0007. Distribution is a Copier template; instances concretize and update

Context

The harness must run inside other repositories, each with its own tracker, branches, gates and toolchain. A library dependency cannot ship agent prompts, hooks, CI files and docs, and a one-off copy cannot receive fixes.

Decision

pdca-harness is a Copier template (copier.yml, first commit 3ca179a, 2026-06-04). A project renders it once; repo-specific facts go into docs/INTEGRATION.md and pdca.toml; later releases arrive with copier update. The driver source is rendered into each instance under src/.

Consequences

An instance can concretize everything the template parameterizes and still receive upstream fixes. Anything an instance changes inside rendered files — especially src/ — is overwritten or conflicts on the next copier update; the wyrd instance carries about 2,300 lines of such local patches. Migration step 5 (ADR-0013, #714) adds a pdca_ext/ boundary that copier update never crosses, so instance behaviour has a supported home.