diff --git a/internal/upgrade/version.go b/internal/upgrade/version.go
index 6b3efe02..be8b246b 100644
--- a/internal/upgrade/version.go
+++ b/internal/upgrade/version.go
@@ -2,4 +2,4 @@ package upgrade
 
 // RequiredSchemaVersion is the schema migration version this binary requires.
 // Bump this whenever adding a new SQL migration file.
-const RequiredSchemaVersion uint = 85
+const RequiredSchemaVersion uint = 86
diff --git a/migrations/000086_fix_channel_contacts_merged_fk.down.sql b/migrations/000086_fix_channel_contacts_merged_fk.down.sql
new file mode 100644
index 00000000..dd7b9d17
--- /dev/null
+++ b/migrations/000086_fix_channel_contacts_merged_fk.down.sql
@@ -0,0 +1,8 @@
+-- Roll back only the corrective FK.
+-- Do not recreate the old self-reference FK because it is incompatible with valid data.
+BEGIN;
+
+ALTER TABLE channel_contacts
+DROP CONSTRAINT IF EXISTS fk_channel_contacts_merged_id;
+
+COMMIT;
diff --git a/migrations/000086_fix_channel_contacts_merged_fk.up.sql b/migrations/000086_fix_channel_contacts_merged_fk.up.sql
new file mode 100644
index 00000000..877fc615
--- /dev/null
+++ b/migrations/000086_fix_channel_contacts_merged_fk.up.sql
@@ -0,0 +1,14 @@
+-- Fix channel_contacts.merged_id FK.
+-- merged_id stores tenant_users.id, not channel_contacts.id.
+BEGIN;
+
+ALTER TABLE channel_contacts
+DROP CONSTRAINT IF EXISTS fk_channel_contacts_merged_id;
+
+ALTER TABLE channel_contacts
+ADD CONSTRAINT fk_channel_contacts_merged_id
+FOREIGN KEY (merged_id)
+REFERENCES tenant_users(id)
+ON DELETE SET NULL;
+
+COMMIT;
diff --git a/migrations/audit_fk_integrity.sql b/migrations/audit_fk_integrity.sql
index be7f0219..2a50efc2 100644
--- a/migrations/audit_fk_integrity.sql
+++ b/migrations/audit_fk_integrity.sql
@@ -66,11 +66,18 @@ FROM webhooks w
 LEFT JOIN channel_instances ci ON ci.id = w.channel_id
 WHERE w.channel_id IS NOT NULL AND ci.id IS NULL;
 
--- channel_contacts: merged_id self-ref orphans
-SELECT 'channel_contacts.merged_id orphans' AS check_name, COUNT(*) AS violations
+-- channel_contacts: merged_id tenant_users orphans
+SELECT 'channel_contacts.merged_id tenant_users orphans' AS check_name, COUNT(*) AS violations
 FROM channel_contacts cc
-LEFT JOIN channel_contacts cc2 ON cc2.id = cc.merged_id
-WHERE cc.merged_id IS NOT NULL AND cc2.id IS NULL;
+LEFT JOIN tenant_users tu ON tu.id = cc.merged_id
+WHERE cc.merged_id IS NOT NULL AND tu.id IS NULL;
+
+-- channel_contacts: merged_id tenant drift
+SELECT 'channel_contacts.merged_id tenant drift' AS check_name, COUNT(*) AS violations
+FROM channel_contacts cc
+JOIN tenant_users tu ON tu.id = cc.merged_id
+WHERE cc.merged_id IS NOT NULL
+  AND cc.tenant_id <> tu.tenant_id;
 
 -- traces: parent_trace_id self-ref orphans
 SELECT 'traces.parent_trace_id orphans' AS check_name, COUNT(*) AS violations