PaperClipAI/ui/src/components/MarkdownEditor.tsx

import { FILE_DROP_TARGET_ATTRIBUTE } from "../lib/file-drop-target";
import { AgentAvatar } from "./AgentAvatar";
import {
  Component,
  type ClipboardEvent,
  type ErrorInfo,
  type KeyboardEvent,
  forwardRef,
  useCallback,
  useEffect,
  useImperativeHandle,
  useMemo,
  useRef,
  useState,
  type DragEvent,
  type MouseEvent as ReactMouseEvent,
  type PointerEvent as ReactPointerEvent,
  type TouchEvent as ReactTouchEvent,
  type ReactElement,
  type ReactNode,
} from "react";
import { createPortal } from "react-dom";
import {
  CodeMirrorEditor,
  MDXEditor,
  codeBlockPlugin,
  codeMirrorPlugin,
  type CodeBlockEditorDescriptor,
  type MDXEditorMethods,
  headingsPlugin,
  imagePlugin,
  linkDialogPlugin,
  linkPlugin,
  listsPlugin,
  markdownShortcutPlugin,
  quotePlugin,
  tablePlugin,
  thematicBreakPlugin,
  defaultSvgIcons,
  type IconKey,
  type RealmPlugin,
} from "@mdxeditor/editor";
import {
  buildAgentMentionHref,
  buildIssueReferenceHref,
  buildProjectMentionHref,
  buildRoutineMentionHref,
  buildUserMentionHref,
} from "@paperclipai/shared";
import { Boxes, CalendarClock, Flag, Hash, User, X } from "lucide-react";
import { applyMentionChipDecoration, clearMentionChipDecoration, parseMentionChipHref } from "../lib/mention-chips";
import { MentionAwareLinkNode, mentionAwareLinkNodeReplacement } from "../lib/mention-aware-link-node";
import { mentionDeletionPlugin } from "../lib/mention-deletion";
import { looksLikeMarkdownPaste } from "../lib/markdownPaste";
import { normalizeMarkdown } from "../lib/normalize-markdown";
import {
  escapeUnsupportedAngleBrackets,
  unescapeAngleBracketEscapes,
} from "../lib/angle-bracket-markdown";
import { unescapeBlockquoteMarkers } from "../lib/blockquote-markdown";
import { unescapeIntrawordUnderscores } from "../lib/underscore-markdown";
import { restoreTrailingMarkdownSpaces } from "../lib/trailing-markdown-spaces";
import { pasteNormalizationPlugin } from "../lib/paste-normalization";
import { cn } from "../lib/utils";
import { useEditorAutocomplete, type SlashCommandOption } from "../context/EditorAutocompleteContext";

/* ---- Mention types ---- */

export interface MentionOption {
  id: string;
  name: string;
  kind?: "agent" | "project" | "user" | "issue";
  agentId?: string;
  agentIcon?: string | null;
  agentAppearance?: import("@paperclipai/shared").AgentAppearance | null;
  projectId?: string;
  projectColor?: string | null;
  userId?: string;
  /** Issue/task references (PAP-95f). `name` carries the searchable identifier + title. */
  issueId?: string;
  issueIdentifier?: string;
}

/* ---- Editor props ---- */

interface MarkdownEditorProps {
  value: string;
  onChange: (value: string) => void;
  ariaLabel?: string;
  placeholder?: string;
  className?: string;
  contentClassName?: string;
  onBlur?: () => void;
  imageUploadHandler?: (file: File) => Promise<string>;
  /** Called when a non-image file is dropped onto the editor (e.g. .zip). */
  onDropFile?: (file: File) => Promise<void>;
  /** When set to `parent`, a wrapper owns drag/drop behavior and visuals. */
  fileDropTarget?: "editor" | "parent";
  bordered?: boolean;
  /** List of mentionable entities. Enables @-mention autocomplete. */
  mentions?: MentionOption[];
  /** Capability-aware action commands supplied by the owning composer. */
  actionCommands?: SlashCommandOption[];
  /** Called on the configured submit shortcut. */
  onSubmit?: () => void;
  /** Task composers use Enter; document editors retain Cmd/Ctrl+Enter by default. */
  submitKey?: "enter" | "mod-enter";
  /** Render the rich editor without allowing edits. */
  readOnly?: boolean;
}

export interface MarkdownEditorRef {
  focus: () => void;
  insertMarkdown: (markdown: string) => void;
  clear: () => void;
}

class MarkdownEditorRichErrorBoundary extends Component<
  { children: ReactNode; onError: (error: unknown) => void },
  { hasError: boolean }
> {
  state = { hasError: false };

  static getDerivedStateFromError() {
    return { hasError: true };
  }

  componentDidCatch(error: unknown, info: ErrorInfo) {
    console.error("Markdown rich editor failed; falling back to raw textarea", {
      error,
      componentStack: info.componentStack,
    });
    this.props.onError(error);
  }

  render() {
    if (this.state.hasError) return null;
    return this.props.children;
  }
}

function readHtmlAttribute(attrs: string, name: string): string | null {
  const match = new RegExp(`${name}\\s*=\\s*("([^"]*)"|'([^']*)'|([^\\s>]+))`, "i").exec(attrs);
  return match?.[2] ?? match?.[3] ?? match?.[4] ?? null;
}

/** MDXEditor icon override: the image chip's delete button gets the lucide X. */
function editorIconFor(name: IconKey): ReactElement {
  if (name === "delete_small") return <X aria-hidden />;
  return defaultSvgIcons[name];
}

function convertHtmlImagesToMarkdown(text: string): string {
  return text.replace(/<img\b([^>]*?)\/?>/gi, (tag, attrs: string) => {
    const src = readHtmlAttribute(attrs, "src");
    if (!src) return tag;
    const alt = readHtmlAttribute(attrs, "alt") ?? "image";
    const title = readHtmlAttribute(attrs, "title");
    const escapedAlt = alt.replace(/[[\]]/g, "\\$&");
    const escapedTitle = title?.replace(/"/g, '\\"');
    return escapedTitle
      ? `![${escapedAlt}](${src} "${escapedTitle}")`
      : `![${escapedAlt}](${src})`;
  });
}

/**
 * Convert a stored value into the exact markdown handed to MDXEditor.
 *
 * The angle-bracket escape runs last, after the `<img>` rewrite, because that
 * rewrite has to match a bare `<img` tag before the escape hides it.
 */
function prepareMarkdownForEditor(value: string): string {
  const normalizedLineEndings = value.replace(/\r\n/g, "\n").replace(/\r/g, "\n");
  // Recover escaped blockquotes (`\>`) so `>`-prefixed content renders as a real
  // blockquote in the editor as well as on display (keeps import/export in sync).
  const withBlockquotes = unescapeBlockquoteMarkers(normalizedLineEndings);
  const withImages = convertHtmlImagesToMarkdown(withBlockquotes);
  // The editor runs with `suppressHtmlProcessing`, so a bare `<` that opens an
  // HTML construct would throw and drop the whole component to raw source.
  // Escaping those brackets keeps ordinary prose — `<name>`, `</close>` — in the
  // rich editor. `toStoredMarkdown` reverses it on the way out.
  return escapeUnsupportedAngleBrackets(withImages);
}

