diff --git a/src/db/queries.ts b/src/db/queries.ts
index e64022d..c3d6c61 100644
--- a/src/db/queries.ts
+++ b/src/db/queries.ts
@@ -69,11 +69,11 @@ export class VConQueries {
         }
       }
 
-      // Insert main vcon
+      // Upsert main vcon — idempotent on re-submission of same UUID
       // Set id = uuid so they match (id is the PK, uuid is the vCon document UUID)
       const { data: vconData, error: vconError } = await this.supabase
         .from('vcons')
-        .insert({
+        .upsert({
           id: vcon.uuid,     // Explicitly set id to match uuid
           uuid: vcon.uuid,
           vcon_version: vcon.vcon ?? '0.3.0',
@@ -85,7 +85,7 @@ export class VConQueries {
           redacted: vcon.redacted || {},
           appended: vcon.appended || {},        // ✅ Added per spec
           tenant_id: tenantId,                  // ✅ Added for RLS multi-tenant support
-        })
+        }, { onConflict: 'id' })
         .select('id, uuid')
         .single();
 
@@ -97,6 +97,14 @@ export class VConQueries {
         throw vconError;
       }
 
+      // Delete existing child rows so re-submission replaces them cleanly
+      await Promise.all([
+        this.supabase.from('parties').delete().eq('vcon_id', vconData.id),
+        this.supabase.from('dialog').delete().eq('vcon_id', vconData.id),
+        this.supabase.from('analysis').delete().eq('vcon_id', vconData.id),
+        this.supabase.from('attachments').delete().eq('vcon_id', vconData.id),
+      ]);
+
     // Insert parties
     if (vcon.parties.length > 0) {
       const partiesData = vcon.parties.map((party, index) => ({
diff --git a/tests/db-queries.test.ts b/tests/db-queries.test.ts
index 1378b93..10bbb11 100644
--- a/tests/db-queries.test.ts
+++ b/tests/db-queries.test.ts
@@ -19,6 +19,7 @@ describe('VConQueries', () => {
         from: vi.fn(),
         select: vi.fn(),
         insert: vi.fn(),
+        upsert: vi.fn(),
         update: vi.fn(),
         delete: vi.fn(),
         eq: vi.fn(),
@@ -70,7 +71,7 @@ describe('VConQueries', () => {
 
       expect(result.uuid).toBe(testVCon.uuid);
       expect(mockSupabase.from).toHaveBeenCalledWith('vcons');
-      expect(mockSupabase.insert).toHaveBeenCalled();
+      expect(mockSupabase.upsert).toHaveBeenCalled();
     });
 
     it('should create vCon with all components (dialog, analysis, attachments)', async () => {