diff --git a/internal/upgrade/version.go b/internal/upgrade/version.go
index ed890c12..ed5f6ffd 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 = 34
+const RequiredSchemaVersion uint = 35
diff --git a/migrations/000035_contact_thread_id.down.sql b/migrations/000035_contact_thread_id.down.sql
new file mode 100644
index 00000000..d390ab3d
--- /dev/null
+++ b/migrations/000035_contact_thread_id.down.sql
@@ -0,0 +1,5 @@
+DROP INDEX IF EXISTS idx_channel_contacts_tenant_type_sender;
+ALTER TABLE channel_contacts DROP COLUMN IF EXISTS thread_type;
+ALTER TABLE channel_contacts DROP COLUMN IF EXISTS thread_id;
+CREATE UNIQUE INDEX idx_channel_contacts_tenant_type_sender
+  ON channel_contacts (tenant_id, channel_type, sender_id);
diff --git a/migrations/000035_contact_thread_id.up.sql b/migrations/000035_contact_thread_id.up.sql
new file mode 100644
index 00000000..ca6f9949
--- /dev/null
+++ b/migrations/000035_contact_thread_id.up.sql
@@ -0,0 +1,22 @@
+ALTER TABLE channel_contacts ADD COLUMN thread_id VARCHAR(100);
+ALTER TABLE channel_contacts ADD COLUMN thread_type VARCHAR(20);
+
+-- Fix sender_id: strip "|username" suffix, keep only numeric ID.
+-- Step 1: Delete "|username" rows where a numeric-only row already exists (avoid UNIQUE conflict).
+DELETE FROM channel_contacts
+WHERE sender_id LIKE '%|%'
+  AND EXISTS (
+    SELECT 1 FROM channel_contacts c2
+    WHERE c2.tenant_id = channel_contacts.tenant_id
+      AND c2.channel_type = channel_contacts.channel_type
+      AND c2.sender_id = split_part(channel_contacts.sender_id, '|', 1)
+      AND COALESCE(c2.thread_id, '') = COALESCE(channel_contacts.thread_id, '')
+  );
+-- Step 2: Update remaining "|username" rows (no numeric counterpart) to strip suffix.
+UPDATE channel_contacts
+SET sender_id = split_part(sender_id, '|', 1)
+WHERE sender_id LIKE '%|%';
+
+DROP INDEX IF EXISTS idx_channel_contacts_tenant_type_sender;
+CREATE UNIQUE INDEX idx_channel_contacts_tenant_type_sender
+  ON channel_contacts (tenant_id, channel_type, sender_id, COALESCE(thread_id, ''));