AGENTS.md: documentation-drift sweep as explicit pre-commit step

Companion to the same addition in the cloud-init and ansible repos.
Caught real drift in those repos in a recent session only because
the user explicitly asked. Codify the sweep with concrete, repo-
specific drift hotspots rather than a vague 'watch for drift' rule
that gets ignored.

Each AGENTS.md addition lists the doc files most likely to fall
behind code changes here, plus a quick-triage one-liner using
'git diff --name-only HEAD | xargs grep -l ...' so the rule is
actionable not aspirational.

AGENTS.md

@@ -195,3 +195,14 @@ future pi-option: a container built with mempalace off should still be
 able to install a functional pi, and that dependency asymmetry is
 cleanest when pi's own config lives in its own repo. Mirrors the
 2026-05-05 split of `opencode-toolkit` out of the same parent.
+
+## Documentation drift sweep
+
+Before committing any non-trivial change, check that prose still matches code. Drift hotspots in this repo:
+
+- `README.md` — install instructions, the file/artifact table, the testing recipe. The installer's behaviour and the README's description of it must stay in lockstep — the README is what users follow.
+- `AGENTS.md` (this file) — the `Conventions` section codifies symlink-vs-cp-vs-template decisions per artifact; if you change how an artifact is installed, update the conventions too.
+- `install.sh` — contains its own usage block at the top; keep the `--help` output and the README in sync.
+- `settings.example.json` — the canonical template for pi settings; if pi adds a new top-level setting that this toolkit blesses with defaults, update the example here.
+
+Quick triage: `git diff --name-only HEAD | xargs -I{} grep -l 'thing-you-changed' README.md AGENTS.md install.sh`.