test(ttp): E.2.14b RuleStore conformance — cross-backend + filesystem-specific + database-specific

tests/ttp/store/conftest.py — parametrized rule_store fixture over
FilesystemRuleStore (skipped on non-Linux) + DatabaseRuleStore.

test_conformance.py — shared assertions (default-state, set_state
isolation/round-trip, subscribe_changes per-rule fan-out, expires_at
auto-revert, set_state failure semantics) parametrize over both.
get_state-default GREEN today on FS (returns RuleState() for empty
cache); rest xfail-gated behind E.3.5/E.3.6.

test_filesystem.py — inotify mask + canonical kernel values + 9
scratch-filename rejections + 4 valid-filename acceptances +
fullmatch anchor + tmp_path construction + CompiledRule frozen
property GREEN today; per-save-style + filter-ordering +
atomic-swap concurrency xfail-gated.

test_database.py — class-level surface (no platform guard, ABC
methods concrete, async coroutines) GREEN today; ttp_rule_state
write + filesystem→DB sync xfail-gated behind E.3.6.

tests/ttp/store/conftest.py

@@ -0,0 +1,47 @@
+"""Parametrized ``rule_store`` fixture for E.2.14b.
+
+The conformance contract from ``development/TTP_TAGGING.md`` §E.2.14b:
+both backends — :class:`FilesystemRuleStore` and
+:class:`DatabaseRuleStore` — must satisfy the same observable
+behavior. Tests that consume :func:`rule_store` are run twice, once
+per backend.
+
+Filesystem is skipped on non-Linux (it raises ``RuntimeError`` from
+``__init__`` on macOS / Windows because the inotify dep is
+Linux-only).
+"""
+from __future__ import annotations
+
+import sys
+from pathlib import Path
+from typing import Iterator
+
+import pytest
+
+from decnet.ttp.store.base import RuleStore
+from decnet.ttp.store.impl.database import DatabaseRuleStore
+from decnet.ttp.store.impl.filesystem import FilesystemRuleStore
+
+
+@pytest.fixture(
+    params=["filesystem", "database"],
+    ids=["filesystem", "database"],
+)
+def rule_store(
+    request: pytest.FixtureRequest, tmp_path: Path,
+) -> Iterator[RuleStore]:
+    """Yield a fresh :class:`RuleStore` instance per parametrization.
+
+    The filesystem backend is constructed against a ``tmp_path``
+    rules dir so tests never touch the real ``./rules/``. The
+    database backend's connection wiring lands at E.3.6; today the
+    fixture just hands out the raw class instance and impl-phase
+    tests are responsible for plumbing it into a session.
+    """
+    backend = request.param
+    if backend == "filesystem":
+        if sys.platform != "linux":
+            pytest.skip("FilesystemRuleStore requires Linux (inotify)")
+        yield FilesystemRuleStore(rules_dir=tmp_path)
+    else:
+        yield DatabaseRuleStore()