feat(tier4): Integrate patch generation into GUI workflow

- Add patch_callback parameter throughout the tool execution chain
- Add _render_patch_modal() to gui_2.py with colored diff display
- Add patch modal state variables to App.__init__
- Add request_patch_from_tier4() to trigger patch generation
- Add run_tier4_patch_callback() to ai_client.py
- Update shell_runner to accept and execute patch_callback
- Diff colors: green for additions, red for deletions, cyan for headers
- 36 tests passing

src/gui_2.py

@@ -1,4 +1,4 @@
-# gui_2.py
+# gui_2.py
 from __future__ import annotations
 import tomli_w
 import time
@@ -114,6 +114,11 @@ class App:
   self._tool_log_dirty: bool = True
   self._last_ui_focus_agent: Optional[str] = None
   self._log_registry: Optional[log_registry.LogRegistry] = None
+  # Patch viewer state for Tier 4 auto-patching
+  self._pending_patch_text: Optional[str] = None
+  self._pending_patch_files: list[str] = []
+  self._show_patch_modal: bool = False
+  self._patch_error_message: Optional[str] = None
 
  def _handle_approve_tool(self, user_data=None) -> None:
   """UI-level wrapper for approving a pending tool execution ask."""
@@ -254,6 +259,7 @@ class App:
    self._process_pending_gui_tasks()
    self._process_pending_history_adds()
    self._render_track_proposal_modal()
+   self._render_patch_modal()
    # Auto-save (every 60s)
    now = time.time()
    if now - self._last_autosave >= self._autosave_interval:
@@ -873,6 +879,82 @@ class App:
     imgui.close_current_popup()
    imgui.end_popup()
 
+ def _render_patch_modal(self) -> None:
+  if not self._show_patch_modal:
+   return
+  imgui.open_popup("Apply Patch?")
+  if imgui.begin_popup_modal("Apply Patch?", True, imgui.ImVec2(600, 500))[0]:
+   imgui.text_colored(imgui.ImVec4(1, 0.9, 0.3, 1), "Tier 4 QA Generated a Patch")
+   imgui.separator()
+   if self._pending_patch_files:
+    imgui.text("Files to modify:")
+    for f in self._pending_patch_files:
+     imgui.text(f"  - {f}")
+   imgui.separator()
+   if self._patch_error_message:
+    imgui.text_colored(imgui.ImVec4(1, 0.3, 0.3, 1), f"Error: {self._patch_error_message}")
+    imgui.separator()
+   imgui.text("Diff Preview:")
+   imgui.begin_child("patch_diff_scroll", imgui.ImVec2(-1, 280), True)
+   if self._pending_patch_text:
+    diff_lines = self._pending_patch_text.split("\n")
+    for line in diff_lines:
+     if line.startswith("+++") or line.startswith("---") or line.startswith("@@"):
+      imgui.text_colored(imgui.ImVec4(0.3, 0.7, 1, 1), line)
+     elif line.startswith("+"):
+      imgui.text_colored(imgui.ImVec4(0.2, 0.9, 0.2, 1), line)
+     elif line.startswith("-"):
+      imgui.text_colored(imgui.ImVec4(0.9, 0.2, 0.2, 1), line)
+     else:
+      imgui.text(line)
+   imgui.end_child()
+   imgui.separator()
+   if imgui.button("Apply Patch", imgui.ImVec2(150, 0)):
+    self._apply_pending_patch()
+   imgui.same_line()
+   if imgui.button("Reject", imgui.ImVec2(150, 0)):
+    self._show_patch_modal = False
+    self._pending_patch_text = None
+    self._pending_patch_files = []
+    self._patch_error_message = None
+    imgui.close_current_popup()
+   imgui.end_popup()
+
+ def _apply_pending_patch(self) -> None:
+  if not self._pending_patch_text:
+   self._patch_error_message = "No patch to apply"
+   return
+  try:
+   from src.diff_viewer import apply_patch_to_file
+   base_dir = str(self.controller.current_project_dir) if hasattr(self.controller, 'current_project_dir') else "."
+   success, msg = apply_patch_to_file(self._pending_patch_text, base_dir)
+   if success:
+    self._show_patch_modal = False
+    self._pending_patch_text = None
+    self._pending_patch_files = []
+    self._patch_error_message = None
+    imgui.close_current_popup()
+   else:
+    self._patch_error_message = msg
+  except Exception as e:
+   self._patch_error_message = str(e)
+
+ def request_patch_from_tier4(self, error: str, file_context: str) -> None:
+  try:
+   from src import ai_client
+   from src.diff_viewer import parse_diff
+   patch_text = ai_client.run_tier4_patch_generation(error, file_context)
+   if patch_text and "---" in patch_text and "+++" in patch_text:
+    diff_files = parse_diff(patch_text)
+    file_paths = [df.old_path for df in diff_files]
+    self._pending_patch_text = patch_text
+    self._pending_patch_files = file_paths
+    self._show_patch_modal = True
+   else:
+    self._patch_error_message = patch_text or "No patch generated"
+  except Exception as e:
+   self._patch_error_message = str(e)
+
  def _render_log_management(self) -> None:
   exp, opened = imgui.begin("Log Management", self.show_windows["Log Management"])
   self.show_windows["Log Management"] = bool(opened)