/**
 * Convert markdown exported by MDXEditor back into the form this product
 * stores. Inverse of the rewrites `prepareMarkdownForEditor` applies, so the
 * stored value never carries the editor's transport escaping — these fields
 * feed agent prompts and must stay in the clean, human-authored form.
 */
function toStoredMarkdown(markdown: string): string {
  const withTrailingSpaces = restoreTrailingMarkdownSpaces(markdown);
  // Unescape underscores first, on the exporter's exact text: removing `\<` or
  // `\>` can turn following lines into HTML or blockquotes and move code ranges.
  return unescapeAngleBracketEscapes(unescapeBlockquoteMarkers(unescapeIntrawordUnderscores(withTrailingSpaces)));
}

function escapeRegExp(value: string): string {
  return value.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
}

function hasMeaningfulEditorContent(node: Node | null): boolean {
  if (!node) return false;
  if (node.nodeType === Node.TEXT_NODE) {
    return (node.textContent ?? "").trim().length > 0;
  }
  if (node.nodeType !== Node.ELEMENT_NODE) {
    return false;
  }

  const element = node as HTMLElement;
  if (["IMG", "HR", "TABLE", "VIDEO", "IFRAME"].includes(element.tagName)) {
    return true;
  }

  return Array.from(element.childNodes).some((child) => hasMeaningfulEditorContent(child));
}

function hasMarkdownImage(value: string): boolean {
  return /!\[[\s\S]*?\]\([^)]+\)/.test(value);
}

function isRichEditorDomEmpty(
  editable: HTMLElement,
  expectedValue: string,
  placeholder?: string,
): boolean {
  const expectedText = expectedValue.trim();
  if (!expectedText) return false;
  const expectedHasImage = hasMarkdownImage(expectedText);

  const visibleText = (editable.textContent ?? "").trim();
  if (visibleText.length === 0) {
    if (expectedHasImage) return false;
    return !Array.from(editable.childNodes).some((child) => hasMeaningfulEditorContent(child));
  }

  const normalizedPlaceholder = placeholder?.trim();
  if (
    normalizedPlaceholder
    && visibleText === normalizedPlaceholder
    && expectedText !== normalizedPlaceholder
  ) {
    if (expectedHasImage) return false;
    return true;
  }

  return false;
}

function isSafeMarkdownLinkUrl(url: string): boolean {
  const trimmed = url.trim();
  if (!trimmed) return true;
  return !/^(javascript|data|vbscript):/i.test(trimmed);
}

function richEditorErrorMessage(error: unknown): string {
  if (error instanceof Error) return error.message;
  if (typeof error === "string") return error;
  return "Rich editor failed to render";
}

/**
 * Why the rich editor was abandoned for this value. Surfaced in the fallback
 * header so a bug report names the path that failed rather than describing the
 * same generic message for three unrelated causes.
 *
 * - `MDE-PARSE`  the markdown importer rejected the source
 * - `MDE-RENDER` the editor threw while rendering
 * - `MDE-EMPTY`  the editor mounted but never painted the content
 */
type RichEditorErrorCode = "MDE-PARSE" | "MDE-RENDER" | "MDE-EMPTY";

interface RichEditorError {
  code: RichEditorErrorCode;
  message: string;
}

/**
 * The editor populates its DOM asynchronously, so "looks empty" is only
 * trustworthy after it has had time to settle and then stayed empty. The first
 * check debounces behind mutations; the second confirms the verdict once.
 */
const RICH_EDITOR_EMPTY_CHECK_MS = 100;
const RICH_EDITOR_EMPTY_CONFIRM_MS = 200;

/* ---- Mention detection helpers ---- */

interface MentionState {
  trigger: "mention" | "skill";
  marker: "@" | "/";
  query: string;
  top: number;
  left: number;
  /**
   * Caret-aligned viewport coords for portal positioning. `viewportTop` /
   * `viewportBottom` describe the active text line, and `viewportLeft` is the
   * caret X (right edge of the last typed character) so the menu can sit on
   * the same line, just to the right of the cursor.
   */
  viewportTop: number;
  viewportBottom: number;
  viewportLeft: number;
  textNode: Text;
  atPos: number;
  endPos: number;
}

type AutocompleteOption = MentionOption | SlashCommandOption;

interface MentionMenuViewport {
  offsetLeft: number;
  offsetTop: number;
  width: number;
  height: number;
}

interface MentionMenuSize {
  width: number;
  height: number;
}

const MENTION_MENU_WIDTH = 188;
const MENTION_MENU_HEIGHT = 208;
const MENTION_MENU_PADDING = 8;
const MENTION_MENU_ROW_HEIGHT = 34;
const MENTION_MENU_CHROME_HEIGHT = 8;
const MAX_AUTOCOMPLETE_OPTIONS = 50;
/** Roughly one space-width of breathing room between the caret and the menu. */
const MENTION_MENU_CARET_GAP = 10;

const CODE_BLOCK_LANGUAGES: Record<string, string> = {
  txt: "Text",
  md: "Markdown",
  js: "JavaScript",
  jsx: "JavaScript (JSX)",
  ts: "TypeScript",
  tsx: "TypeScript (TSX)",
  json: "JSON",
  bash: "Bash",
  sh: "Shell",
  python: "Python",
  go: "Go",
  rust: "Rust",
  sql: "SQL",
  html: "HTML",
  css: "CSS",
  yaml: "YAML",
  yml: "YAML",
};

const FALLBACK_CODE_BLOCK_DESCRIPTOR: CodeBlockEditorDescriptor = {
  // Keep this lower than codeMirrorPlugin's descriptor priority so known languages
  // still use the standard matching path; this catches malformed/unknown fences.
  priority: 0,
  match: () => true,
  Editor: CodeMirrorEditor,
};

export function findMentionMatch(
  text: string,
  offset: number,
): Pick<MentionState, "trigger" | "marker" | "query" | "atPos" | "endPos"> | null {
  let atPos = -1;
  let trigger: MentionState["trigger"] | null = null;
  let marker: MentionState["marker"] | null = null;
  for (let i = offset - 1; i >= 0; i--) {
    const ch = text[i];
    if (ch === "@" || ch === "/") {
      if (i === 0 || /\s/.test(text[i - 1])) {
        atPos = i;
        trigger = ch === "@" ? "mention" : "skill";
        marker = ch;
      }
      break;
    }
    if (ch === "\n" || ch === "\r") break;
  }

  if (atPos === -1) return null;
  const query = text.slice(atPos + 1, offset);
  if (trigger === "skill" && /\s/.test(query) && !query.toLowerCase().startsWith("routine:")) {
    return null;
  }

  return {
    trigger: trigger ?? "mention",
    marker: marker ?? "@",
    query,
    atPos,
    endPos: offset,
  };
}

interface CaretRect {
  top: number;
  bottom: number;
  /** Caret X — the right edge of the last typed character (or left edge of the next). */
  x: number;
}

function measureCaretRect(textNode: Text, offset: number, atPos: number): CaretRect {
  const length = textNode.textContent?.length ?? 0;
  const rectFromRange = (start: number, end: number, side: "right" | "left"): CaretRect | null => {
    if (start < 0 || end > length || end <= start) return null;
    const range = document.createRange();
    range.setStart(textNode, start);
    range.setEnd(textNode, end);
    const rect = range.getBoundingClientRect();
    if (rect.width === 0 && rect.height === 0) return null;
    return { top: rect.top, bottom: rect.bottom, x: side === "right" ? rect.right : rect.left };
  };

  // Prefer the character immediately before the caret — its right edge IS the caret X
  // and its top/bottom describe the active line. Falls back to the char after the caret
  // and finally the @ marker if nothing else gives us a valid rect.
  return (
    rectFromRange(Math.max(0, offset - 1), offset, "right")
    ?? rectFromRange(offset, Math.min(length, offset + 1), "left")
    ?? rectFromRange(atPos, atPos + 1, "right")
    ?? { top: 0, bottom: 0, x: 0 }
  );
}

function detectMention(container: HTMLElement): MentionState | null {
  const sel = window.getSelection();
  if (!sel || sel.rangeCount === 0 || !sel.isCollapsed) return null;

  const range = sel.getRangeAt(0);
  const textNode = range.startContainer;
  if (textNode.nodeType !== Node.TEXT_NODE) return null;
  if (!container.contains(textNode)) return null;

  const text = textNode.textContent ?? "";
  const offset = range.startOffset;
  const match = findMentionMatch(text, offset);
  if (!match) return null;

