docs: add AGENTS.md repository guidance

AGENTS.md

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+# Repository guidance
+
+## Development and verification
+
+- Python minimum is 3.13; CI tests 3.13 and 3.14 on Linux/macOS. Use `uv`;
+  `uv sync --extra telemetry` includes the optional dependencies exercised in CI.
+- Run checks from the repo root, in CI order:
+  ```sh
+  uv run ruff check
+  uv run ruff format --check
+  uv run python -m pytest
+  ```
+- Focused test: `uv run python -m pytest tests/test_agent_builder.py`; append
+  `::test_read_only_mode_denies_writes` to run one case.
+- CLI startup requires `fd`, `rg`, and `rtk` on PATH. Debian's `fd-find` installs
+  `fdfind`, so expose it as `fd`. Search tests skip without their binaries;
+  CI supplies an RTK pass-through shim, not real compaction coverage.
+- `.pre-commit-config.yaml` runs Ruff checks and formatting on commit, the full
+  pytest suite on pre-push. The formatting hook modifies files.
+
+## Runtime boundaries
+
+- `src/lecode/cli.py` dispatches interactive, headless, loop, and chain modes.
+  They share `agent/builder.py:build_runtime()` for wiring and
+  `agent/runner.py:AgentRunner` for the model/tool loop. Keep builder wiring
+  network-free; interactive catalog/MCP startup is deferred until chat opens.
+- Route tool execution through `agent/tools/base.py:ToolRegistry.dispatch_result()`:
+  it validates arguments and enforces permissions/approval. Auto-approval never
+  overrides Deny; hooks and agent overlays can only narrow permissions.
+- TUI changes must preserve normal terminal scrollback, not an alternate-screen UI.
+  `tui/feed.py` keeps live tokens in the layout and flushes completed text to
+  scrollback; partial-line printing through `patch_stdout` can erase streaming output.
+  Check `tests/test_tui_feed.py`, `tests/test_tui_app.py`, and
+  `tests/test_tui_streaming_pty.py` for rendering changes.
+- `session/storage.py` stores append-only JSONL. Replay through `load_for_model()`
+  so compaction, clear events, and undo tombstones apply. Keep lock sidecars on
+  release: unlinking them allows competing processes to lock different inodes.
+
+## Isolation and sources of truth
+
+- `config/loader.py:load_config()` creates defaults and rewrites migrated config.
+  Tests constructing runtimes/config/session stores should isolate
+  `LECODE_CONFIG_DIR`, `LECODE_SKILLS_DIR`, and project cwd under `tmp_path`.
+  The shared `tool_ctx` fixture is not autouse and isolates only the config directory.
+- Reuse `tests/fakes.py` for providers/catalogs. MCP tests launch mock subprocesses
+  and localhost servers; disable auto servers as in `tests/test_mcp.py:mcp_config`
+  to avoid ambient credentials activating Exa. Keep the SSE shutdown reset in
+  `tests/conftest.py`; it prevents order-dependent failures across server tests.
+- `docs/build-plan.md` is historical, not the current spec: permissions now have
+  two modes, config is TOML-only, and the catalog is live with an empty fallback.
+  For config or hook changes, consult `docs/configuration.md` or `docs/hooks.md`
+  and reconcile with the implementation.
+- Releases use conventional commits and release-please, with wheel/sdist attached
+  to GitHub Releases, not PyPI. `.github/workflows/release.yml` separately re-locks
+  `uv.lock` after release-please bumps `pyproject.toml`.