lint: ruff cleanup pass across bal/ and tests/

- Sort imports and fix pyproject ruff config (per-file ignores for
  intentional Qt/core exceptions)
- Mark Heirs.validate_* helpers as @staticmethod
- Clean up dead code, rename shadowing vars, use raise ... from
- Add AGENTS.md with env/lint/test/release guidance

AGENTS.md

@@ -0,0 +1,76 @@
+# AGENTS.md
+
+BAL — Bitcoin After Life, an Electrum plugin (inheritance / dead-man's-switch).
+Source-of-truth docs: `README.md`, `HANDOFF.md`, `COMPATIBILITY.md`.
+
+## Environments (critical)
+
+Two separate venvs; using the wrong one is the #1 mistake.
+
+- **Runtime env** (Electrum + PyQt6, has `electrum` importable):
+  `source /home/steal/devel/bal/electrum/env/bin/activate`
+  This is an editable install of the Electrum 4.8.0 checkout at
+  `/home/steal/devel/bal/electrum`. Use it for anything that imports
+  `electrum`, runs GUI code, or runs tests.
+- **Lint venv** (repo-local `venv/`): ruff, black, flake8 only. It cannot
+  import `electrum` or `PyQt6`. Do NOT use it to run tests.
+
+The plugin's `bal/` directory is symlinked into
+`electrum/electrum/plugins/bal` (internal-plugin install used during dev).
+
+## Test & verify
+
+Tests are **standalone scripts**, not pytest. Each `tests/test_*.py` file runs
+its `test_*` functions from `if __name__ == "__main__"`. Run a file directly:
+
+```bash
+source /home/steal/devel/bal/electrum/env/bin/activate
+python3 tests/test_core_heirs.py        # core, no Qt needed
+QT_QPA_PLATFORM=offscreen python3 tests/test_gui_common.py   # GUI tests need offscreen
+```
+
+- Most core tests run offline (no wallet/network). Some files
+  (`test_group_*.py`, `test_no_willexecutor_karen7.py`, `parallel_ping_test.py`)
+  exercise will-executor/network flows and need the live servers — don't rely on
+  them for quick verification.
+- `tests/smoke_test.py` proves clean import under real Electrum:
+  `QT_QPA_PLATFORM=offscreen python3 tests/smoke_test.py electrum.plugins.bal`
+- `tests/external_zip_test.py` loads the built zip the way Electrum's plugin
+  dialog does (`electrum_external_plugins.bal`); run it after `build_zip.py`.
+
+## Lint / typecheck
+
+- **Ruff is NOT clean** (hundreds of pre-existing errors in `bal/` and
+  `tests/`). Do not run `--fix` wholesale and do not try to silence everything;
+  just avoid adding new violations. Config: `pyproject.toml` (line-length 88,
+  E501 ignored).
+- Lint via the repo venv: `/home/steal/devel/bal/bal-electrum-plugin/venv/bin/ruff`
+- Typecheck: `pyright` (npm, `node_modules/`), config `pyrightconfig.json`
+  (`extraPaths: ["../electrum"]`). Pyright reports many false positives on
+  dynamically-attached attrs (e.g. `self.window`, `BalPlugin.*`); don't chase
+  them.
+
+## Architecture
+
+- `bal/core/` = GUI-free logic (`heirs.py`, `will.py`, `willexecutors.py`,
+  `plugin_base.py`, `util.py`). Must never import Qt.
+- `bal/gui/qt/` = PyQt6 layer. `window.py` is the per-wallet controller,
+  `plugin.py` is the Electrum `@hooks` entry, `qt.py` is a zipimport shim.
+- `bal/manifest.json` = version source of truth (Electrum reads it; also read by
+  `make-release.sh`).
+- Compatibility constraint: must support Electrum **4.7.2 and 4.8.0**; the DB
+  registration API differs between them (`json_db.register_dict` vs
+  `stored_dict.register_name`).
+
+## Build / release
+
+```bash
+python3 build_zip.py   # -> bal-electrum-plugin.zip (deterministic, prints sha256)
+./make-release.sh [v0.x.y]   # bump manifest version, tag, sign, push Gitea release
+```
+
+- `make-release.sh` requires gpg and Gitea credentials (`~/.git-credentials`
+  or `GITEA_USER`/`GITEA_TOKEN`). It bumps `bal/manifest.json` — bump the
+  version there, never invent a new source of truth.
+- Remote is Gitea (`origin` = bitcoin-after.life). `.env` holds a Gitea token
+  (gitignored, never commit it).