  // Anchor the menu to the live caret so it tracks each typed character instead of
  // staying glued to the @ marker.
  const caret = measureCaretRect(textNode as Text, offset, match.atPos);
  const containerRect = container.getBoundingClientRect();

  return {
    trigger: match.trigger,
    marker: match.marker,
    query: match.query,
    top: caret.top - containerRect.top,
    left: caret.x - containerRect.left,
    viewportTop: caret.top,
    viewportBottom: caret.bottom,
    viewportLeft: caret.x,
    textNode: textNode as Text,
    atPos: match.atPos,
    endPos: match.endPos,
  };
}

function getMentionMenuViewport(): MentionMenuViewport {
  const viewport = window.visualViewport;
  if (viewport) {
    return {
      offsetLeft: viewport.offsetLeft,
      offsetTop: viewport.offsetTop,
      width: viewport.width,
      height: viewport.height,
    };
  }

  return {
    offsetLeft: 0,
    offsetTop: 0,
    width: window.innerWidth,
    height: window.innerHeight,
  };
}

export function computeMentionMenuPosition(
  anchor: Pick<MentionState, "viewportTop" | "viewportBottom" | "viewportLeft">,
  viewport: MentionMenuViewport,
  menuSize: MentionMenuSize = { width: MENTION_MENU_WIDTH, height: MENTION_MENU_HEIGHT },
) {
  const minLeft = viewport.offsetLeft + MENTION_MENU_PADDING;
  const maxLeft = viewport.offsetLeft + viewport.width - menuSize.width;
  const minTop = viewport.offsetTop + MENTION_MENU_PADDING;
  const maxTop = viewport.offsetTop + viewport.height - menuSize.height;

  // Place the menu's top edge on the current line so it sits next to the caret.
  // If it would overflow below, flip above so the menu's bottom hugs the line.
  const desiredTop = viewport.offsetTop + anchor.viewportTop;
  let top: number;
  if (desiredTop > maxTop) {
    const flipped = viewport.offsetTop + anchor.viewportBottom - menuSize.height;
    top = Math.max(minTop, Math.min(flipped, maxTop));
  } else {
    top = Math.max(minTop, desiredTop);
  }

  // Place the menu's left edge a small gap to the right of the caret X so
  // there's roughly a space-width of breathing room between cursor and menu.
  const desiredLeft = viewport.offsetLeft + anchor.viewportLeft + MENTION_MENU_CARET_GAP;
  const left = Math.max(minLeft, Math.min(desiredLeft, maxLeft));

  // The menu can grow beyond its estimated width for long task names.
  // Constrain its actual layout to the space remaining beside the caret.
  const maxWidth = Math.max(0, viewport.offsetLeft + viewport.width - MENTION_MENU_PADDING - left);
  return { top, left, maxWidth };
}

function getMentionMenuSize(optionCount: number): MentionMenuSize {
  const visibleRows = Math.max(1, Math.min(optionCount, 8));
  return {
    width: MENTION_MENU_WIDTH,
    height: Math.min(
      MENTION_MENU_HEIGHT,
      visibleRows * MENTION_MENU_ROW_HEIGHT + MENTION_MENU_CHROME_HEIGHT,
    ),
  };
}

// CodeMirror's editable surface is `.cm-content`, not a `pre` or `code` node.
// MDXEditor wraps that surface in a hashed `codeMirrorWrapper` class. A paste
// that starts inside either of those belongs to the nested editor.
const CODE_LIKE_SELECTOR = [
  "pre",
  "code",
  ".cm-editor",
  ".cm-content",
  "[class*='codeMirrorWrapper']",
  "[class*='codeBlockEditor']",
].join(",");

function nodeInsideCodeLike(container: HTMLElement, node: Node | null): boolean {
  if (!node || !container.contains(node)) return false;
  const el = node instanceof Element ? node : node.parentElement;
  return Boolean(el?.closest(CODE_LIKE_SELECTOR));
}

function isSelectionInsideCodeLikeElement(container: HTMLElement | null) {
  if (!container) return false;
  const selection = window.getSelection();
  if (!selection) return false;
  for (const node of [selection.anchorNode, selection.focusNode]) {
    if (nodeInsideCodeLike(container, node)) return true;
  }
  return false;
}

function isPasteInsideCodeLikeElement(
  container: HTMLElement | null,
  event: { target: EventTarget | null },
): boolean {
  if (!container) return false;
  if (event.target instanceof Node && nodeInsideCodeLike(container, event.target)) return true;
  const active = typeof document !== "undefined" ? document.activeElement : null;
  if (active instanceof Node && nodeInsideCodeLike(container, active)) return true;
  return isSelectionInsideCodeLikeElement(container);
}

/** The human title of an issue mention — `name` minus its leading identifier. */
export function issueMentionTitle(option: MentionOption): string {
  const name = option.name.trim();
  const identifier = option.issueIdentifier?.trim();
  if (identifier && name.toLowerCase().startsWith(identifier.toLowerCase())) {
    return name.slice(identifier.length).trim();
  }
  return name;
}

function mentionMarkdown(option: MentionOption): string {
  if (option.kind === "issue" && option.issueIdentifier) {
    // Insert a compact issue link (e.g. `[PAP-123](/issues/PAP-123)`). The chip
    // decorator recognizes this href as an `issue` mention and renders it as a
    // task chip; MarkdownBody linkifies the same href on display.
    return `[${option.issueIdentifier}](${buildIssueReferenceHref(option.issueIdentifier)}) `;
  }
  if (option.kind === "project" && option.projectId) {
    return `[@${option.name}](${buildProjectMentionHref(option.projectId, option.projectColor ?? null)}) `;
  }
  if (option.kind === "user" && option.userId) {
    return `[@${option.name}](${buildUserMentionHref(option.userId)}) `;
  }
  const agentId = option.agentId ?? option.id.replace(/^agent:/, "");
  return `[@${option.name}](${buildAgentMentionHref(agentId, option.agentIcon ?? null)}) `;
}

function slashCommandLabel(option: SlashCommandOption): string {
  if (option.kind === "routine") return `/routine:${option.name}`;
  if (option.kind === "action") return `/${option.command}`;
  return `/${option.slug}`;
}

function slashCommandMarkdown(option: SlashCommandOption): string {
  // MDXEditor trims an ordinary trailing space when setMarkdown re-imports the
  // command. Keep a non-breaking separator in the document so subsequent text
  // is inserted as the command argument instead of being glued to the token.
  if (option.kind === "action") return `/${option.command}\u00a0`;
  if (option.kind === "routine") {
    return `[${slashCommandLabel(option)}](${buildRoutineMentionHref(option.routineId)}) `;
  }
  return `[/${option.slug}](${option.href}) `;
}

function autocompleteMarkdown(option: AutocompleteOption): string {
  return option.kind === "skill" || option.kind === "routine" || option.kind === "action"
    ? slashCommandMarkdown(option)
    : mentionMarkdown(option);
}

export function shouldAcceptAutocompleteKey(
  key: string,
  trigger: MentionState["trigger"] | null,
  skillEnterArmed = false,
): boolean {
  if (key === "Tab") return true;
  if (key !== "Enter") return false;
  return trigger === "mention" || (trigger === "skill" && skillEnterArmed);
}

export function isSameAutocompleteSession(
  left: Pick<MentionState, "trigger" | "marker" | "query" | "textNode" | "atPos" | "endPos"> | null,
  right: Pick<MentionState, "trigger" | "marker" | "query" | "textNode" | "atPos" | "endPos"> | null,
): boolean {
  if (!left || !right) return false;
  return left.trigger === right.trigger
    && left.marker === right.marker
    && left.query === right.query
    && left.textNode === right.textNode
    && left.atPos === right.atPos
    && left.endPos === right.endPos;
}

function autocompleteOptionMatchesLink(option: AutocompleteOption, href: string): boolean {
  if (option.kind === "action") return false;
  const parsed = parseMentionChipHref(href);
  if (!parsed) return false;

  if (option.kind === "skill") {
    return parsed.kind === "skill" && parsed.skillId === option.skillId;
  }
  if (option.kind === "routine") {
    return parsed.kind === "routine" && parsed.routineId === option.routineId;
  }

  if (option.kind === "issue" && option.issueIdentifier) {
    return parsed.kind === "issue" && parsed.identifier === option.issueIdentifier;
  }
  if (option.kind === "project" && option.projectId) {
    return parsed.kind === "project" && parsed.projectId === option.projectId;
  }
  if (option.kind === "user" && option.userId) {
    return parsed.kind === "user" && parsed.userId === option.userId;
  }

  const agentId = option.agentId ?? option.id.replace(/^agent:/, "");
  return parsed.kind === "agent" && parsed.agentId === agentId;
}

