Function windowFor

src/ui-server/api/flow.ts:408–450

* The ±SOURCE_WINDOW lines a card shows. * * Anchored on the line that makes the next call. The last card has no next * call, so it anchors on the definition instead — a reader who followed seven * hops to get there wants to see what they arrived at.

(
  cg: CodeGraph,
  projectRoot: string,
  cache: Map<string, FileCache>,
  node: Node,
  anchor: number
)

 * hops to get there wants to see what they arrived at.
 */
async function windowFor(
  cg: CodeGraph,
  projectRoot: string,
  cache: Map<string, FileCache>,
  node: Node,
  anchor: number
): Promise<WireFlowSource | null> {
  const file = loadFile(cg, projectRoot, cache, node.filePath);
  if (!file) return null;
  const posix = toRequestPath(node.filePath);
  if (file.lines === null) {
    return {
      file: posix,
      language: file.language,
      from: anchor,
      to: anchor,
      drift: file.drift,
      ...(file.reason ? { reason: file.reason } : {}),
    };
  }

  const total = file.lines.length;
  const from = Math.max(1, Math.min(anchor - SOURCE_WINDOW, total));
  const to = Math.max(from, Math.min(anchor + SOURCE_WINDOW, total));
  // Tokenise with the lead-in, then keep only the window — see HIGHLIGHT_LEAD_MAX.
  const leadFrom = Math.max(1, Math.min(from, Math.max(node.startLine, from - HIGHLIGHT_LEAD_MAX)));
  const highlighted = await highlightLines(file.lines.slice(leadFrom - 1, to), {
    language: file.language,
    cacheKey: `${posix}:${leadFrom}:${to}`,
  });
  return {
    file: posix,
    language: file.language,
    from,
    to,
    lines: file.lines.slice(from - 1, to),
    highlight: {
      ...highlighted,
      lines: highlighted.lines.slice(from - leadFrom),
    },
    drift: false,
  };
}

/** The branch label for `edge`'s call site in `siteNode`'s file, or ''. */
async function whenAt(