feat(gui): Implement per-response token metrics and AI discussion compression

- Display token metrics (input/output/cache) per response in Discussion Hub.
- Add total Discussion Token usage in the panel header.
- Implement 'Compress' feature to intelligently summarize and replace exhausted discussion histories using an AI subagent.

src/gui_2.py

@@ -3416,17 +3416,29 @@ def render_discussion_entry(app: App, entry: dict, index: int) -> None:
    imgui.same_line()
    if imgui.button("[Edit]" if read_mode else "[Read]"): entry["read_mode"] = not read_mode
   ts_str = entry.get("ts", "")
-  if ts_str:
-   imgui.same_line(); imgui.text_colored(vec4(120, 120, 100), str(ts_str)); e_dt = project_manager.parse_ts(ts_str)
-   if e_dt:
-    e_unix, next_unix = e_dt.timestamp(), float('inf')
-    if index + 1 < len(app.disc_entries):
-     n_ts = app.disc_entries[index+1].get("ts", ""); n_dt = project_manager.parse_ts(n_ts)
-     if n_dt: next_unix = n_dt.timestamp()
-    injected = [f for f in app.files if hasattr(f, 'injected_at') and f.injected_at and e_unix <= f.injected_at < next_unix]
-    if injected:
-     imgui.same_line(); imgui.text_colored(vec4(100, 255, 100), f"[{len(injected)}+]")
-     if imgui.is_item_hovered(): imgui.set_tooltip("Files injected at this point:\n" + "\n".join([f.path for f in injected]))
+  usage = entry.get("usage", {})
+  if ts_str or usage:
+   imgui.same_line()
+   if ts_str:
+    imgui.text_colored(vec4(120, 120, 100), str(ts_str))
+    e_dt = project_manager.parse_ts(ts_str)
+    if e_dt:
+     e_unix, next_unix = e_dt.timestamp(), float('inf')
+     if index + 1 < len(app.disc_entries):
+      n_ts = app.disc_entries[index+1].get("ts", ""); n_dt = project_manager.parse_ts(n_ts)
+      if n_dt: next_unix = n_dt.timestamp()
+     injected = [f for f in app.files if hasattr(f, 'injected_at') and f.injected_at and e_unix <= f.injected_at < next_unix]
+     if injected:
+      imgui.same_line(); imgui.text_colored(vec4(100, 255, 100), f"[{len(injected)}+]")
+      if imgui.is_item_hovered(): imgui.set_tooltip("Files injected at this point:\n" + "\n".join([f.path for f in injected]))
+   if usage:
+    inp = usage.get("input_tokens", 0)
+    out = usage.get("output_tokens", 0)
+    cache = usage.get("cache_read_input_tokens", 0)
+    usage_str = f" in:{inp} out:{out}"
+    if cache: usage_str += f" cache:{cache}"
+    imgui.same_line()
+    imgui.text_colored(vec4(100, 150, 180), usage_str)
   if collapsed:
    imgui.same_line()
    if imgui.button("Ins"): app.disc_entries.insert(index, {"role": "User", "content": "", "collapsed": True, "ts": project_manager.now_ts()})
@@ -3794,6 +3806,8 @@ def render_discussion_entry_controls(app: App) -> None:
  if imgui.button("Clear All"): app.disc_entries.clear()
  imgui.same_line()
  if imgui.button("Save"): app._flush_to_project(); app._flush_to_config(); models.save_config(app.config); app.ai_status = "discussion saved"
+ imgui.same_line()
+ if imgui.button("Compress"): app.controller._handle_compress_discussion()
  _, app.ui_auto_add_history = imgui.checkbox("Auto-add message & response to history", app.ui_auto_add_history)
  imgui.text("Keep Pairs:"); imgui.same_line(); imgui.set_next_item_width(80)
  ch, app.ui_disc_truncate_pairs = imgui.input_int("##trunc_pairs", app.ui_disc_truncate_pairs, 1)
@@ -3806,6 +3820,17 @@ def render_discussion_entry_controls(app: App) -> None:
 def render_discussion_metadata(app: App) -> None:
  disc_data = app.project.get("discussion", {}).get("discussions", {}).get(app.active_discussion, {})
  git_commit, last_updated = disc_data.get("git_commit", ""), disc_data.get("last_updated", "")
+ 
+ total_in, total_out, total_cache = 0, 0, 0
+ for entry in app.disc_entries:
+  if "usage" in entry:
+   total_in += entry["usage"].get("input_tokens", 0)
+   total_out += entry["usage"].get("output_tokens", 0)
+   total_cache += entry["usage"].get("cache_read_input_tokens", 0)
+ if total_in > 0 or total_out > 0:
+  imgui.text_colored(vec4(100, 150, 180), f"Discussion Tokens: {total_in} In | {total_out} Out | {total_cache} Cache")
+  imgui.separator()
+
  imgui.text_colored(C_LBL, "commit:"); imgui.same_line()
  render_selectable_label(app, 'git_commit_val', git_commit[:12] if git_commit else '(none)', width=100, color=(C_IN if git_commit else C_LBL))
  imgui.same_line()