export function findClosestAutocompleteAnchor(
  editable: HTMLElement,
  option: AutocompleteOption,
  origin?: Pick<MentionState, "left" | "top"> | null,
): HTMLAnchorElement | null {
  const matchingMentions = Array.from(editable.querySelectorAll("a"))
    .filter((node): node is HTMLAnchorElement => node instanceof HTMLAnchorElement)
    .filter((link) => autocompleteOptionMatchesLink(option, link.getAttribute("href") ?? ""));

  if (matchingMentions.length === 0) return null;
  if (!origin) return matchingMentions[0] ?? null;

  const containerRect = editable.getBoundingClientRect();
  return matchingMentions.sort((a, b) => {
    const rectA = a.getBoundingClientRect();
    const rectB = b.getBoundingClientRect();
    const leftA = rectA.left - containerRect.left;
    const topA = rectA.top - containerRect.top;
    const leftB = rectB.left - containerRect.left;
    const topB = rectB.top - containerRect.top;
    const distA = Math.hypot(leftA - origin.left, topA - origin.top);
    const distB = Math.hypot(leftB - origin.left, topB - origin.top);
    return distA - distB;
  })[0] ?? null;
}

export function placeCaretAfterMentionAnchor(target: HTMLAnchorElement): boolean {
  const selection = window.getSelection();
  if (!selection) return false;

  const range = document.createRange();
  const nextSibling = target.nextSibling;
  if (nextSibling?.nodeType === Node.TEXT_NODE) {
    const text = nextSibling.textContent ?? "";
    if (text.startsWith(" ")) {
      range.setStart(nextSibling, 1);
      range.collapse(true);
      selection.removeAllRanges();
      selection.addRange(range);
      return true;
    }
    if (text.length > 0) {
      range.setStart(nextSibling, 0);
      range.collapse(true);
      selection.removeAllRanges();
      selection.addRange(range);
      return true;
    }
  }

  range.setStartAfter(target);
  range.collapse(true);
  selection.removeAllRanges();
  selection.addRange(range);
  return true;
}

export function placeCaretAtEditableEnd(target: HTMLElement): boolean {
  const selection = window.getSelection();
  if (!selection) return false;
  const range = document.createRange();
  range.selectNodeContents(target);
  range.collapse(false);
  selection.removeAllRanges();
  selection.addRange(range);
  return true;
}

/** Replace the active autocomplete token in the markdown string with the selected token. */
function applyMention(markdown: string, state: MentionState, option: AutocompleteOption): string {
  const search = `${state.marker}${state.query}`;
  const replacement = autocompleteMarkdown(option);
  const idx = markdown.lastIndexOf(search);
  if (idx === -1) return markdown;
  return markdown.slice(0, idx) + replacement + markdown.slice(idx + search.length);
}

/* ---- Component ---- */

export const MarkdownEditor = forwardRef<MarkdownEditorRef, MarkdownEditorProps>(function MarkdownEditor({
  value,
  onChange,
  ariaLabel,
  placeholder,
  className,
  contentClassName,
  onBlur,
  imageUploadHandler,
  onDropFile,
  fileDropTarget = "editor",
  bordered = true,
  mentions,
  actionCommands = [],
  onSubmit,
  submitKey = "mod-enter",
  readOnly = false,
}: MarkdownEditorProps, forwardedRef) {
  const editorValue = useMemo(() => prepareMarkdownForEditor(value), [value]);
  function isSubmitShortcut(event: KeyboardEvent<HTMLElement>): boolean {
    return !readOnly
      && event.key === "Enter"
      && !event.nativeEvent.isComposing
      && event.keyCode !== 229
      && !event.shiftKey
      && !event.altKey
      && (submitKey === "enter" || event.metaKey || event.ctrlKey);
  }
  const { slashCommands: sharedSlashCommands } = useEditorAutocomplete();
  const slashCommands = useMemo(
    () => [...actionCommands, ...sharedSlashCommands],
    [actionCommands, sharedSlashCommands],
  );
  const containerRef = useRef<HTMLDivElement>(null);
  const ref = useRef<MDXEditorMethods>(null);
  const fallbackTextareaRef = useRef<HTMLTextAreaElement>(null);
  const valueRef = useRef(editorValue);
  valueRef.current = editorValue;
  const latestValueRef = useRef(editorValue);
  const initialChildOnChangeRef = useRef(true);
  /**
   * After imperative `setMarkdown` (prop sync, mentions, image upload), MDXEditor may emit `onChange`
   * with the same markdown. Skip notifying the parent for that echo so controlled parents that
   * normalize or transform values cannot loop. Replaces the older blur/focus gate for the same concern.
   */
  const echoIgnoreMarkdownRef = useRef<string | null>(null);
  const [uploadError, setUploadError] = useState<string | null>(null);
  const [isDragOver, setIsDragOver] = useState(false);
  const [richEditorError, setRichEditorError] = useState<RichEditorError | null>(null);
  const dragDepthRef = useRef(0);

  // Stable ref for imageUploadHandler so plugins don't recreate on every render
  const imageUploadHandlerRef = useRef(imageUploadHandler);
  imageUploadHandlerRef.current = imageUploadHandler;

  // Mention state (ref kept in sync so callbacks always see the latest value)
  const [mentionState, setMentionState] = useState<MentionState | null>(null);
  const mentionStateRef = useRef<MentionState | null>(null);
  const [mentionIndex, setMentionIndex] = useState(0);
  const autocompleteOptionRefs = useRef<Array<HTMLButtonElement | null>>([]);
  const skillEnterArmedRef = useRef(false);
  const autocompleteSelectionHandledRef = useRef(false);
  const mentionActive = mentionState !== null && (
    (mentionState.trigger === "mention" && Boolean(mentions?.length))
    || (mentionState.trigger === "skill" && slashCommands.length > 0)
  );
  const mentionOptionByKey = useMemo(() => {
    const map = new Map<string, MentionOption>();
    for (const mention of mentions ?? []) {
      if (mention.kind === "agent") {
        const agentId = mention.agentId ?? mention.id.replace(/^agent:/, "");
        map.set(`agent:${agentId}`, mention);
      }
      if (mention.kind === "user" && mention.userId) {
        map.set(`user:${mention.userId}`, mention);
      }
      if (mention.kind === "project" && mention.projectId) {
        map.set(`project:${mention.projectId}`, mention);
      }
    }
    return map;
  }, [mentions]);

  const setEditorRef = useCallback((instance: MDXEditorMethods | null) => {
    ref.current = instance;
    if (!instance) {
      return;
    }
    if (valueRef.current !== latestValueRef.current) {
      // Re-apply the latest controlled value once MDXEditor exposes its imperative API.
      echoIgnoreMarkdownRef.current = valueRef.current;
      instance.setMarkdown(valueRef.current);
      latestValueRef.current = valueRef.current;
    }
  }, []);

  const filteredMentions = useMemo<AutocompleteOption[]>(() => {
    if (!mentionState) return [];
    const q = mentionState.query.trim().toLowerCase();
    if (mentionState.trigger === "skill") {
      return slashCommands
        .filter((command) => {
          if (!q) return true;
          return command.aliases.some((alias) => alias.toLowerCase().includes(q));
        })
        .slice(0, MAX_AUTOCOMPLETE_OPTIONS);
    }
    if (!mentions) return [];
    return mentions
      .filter((m) => m.name.toLowerCase().includes(q))
      .slice(0, MAX_AUTOCOMPLETE_OPTIONS);
  }, [mentionState, mentions, slashCommands]);

