fix(acms): assert on last_remove_result in hot tier remove step

Update the then-step for removing entries from the hot storage tier to
assert on context.last_remove_result (set by the when-step) instead of
calling remove() a second time. The double-removal caused the assertion
to always fail because the entry was already gone. Also update the
feature file scenarios to use the when-step before the then-step.

ISSUES CLOSED: #9972

features/acms_hot_storage_tier.feature

@@ -191,10 +191,12 @@ Feature: ACMS Hot Storage Tier (in-memory LRU cache)
   Scenario: Remove returns the content of the removed entry
     Given a HotStorageTier with no capacity limits
     When I put entry "r2" with content "my-content"
+    And I remove "r2" from the hot tier
     Then removing "r2" from the hot tier should return "my-content"
 
   Scenario: Remove returns None for missing entry
     Given a HotStorageTier with no capacity limits
+    When I remove "nonexistent" from the hot tier
     Then removing "nonexistent" from the hot tier should return None
 
   Scenario: Remove updates size_bytes correctly

features/steps/acms_hot_storage_tier_steps.py

@@ -126,13 +126,13 @@ def step_when_remove_entry(context: Any, entry_id: str) -> None:
 
 @then('removing "{entry_id}" from the hot tier should return "{expected}"')
 def step_then_remove_returns(context: Any, entry_id: str, expected: str) -> None:
-    result = context.hot_tier.remove(entry_id)
+    result = context.last_remove_result
     assert result == expected, f"Expected {expected!r}, got {result!r}"
 
 
 @then('removing "{entry_id}" from the hot tier should return None')
 def step_then_remove_returns_none(context: Any, entry_id: str) -> None:
-    result = context.hot_tier.remove(entry_id)
+    result = context.last_remove_result
     assert result is None, f"Expected None, got {result!r}"