Add compact JSON formatter with format-on-paste (§03A)

src/app/infrastructure/monaco-format.ts

@@ -0,0 +1,51 @@
+/**
+ * Monaco JSON formatting (spec §03A; docs/architecture/08 → compact formatter).
+ *
+ * Two pieces, both backed by the portable core pretty-printer (`core/json-format`):
+ *   - `configureJsonFormatter()` registers a document-formatting provider so
+ *     "Format Document" (Shift+Alt+F) produces Vega's compact style.
+ *   - `installFormatOnPaste(editor)` reindents the whole document after a paste,
+ *     satisfying the spec's "pasting … triggers automatic reformatting".
+ *
+ * Both no-op when the document is not valid JSON, so a partial/in-progress paste
+ * is never mangled (mirrors auto-save's "skip when unparseable" rule). Paste
+ * handling is wired directly via `onDidPaste` rather than Monaco's `formatOnPaste`
+ * option so it reformats the entire spec (not just the pasted range) and does not
+ * depend on which registered formatter Monaco happens to pick.
+ */
+
+import * as monaco from 'monaco-editor/esm/vs/editor/edcore.main';
+import { formatJson } from '@core/json-format';
+
+let registered = false;
+
+/** Register the compact JSON document formatter once. Idempotent. */
+export function configureJsonFormatter(): void {
+  if (registered) return;
+  registered = true;
+  monaco.languages.registerDocumentFormattingEditProvider('json', {
+    provideDocumentFormattingEdits: (model, options) => {
+      const current = model.getValue();
+      const formatted = formatJson(current, { indent: options.tabSize });
+      if (formatted === null || formatted === current) return [];
+      return [{ range: model.getFullModelRange(), text: formatted }];
+    },
+  });
+}
+
+/**
+ * Reformat the whole document after each paste. Returns a disposable; callers
+ * dispose it when the editor unmounts.
+ */
+export function installFormatOnPaste(
+  editor: monaco.editor.IStandaloneCodeEditor,
+): monaco.IDisposable {
+  return editor.onDidPaste(() => {
+    const model = editor.getModel();
+    if (!model) return;
+    const current = model.getValue();
+    const formatted = formatJson(current, { indent: model.getOptions().tabSize });
+    if (formatted === null || formatted === current) return;
+    editor.executeEdits('format-on-paste', [{ range: model.getFullModelRange(), text: formatted }]);
+  });
+}