E.3.9.0 prerequisite for the per-source lifters (E.3.9-E.3.13). The
dispatch index, install/evict/apply_change atomic-swap protocol, and
state-modulation helpers (is_active / apply_ceiling) move out of
rule_engine.py into _rule_index.py and _state.py. RuleEngine wraps a
RuleIndex; back-compat shims preserve _by_kind / _by_rule / _install
attribute access for tests poking at the dispatch internals.
Lifters in E.3.9-E.3.12 will each hold their own RuleIndex, watching
the same RuleStore via subscribe_changes() fan-out. Hot-reload
semantics (disable / clip / TTL via set_state API) now reach
lifter-bound rules through the same atomic-swap path the engine uses,
not a future composite-rebuild compromise.
Implements the rule engine body left empty at contract phase: evaluate()
dispatches by source_kind through self._by_kind, runs the rule's match
spec against event.payload, and emits one TTPTag per emits entry.
watch_store() loads the initial corpus from RuleStore.load_compiled,
then drains subscribe_changes, applying definition changes via
single-statement dict assignment (atomic swap, GIL-atomic to readers)
and state changes via NamedTuple._replace on the existing CompiledRule.
Why: with the FS + DB stores in place (E.3.5/E.3.6), the engine is the
last piece of the rule plane. Lifters (E.3.9–E.3.13) consume the
engine; the worker bootstrap (E.3.14) wires watch_store into the
asyncio event loop. After this commit a CompositeTagger constructed
with a RuleEngine + a populated rules dir will produce real tags.
Notes:
- CompiledRule.emits extended to 4-tuple
(technique_id, sub_technique_id, tactic, confidence). Tactic + confidence
ride per-emit so a single rule can carry multiple precision targets
(the "one event maps to many techniques" property). Compile helpers in
both backends extract them from the YAML emits dict; missing tactic
or confidence is a deploy-time error.
- v0 match operator is "pattern" (regex). The field defaults per
source_kind (command_text / raw_url / subject / verdict / …) and is
overridable via match.field. Future ops (contains, equals, in_set)
extend _match_event without touching the engine surface.
- Confidence model: rules with state="clipped" + confidence_max set
cap the per-emit confidence downward; clipped is a soft suppress, not
a hard skip. Disabled rules are skipped wholly; expires_at past is
re-checked at evaluate as defense-in-depth (the store auto-reverts,
but a racing read between expiry and revert must not fire the rule).
- _span(name, **attrs) helper in engine + both stores short-circuits on
decnet.telemetry._ENABLED — matches the project's @traced /
wrap_repository zero-overhead-when-disabled pattern instead of relying
solely on the no-op tracer indirection.
- Late-bound tracer (telemetry.get_tracer called per-span, not at
module load) so test_tracing's monkeypatch reaches the production
code path.
xfails flipped: tests/ttp/test_rule_engine.py multi-emit fan-out +
rule_version-collision-via-engine; tests/ttp/test_multi_mapping.py
N×M engine fan-out + idempotent replay; tests/ttp/test_tracing.py
ttp.eval span hierarchy + ttp.rule.fire span attributes.
Tests: 214 passed, 19 xfailed (gated on E.3.8 lifters / rule pack /
worker bootstrap).
mypy: clean on prod code; pre-existing test-stub arg-type warnings
unchanged.
