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)

src/gui_2.py

@@ -3535,13 +3535,11 @@ def render_context_batch_actions(app: App, total_lines: int, total_ast: int) ->
   if not app.context_files:
     app.context_preview_text = "# Context Composition Empty\n\nNo files have been added to the context composition yet."
   else:
-    try:
-     app.controller.context_files = app.context_files
-     app.context_preview_text = app.controller._do_generate()[0]
-    except Exception as e:
-     import traceback
-     err = traceback.format_exc()
-     app.context_preview_text = f"# Error generating preview\n\n```python\n{err}\n```"
+    preview_result = _render_context_batch_actions_preview_result(app)
+    app.context_preview_text = preview_result.data
+    if not preview_result.ok:
+     if not hasattr(app, '_last_request_errors'): app._last_request_errors = []
+     app._last_request_errors.append(("_render_context_batch_actions_preview", preview_result.errors[0]))
   app.show_windows["Context Preview"] = True
  imgui.same_line()
  imgui.text(f" | Total: {len(app.context_files)} files, {total_lines} lines, {total_ast} AST elements")
@@ -7931,6 +7929,37 @@ def _render_tool_preset_bias_save_result(app: "App") -> Result[bool]:
    original=e,
   )])
 
+
+def _render_context_batch_actions_preview_result(app: "App") -> Result[str]:
+ """Drain-aware variant of L3582 render_context_batch_actions Preview button.
+
+ Extracts the _do_generate preview try/except from
+ render_context_batch_actions into a Result-returning helper. On success,
+ returns Result(data=preview_text) where preview_text is the
+ controller._do_generate() output. On exception, captures the traceback,
+ returns Result(data="<error markdown>", errors=[ErrorInfo]).
+
+ The legacy wrapper (the imgui.button callback) drains errors to
+ app._last_request_errors (per FR-BC-4 event-handler drain pattern;
+ data plane attribute).
+
+ [C: src/gui_2.py:render_context_batch_actions (L3582 legacy wrapper)]
+ """
+ try:
+  app.controller.context_files = app.context_files
+  preview_text = app.controller._do_generate()[0]
+  return Result(data=preview_text)
+ except Exception as e:
+  import traceback
+  err = traceback.format_exc()
+  preview_text = f"# Error generating preview\n\n```python\n{err}\n```"
+  return Result(data=preview_text, errors=[ErrorInfo(
+   kind=ErrorKind.INTERNAL,
+   message=f"Context preview generation failed: {e}",
+   source="gui_2._render_context_batch_actions_preview_result",
+   original=e,
+  )])
+
 #endregion: Phase 5 Event Handler Result Helpers
 
 #endregion: MMA

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