feat: parse inbound post (rich text) messages

- parsePostMessage: full Feishu post payload parser with locale fallback,
  supports text/a/at/img/media/file/code_block/br/hr/emotion elements
- Trigger accepts post messages, extracts text + downloads attachments
- Post messages with attachments bypass batching, text-only posts batch
- Add unit tests (10) for all element types and edge cases

hub/src/feishu/client.ts

@@ -126,6 +126,29 @@ export function _stripMarkdownToPlainText(text: string): string {
     .replace(/(^|[^_])_([^_\n]+)_/g, "$1$2");
 }
 
+export function parsePostMessage(content: string): { text: string; imageKeys: string[]; fileKeys: string[] } {
+  const parsed = parseJsonObject(content);
+  const root = parsed === null ? null : postRoot(parsed);
+  const locale = root === null ? null : selectPostLocale(root);
+  if (locale === null) {
+    return { text: "", imageKeys: [], fileKeys: [] };
+  }
+
+  const imageKeys: string[] = [];
+  const fileKeys: string[] = [];
+  const rows = Array.isArray(locale["content"]) ? locale["content"] : [];
+  const body = rows
+    .map((row) => {
+      const elements = Array.isArray(row) ? row : [row];
+      return elements.map((element) => renderPostElement(element, imageKeys, fileKeys)).join("");
+    })
+    .join("\n");
+
+  const title = stringField(locale, "title");
+  const text = title === undefined || title === "" ? body : body === "" ? `# ${title}` : `# ${title}\n\n${body}`;
+  return { text, imageKeys, fileKeys };
+}
+
 /** Send a text message using the best Feishu message type for the content. */
 export async function sendTextMessage(rt: FeishuRuntime, chatId: string, text: string): Promise<string | null> {
   const payload = buildOutboundPayload(text);
@@ -389,6 +412,157 @@ function reactionIdFromResponse(res: ReactionCreateResponse): string | null {
   return res?.data?.reaction_id ?? res?.reaction_id ?? null;
 }
 
+function parseJsonObject(content: string): Record<string, unknown> | null {
+  try {
+    const parsed = JSON.parse(content) as unknown;
+    return isRecord(parsed) ? parsed : null;
+  } catch {
+    return null;
+  }
+}
+
+function postRoot(parsed: Record<string, unknown>): Record<string, unknown> {
+  const post = parsed["post"];
+  return isRecord(post) ? post : parsed;
+}
+
+function selectPostLocale(root: Record<string, unknown>): Record<string, unknown> | null {
+  if (Array.isArray(root["content"])) return root;
+
+  for (const locale of ["zh_cn", "en_us"]) {
+    const candidate = root[locale];
+    if (isPostLocale(candidate)) return candidate;
+  }
+
+  for (const candidate of Object.values(root)) {
+    if (isPostLocale(candidate)) return candidate;
+  }
+  return null;
+}
+
+function isPostLocale(value: unknown): value is Record<string, unknown> {
+  return isRecord(value) && (Array.isArray(value["content"]) || typeof value["title"] === "string");
+}
+
+function renderPostElement(element: unknown, imageKeys: string[], fileKeys: string[]): string {
+  if (!isRecord(element)) return "";
+
+  switch (stringField(element, "tag")) {
+    case "text":
+      return applyTextStyles(stringField(element, "text") ?? "", element);
+    case "a":
+      return renderLink(element);
+    case "at":
+      return renderMention(element);
+    case "img":
+    case "image":
+      pushStringField(imageKeys, element, "image_key");
+      return "[Image]";
+    case "media":
+    case "file":
+    case "audio":
+    case "video":
+      pushStringField(fileKeys, element, "file_key");
+      return renderAttachmentPlaceholder(element);
+    case "code":
+    case "code_block":
+      return renderCodeBlock(element);
+    case "br":
+      return "\n";
+    case "hr":
+    case "divider":
+      return "\n\n---\n\n";
+    case "emotion":
+    case "emoji":
+      return renderEmoji(element);
+    case "md":
+      return stringField(element, "text") ?? "";
+    default:
+      return stringField(element, "text") ?? "";
+  }
+}
+
+function renderLink(element: Record<string, unknown>): string {
+  const text = stringField(element, "text") ?? "";
+  const href = stringField(element, "href") ?? "";
+  if (href === "") return text;
+  return `[${text}](${href})`;
+}
+
+function renderMention(element: Record<string, unknown>): string {
+  if (stringField(element, "user_id") === "@_all") return "@all";
+  const name =
+    stringField(element, "user_name") ??
+    stringField(element, "name") ??
+    stringField(element, "text") ??
+    stringField(element, "user_id") ??
+    "";
+  return name === "" ? "" : `@${name.replace(/^@/, "")}`;
+}
+
+function renderAttachmentPlaceholder(element: Record<string, unknown>): string {
+  const fileName = stringField(element, "file_name") ?? stringField(element, "name");
+  return fileName === undefined || fileName === "" ? "[Attachment]" : `[Attachment: ${fileName}]`;
+}
+
+function renderCodeBlock(element: Record<string, unknown>): string {
+  const language = stringField(element, "language") ?? "";
+  const text = stringField(element, "text") ?? "";
+  return `\`\`\`${language}\n${text}\n\`\`\``;
+}
+
+function renderEmoji(element: Record<string, unknown>): string {
+  const emojiType =
+    stringField(element, "emoji_type") ??
+    stringField(element, "emotion_key") ??
+    stringField(element, "name") ??
+    stringField(element, "text");
+  return emojiType === undefined || emojiType === "" ? "" : `:${emojiType}:`;
+}
+
+function applyTextStyles(text: string, element: Record<string, unknown>): string {
+  let rendered = text;
+  if (hasPostStyle(element, "bold")) rendered = `**${rendered}**`;
+  if (hasPostStyle(element, "italic")) rendered = `*${rendered}*`;
+  if (hasPostStyle(element, "strikethrough", "strike", "line_through", "lineThrough")) rendered = `~~${rendered}~~`;
+  if (hasPostStyle(element, "code", "inline_code", "inlineCode")) rendered = `\`${rendered}\``;
+  return rendered;
+}
+
+function hasPostStyle(element: Record<string, unknown>, ...names: string[]): boolean {
+  const style = element["style"] ?? element["styles"];
+  if (styleMatches(style, names)) return true;
+  return names.some((name) => element[name] === true);
+}
+
+function styleMatches(style: unknown, names: readonly string[]): boolean {
+  if (Array.isArray(style)) {
+    return style.some((entry) => typeof entry === "string" && names.includes(entry));
+  }
+  if (typeof style === "string") {
+    const tokens = style.split(/[\s,]+/).filter((token) => token !== "");
+    return tokens.some((token) => names.includes(token));
+  }
+  if (isRecord(style)) {
+    return names.some((name) => style[name] === true || style[name] === "true");
+  }
+  return false;
+}
+
+function pushStringField(target: string[], record: Record<string, unknown>, field: string): void {
+  const value = stringField(record, field);
+  if (value !== undefined && value !== "") target.push(value);
+}
+
+function stringField(record: Record<string, unknown>, field: string): string | undefined {
+  const value = record[field];
+  return typeof value === "string" ? value : undefined;
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null && !Array.isArray(value);
+}
+
 function containsMarkdownSyntax(content: string): boolean {
   const patterns = [
     /^ {0,3}#{1,6}\s+\S/m,