From ffa08d76f54cece5b75841f3689fd3ec3859bee2 Mon Sep 17 00:00:00 2001
From: cliffhall <cliff@futurescale.com>
Date: Wed, 26 Aug 2026 13:09:54 -0400
Subject: [PATCH] =?UTF-8?q?fix:=20address=20Copilot=20review=20round=2033?=
 =?UTF-8?q?=20=E2=80=94=20keep=20a=20cleared=20field=20cleared=20across=20?=
 =?UTF-8?q?a=20branch=20switch?=
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The carry filter dropped a name whose value was `undefined`, but clearing a
number or JSON field leaves exactly that: the name present with no value, which
is the user's answer rather than an absence. The incoming branch's defaults
then put the field's default back and undid the clear. Own-property presence
alone is now the test.

Signed-off-by: cliffhall <cliff@futurescale.com>
---
 .../groups/SchemaForm/SchemaForm.test.tsx     | 25 +++++++++++++++++++
 .../groups/SchemaForm/SchemaForm.tsx          |  5 +++-
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/clients/web/src/components/groups/SchemaForm/SchemaForm.test.tsx b/clients/web/src/components/groups/SchemaForm/SchemaForm.test.tsx
index 575c52d0..0d492714 100644
--- a/clients/web/src/components/groups/SchemaForm/SchemaForm.test.tsx
+++ b/clients/web/src/components/groups/SchemaForm/SchemaForm.test.tsx
@@ -2291,6 +2291,31 @@ describe("SchemaForm multiline strings (#2042)", () => {
       expect(onChange).not.toHaveBeenCalled();
     });
 
+    it("keeps a cleared root field cleared across a branch switch", async () => {
+      const user = userEvent.setup();
+      const onChange = vi.fn();
+      const schema: InspectorFormSchema = {
+        type: "object",
+        properties: { count: { type: "number", default: 7, title: "Count" } },
+        anyOf: [
+          { type: "object", title: "A", properties: { x: {} } },
+          { type: "object", title: "B", properties: { y: {} } },
+        ],
+      };
+      renderWithMantine(
+        <SchemaForm
+          schema={schema}
+          // What clearing a number field leaves behind: the name is present
+          // with no value, which is the user's answer and not an absence.
+          values={{ count: undefined }}
+          onChange={onChange}
+        />,
+      );
+      await user.click(screen.getByRole("textbox", { name: /Variant/ }));
+      await user.click(screen.getByRole("option", { name: "B" }));
+      expect(onChange).toHaveBeenCalledWith({ count: undefined });
+    });
+
     it("renders no picker for a single-branch union but still shows its fields", () => {
       const schema: InspectorFormSchema = {
         type: "object",
diff --git a/clients/web/src/components/groups/SchemaForm/SchemaForm.tsx b/clients/web/src/components/groups/SchemaForm/SchemaForm.tsx
index 8dfde16f..7cd2b174 100644
--- a/clients/web/src/components/groups/SchemaForm/SchemaForm.tsx
+++ b/clients/web/src/components/groups/SchemaForm/SchemaForm.tsx
@@ -799,8 +799,11 @@ export function SchemaForm({
       Object.entries(nextProperties)
         .filter(
           ([name, fieldSchema]) =>
+            // Own-property presence alone, `undefined` included: clearing a
+            // number or JSON field leaves the name present with no value, and
+            // that is the user's answer. Dropping it would let the defaults
+            // below put the field's default back and undo the clear.
             Object.hasOwn(values, name) &&
-            values[name] !== undefined &&
             fieldSchema.const === undefined &&
             // Carried only where the incoming branch leaves the root's
             // declaration as it found it. Anything the incoming branch declares