test(acms): add direct _read_file and add_command traversal coverage

Adds a focused feature file that directly exercises the diff-coverage
gaps reported by the coverage gate across 13 prior attempts:

  acms/index.py  lines 597-612  (_read_file: stat + size-check + read_text)
  context.py     lines 111-112  (add_command: traverser invocation)

Three scenarios, each targeting specific line ranges:
1. _read_file with default traverser covers lines 597-598, 611-612
2. _read_file with max_file_size=1 covers lines 602-607
3. add_command with real ChunkedFileTraverser covers lines 111-112
   (also transitively covers 597-612 via _read_file)

ISSUES CLOSED: #9982

features/acms_read_file_coverage.feature

@@ -0,0 +1,20 @@
+Feature: ChunkedFileTraverser _read_file and add_command traversal coverage
+  Direct coverage for diff lines that the parallel test runner may not
+  reach via the acms_context_add.feature scenarios:
+    acms/index.py  lines 597-612  (_read_file stat + size-check + read_text)
+    context.py     lines 111-112  (add_command traverser invocation)
+
+  Background:
+    Given a temp file exists for read file coverage
+
+  Scenario: _read_file returns AcmsIndexEntry for a normal readable file
+    When I directly call _read_file with default traverser
+    Then the direct read file result should be an AcmsIndexEntry
+
+  Scenario: _read_file returns None when file exceeds max_file_size
+    When I directly call _read_file with max_file_size 1
+    Then the direct read file result should be None
+
+  Scenario: add_command invokes the real traverser for an existing path
+    When I call add_command with the real traverser and a mocked container
+    Then the mocked add_to_context should have been called

features/steps/acms_read_file_coverage_steps.py

@@ -0,0 +1,84 @@
+"""Step definitions for direct _read_file and add_command traversal coverage.
+
+Targets diff-coverage gaps:
+  acms/index.py  lines 597-612  (_read_file stat/size-check/read_text paths)
+  context.py     lines 111-112  (add_command traverser invocation)
+
+Step names are prefixed with ``rf_`` / ``ac_`` context attributes and use
+unique step text to avoid AmbiguousStep conflicts with existing steps.
+"""
+
+from __future__ import annotations
+
+import tempfile
+from pathlib import Path
+from unittest.mock import MagicMock, patch
+
+from behave import given, then, when
+from behave.runner import Context
+
+from cleveragents.acms.index import AcmsIndexEntry, ChunkedFileTraverser
+
+
+@given("a temp file exists for read file coverage")
+def step_rf_temp_file(context: Context) -> None:
+    """Create a small temp file used by all scenarios in this feature."""
+    context.rf_tmpdir = tempfile.mkdtemp()
+    path = Path(context.rf_tmpdir) / "sample.py"
+    path.write_text("# sample content\n", encoding="utf-8")
+    context.rf_path = path
+
+
+@when("I directly call _read_file with default traverser")
+def step_rf_direct_default(context: Context) -> None:
+    """Call _read_file directly — exercises lines 597-598 and 611-612."""
+    traverser = ChunkedFileTraverser()
+    context.rf_result = traverser._read_file(context.rf_path)
+
+
+@when("I directly call _read_file with max_file_size 1")
+def step_rf_direct_max_size(context: Context) -> None:
+    """Call _read_file with max_file_size=1 — exercises lines 602-607."""
+    traverser = ChunkedFileTraverser(max_file_size=1)
+    context.rf_result = traverser._read_file(context.rf_path)
+
+
+@then("the direct read file result should be an AcmsIndexEntry")
+def step_rf_result_is_entry(context: Context) -> None:
+    assert isinstance(context.rf_result, AcmsIndexEntry), (
+        f"Expected AcmsIndexEntry, got {type(context.rf_result)!r}"
+    )
+
+
+@then("the direct read file result should be None")
+def step_rf_result_is_none(context: Context) -> None:
+    assert context.rf_result is None, (
+        f"Expected None from _read_file, got {context.rf_result!r}"
+    )
+
+
+@when("I call add_command with the real traverser and a mocked container")
+def step_ac_call_add_command_real_traverser(context: Context) -> None:
+    """Call add_command with the REAL ChunkedFileTraverser — exercises lines 111-112."""
+    from cleveragents.cli.commands.context import add_command
+
+    container = MagicMock()
+    context_service = MagicMock()
+    context_service.add_to_context.return_value = ([context.rf_path], [])
+    container.context_service.return_value = context_service
+    project_service = MagicMock()
+    project_service.get_current_project.return_value = MagicMock()
+    container.project_service.return_value = project_service
+
+    with patch(
+        "cleveragents.application.container.get_container",
+        return_value=container,
+    ):
+        add_command([str(context.rf_path)])
+
+    context.ac_context_service = context_service
+
+
+@then("the mocked add_to_context should have been called")
+def step_ac_add_to_context_called(context: Context) -> None:
+    context.ac_context_service.add_to_context.assert_called_once()