fix(acms): format __init__.py, add coverage for budget_enforcement paths

- Remove unnecessary parentheses from __all__ concatenation in acms/__init__.py
  to satisfy ruff format (lint gate was failing)
- Mark unreachable RuntimeError branch in add_file with # pragma: no cover
- Add 8 Behave scenarios covering previously uncovered lines:
  get_assembled_context(), reset(), BudgetEnforcer.__post_init__ validation
  errors, add_file validation errors, BudgetViolation unknown type
- Add corresponding step definitions; import BudgetViolation in steps module

ISSUES CLOSED: #9583

features/acms/acms_budget_enforcement.feature

@@ -71,3 +71,31 @@ Feature: ACMS Budget Enforcement for max_file_size and max_total_size constraint
     When I add a file with multi-byte UTF-8 content of 250 characters to the context
     Then the file should be excluded from the assembled context
     And a budget violation warning should be generated for the file
+
+  Scenario: Assembled context joins included file contents
+    When I add a file of 100 bytes to the context
+    And I add a file of 200 bytes to the context
+    Then the assembled context should be non-empty
+
+  Scenario: Reset clears enforcer state for re-use
+    When I add a file of 500 bytes to the context
+    And I reset the budget enforcer
+    Then the total context size should be 0 bytes
+
+  Scenario: BudgetEnforcer rejects negative max_file_size
+    Then creating an enforcer with negative max_file_size raises ValueError
+
+  Scenario: BudgetEnforcer rejects zero max_total_size
+    Then creating an enforcer with zero max_total_size raises ValueError
+
+  Scenario: BudgetEnforcer rejects max_file_size larger than max_total_size
+    Then creating an enforcer with max_file_size larger than max_total_size raises ValueError
+
+  Scenario: add_file rejects empty filename
+    Then adding a file with an empty name raises ValueError
+
+  Scenario: add_file rejects non-string content
+    Then adding a file with non-string content raises TypeError
+
+  Scenario: BudgetViolation rejects unknown violation_type
+    Then creating a BudgetViolation with an unknown type raises ValueError

features/steps/acms_budget_enforcement_steps.py

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 from behave import given, then, when
 
-from cleveragents.acms.budget_enforcement import BudgetEnforcer
+from cleveragents.acms.budget_enforcement import BudgetEnforcer, BudgetViolation
 
 
 @given("a budget enforcer with max_file_size of {size:d} bytes")
@@ -246,3 +246,78 @@ def step_both_files_included(context: object) -> None:
     """Verify that both files were included."""
     files = context.budget_enforcer.get_included_files()
     assert len(files) == 2, f"Expected 2 files, got {len(files)}"
+
+
+@then("the assembled context should be non-empty")
+def step_assembled_context_non_empty(context: object) -> None:
+    """Verify the assembled context is non-empty."""
+    ctx = context.budget_enforcer.get_assembled_context()
+    assert len(ctx) > 0, "Expected non-empty assembled context"
+
+
+@when("I reset the budget enforcer")
+def step_reset_budget_enforcer(context: object) -> None:
+    """Reset the budget enforcer to its initial state."""
+    context.budget_enforcer.reset()
+
+
+@then("creating an enforcer with negative max_file_size raises ValueError")
+def step_negative_max_file_size_raises(context: object) -> None:
+    """Verify ValueError is raised for negative max_file_size."""
+    try:
+        BudgetEnforcer(max_file_size=-1, max_total_size=5000)
+        raise AssertionError("Expected ValueError for negative max_file_size")
+    except ValueError as e:
+        assert "max_file_size" in str(e), f"Error should mention max_file_size: {e}"
+
+
+@then("creating an enforcer with zero max_total_size raises ValueError")
+def step_zero_max_total_size_raises(context: object) -> None:
+    """Verify ValueError is raised for zero max_total_size."""
+    try:
+        BudgetEnforcer(max_file_size=100, max_total_size=0)
+        raise AssertionError("Expected ValueError for zero max_total_size")
+    except ValueError as e:
+        assert "max_total_size" in str(e), f"Error should mention max_total_size: {e}"
+
+
+@then(
+    "creating an enforcer with max_file_size larger than max_total_size raises ValueError"
+)
+def step_max_file_size_exceeds_total_raises(context: object) -> None:
+    """Verify ValueError is raised when max_file_size > max_total_size."""
+    try:
+        BudgetEnforcer(max_file_size=5000, max_total_size=1000)
+        raise AssertionError("Expected ValueError for max_file_size > max_total_size")
+    except ValueError as e:
+        assert "cannot exceed" in str(e), f"Error should mention cannot exceed: {e}"
+
+
+@then("adding a file with an empty name raises ValueError")
+def step_empty_name_raises(context: object) -> None:
+    """Verify ValueError is raised for an empty filename."""
+    try:
+        context.budget_enforcer.add_file("", "some content")
+        raise AssertionError("Expected ValueError for empty name")
+    except ValueError as e:
+        assert "name" in str(e).lower(), f"Error should mention name: {e}"
+
+
+@then("adding a file with non-string content raises TypeError")
+def step_non_string_content_raises(context: object) -> None:
+    """Verify TypeError is raised for non-string content."""
+    try:
+        context.budget_enforcer.add_file("file.txt", object())
+        raise AssertionError("Expected TypeError for non-string content")
+    except TypeError as e:
+        assert "content" in str(e).lower(), f"Error should mention content: {e}"
+
+
+@then("creating a BudgetViolation with an unknown type raises ValueError")
+def step_unknown_violation_type_raises(context: object) -> None:
+    """Verify ValueError is raised for an unknown violation_type."""
+    try:
+        BudgetViolation(violation_type="unknown_type")
+        raise AssertionError("Expected ValueError for unknown violation_type")
+    except ValueError as e:
+        assert "unknown_type" in str(e), f"Error should mention the bad type: {e}"

src/cleveragents/acms/__init__.py

@@ -94,6 +94,4 @@ _index_exports = [
 _storage_exports = ["HotStorageTier"]
 _budget_exports = ["BudgetEnforcer", "BudgetViolation", "ContextFile"]
 
-__all__: list[str] = (
-    _uko_exports + _index_exports + _storage_exports + _budget_exports
-)
+__all__: list[str] = _uko_exports + _index_exports + _storage_exports + _budget_exports

src/cleveragents/acms/budget_enforcement.py

@@ -115,7 +115,7 @@ class BudgetEnforcer:
         file_obj = ContextFile(name=name, content=content)
 
         # Check max_file_size constraint
-        if file_obj.size is None:
+        if file_obj.size is None:  # pragma: no cover
             raise RuntimeError(
                 f"Internal error: {name} has no size; budget enforcement logic error"
             )