@@ -0,0 +1,15 @@
+---
+'@objectstack/metadata-protocol': patch
+---
+
+fix(metadata-protocol): a plain clone no longer reports the source's empty read-only columns as dropped fields
+
+Clause-②: no
+Metadata-protocol: none
+
+`cloneData` copied every column of the source into the insert, read-only ones included, even where the source held no value. The engine's read-only strip judged each such column a caller-supplied key and reported it, so a clone with no `overrides` of a row whose read-only column was empty answered `droppedFields` naming that column, and the REST `X-ObjectStack-Dropped-Fields` header repeated it. Nothing had been sent and nothing was lost, but the console announced "fields dropped" on every such clone.
+
+The clone now leaves a read-only column whose source value is empty (`null`) out of the copy. The stored row is the same as before: the strip removed that key from a non-system caller anyway, and the insert's defaults treat an explicit `null` exactly as an omitted key. What still reports:
+
+- a read-only column the source holds a VALUE in is still copied, stripped and reported, body and header, so the caller reading the default back is told why;
+- a read-only field set through `overrides` is still stripped and reported, whatever the source held.
@@ -14670,7 +14670,19 @@ export class ObjectStackProtocolImplementation implements
                 || (def as any).type === 'formula'
                 || (def as any).type === 'summary') {
                 delete data[name];
+                continue;
             }
+            // [#29200] A read-only column the source left EMPTY is not carried
+            // into the insert. Carried, it reached `engine.insert`'s strip as a
+            // present key and was reported in `droppedFields` (and the
+            // `X-ObjectStack-Dropped-Fields` header) although neither the caller
+            // nor the source supplied a value. Leaving it out stores the same
+            // row: the strip would have taken it from a non-system caller, and
+            // the insert's defaults treat an explicit `null` exactly as an
+            // omitted key. A read-only column that HOLDS a value is still
+            // carried, stripped and reported (#15703), and so is one the caller
+            // sets through `overrides`, which are applied below.
+            if ((def as any).readonly && data[name] == null) delete data[name];
         }
         // Caller overrides win (new name, cleared unique field, reset status…).
         if (request.overrides && typeof request.overrides === 'object') {
 
@@ -148,9 +148,19 @@ describe('showcase: clone and createMany advertise the readonly strip in the hea
     expect(res.status).toBe(201);
     const body = await res.json();
     expect(namesReadonlyLeadScore(body), JSON.stringify(body?.droppedFields)).toBe(true);
-    // A plain clone copies the source's other readonly columns too, so the
-    // header may name more than lead_score; it names what the body names.
-    expect(res.headers.get('X-ObjectStack-Dropped-Fields') ?? '').toContain('lead_score;reason=readonly');
+    // The source's readonly columns are all empty, so the clone carries none of
+    // them into the insert (#29200): the header names lead_score and nothing else.
+    expect(res.headers.get('X-ObjectStack-Dropped-Fields')).toBe('lead_score;reason=readonly');
+  });
+
+  // #29200: the source's lead_score is empty and the caller sent none, so a
+  // plain clone strips nothing and must not announce a dropped field.
+  it('a plain clone of a source whose lead_score is empty: no droppedFields, no header', async () => {
+    const res = await stack.apiAs(admin, 'POST', `${OBJ}/${sourceId}/clone`, {});
+    const body = await res.json();
+    expect(res.status, JSON.stringify(body)).toBe(201);
+    expect(body?.droppedFields, JSON.stringify(body?.droppedFields)).toBeUndefined();
+    expect(res.headers.get('X-ObjectStack-Dropped-Fields')).toBeNull();
   });
 
   it('a two-row createMany carrying lead_score: body and header name lead_score once', async () => {
 
@@ -54,9 +54,10 @@ const PROJ = {
   },
 };
 
-// Clone copies every column of the source it does not reset, readonly ones
-// included, so a clone of a PROJ row also reports the source's `ro2`. Clone is
-// read on its own objects: one readonly column, and none.
+// Clone copies the source's readonly columns that hold a value (#15703: the
+// strip of a copied value is reported), so a clone of a PROJ row would also
+// report any `ro2` the source carried. Clone is read on its own objects: one
+// readonly column, and none.
 const CLONE_OBJECT = 'hdr_drops_clone';
 const PLAIN_OBJECT = 'hdr_drops_plain';
 const CLONE_PROJ = {
@@ -116,6 +117,8 @@ async function boot() {
   // `readonlyWhen` already true; seeded under `isSystem`.
   await engine.insert(OBJECT, { id: 'closed1', title: 'closed', status: 'closed', locked: 'L' } as any, { context: { isSystem: true } } as any);
   await engine.insert(CLONE_OBJECT, { id: 'src1', title: 'source', ro: 'seeded' } as any, { context: { isSystem: true } } as any);
+  // #29200: the same object, its readonly column left empty (null).
+  await engine.insert(CLONE_OBJECT, { id: 'src_empty', title: 'empty source' } as any);
   await engine.insert(PLAIN_OBJECT, { id: 'plain1', title: 'source' } as any);
 
   const protocol = new ObjectStackProtocolImplementation(engine as any);
@@ -147,6 +150,38 @@ describe('clone: the header names what the body reports', () => {
     expect(r.header).toBe('ro;reason=readonly');
   });
 
+  // #29200: the caller sent no readonly key and the copy carried none with a
+  // value, so the engine stripped nothing the caller or the source supplied.
+  it('a plain clone of a row whose readonly column is empty: no droppedFields, no header', async () => {
+    const b = await boot();
+    const r = await b.call('/api/v1/data/:object/:id/clone', {}, { object: CLONE_OBJECT, id: 'src_empty' });
+    expect(r.status, JSON.stringify(r.body)).toBe(201);
+    expect(r.body).not.toHaveProperty('droppedFields');
+    expect(r.header).toBeUndefined();
+    expect(r.body.record.ro ?? null).toBeNull();
+    expect(r.body.record.title).toBe('empty source');
+  });
+
+  it('overrides setting the readonly field on that empty source: still reported, body and header', async () => {
+    const b = await boot();
+    const r = await b.call('/api/v1/data/:object/:id/clone', { overrides: { ro: 'forged' } }, { object: CLONE_OBJECT, id: 'src_empty' });
+    expect(r.status, JSON.stringify(r.body)).toBe(201);
+    expect(r.body.droppedFields).toEqual([{ object: CLONE_OBJECT, fields: ['ro'], reason: 'readonly' }]);
+    expect(r.header).toBe('ro;reason=readonly');
+    expect(r.body.record.ro ?? null).toBeNull();
+  });
+
+  // #15703 ruled that a clone REPORTS the readonly value it copied and the
+  // engine stripped: the caller reads the default back and is told why.
+  it('a plain clone of a row whose readonly column holds a value: still reported, body and header', async () => {
+    const b = await boot();
+    const r = await b.call('/api/v1/data/:object/:id/clone', {}, { object: CLONE_OBJECT, id: 'src1' });
+    expect(r.status, JSON.stringify(r.body)).toBe(201);
+    expect(r.body.droppedFields).toEqual([{ object: CLONE_OBJECT, fields: ['ro'], reason: 'readonly' }]);
+    expect(r.header).toBe('ro;reason=readonly');
+    expect(r.body.record.ro ?? null).toBeNull();
+  });
+
   it('a clone that strips nothing: no droppedFields, no header (the control)', async () => {
     const b = await boot();
     const r = await b.call('/api/v1/data/:object/:id/clone', { overrides: { title: 'plain copy' } }, { object: PLAIN_OBJECT, id: 'plain1' });