The customer problem
A platform team must migrate a 200-file codebase from library A to library B. Done by hand it is a quarter of grind; done by an agent in one heroic session it fails on context limits and unreviewable diffs. The work must span sessions, parallelize safely, and prove itself.
Architecture shape
A planner produces a migration plan as a file in the repo. Workers take file-scoped tasks in isolated worktrees; the test suite is the done criterion per task; a ratchet forbids regressions. Sessions hand off through the plan and progress files, so any session can die and the next one continues. The codebase itself is the durable state.
The decisions that matter
- The repo is the checkpoint store. Plans, progress and diffs live in files and branches, which makes resume trivial and review natural.
- Verification is separate from generation. The test ratchet, not the model’s summary, decides whether a task is done.
- Parallelism is bounded by isolation. Worktrees keep workers from stepping on each other, the same ownership problem as any long-running system.
Where Course 001 uses this case
The Deep Agents bridge (Module 12) studies this shape directly, and it recurs across the industry architectures survey.