  const insertMarkdown = useCallback((markdown: string) => {
    if (readOnly) return;
    if (!richEditorError && ref.current) {
      // MDXEditor's insertMarkdown silently no-ops without a Lexical selection
      // (an editor that was never focused). Focus first — the callback runs
      // once focus (and a selection: caret kept, else rootEnd) is in place.
      const editor = ref.current;
      // Inserted markdown reaches the same importer as the mounted document, so
      // it needs the same angle-bracket escaping to survive it.
      const editorMarkdown = escapeUnsupportedAngleBrackets(markdown);
      editor.focus(() => editor.insertMarkdown(editorMarkdown), { defaultSelection: "rootEnd" });
      return;
    }
    const textarea = fallbackTextareaRef.current;
    if (!textarea) {
      onChange(`${value}${markdown}`);
      return;
    }
    const start = textarea.selectionStart ?? value.length;
    const end = textarea.selectionEnd ?? value.length;
    const next = `${value.slice(0, start)}${markdown}${value.slice(end)}`;
    onChange(next);
    requestAnimationFrame(() => {
      textarea.focus();
      const cursor = start + markdown.length;
      textarea.setSelectionRange(cursor, cursor);
    });
  }, [onChange, readOnly, richEditorError, value]);

  useImperativeHandle(forwardedRef, () => ({
    focus: () => {
      if (richEditorError) {
        fallbackTextareaRef.current?.focus();
        return;
      }
      ref.current?.focus(undefined, { defaultSelection: "rootEnd" });
    },
    insertMarkdown,
    clear: () => {
      latestValueRef.current = "";
      echoIgnoreMarkdownRef.current = "";
      ref.current?.setMarkdown("");
      if (fallbackTextareaRef.current) fallbackTextareaRef.current.value = "";
    },
  }), [insertMarkdown, richEditorError]);

  const autoSizeFallbackTextarea = useCallback((element: HTMLTextAreaElement | null) => {
    if (!element) return;
    element.style.height = "auto";
    element.style.height = `${element.scrollHeight}px`;
  }, []);

  useEffect(() => {
    if (!richEditorError) return;
    autoSizeFallbackTextarea(fallbackTextareaRef.current);
  }, [autoSizeFallbackTextarea, richEditorError, value]);

  useEffect(() => {
    if (richEditorError || editorValue.trim().length === 0) return;
    const container = containerRef.current;
    if (!container) return;

    let checkTimeoutId = 0;
    let confirmTimeoutId = 0;
    let mutationCount = 0;

    const looksEmpty = () => {
      const editable = container.querySelector('[contenteditable="true"]');
      if (!(editable instanceof HTMLElement)) return false;
      const activeElement = document.activeElement;
      // A focused editor is the user's, not ours to second-guess.
      if (activeElement === editable || editable.contains(activeElement)) return false;
      return isRichEditorDomEmpty(editable, editorValue, placeholder);
    };

    // Two phases. Mounting (and especially remounting after "Retry rich
    // editor", where focus sits on the button rather than the editor) leaves
    // the editable momentarily empty, so a single immediate check reads a
    // still-populating editor as a broken one. Wait, then confirm once; any
    // mutation in between means content arrived and restarts the whole thing.
    const scheduleCheck = () => {
      window.clearTimeout(checkTimeoutId);
      window.clearTimeout(confirmTimeoutId);
      checkTimeoutId = window.setTimeout(() => {
        if (!looksEmpty()) return;
        const mutationsAtCheck = mutationCount;
        confirmTimeoutId = window.setTimeout(() => {
          if (mutationCount !== mutationsAtCheck) return;
          if (!looksEmpty()) return;
          setRichEditorError({
            code: "MDE-EMPTY",
            message: "Rich editor failed to load content",
          });
        }, RICH_EDITOR_EMPTY_CONFIRM_MS);
      }, RICH_EDITOR_EMPTY_CHECK_MS);
    };

    scheduleCheck();
    const observer = new MutationObserver(() => {
      mutationCount += 1;
      scheduleCheck();
    });
    observer.observe(container, {
      subtree: true,
      childList: true,
      characterData: true,
    });

    return () => {
      window.clearTimeout(checkTimeoutId);
      window.clearTimeout(confirmTimeoutId);
      observer.disconnect();
    };
  }, [editorValue, placeholder, richEditorError]);

  const hasImageUpload = Boolean(imageUploadHandler);

  const plugins = useMemo<RealmPlugin[]>(() => {
    const imageHandler = hasImageUpload
      ? async (file: File) => {
          const handler = imageUploadHandlerRef.current;
          if (!handler) throw new Error("No image upload handler");
          try {
            const src = await handler(file);
            setUploadError(null);
            // After MDXEditor inserts the image, ensure two newlines follow it
            // so the cursor isn't stuck right next to the image.
            setTimeout(() => {
              const current = latestValueRef.current;
              const escapedSrc = escapeRegExp(src);
              const updated = current.replace(
                new RegExp(`(!\\[[^\\]]*\\]\\(${escapedSrc}\\))(?!\\n\\n)`, "g"),
                "$1\n\n",
              );
              if (updated !== current) {
                latestValueRef.current = updated;
                echoIgnoreMarkdownRef.current = updated;
                ref.current?.setMarkdown(updated);
                // `updated` derives from `latestValueRef`, which is editor
                // space; the parent only ever sees stored space.
                onChange(toStoredMarkdown(updated));
                requestAnimationFrame(() => {
                  ref.current?.focus(undefined, { defaultSelection: "rootEnd" });
                });
              }
            }, 100);
            return src;
          } catch (err) {
            const message = err instanceof Error ? err.message : "Image upload failed";
            setUploadError(message);
            throw err;
          }
        }
      : undefined;
    const all: RealmPlugin[] = [
      headingsPlugin(),
      listsPlugin(),
      quotePlugin(),
      tablePlugin(),
      linkPlugin({ validateUrl: isSafeMarkdownLinkUrl }),
      linkDialogPlugin(),
      mentionDeletionPlugin(),
      pasteNormalizationPlugin(),
      thematicBreakPlugin(),
      codeBlockPlugin({
        defaultCodeBlockLanguage: "txt",
        codeBlockEditorDescriptors: [FALLBACK_CODE_BLOCK_DESCRIPTOR],
      }),
      codeMirrorPlugin({ codeBlockLanguages: CODE_BLOCK_LANGUAGES }),
      markdownShortcutPlugin(),
    ];
    all.push(imagePlugin({ imageUploadHandler: imageHandler, disableImageSettingsButton: true }));
    return all;
  }, [hasImageUpload]);

  useEffect(() => {
    if (editorValue !== latestValueRef.current) {
      if (ref.current) {
        // Pair with onChange echo suppression (echoIgnoreMarkdownRef).
        echoIgnoreMarkdownRef.current = editorValue;
        ref.current.setMarkdown(editorValue);
        latestValueRef.current = editorValue;
      }
    }
  }, [editorValue]);

  const decorateProjectMentions = useCallback(() => {
    const editable = containerRef.current?.querySelector('[contenteditable="true"]');
    if (!editable) return;
    const links = editable.querySelectorAll("a");
    for (const node of links) {
      const link = node as HTMLAnchorElement;
      const parsed = parseMentionChipHref(link.getAttribute("href") ?? "");
      if (!parsed) {
        clearMentionChipDecoration(link);
        continue;
      }

      if (parsed.kind === "project") {
        const option = mentionOptionByKey.get(`project:${parsed.projectId}`);
        applyMentionChipDecoration(link, {
          ...parsed,
          color: parsed.color ?? option?.projectColor ?? null,
        });
        continue;
      }

      if (parsed.kind === "skill" || parsed.kind === "routine") {
        applyMentionChipDecoration(link, parsed);
        continue;
      }

      if (parsed.kind === "user" || parsed.kind === "issue") {
        applyMentionChipDecoration(link, parsed);
        continue;
      }

      const option = mentionOptionByKey.get(`agent:${parsed.agentId}`);
      applyMentionChipDecoration(link, {
        ...parsed,
        appearance: option?.agentAppearance,
      });
    }
  }, [mentionOptionByKey]);

