Scoped guidance

Root AGENTS.md is authoritative and cannot be weakened here; on conflict, the root wins — flag and fix the conflict in the same PR. This file adds durable local rules only.

Public harness contract

• This package is the public test harness for flows: users import from chainweaver.testing directly. Its symbols are deliberately not in the top-level chainweaver/__init__.py __all__ (the one exception is FixtureStaleError, which follows the error-catalog convention) — keep it that way so the public-API snapshot stays runtime-focused.
• The harness hooks at the Tool._call_fn / _call_fn_async boundary — never inside executor.py — so schema validation still runs during replay and the executor's invariants stay untouched. See architecture.md § Design traps before changing the record/replay patching.
• protocol_suites.py imports pytest, so it must remain a submodule that testing/__init__.py never imports — the harness itself stays pytest-free.
• The pytest plugin lives at the repo root (pytest_chainweaver.py), not in this package — that placement is deliberate (coverage measurement); do not move it here.