[bobsingor]

What changes

A signature field's style panel offered a border colour, background, border width and style, but picking one made the field flicker and go back. The engine wrote /MK and /BS and then had nothing to draw them with: the fork's form generator had no /Sig branch, so a restyle reported generation-unavailable, and the form painter skipped signature fields. The viewer drew the new style while the change was pending, then fell back to the engine's picture, which was empty.

Now a signature field's widget draws its box in its style, like every other widget, in both places that draw it:

• Engine: placing a signature field writes its box (the fork bakes it on attach), and a restyle draws it again. A widget in no field draws its box too.
• Viewer: the form painter draws the same box live, so the drawing while a change is pending and the engine's picture after it are the same.

Once a mark is in the field, it shows the mark instead. That happens when the field is signed, or a mark was drawn in with forms.setSignatureAppearance:

• The widget reads hasMark: true.
• Its style no longer applies. A style change is refused with InvalidArg; the style it reads, sent back, is no change.
• The engine never draws over the mark. A resize keeps it.
• The viewer treats it as the widget-mark kind, which has no style rows, so the style panel offers nothing that wouldn't show.

const { field } = await doc.forms.create({
  family: 'signature',
  name: 'approval',
  widgets: [{ page, rect, color: '#1a1a1a', interiorColor: '#eeeeee' }],
});
await doc.forms.updateWidget(field.widgets[0].ref, { interiorColor: '#d43c2c' }); // redrawn
await doc.forms.setSignatureAppearance(field.ref, { pdf: artwork });
// the widget now reads hasMark: true, and a style change fails with InvalidArg

By layer:

• Runtime: pinned to 4346c5131. It brings Draw a signature field's box runtime#114 (GenerateBoxFormAP, the /Sig and no-field branches, the bake on attach) and Zooming with Ctrl + mouse wheel #113 (a comment's rich text reads over the reader's defaults, safe since Read and write a markup annotation's comment as rich text #978). No function is added.
• Engine core:
  • The widget declaration gains hasMark, an engine field.
  • A placed signature widget is predicted with its appearance.
  • WIDGET_STYLE_NAMES lists a widget's style fields. It lives in a zod-free module, so the runtime entry still reaches no zod.
• Engine services:
  • The widget read joins hasMark: a signature field's widget, with a value (signed) or a recorded fit.
  • assertMarkKeepsItsLook refuses a style change on a marked widget before anything is written.
  • A marked widget is never redrawn.
  • A visual fill records its fit in /EMBD_Metadata/AppearanceFit, the key a stamp records its own in. The key's read and write move to appearanceFit.ts, shared by both. Signing records nothing: a signing changes no other key of its widget, and the signing analysis holds it to that.
• Viewer:
  • core-form paints signature fields: fieldBoxOps, the port of the fork's WriteFieldBox, shared with the text field.
  • core-annotation adds the widget-mark kind; widgetKindOf takes the widget.
  • plugin-form gives a marked widget no painter.
  • plugin-annotation: a lent record with no live drawing keeps its picture while a new look is pending, instead of drawing its bare style.
• Contract and SDKs: api:sync. The TypeScript SDK's WidgetAnnotation gains hasMark.
• Docs: "Move and style widgets" and the signature family row on the forms authoring page, and the visual fill on the signatures page, synced to both sites.
• Changesets: engine-core, engine-services, core-annotation, core-form, cloudpdf-contract and cloudpdf-sdk (minor); plugin-form and plugin-annotation (patch).

Not in this PR:

• The empty-panel message: a selected field with a mark in it shows the style panel's generic empty text ("Pick a draw tool or select an annotation to edit its style."), the same text a locked annotation shows.
• Re-fitting a mark: a resized mark stretches as the file places it; it isn't re-fitted into the new box the way a stamp is.

Testing

Run on the branch with main merged in, against the pinned runtime's code (native and wasm, built from the same tree as 4346c5131):

• Engine (signature-visual-fill.test.ts):
  • a placed field has its box in its style;
  • a restyle is regenerated and drawn in the new colour;
  • after a visual fill the widget reads hasMark;
  • a style change is refused, and the same style sent back is accepted;
  • a resize keeps the mark, with no box drawn over it;
  • a field signed without artwork reads hasMark and refuses a style change too.
• Painter parity: 12 new signature cases (every border style, no colours, three turns). The painter draws what the engine writes, item by item.
• Viewer:
  • design.integration.test.ts: a restyled signature field draws live by the painter, then is confirmed by the engine. A marked one is widget-mark with no live drawing.
  • Kind tests: a marked widget has no style rows.
• Suites: engine 1,943, engine-core 1,059, core-annotation 672, plugin-annotation 289, plugin-form 189 and core-form 15 pass, and the touched packages typecheck.
• In the viewer: a placed field restyled red keeps its colour after the engine confirms. With a mark placed in it, the field shows the mark, and its style panel offers nothing.

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