docs(agent): require Conventional Commits in contribution guide

Author: rdavid

AGENT.md

@@ -0,0 +1,34 @@
+# SPDX-FileCopyrightText: 2026 David Rabkin
+# SPDX-License-Identifier: 0BSD
+
+# AGENT
+
+Purpose: quick operating notes for humans and automation working in this repo.
+
+## Project
+- Name: `toolbox`
+- Language: POSIX shell (`#!/bin/sh`) scripts in `app/`
+- Build/lint entrypoint: `redo lint` (via `all.do` / `lint.do`)
+
+## Repo Layout
+- `app/`: executable utilities
+- `cfg/`: configuration files used by scripts
+- `*.do`: `redo` build/lint tasks
+- `README.adoc`: user-facing docs
+
+## Conventions
+- Keep scripts POSIX-friendly for `sh`.
+- Use `shellcheck` + `shfmt` compatible style.
+- Preserve SPDX headers in edited files.
+- Use Conventional Commits for commit subjects (for example: `fix: ...`,
+  `style: ...`, `chore: ...`).
+- Prefer minimal, focused commits.
+
+## Common Commands
+- Run lint: `redo lint`
+- Run shell syntax check on all apps:
+  `for f in app/*; do sh -n "$f"; done`
+
+## Safety
+- Avoid destructive git/history operations unless explicitly requested.
+- Do not rewrite unrelated files.