  // Mention detection: listen for selection changes and input events
  const checkMention = useCallback(() => {
    if (!containerRef.current || isSelectionInsideCodeLikeElement(containerRef.current)) {
      mentionStateRef.current = null;
      skillEnterArmedRef.current = false;
      setMentionState(null);
      return;
    }
    const result = detectMention(containerRef.current);
    if (
      result
      && result.trigger === "mention"
      && (!mentions || mentions.length === 0)
    ) {
      mentionStateRef.current = null;
      skillEnterArmedRef.current = false;
      setMentionState(null);
      return;
    }
    if (
      result
      && result.trigger === "skill"
      && slashCommands.length === 0
    ) {
      mentionStateRef.current = null;
      skillEnterArmedRef.current = false;
      setMentionState(null);
      return;
    }
    const previous = mentionStateRef.current;
    const sameSession = isSameAutocompleteSession(previous, result);
    mentionStateRef.current = result;
    if (!sameSession) {
      skillEnterArmedRef.current = false;
      setMentionIndex(0);
    }
    setMentionState(result);
  }, [mentions, slashCommands.length]);

  useEffect(() => {
    if ((!mentions || mentions.length === 0) && slashCommands.length === 0) return;

    const el = containerRef.current;
    // Listen for input events on the container so mention detection
    // also fires after typing (e.g. space to dismiss).
    const onInput = () => requestAnimationFrame(checkMention);

    document.addEventListener("selectionchange", checkMention);
    el?.addEventListener("input", onInput, true);
    return () => {
      document.removeEventListener("selectionchange", checkMention);
      el?.removeEventListener("input", onInput, true);
    };
  }, [checkMention, mentions, slashCommands.length]);

  useEffect(() => {
    if (!mentionActive) return;

    const updatePosition = () => requestAnimationFrame(checkMention);
    const viewport = window.visualViewport;

    viewport?.addEventListener("resize", updatePosition);
    viewport?.addEventListener("scroll", updatePosition);
    window.addEventListener("resize", updatePosition);
    window.addEventListener("scroll", updatePosition, true);

    return () => {
      viewport?.removeEventListener("resize", updatePosition);
      viewport?.removeEventListener("scroll", updatePosition);
      window.removeEventListener("resize", updatePosition);
      window.removeEventListener("scroll", updatePosition, true);
    };
  }, [checkMention, mentionActive]);

  useEffect(() => {
    if (!mentionActive) return;
    autocompleteOptionRefs.current.length = filteredMentions.length;
    if (mentionIndex >= filteredMentions.length) {
      setMentionIndex(Math.max(0, filteredMentions.length - 1));
      return;
    }
    const activeOption = autocompleteOptionRefs.current[mentionIndex];
    if (!activeOption || typeof activeOption.scrollIntoView !== "function") return;
    activeOption.scrollIntoView({ block: "nearest" });
  }, [filteredMentions.length, mentionActive, mentionIndex]);

  useEffect(() => {
    if (mentionActive) return;
    autocompleteSelectionHandledRef.current = false;
  }, [mentionActive]);

  useEffect(() => {
    const editable = containerRef.current?.querySelector('[contenteditable="true"]');
    if (!editable) return;
    let frameId: number | null = null;
    let disposed = false;
    const observe = () => {
      observer.observe(editable, {
        subtree: true,
        childList: true,
        characterData: true,
      });
    };
    const flushDecorations = () => {
      frameId = null;
      if (disposed) return;
      observer.disconnect();
      decorateProjectMentions();
      if (!disposed) observe();
    };
    const scheduleDecorations = () => {
      if (frameId !== null) return;
      frameId = requestAnimationFrame(flushDecorations);
    };
    const observer = new MutationObserver(() => {
      scheduleDecorations();
    });

    flushDecorations();
    return () => {
      disposed = true;
      observer.disconnect();
      if (frameId !== null) {
        cancelAnimationFrame(frameId);
      }
    };
  }, [decorateProjectMentions]);

  const selectMention = useCallback(
    (option: AutocompleteOption) => {
      // Read from ref to avoid stale-closure issues (selectionchange can
      // update state between the last render and this callback firing).
      const state = mentionStateRef.current;
      if (!state) return false;
      if (option.kind === "action" && option.disabled) return false;
      const current = latestValueRef.current;
      const next = applyMention(current, state, option);
      if (next !== current) {
        latestValueRef.current = next;
        echoIgnoreMarkdownRef.current = next;
        ref.current?.setMarkdown(next);
        // `next` derives from `latestValueRef`, which is editor space; the
        // parent only ever sees stored space.
        onChange(toStoredMarkdown(next));
      }

      const restoreSelection = (attemptsRemaining: number) => {
        const editable = containerRef.current?.querySelector('[contenteditable="true"]');
        if (!(editable instanceof HTMLElement)) return;

        decorateProjectMentions();
        editable.focus();

        if (option.kind === "action") {
          placeCaretAtEditableEnd(editable);
          return;
        }

        const target = findClosestAutocompleteAnchor(editable, option, state);
        if (!target) {
          if (attemptsRemaining > 0) {
            requestAnimationFrame(() => restoreSelection(attemptsRemaining - 1));
          }
          return;
        }

        placeCaretAfterMentionAnchor(target);
      };

      requestAnimationFrame(() => restoreSelection(4));

      mentionStateRef.current = null;
      skillEnterArmedRef.current = false;
      setMentionState(null);
      return true;
    },
    [decorateProjectMentions, onChange],
  );

  const handleAutocompletePress = useCallback((
    event: ReactMouseEvent<HTMLButtonElement> | ReactPointerEvent<HTMLButtonElement> | ReactTouchEvent<HTMLButtonElement>,
    option: AutocompleteOption,
  ) => {
    event.preventDefault();
    event.stopPropagation();
    if (autocompleteSelectionHandledRef.current) return;
    const handled = selectMention(option);
    if (handled) {
      autocompleteSelectionHandledRef.current = true;
    }
  }, [selectMention]);

  // Touch handling for the mention menu. We deliberately do NOT preventDefault
  // on touchstart so the browser can still scroll the menu vertically; instead
  // we record the start point and only treat the gesture as a selection if the
  // finger lifted with negligible movement (i.e., a tap, not a scroll).
  const touchStartPointRef = useRef<{ x: number; y: number } | null>(null);
  const TOUCH_TAP_THRESHOLD_PX = 8;

  const handleAutocompleteTouchStart = useCallback((event: ReactTouchEvent<HTMLButtonElement>) => {
    const touch = event.touches[0];
    if (!touch) return;
    touchStartPointRef.current = { x: touch.clientX, y: touch.clientY };
  }, []);

  const handleAutocompleteTouchMove = useCallback((event: ReactTouchEvent<HTMLButtonElement>) => {
    const start = touchStartPointRef.current;
    if (!start) return;
    const touch = event.touches[0];
    if (!touch) return;
    if (Math.hypot(touch.clientX - start.x, touch.clientY - start.y) > TOUCH_TAP_THRESHOLD_PX) {
      touchStartPointRef.current = null;
    }
  }, []);

  const handleAutocompleteTouchEnd = useCallback((
    event: ReactTouchEvent<HTMLButtonElement>,
    option: AutocompleteOption,
  ) => {
    const start = touchStartPointRef.current;
    touchStartPointRef.current = null;
    if (!start) return;
    const touch = event.changedTouches[0];
    if (!touch) return;
    if (Math.hypot(touch.clientX - start.x, touch.clientY - start.y) > TOUCH_TAP_THRESHOLD_PX) {
      return;
    }
    handleAutocompletePress(event, option);
  }, [handleAutocompletePress]);

  function hasFilePayload(evt: DragEvent<HTMLDivElement>) {
    return Array.from(evt.dataTransfer?.types ?? []).includes("Files");
  }

  const canDropFile = fileDropTarget === "editor" && Boolean(imageUploadHandler || onDropFile);
  const handlePasteCapture = useCallback((event: ClipboardEvent<HTMLDivElement>) => {
    const clipboard = event.clipboardData;
    if (!clipboard || !ref.current) return;
    const types = new Set(Array.from(clipboard.types));
    if (types.has("Files") || types.has("text/html")) return;
    if (isPasteInsideCodeLikeElement(containerRef.current, event)) return;

    const rawText = clipboard.getData("text/plain");
    if (!looksLikeMarkdownPaste(rawText)) return;

    event.preventDefault();
    // Lexical also handles paste on the editable element. Once Markdown is
    // inserted here, prevent that handler from inserting the plain text again.
    event.stopPropagation();
    ref.current.insertMarkdown(escapeUnsupportedAngleBrackets(normalizeMarkdown(rawText)));
  }, []);

