fix: remove weak postcheck from validator removal to prevent idempotency skip

The validator-removal operation used a postcheck that matched
options.validationLevel=strict, which was already satisfied when
the original validator also used strict. This caused the idempotency
probe to skip the collMod entirely, leaving the validator in place.

Empty the postcheck array so the operation always executes. The collMod
with validator:{} is inherently idempotent so no safety is lost.

Author: wmadden

packages/3-mongo-target/2-mongo-adapter/src/core/mongo-planner.ts

@@ -243,17 +243,7 @@ function planValidatorDiff(
         }),
       },
     ],
-    postcheck: [
-      {
-        description: `validator removed from ${collName}`,
-        source: new ListCollectionsCommand(),
-        filter: MongoAndExpr.of([
-          MongoFieldFilter.eq('name', collName),
-          MongoFieldFilter.eq('options.validationLevel', 'strict'),
-        ]),
-        expect: 'exists' as const,
-      },
-    ],
+    postcheck: [],
   };
 }
 

packages/3-mongo-target/2-mongo-adapter/test/mongo-planner.test.ts

@@ -584,7 +584,7 @@ describe('MongoMigrationPlanner', () => {
       expect(op.postcheck[0]!.expect).toBe('exists');
     });
 
-    it('validator remove has precheck and postcheck', () => {
+    it('validator remove has precheck and empty postcheck', () => {
       const contract = makeContract({ users: {} });
       const origin: MongoSchemaIR = {
         collections: {
@@ -607,9 +607,7 @@ describe('MongoMigrationPlanner', () => {
       expect(op.precheck[0]!.source.kind).toBe('listCollections');
       expect(op.precheck[0]!.expect).toBe('exists');
 
-      expect(op.postcheck).toHaveLength(1);
-      expect(op.postcheck[0]!.source.kind).toBe('listCollections');
-      expect(op.postcheck[0]!.expect).toBe('exists');
+      expect(op.postcheck).toHaveLength(0);
     });
 
     it('classifies validator removal as widening', () => {