Add CLAUDE.md agent guide

CLAUDE.md

@@ -0,0 +1,41 @@
+# door-sync — agent guide
+
+CiviCRM → UniFi Access reconciliation daemon. Runs on a Raspberry Pi under systemd.
+
+**Status: pre-implementation.** Module skeleton exists in `src/door_sync/` but reconciler/safety/clients are not yet written. Architecture is locked; see `docs/architecture.md` before adding code.
+
+## Commands
+
+```bash
+uv sync                       # install
+uv run pytest                 # tests
+uv run mypy src tests         # type check (strict)
+uv run ruff check .           # lint
+uv run door-sync --once       # one reconcile cycle, exit
+uv run door-sync --dry-run    # compute + log diff; no UniFi writes
+```
+
+All tooling goes through `uv run` — the venv is managed by uv, not pip.
+
+## Architecture
+
+`docs/architecture.md` is authoritative for module layout, data contracts, and the pure/impure boundary. Read it before designing changes that cross module boundaries.
+
+## Hard rules (from architecture doc — do not violate without a human in the loop)
+
+- **No asyncio.** Sync `httpx` only. Do not "modernize" to async; the design rejects it deliberately (architecture.md §3).
+- **Pure modules stay pure.** `reconciler.py`, `safety.py`, `tier_mapping.py` take dataclasses, return dataclasses. No logging, no config lookups, no HTTP, no exceptions on data issues — return a sentinel instead (architecture.md §5).
+- **Frozen dataclasses.** All domain models in `models.py` are `@dataclass(frozen=True)`. Never mutate; construct a new instance.
+- **Strict layering.** Nothing imports `orchestrator` except `scheduler` and (future) `webhook`. See dependency table in architecture.md §4.
+- **Card ID redaction.** Logs show last-4 only. Never log a full card ID at any level (architecture.md §11).
+- **Dry-run is sacred.** Dry-run flips a flag inside `UnifiClient` that turns writes into no-ops. Pure modules behave identically in dry-run and live — do not branch on dry-run in pure code.
+- **Fail-secure on safety guards.** Any guard firing means zero writes that cycle. No partial application.
+
+## Testing
+
+- Pure-module tests use plain dataclass construction — no mocks, no HTTP fixtures.
+- Idempotency canary: `compute_diff` immediately after `unifi.apply()` must yield all-empty diff sets. Include this test for the reconciler (architecture.md §8).
+
+## Config
+
+Two-file split: secrets in env (`.env` dev, `/etc/door-sync/env` prod, mode 0400), everything else in TOML (`config.toml` dev, `/etc/door-sync/config.toml` prod). Schema is not yet implemented.