Function extractCompletionToken

src/hooks/useTypeahead.tsx:261–325

(text: string, cursorPos: number, includeAtSymbol = false)

 * @returns The completable token and its start position, or null if not found
 */
export function extractCompletionToken(text: string, cursorPos: number, includeAtSymbol = false): {
  token: string;
  startPos: number;
  isQuoted?: boolean;
} | null {
  // Empty input check
  if (!text) return null;

  // Get text up to cursor
  const textBeforeCursor = text.substring(0, cursorPos);

  // Check for quoted @ mention first (e.g., @"my file with spaces")
  if (includeAtSymbol) {
    const quotedAtRegex = /@"([^"]*)"?$/;
    const quotedMatch = textBeforeCursor.match(quotedAtRegex);
    if (quotedMatch && quotedMatch.index !== undefined) {
      // Include any remaining quoted content after cursor until closing quote or end
      const textAfterCursor = text.substring(cursorPos);
      const afterQuotedMatch = textAfterCursor.match(/^[^"]*"?/);
      const quotedSuffix = afterQuotedMatch ? afterQuotedMatch[0] : '';
      return {
        token: quotedMatch[0] + quotedSuffix,
        startPos: quotedMatch.index,
        isQuoted: true
      };
    }
  }

  // Fast path for @ tokens: use lastIndexOf to avoid expensive $ anchor scan
  if (includeAtSymbol) {
    const atIdx = textBeforeCursor.lastIndexOf('@');
    if (atIdx >= 0 && (atIdx === 0 || /\s/.test(textBeforeCursor[atIdx - 1]!))) {
      const fromAt = textBeforeCursor.substring(atIdx);
      const atHeadMatch = fromAt.match(AT_TOKEN_HEAD_RE);
      if (atHeadMatch && atHeadMatch[0].length === fromAt.length) {
        const textAfterCursor = text.substring(cursorPos);
        const afterMatch = textAfterCursor.match(PATH_CHAR_HEAD_RE);
        const tokenSuffix = afterMatch ? afterMatch[0] : '';
        return {
          token: atHeadMatch[0] + tokenSuffix,
          startPos: atIdx,
          isQuoted: false
        };
      }
    }
  }

  // Non-@ token or cursor outside @ token — use $ anchor on (short) tail
  const tokenRegex = includeAtSymbol ? TOKEN_WITH_AT_RE : TOKEN_WITHOUT_AT_RE;
  const match = textBeforeCursor.match(tokenRegex);
  if (!match || match.index === undefined) {
    return null;
  }

  // Check if cursor is in the MIDDLE of a token (more word characters after cursor)
  // If so, extend the token to include all characters until whitespace or end of string
  const textAfterCursor = text.substring(cursorPos);
  const afterMatch = textAfterCursor.match(PATH_CHAR_HEAD_RE);