  const handleRichEditorRenderError = useCallback((error: unknown) => {
    setRichEditorError({ code: "MDE-RENDER", message: richEditorErrorMessage(error) });
  }, []);

  const handleRichEditorParseError = useCallback((error: unknown) => {
    setRichEditorError({ code: "MDE-PARSE", message: richEditorErrorMessage(error) });
  }, []);

  const mentionMenuPosition = mentionState
    ? computeMentionMenuPosition(
        mentionState,
        getMentionMenuViewport(),
        getMentionMenuSize(filteredMentions.length),
      )
    : null;

  if (richEditorError) {
    return (
      <div
        ref={containerRef}
        className={cn(
          "relative paperclip-mdxeditor-scope",
          bordered ? "rounded-md border border-border bg-transparent" : "bg-transparent",
          className,
        )}
      >
        <div className="flex items-start justify-between gap-3 px-3 pt-2 text-xs text-muted-foreground">
          <p>
            Rich editor unavailable for this markdown. Showing raw source instead.{" "}
            <span data-testid="markdown-editor-fallback-code" className="font-mono">
              {richEditorError.code}
            </span>
          </p>
          <button
            type="button"
            className="shrink-0 underline underline-offset-2 hover:text-foreground"
            onClick={() => {
              // The retry remounts MDXEditor, so re-arm the mount-time guard:
              // a fresh mount can emit an empty onChange that would otherwise
              // wipe the parent's value.
              initialChildOnChangeRef.current = true;
              setRichEditorError(null);
            }}
          >
            Retry rich editor
          </button>
        </div>
        <textarea
          ref={fallbackTextareaRef}
          aria-label={ariaLabel}
          value={value}
          placeholder={placeholder}
          readOnly={readOnly}
          onChange={(event) => {
            if (readOnly) return;
            onChange(event.target.value);
            autoSizeFallbackTextarea(event.target);
          }}
          onBlur={() => onBlur?.()}
          onKeyDown={(event) => {
            if (onSubmit && isSubmitShortcut(event)) {
              event.preventDefault();
              event.stopPropagation();
              onSubmit();
            }
          }}
          className={cn(
            "min-h-(--sz-12rem) w-full resize-none bg-transparent px-3 pb-3 pt-2 font-mono text-sm leading-6 outline-none",
            contentClassName,
          )}
        />
      </div>
    );
  }

  return (
    <div
      ref={containerRef}
      {...(canDropFile && !readOnly ? { [FILE_DROP_TARGET_ATTRIBUTE]: "" } : {})}
      className={cn(
        "relative paperclip-mdxeditor-scope",
        bordered ? "rounded-md border border-border bg-transparent" : "bg-transparent",
        isDragOver && "ring-1 ring-primary/60 bg-accent/20",
        className,
      )}
      onInputCapture={(event) => {
        if (
          !readOnly
          && event.target instanceof HTMLElement
          && event.target.closest('[contenteditable="true"]')
        ) {
          // Actual input may be the editor's first change. An intentional clear
          // must not be mistaken for its programmatic empty mount reset.
          initialChildOnChangeRef.current = false;
        }
      }}
      onKeyDownCapture={(e) => {
        if (readOnly || e.nativeEvent.isComposing || e.keyCode === 229) return;
        if (e.key === "Enter" && (e.shiftKey || e.altKey)) return;
        if (
          (e.key === "Backspace" || e.key === "Delete")
          && e.target instanceof HTMLElement
          && e.target.closest('[contenteditable="true"]')
        ) {
          // Lexical handles deletion on keydown and may suppress DOM input.
          initialChildOnChangeRef.current = false;
        }
        // An explicit Cmd/Ctrl+Enter sends even while autocomplete is open.
        if (onSubmit && isSubmitShortcut(e) && (e.metaKey || e.ctrlKey)) {
          e.preventDefault();
          e.stopPropagation();
          onSubmit();
          return;
        }

        // Mention keyboard handling
        if (mentionActive) {
          if (e.key === " " && mentionStateRef.current?.trigger === "skill") {
            mentionStateRef.current = null;
            skillEnterArmedRef.current = false;
            setMentionState(null);
            return;
          }
          // Escape always dismisses
          if (e.key === "Escape") {
            e.preventDefault();
            e.stopPropagation();
            mentionStateRef.current = null;
            skillEnterArmedRef.current = false;
            setMentionState(null);
            return;
          }
          // Arrow / Enter / Tab only when there are filtered results
          if (filteredMentions.length > 0) {
            if (e.key === "ArrowDown") {
              e.preventDefault();
              e.stopPropagation();
              skillEnterArmedRef.current = mentionStateRef.current?.trigger === "skill";
              setMentionIndex((prev) => Math.min(prev + 1, filteredMentions.length - 1));
              return;
            }
            if (e.key === "ArrowUp") {
              e.preventDefault();
              e.stopPropagation();
              skillEnterArmedRef.current = mentionStateRef.current?.trigger === "skill";
              setMentionIndex((prev) => Math.max(prev - 1, 0));
              return;
            }
            if (
              shouldAcceptAutocompleteKey(
                e.key,
                mentionStateRef.current?.trigger ?? null,
                skillEnterArmedRef.current,
              )
            ) {
              e.preventDefault();
              e.stopPropagation();
              selectMention(filteredMentions[mentionIndex]);
              return;
            }
          }
        }

        // Leave an unselected slash menu's Enter with the editor.
        if (
          onSubmit && isSubmitShortcut(e)
          && !(mentionActive && filteredMentions.length > 0)
          && e.target instanceof HTMLElement
          && e.target.closest('[contenteditable="true"]')
        ) {
          e.preventDefault();
          e.stopPropagation();
          onSubmit();
        }
      }}
      onDragEnter={(evt) => {
        if (readOnly) return;
        if (!canDropFile || !hasFilePayload(evt)) return;
        dragDepthRef.current += 1;
        setIsDragOver(true);
      }}
      onDragOver={(evt) => {
        if (readOnly) return;
        if (!canDropFile || !hasFilePayload(evt)) return;
        evt.preventDefault();
        evt.dataTransfer.dropEffect = "copy";
      }}
      onDragLeave={() => {
        if (readOnly) return;
        if (!canDropFile) return;
        dragDepthRef.current = Math.max(0, dragDepthRef.current - 1);
        if (dragDepthRef.current === 0) setIsDragOver(false);
      }}
      onDrop={(evt) => {
        if (readOnly) return;
        dragDepthRef.current = 0;
        setIsDragOver(false);
        if (!onDropFile) return;
        const files = evt.dataTransfer?.files;
        if (!files || files.length === 0) return;
        const allFiles = Array.from(files);
        const nonImageFiles = allFiles.filter(
          (f) => !f.type.startsWith("image/"),
        );
        if (nonImageFiles.length === 0) return;
        // If all dropped files are non-image, prevent default so MDXEditor
        // doesn't try to handle them. If mixed, let images flow through to
        // the image plugin and only handle the non-image files ourselves.
        if (nonImageFiles.length === allFiles.length) {
          evt.preventDefault();
          evt.stopPropagation();
        }
        for (const file of nonImageFiles) {
          void onDropFile(file);
        }
      }}
      onPasteCapture={handlePasteCapture}
    >
      <MarkdownEditorRichErrorBoundary onError={handleRichEditorRenderError}>
        <MDXEditor
          ref={setEditorRef}
          translation={(key, fallback, interpolations = {}) =>
            key === "contentArea.editableMarkdown" && ariaLabel
              ? ariaLabel
              : Object.entries(interpolations).reduce(
                  (text, [name, value]) => text.replaceAll(`{{${name}}}`, String(value)),
                  fallback,
                )
          }
          markdown={editorValue}
          iconComponentFor={editorIconFor}
          suppressHtmlProcessing
          placeholder={placeholder}
          readOnly={readOnly}
          onChange={(rawNext, initialMarkdownNormalize) => {
            if (readOnly) return;
            // Reverse the editor-only rewrites: blockquotes the exporter escaped
            // as `\>` (so a `>`-prefixed line the user typed survives even when
            // the WYSIWYG shortcut didn't fire), and the `\<` transport escaping
            // that keeps bare angle brackets off the HTML parser.
            const next = toStoredMarkdown(rawNext);
            const echo = echoIgnoreMarkdownRef.current;
            if (echo !== null) {
              echoIgnoreMarkdownRef.current = null;
              // `echo` is what we handed to `setMarkdown`, so it is in editor
              // space while `next` is in stored space. Accept either form —
              // otherwise every prop sync of a value containing an escaped
              // bracket reads as a real edit and notifies the parent.
              if (next === echo || next === toStoredMarkdown(echo)) {
                latestValueRef.current = echo;
                return;
              }
            }

