test: cover pytest launch fields in child-process attach regression

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Co-authored-by: rchiodo <19672699+rchiodo@users.noreply.github.com>

Author: Copilot

src/test/unittest/hooks/childProcessAttachService.unit.test.ts

@@ -235,4 +235,32 @@ suite('Debug - Attach to Child Process', () => {
         // The original data object must not be mutated.
         expect(data).to.have.property('purpose').deep.equal(['debug-test']);
     });
+    test('Child process attach keeps pytest launch fields while removing debug-test purpose', async () => {
+        const data: AttachRequestArguments = {
+            request: 'attach',
+            type: debuggerTypeName,
+            name: 'Attach',
+            port: 1234,
+            subProcessId: 2,
+            purpose: ['debug-test'],
+            module: 'pytest',
+            args: ['-s', '${workspaceFolder}/tests/test_multiproc.py'],
+            console: 'integratedTerminal',
+        };
+        const session: any = {};
+
+        getWorkspaceFoldersStub.returns(undefined);
+        startDebuggingStub.resolves(true);
+
+        await attachService.attach(data, session);
+
+        sinon.assert.calledOnce(startDebuggingStub);
+        const [, secondArg] = startDebuggingStub.args[0];
+        expect(secondArg).to.include({
+            module: 'pytest',
+            console: 'integratedTerminal',
+        });
+        expect(secondArg).to.have.property('args').deep.equal(['-s', '${workspaceFolder}/tests/test_multiproc.py']);
+        expect(secondArg).to.not.have.property('purpose');
+    });
 });