fix(tui): stabilize live todo panel count and anchor position

Two bugs surfaced together while the model fired the todo tool:

1. Count flickered (e.g. 3 → 1 → 3) because tool.start echoed
   args.todos as the live state. With merge=true (or any partial
   replacement) args.todos is just the items being updated, not the
   full list. Drop the early echo — tool.complete already carries the
   canonical full list from the tool result.

2. After turn end the panel jumped from under the user prompt to below
   thinking/tools because archiveDoneTodos() was pushed AFTER segments
   in finalMessages. Prepend the archive trail msg so it sits right
   after the user prompt — same visual slot the live panel occupied
   during streaming.

tui_gateway/server.py

@@ -1040,13 +1040,14 @@ def _on_tool_start(sid: str, tool_call_id: str, name: str, args: dict):
             pass
         session.setdefault("tool_started_at", {})[tool_call_id] = time.time()
     if _tool_progress_enabled(sid):
-        payload = {"tool_id": tool_call_id, "name": name, "context": _tool_ctx(name, args)}
-        if name == "todo" and isinstance(args, dict) and isinstance(args.get("todos"), list):
-            payload["todos"] = args.get("todos")
+        # Don't echo args.todos on tool.start — for merge=true (or partial
+        # replacement) it's only the items being updated, not the full list,
+        # and would flicker the live count. tool.complete is the source of
+        # truth (always returns the full list from the tool result).
         _emit(
             "tool.start",
             sid,
-            payload,
+            {"tool_id": tool_call_id, "name": name, "context": _tool_ctx(name, args)},
         )
 
 

ui-tui/src/app/createGatewayEventHandler.ts

@@ -537,10 +537,10 @@ export function createGatewayEventHandler(ctx: GatewayEventHandlerContext): (ev:
         const { finalMessages, finalText, wasInterrupted } = turnController.recordMessageComplete(ev.payload ?? {})
 
         if (!wasInterrupted) {
-          // Archive the todo list FIRST so it sits above the final assistant
-          // text in the transcript — same position it held during streaming.
-          // Otherwise the panel would visibly jump from "above live answer" to
-          // "below final answer" at message.complete.
+          // Defensive: turnController.recordMessageComplete already prepends
+          // the archive at the head of finalMessages. This is a no-op in the
+          // normal path (state.todos is empty) but covers any edge where
+          // todos linger past the controller archive.
           archiveTodosAtTurnEnd().forEach(appendMessage)
 
           const msgs: Msg[] = finalMessages.length ? finalMessages : [{ role: 'assistant', text: finalText }]

ui-tui/src/app/turnController.ts

@@ -469,9 +469,12 @@ class TurnController {
       ...(tools.length && { tools })
     }
 
-    const finalMessages = hasDetails(finalDetails) ? [...segments, finalDetails] : [...segments]
-
-    finalMessages.push(...archiveDoneTodos())
+    // Archive todos FIRST so the trail msg sits right after the user prompt,
+    // not between thinking/tools and the final assistant text. Keeps the
+    // panel visually anchored where it lived during streaming.
+    const archived = archiveDoneTodos()
+    const body = hasDetails(finalDetails) ? [...segments, finalDetails] : segments
+    const finalMessages: Msg[] = [...archived, ...body]
 
     if (finalText) {
       finalMessages.push({ role: 'assistant', text: finalText })