/**
 * Cross-rung identity (F5, spec §6.3 fork c): `email` is git's own join key —
 * forges already map email → account. Resolved from the workspace git config,
 * cached per root, FAIL-OPEN: absence just omits the optional field and the
 * sidecar stays valid (spec §6.9). vscode-free, so it is unit-testable.
 */
import { execFileSync } from "node:child_process";

const cache = new Map<string, string | undefined>();

export function gitUserEmail(rootDir: string): string | undefined {
  if (!cache.has(rootDir)) {
    try {
      const out = execFileSync("git", ["config", "user.email"], {
        cwd: rootDir,
        encoding: "utf8",
        stdio: ["ignore", "pipe", "ignore"],
      }).trim();
      cache.set(rootDir, out || undefined);
    } catch {
      cache.set(rootDir, undefined);
    }
  }
  return cache.get(rootDir);
}