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

@@ -43,6 +43,8 @@ When bumping the opencode version, bump `OPENCODE_VERSION` in `Dockerfile.varian
   - `.env.example` must be hand-updated to match Dockerfile/entrypoint behavior — it is not auto-generated.
 
   Release-day checklist: README → (regenerate DOCKER_HUB.md only if HUB_TEMPLATE changed) → promote CHANGELOG Unreleased → grep AGENTS.md for stale counts → commit → tag → push tag.
+
+  **Between releases the same coupling applies.** Doc drift is not just a release-day concern — a workflow tweak, entrypoint change, or `generate-config.py` refactor can leave any of these four files lying. Before committing a non-release change, grep the docs for references to what you touched: `git diff --name-only HEAD | xargs -I{} grep -l 'thing-you-changed' README.md AGENTS.md DOCKER_HUB.md .gitea/README.md .env.example`. If a doc says "four variants" / "two phases" / "runs on amd64 only" and your change made that no longer true, fix it in the same commit.
 - **GitHub/Gitea-sourced binaries float by default** — gosu, fzf, git-lfs, nvim, bat, eza, zoxide, uv, gitea-mcp, Go, oh-my-opencode-slim all default to `latest`. Each build-time install step reads the `/releases/latest` Location redirect (or the go.dev JSON feed for Go) and derives the concrete version. Use the same `ARCH` case-switch pattern for multi-arch support (amd64/arm64). Intentional pins: `OPENCODE_VERSION` (drives the image tag), `NODE_VERSION=22` (major pin), `DEBIAN_VERSION=trixie-slim` (OS base). Adding a new upstream tool: follow the existing floated-version pattern, don't hardcode a specific tag.
 - **Resolved versions are logged by the smoke test** — `scripts/smoke-test.sh` prints a "Resolved component versions" table as its first step. CI logs always capture what got baked into a given image even when ARGs default to `latest`.
 - **Shell scripts use `set -euo pipefail`** — both entrypoints are strict. Errors in volume chown or SSH permission operations are intentionally suppressed with `|| true`.