Method backtrack

src/agent/git-sandbox.ts:306–326

* Autonomous backtrack: hard-reset to the last checkpoint (or the sandbox base * if none). This is the "this approach is wrong — undo it" lever. Returns the * SHA we reset to, or null on failure. * * The last checkpoint is RETAINED (not popped): backtracking means "return to * the las

(signal?: AbortSignal)

   * dropCheckpoint() first.
   */
  async backtrack(signal?: AbortSignal): Promise<string | null> {
    if (!this.state?.active) return null;
    try {
      // Safety: a `reset --hard` blows away the whole working tree of whatever
      // branch HEAD points at. NEVER do that unless HEAD is still our sandbox
      // branch — otherwise we'd destroy the user's real branch state.
      const cur = await this.currentBranch(signal);
      if (cur !== this.state.branch) {
        logger.warn('GitSandbox.backtrack: HEAD is not the sandbox branch — aborting reset --hard', { expected: this.state.branch, actual: cur });
        return null;
      }
      const target = this.state.checkpoints[this.state.checkpoints.length - 1] ?? this.state.baseCommit;
      const r = await git(['reset', '--hard', target], { cwd: this.cwd, signal });
      if (!(r.exitCode === 0)) return null;
      logger.info('GitSandbox backtracked', { to: target.slice(0, 8) });
      return target;
    } catch (e: any) {
      logger.debug('GitSandbox.backtrack failed', { err: e?.message });
      return null;
    }
  }

  /** Discard the most recent checkpoint so the next backtrack walks further back. */
  dropCheckpoint(): void {