TIER-2 READ conductor/code_styleguides/error_handling.md end-to-end before Phase 5: refactor(gui_2): migrate L3582 render_context_batch_actions preview to Result[T] (Phase 5)

Extract _render_context_batch_actions_preview_result helper from the
_do_generate preview try/except in render_context_batch_actions. The
imgui.button callback drains errors to app._last_request_errors per FR-BC-4
event-handler pattern.

[pre-audit] L3582 INTERNAL_BROAD_CATCH
[post-audit] V count: 8 -> 7 (L3582 removed)

tests/test_gui_2_result.py

@@ -1068,3 +1068,42 @@ def test_phase_5_l3163_render_tool_preset_bias_save_result_failure():
  assert err.source == "gui_2._render_tool_preset_bias_save_result"
  assert "bias validation failed" in err.message
  assert "Error:" in app.ai_status
+
+
+def test_phase_5_l3582_render_context_batch_actions_preview_result_success():
+ """
+ L3582 _render_context_batch_actions_preview_result returns Result.ok=True on success.
+
+ The helper wraps the _do_generate preview try/except in
+ render_context_batch_actions. On success, returns Result(data=preview_text)
+ where preview_text is the controller._do_generate() output.
+ """
+ from src import gui_2
+ from unittest.mock import MagicMock
+ app = MagicMock()
+ app.context_files = ["foo.py", "bar.py"]
+ app.controller._do_generate.return_value = ("# Generated Preview\n\nContent here", "preview.md")
+ result = gui_2._render_context_batch_actions_preview_result(app)
+ assert result.ok, f"Expected ok=True on success, got errors: {result.errors}"
+ assert "Generated Preview" in result.data
+
+
+def test_phase_5_l3582_render_context_batch_actions_preview_result_failure():
+ """
+ L3582 _render_context_batch_actions_preview_result returns Result.ok=False on failure.
+
+ When _do_generate raises, the helper captures the traceback and returns
+ Result(data="<error message>", errors=[ErrorInfo]).
+ """
+ from src import gui_2
+ from unittest.mock import MagicMock
+ app = MagicMock()
+ app.context_files = ["foo.py"]
+ app.controller._do_generate.side_effect = RuntimeError("generate failed")
+ result = gui_2._render_context_batch_actions_preview_result(app)
+ assert not result.ok, f"Expected ok=False on failure, got data: {result.data}"
+ assert result.errors, "Expected at least one error on failure"
+ err = result.errors[0]
+ assert err.source == "gui_2._render_context_batch_actions_preview_result"
+ assert "generate failed" in err.message
+ assert "Error" in result.data