            if (initialChildOnChangeRef.current) {
              initialChildOnChangeRef.current = false;
              if (next === "" && editorValue !== "") {
                echoIgnoreMarkdownRef.current = editorValue;
                ref.current?.setMarkdown(editorValue);
                return;
              }
            }
            // MDXEditor re-serialises the initial markdown on load (bullet
            // markers, escapes, blank lines) and flags that emission. It is not
            // a user edit: forwarding it marks every controlled parent with
            // dirty tracking as unsaved before any keystroke. `latestValueRef`
            // stays on the parent's value, so the prop-sync effect does not
            // push the original back over the editor.
            if (initialMarkdownNormalize) return;
            // `latestValueRef` is compared against `editorValue`, so it has to
            // hold editor space; storing `next` would make every edit containing
            // an escaped bracket look like a pending prop sync and trigger a
            // redundant `setMarkdown` that resets the caret.
            latestValueRef.current = prepareMarkdownForEditor(next);
            onChange(next);
          }}
          onBlur={() => onBlur?.()}
          onError={(payload) => {
            handleRichEditorParseError(payload.error);
          }}
          className={cn("paperclip-mdxeditor", !bordered && "paperclip-mdxeditor--borderless")}
          contentEditableClassName={cn(
            "paperclip-mdxeditor-content focus:outline-none [&_ul]:list-disc [&_ul]:pl-5 [&_ol]:list-decimal [&_ol]:pl-5 [&_li]:list-item",
            contentClassName,
          )}
          additionalLexicalNodes={[MentionAwareLinkNode, mentionAwareLinkNodeReplacement]}
          plugins={plugins}
        />
      </MarkdownEditorRichErrorBoundary>

      {/* Mention dropdown — rendered via portal so it isn't clipped by overflow containers */}
      {mentionActive && filteredMentions.length > 0 && mentionMenuPosition &&
        createPortal(
          <div
            data-paperclip-floating-ui=""
            data-testid="mention-autocomplete-menu"
            className="pointer-events-auto fixed z-(--z-9999) min-w-(--sz-180px) max-w-(--sz-calc-15) max-h-(--sz-208px) overflow-y-auto overscroll-contain rounded-md border border-border bg-popover shadow-md"
            style={{
              top: mentionMenuPosition.top,
              left: mentionMenuPosition.left,
              maxWidth: mentionMenuPosition.maxWidth,
              touchAction: "pan-y",
              WebkitOverflowScrolling: "touch",
            }}
            onWheelCapture={(event) => {
              // Modal scroll locks treat this body-level portal as outside the
              // dialog. Keep wheel input on the menu so the lock cannot cancel it.
              event.stopPropagation();
            }}
            onTouchMove={(event) => {
              // Let the touched option observe movement first, then keep the
              // native event from reaching a modal's document-level scroll lock.
              event.stopPropagation();
            }}
          >
            {filteredMentions.map((option, i) => (
              <button
                key={option.id}
                type="button"
                tabIndex={-1}
                disabled={option.kind === "action" && option.disabled === true}
                aria-disabled={option.kind === "action" && option.disabled === true}
                title={option.kind === "action" && option.disabled ? option.disabledReason ?? undefined : undefined}
                ref={(node) => {
                  autocompleteOptionRefs.current[i] = node;
                }}
                className={cn(
                  "flex items-center gap-2 w-full px-3 py-1.5 text-sm text-left hover:bg-accent/50 transition-colors",
                  i === mentionIndex && "bg-accent",
                  option.kind === "action" && option.disabled && "cursor-not-allowed opacity-60 hover:bg-transparent",
                )}
                onPointerDown={(e) => {
                  // Touch is handled via onTouchStart/onTouchEnd so vertical scrolling
                  // isn't swallowed; only handle mouse/pen here.
                  if (e.pointerType === "touch") return;
                  handleAutocompletePress(e, option);
                }}
                onMouseDown={(e) => handleAutocompletePress(e, option)}
                onTouchStart={handleAutocompleteTouchStart}
                onTouchMove={handleAutocompleteTouchMove}
                onTouchEnd={(e) => handleAutocompleteTouchEnd(e, option)}
                onMouseEnter={() => {
                  if (mentionStateRef.current?.trigger === "skill") {
                    skillEnterArmedRef.current = true;
                  }
                  setMentionIndex(i);
                }}
              >
                {option.kind === "routine" ? (
                  <CalendarClock className="h-3.5 w-3.5 shrink-0 text-muted-foreground" />
                ) : option.kind === "action" ? (
                  <Flag className="h-3.5 w-3.5 shrink-0 text-muted-foreground" />
                ) : option.kind === "skill" ? (
                  <Boxes className="h-3.5 w-3.5 shrink-0 text-muted-foreground" />
                ) : option.kind === "issue" ? (
                  <Hash className="h-3.5 w-3.5 shrink-0 text-muted-foreground" />
                ) : option.kind === "project" && option.projectId ? (
                  <span
                    className="inline-flex h-2 w-2 rounded-full border border-border/50"
                    style={{ backgroundColor: option.projectColor ?? "var(--project-none)" }}
                  />
                ) : option.kind === "user" ? (
                  <User className="h-3.5 w-3.5 shrink-0 text-muted-foreground" />
                ) : (
                  <AgentAvatar agent={{ id: option.agentId ?? option.id, name: option.name, appearance: option.agentAppearance }} size={16} />
                )}
                {option.kind === "issue" && option.issueIdentifier ? (
                  <span className="flex min-w-0 items-baseline gap-1.5">
                    <span className="shrink-0 font-mono text-(length:--text-micro) text-muted-foreground">
                      {option.issueIdentifier}
                    </span>
                    <span className="truncate">{issueMentionTitle(option)}</span>
                  </span>
                ) : (
                  <span className="truncate">
                    {option.kind === "skill" || option.kind === "routine" || option.kind === "action"
                      ? slashCommandLabel(option)
                      : option.name}
                  </span>
                )}
                {option.kind === "issue" && (
                  <span className="ml-auto text-(length:--text-nano) uppercase tracking-wide text-muted-foreground">
                    Task
                  </span>
                )}
                {option.kind === "project" && option.projectId && (
                  <span className="ml-auto text-(length:--text-nano) uppercase tracking-wide text-muted-foreground">
                    Project
                  </span>
                )}
                {option.kind === "user" && (
                  <span className="ml-auto text-(length:--text-nano) uppercase tracking-wide text-muted-foreground">
                    User
                  </span>
                )}
                {option.kind === "skill" && (
                  <span className="ml-auto text-(length:--text-nano) uppercase tracking-wide text-muted-foreground">
                    Skill
                  </span>
                )}
                {option.kind === "routine" && (
                  <span className="ml-auto text-(length:--text-nano) uppercase tracking-wide text-muted-foreground">
                    Routine
                  </span>
                )}
                {option.kind === "action" && (
                  <span className="ml-auto max-w-28 truncate text-(length:--text-nano) text-muted-foreground">
                    {option.disabled ? option.disabledReason : option.description}
                  </span>
                )}
              </button>
            ))}
          </div>,
          document.body,
        )}

      {isDragOver && canDropFile && (
        <div
          className={cn(
            "pointer-events-none absolute inset-1 z-40 flex items-center justify-center rounded-md border border-dashed border-primary/80 bg-primary/10 text-xs font-medium text-primary",
            !bordered && "inset-0 rounded-sm",
          )}
        >
          Drop {onDropFile ? "file" : "image"} to upload
        </div>
      )}
      {uploadError && (
        <p className="px-3 pb-2 text-xs text-destructive">{uploadError}</p>
      )}
    </div>
  );
});