ADR 0005 — Answers file from day one; three-way-merge updates postponed

Status: Accepted · Date: 2026-08-01

Context

The most valuable (and hardest) feature in the ecosystem is Copier's: updating an already-generated project when its template improves, via three-way merge (original template + current project + new template). It requires knowing which template, version, and values were used at generation time. Without that record, it is retroactively impossible.

Decision

• Every generated project includes .templetry-answers.yml: template, commit/version, variable values and features. Cost: zero.
• Three-way-merge updates are postponed to Phase 4+ — they don't gate the MVP.

Outcome (2026-08-05): fully realized. Engine v0.2.2 records the resolved template commit; the desktop app ships drift detection, assisted updates (re-render with recorded inputs + diff) and real three-way merges via git merge-file when both the user and the template changed a file.

Consequences

• The door to updates stays open for every project generated from day one.
• The answers-file format is part of the public API (version it just like the manifest).