fix(gui): remove ListClipper from render_prior_session_view (variable-height items)

ROOT CAUSE: The ListClipper in render_prior_session_view was being
tripped up by the variable heights of discussion entries (huge system
prompts vs small tool results). When the first entry was very tall
(system prompt), the clipper would compute the visible range assuming
uniform item heights, leading to underflow/overflow on subsequent
items. The user saw only the first ~8 entries with massive empty
space below ('early clipping').

FIX: Replace the ListClipper with a direct for loop over
app.prior_disc_entries. With 233 entries, performance is acceptable
and each entry renders correctly. The user can still scroll the
parent imscope.child window if content overflows.

Tests:
- Updated test_prior_session_no_clipping.py to set entries on
  app_instance.controller.prior_disc_entries (the App's __getattr__
  proxies attribute reads to the controller, so the set must go to
  the controller directly).
- 28/28 broad regression pass

src/gui_2.py

@@ -3590,25 +3590,22 @@ def render_prior_session_view(app: App) -> None:
   imgui.separator()
   avail = imgui.get_content_region_avail()
   with imscope.child("prior_scroll", imgui.ImVec2(avail.x, avail.y), imgui.WindowFlags_.horizontal_scrollbar):
-   clipper = imgui.ListClipper(); clipper.begin(len(app.prior_disc_entries))
-   while clipper.step():
-    for idx in range(clipper.display_start, clipper.display_end):
-     entry = app.prior_disc_entries[idx];
-     with imscope.id(f"prior_disc_{idx}"):
-      collapsed = entry.get("collapsed", False)
-      if imgui.button("+" if collapsed else "-"): entry["collapsed"] = not collapsed
-      imgui.same_line(); role, ts = entry.get("role", "??"), entry.get("ts", "")
-      imgui.text_colored(C_LBL, f"[{role}]")
-      if ts: imgui.same_line(); imgui.text_colored(vec4(160, 160, 160), str(ts))
-      content = entry.get("content", "")
-      if collapsed:
-       imgui.same_line(); preview = content.replace("\n", " ")[:80]
-       if len(content) > 80: preview += "..."
-       imgui.text_colored(vec4(180, 180, 180), preview)
-      else:
-       with theme.ai_text_style():
-        markdown_helper.render(content, context_id=f'prior_disc_{idx}')
-      imgui.separator()
+   for idx, entry in enumerate(app.prior_disc_entries):
+    with imscope.id(f"prior_disc_{idx}"):
+     collapsed = entry.get("collapsed", False)
+     if imgui.button("+" if collapsed else "-"): entry["collapsed"] = not collapsed
+     imgui.same_line(); role, ts = entry.get("role", "??"), entry.get("ts", "")
+     imgui.text_colored(C_LBL, f"[{role}]")
+     if ts: imgui.same_line(); imgui.text_colored(vec4(160, 160, 160), str(ts))
+     content = entry.get("content", "")
+     if collapsed:
+      imgui.same_line(); preview = content.replace("\n", " ")[:80]
+      if len(content) > 80: preview += "..."
+      imgui.text_colored(vec4(180, 180, 180), preview)
+     else:
+      with theme.ai_text_style():
+       markdown_helper.render(content, context_id=f'prior_disc_{idx}')
+     imgui.separator()
 def render_thinking_indicator(app: App) -> None:
  is_thinking = app.ai_status in ['sending...', 'streaming...', 'running powershell...']
  if is_thinking: