TIER-2 READ conductor/code_styleguides/error_handling.md end-to-end before Phase 10: refactor(gui_2): migrate L1693 render_main_interface autosave to Result[T] (Phase 10 site 9)

Extracted _autosave_flush_result(app) -> Result[None] helper above the
call site in render_main_interface.
ANTI-SLIMING: full Result[T] propagation (NO except+pass with comment).
The helper returns Result(data=None) on success or Result(data=None,
errors=[ErrorInfo]) on exception (logging NOT a drain per the user's
principle 2026-06-17). The 'don't disrupt the GUI loop' intent is
preserved via the data plane (app._last_request_errors) rather than
silent swallow.

The legacy render_main_interface code preserves its behavior, calls the
helper, and drains errors to app._last_request_errors.

Tests: 2 new tests verify both paths (success and OSError).

Audit: L1693 reclassified from INTERNAL_SILENT_SWALLOW (5 sites remaining,
was 6). New helper L1693 is INTERNAL_COMPLIANT.

src/gui_2.py

@@ -1690,12 +1690,36 @@ def _focus_response_window_result() -> Result[None]:
  now = time.time()
  if now - app._last_autosave >= app._autosave_interval:
   app._last_autosave = now
-  try:
-   app._flush_to_project()
-   app._flush_to_config()
-   app.save_config()
-  except Exception:
-   pass  # silent — don't disrupt the GUI loop
+  autosave_result = _autosave_flush_result(app)
+  if not autosave_result.ok:
+   if not hasattr(app, '_last_request_errors'): app._last_request_errors = []
+   app._last_request_errors.append(("render_main_interface.autosave", autosave_result.errors[0]))
+
+def _autosave_flush_result(app: "App") -> Result[None]:
+ """Drain-aware variant of render_main_interface auto-save try block (L1693 INTERNAL_SILENT_SWALLOW).
+
+ Extracts the auto-save flush_to_project + flush_to_config + save_config
+ try/except from render_main_interface into a Result-returning helper. On
+ exception (disk full, JSON parse error), converts to ErrorInfo (logging
+ NOT a drain per the user's principle 2026-06-17). The caller drains to
+ app._last_request_errors and continues with the GUI loop, preserving
+ the original "don't disrupt the GUI loop" intent via the data plane
+ rather than silent swallow.
+
+ [C: src/gui_2.py:render_main_interface (L1693 legacy wrapper)]
+ """
+ try:
+  app._flush_to_project()
+  app._flush_to_config()
+  app.save_config()
+  return Result(data=None)
+ except Exception as e:
+  return Result(data=None, errors=[ErrorInfo(
+   kind=ErrorKind.INTERNAL,
+   message=f"autosave flush failed: {e}",
+   source="gui_2._autosave_flush_result",
+   original=e,
+  )])
  
  # Sync pending comms
  with app._pending_comms_lock: