fix(web): numbered composer lists nest and lift correctly#17138

@@ -0,0 +1,107 @@
+// Run in the isolated dev app's preview_evaluate context. Never sends a turn.
+export const fixtures = {
+  A: ["1. parent\n2. ch|ild", "10. parent\n11. ch|ild"],
+  B: ["2. parent\n   1. sibling\n      1. grandchild\n3. ch|ild"],
+  C: ["1. parent\n   1. child\n      1. |"],
+  D: ["7. solo|", "1. parent\n\n2. ch|ild", "10. parent\n|11. child"],
+  E: [
+    "- parent\n- ch|ild",
+    "- [x] parent\n- [ ] ch|ild",
+    "1. parent\n   09) sibling\n2) ch|ild",
+    "1. parent\n   09) sibling\n2. ch|ild",
+  ],
+};
+
+export async function seed(marked) {
+  const { buildDocJson, serializeEditorDoc } = await import("/src/composer-rich-text-doc.ts");
+  const element = document.querySelector('[data-testid="composer-editor"]');
+  if (!element?.editor) throw new Error("Open an empty synthetic ChatComposer first");
+  const editor = element.editor;
+  const rich = element.dataset.composerRichText === "true";
+  const offset = marked.indexOf("|");
+  const text = marked.replace("|", "");
+  const doc = editor.schema.nodeFromJSON(buildDocJson(text, () => null, { styling: rich }));
+  editor.view.dispatch(editor.state.tr.replaceWith(0, editor.state.doc.content.size, doc.content));
+  const map = serializeEditorDoc(editor.state.doc);
+  // Structural rich markers have no editable prefix position. Use content start.
+  const run =
+    map.runs.find(
+      (r) => r.kind === "text" && offset >= r.mdStart && offset <= r.mdStart + r.mdLen,
+    ) ??
+    map.runs.find((r) => r.mdStart >= offset && r.kind !== "prefix") ??
+    map.runs.at(-1);
+  const pos = Math.min(
+    editor.state.doc.content.size - 1,
+    run ? run.pmPos + Math.max(0, Math.min(run.docLen, offset - run.mdStart)) : 1,
+  );
+  editor.view.dispatch(
+    editor.state.tr.setSelection(editor.state.selection.constructor.create(editor.state.doc, pos)),
+  );
+  editor.view.focus();
+  return { requested: text, canonical: map.value, requestedOffset: offset, pmPos: pos, rich };
+}
+
+export async function observe() {
+  const { serializeEditorDoc } = await import("/src/composer-rich-text-doc.ts");
+  const editor = document.querySelector('[data-testid="composer-editor"]').editor;
+  return {
+    text: serializeEditorDoc(editor.state.doc).value,
+    selection: editor.state.selection.toJSON(),
+  };
+}
+
+export async function installRpc(environmentId) {
+  const { createEnvironmentRpcCommand } =
+    await import("/@fs/home/ubuntu/wt/issue-17124/packages/client-runtime/src/state/runtime.ts");

@@ -149,6 +149,27 @@ function currentLine(value: string, cursor: number): { start: number; end: numbe
   return { start, end, text: value.slice(start, end) };
 }
 
+function* listMarkersAbove(
+  value: string,
+  start: number,
+  tokens: ReturnType<typeof inlineTokenRanges>,
+) {
+  let tokenIndex = tokens.length - 1;
+  while (start > 0) {
+    let lineStart = value.lastIndexOf("\n", start - 2) + 1;
+    // A newline inside a chip does not start a list item.
+    for (let token = tokens[tokenIndex]; token; token = tokens[tokenIndex]) {
+      if (token.start >= lineStart) tokenIndex -= 1;
+      else if (token.end > lineStart) lineStart = value.lastIndexOf("\n", token.start - 1) + 1;
+      else break;
+    }
+    const parsed = parseListMarker(value.slice(lineStart, start - 1));
+    if (!parsed) return;