tc.table_schema = kcu.table_schema
+  WHERE tc.table_schema='public'
+    AND tc.table_name='evenements'
+    AND tc.constraint_type='FOREIGN KEY'
+    AND kcu.column_name='cree_par';
+  IF conname IS NOT NULL THEN
+    EXECUTE format('ALTER TABLE public.evenements DROP CONSTRAINT %I', conname);
+  END IF;
+  EXECUTE $sql$
+    ALTER TABLE public.evenements
+    ADD CONSTRAINT fk_evenements_cree_par
+    FOREIGN KEY (cree_par) REFERENCES public.utilisateurs(id) ON DELETE SET NULL
+  $sql$;
+END $$;
+
+-- ========== signalements_bugs.id_utilisateur -> utilisateurs.id : SET NULL
+DO $$
+DECLARE conname text;
+BEGIN
+  SELECT tc.constraint_name INTO conname
+  FROM information_schema.table_constraints tc
+  JOIN information_schema.key_column_usage kcu
+    ON tc.constraint_name = kcu.constraint_name AND tc.table_schema = kcu.table_schema
+  WHERE tc.table_schema='public'
+    AND tc.table_name='signalements_bugs'
+    AND tc.constraint_type='FOREIGN KEY'
+    AND kcu.column_name='id_utilisateur';
+  IF conname IS NOT NULL THEN
+    EXECUTE format('ALTER TABLE public.signalements_bugs DROP CONSTRAINT %I', conname);
+  END IF;
+  EXECUTE $sql$
+    ALTER TABLE public.signalements_bugs
+    ADD CONSTRAINT fk_signalements_bugs_id_utilisateur
+    FOREIGN KEY (id_utilisateur) REFERENCES public.utilisateurs(id) ON DELETE SET NULL
+  $sql$;
+END $$;
+
+-- ========== validations.id_utilisateur -> utilisateurs.id : SET NULL
+DO $$
+DECLARE conname text;
+BEGIN
+  SELECT tc.constraint_name INTO conname
+  FROM information_schema.table_constraints tc
+  JOIN information_schema.key_column_usage kcu
+    ON tc.constraint_name = kcu.constraint_name AND tc.table_schema = kcu.table_schema
+  WHERE tc.table_schema='public'
+    AND tc.table_name='validations'
+    AND tc.constraint_type='FOREIGN KEY'
+    AND kcu.column_name='id_utilisateur';
+  IF conname IS NOT NULL THEN
+    EXECUTE format('ALTER TABLE public.validations DROP CONSTRAINT %I', conname);
+  END IF;
+  EXECUTE $sql$
+    ALTER TABLE public.validations
+    ADD CONSTRAINT fk_validations_id_utilisateur
+    FOREIGN KEY (id_utilisateur) REFERENCES public.utilisateurs(id) ON DELETE SET NULL
+  $sql$;
+END $$;
+
+-- NB:
+-- D'autres FK déjà correctes : CASCADE (assistantes_maternelles, parents, enfants_parents, dossiers, messages.id_dossier, contrats, avenants_contrats.id_contrat, evenements.id_enfant), SET NULL (uploads).
+-- On laisse ON UPDATE par défaut (NO ACTION), car les UUID ne changent pas.