fix(concurrency): fix lint and Behave step conflict in thread-safety tests

- Remove unused imports (Invariant, ULID) from step definitions
- Rename ambiguous parameter l -> num_listers (E741)
- Fix import ordering in invariant_service.py (RLock before structlog)
- Fix line too long in invariant_service.py:208
- Apply ruff format to steps file
- Disambiguate @then step text that conflicted with context_tier_thread_safety_steps.py

ISSUES CLOSED: #7524

features/invariant_service_thread_safety.feature

@@ -15,7 +15,7 @@ Feature: InvariantService thread safety (Issue #7524)
 
   Scenario: InvariantService has a reentrant lock attribute
     Then the invariant service should have a _lock attribute
-    And the _lock should be a threading.RLock
+    And the invariant service _lock should be a threading.RLock
 
   # -----------------------------------------------------------------
   # Concurrent adds

features/steps/invariant_service_thread_safety_steps.py

@@ -13,13 +13,9 @@ import threading
 from typing import Any
 
 from behave import given, then, when
-from ulid import ULID
 
 from cleveragents.application.services.invariant_service import InvariantService
-from cleveragents.domain.models.core.invariant import (
-    Invariant,
-    InvariantScope,
-)
+from cleveragents.domain.models.core.invariant import InvariantScope
 
 __all__: list[str] = []
 
@@ -58,7 +54,7 @@ def step_then_has_lock(context: Any) -> None:
     )
 
 
-@then("the _lock should be a threading.RLock")
+@then("the invariant service _lock should be a threading.RLock")
 def step_then_lock_is_rlock(context: Any) -> None:
     lock = context.invariant_svc._lock
     assert hasattr(lock, "acquire"), "_lock must have acquire()"
@@ -75,9 +71,7 @@ def step_then_lock_is_rlock(context: Any) -> None:
 # ---------------------------------------------------------------------------
 
 
-@when(
-    "{n:d} threads concurrently add {k:d} invariants each to the invariant service"
-)
+@when("{n:d} threads concurrently add {k:d} invariants each to the invariant service")
 def step_when_concurrent_adds(context: Any, n: int, k: int) -> None:
     errors: list[Exception] = []
     lock = threading.Lock()
@@ -111,9 +105,7 @@ def step_then_no_runtime_error(context: Any) -> None:
     )
 
 
-@then(
-    "the invariant service should contain at least {n:d} active invariants"
-)
+@then("the invariant service should contain at least {n:d} active invariants")
 def step_then_at_least_invariants(context: Any, n: int) -> None:
     snapshot = context.invariant_svc.get_invariants_snapshot()
     assert len(snapshot) >= n, (
@@ -175,9 +167,9 @@ def step_then_no_exc_list(context: Any) -> None:
 
 @when(
     "{a:d} threads concurrently add invariants and "
-    "{l:d} threads concurrently list invariants"
+    "{num_listers:d} threads concurrently list invariants"
 )
-def step_when_mixed_access(context: Any, a: int, l: int) -> None:
+def step_when_mixed_access(context: Any, a: int, num_listers: int) -> None:
     errors: list[Exception] = []
     lock = threading.Lock()
 
@@ -203,7 +195,9 @@ def step_when_mixed_access(context: Any, a: int, l: int) -> None:
                     errors.append(exc)
 
     threads = [threading.Thread(target=add_worker, args=(t,)) for t in range(a)]
-    threads += [threading.Thread(target=list_worker, args=(t,)) for t in range(l)]
+    threads += [
+        threading.Thread(target=list_worker, args=(t,)) for t in range(num_listers)
+    ]
     for t in threads:
         t.start()
     for t in threads:
@@ -224,9 +218,7 @@ def step_then_no_exc_mixed(context: Any) -> None:
 # ---------------------------------------------------------------------------
 
 
-@given(
-    "{n:d} invariants pre-stored in the invariant service with plan \"{plan_id}\""
-)
+@given('{n:d} invariants pre-stored in the invariant service with plan "{plan_id}"')
 def step_given_pre_stored_with_plan(context: Any, n: int, plan_id: str) -> None:
     context.pre_stored_ids = []
     for i in range(n):
@@ -239,7 +231,7 @@ def step_given_pre_stored_with_plan(context: Any, n: int, plan_id: str) -> None:
 
 
 @when(
-    "{n:d} threads concurrently enforce all stored invariants each from plan \"{plan_id}\""
+    '{n:d} threads concurrently enforce all stored invariants each from plan "{plan_id}"'
 )
 def step_when_concurrent_enforcement(context: Any, n: int, plan_id: str) -> None:
     errors: list[Exception] = []
@@ -254,8 +246,7 @@ def step_when_concurrent_enforcement(context: Any, n: int, plan_id: str) -> None
                 filtered = [
                     inv
                     for inv in snapshot
-                    if inv.scope == InvariantScope.PLAN
-                    and inv.source_name == plan_id
+                    if inv.scope == InvariantScope.PLAN and inv.source_name == plan_id
                 ]
                 if not filtered:
                     continue
@@ -284,9 +275,7 @@ def step_then_no_exc_enforce(context: Any) -> None:
     )
 
 
-@then(
-    "the invariant service should contain at least {n:d} enforcement records"
-)
+@then("the invariant service should contain at least {n:d} enforcement records")
 def step_then_at_least_records(context: Any, n: int) -> None:
     records = context.invariant_svc.get_enforcement_records()
     assert len(records) >= n, (

src/cleveragents/application/services/invariant_service.py

@@ -27,10 +27,10 @@ Based on ``docs/specification.md`` and implementation plan Stage M3.5.
 
 from __future__ import annotations
 
+from threading import RLock
 from typing import TYPE_CHECKING
 
 import structlog
-from threading import RLock
 from ulid import ULID
 
 from cleveragents.application.services.prompt_sanitizer import PromptSanitizer
@@ -205,7 +205,9 @@ class InvariantService:
             # Invariant is frozen (immutable); create a new instance with active=False
             deactivated = inv.model_copy(update={"active": False})
             self._invariants[invariant_id] = deactivated
-            self._logger.info("Invariant removed (soft-delete)", invariant_id=invariant_id)
+            self._logger.info(
+                "Invariant removed (soft-delete)", invariant_id=invariant_id
+            )
         return deactivated
 
     def get_effective_invariants(