hide the status indicator when the answer stream starts (#4101)

This eliminates a "bounce" at the end of streaming where we hide the
status indicator at the end of the turn and the composer moves up two
lines.

Also, simplify streaming further by removing the HistorySink and
inverting control, and collapsing a few single-element structures.

codex-rs/tui/src/streaming/mod.rs

@@ -1,10 +1,13 @@
-use crate::markdown_stream::AnimatedLineStreamer;
+use std::collections::VecDeque;
+
+use ratatui::text::Line;
+
 use crate::markdown_stream::MarkdownStreamCollector;
 pub(crate) mod controller;
 
 pub(crate) struct StreamState {
     pub(crate) collector: MarkdownStreamCollector,
-    pub(crate) streamer: AnimatedLineStreamer,
+    queued_lines: VecDeque<Line<'static>>,
     pub(crate) has_seen_delta: bool,
 }
 
@@ -12,25 +15,25 @@ impl StreamState {
     pub(crate) fn new() -> Self {
         Self {
             collector: MarkdownStreamCollector::new(),
-            streamer: AnimatedLineStreamer::new(),
+            queued_lines: VecDeque::new(),
             has_seen_delta: false,
         }
     }
     pub(crate) fn clear(&mut self) {
         self.collector.clear();
-        self.streamer.clear();
+        self.queued_lines.clear();
         self.has_seen_delta = false;
     }
-    pub(crate) fn step(&mut self) -> crate::markdown_stream::StepResult {
-        self.streamer.step()
+    pub(crate) fn step(&mut self) -> Vec<Line<'static>> {
+        self.queued_lines.pop_front().into_iter().collect()
     }
-    pub(crate) fn drain_all(&mut self) -> crate::markdown_stream::StepResult {
-        self.streamer.drain_all()
+    pub(crate) fn drain_all(&mut self) -> Vec<Line<'static>> {
+        self.queued_lines.drain(..).collect()
     }
     pub(crate) fn is_idle(&self) -> bool {
-        self.streamer.is_idle()
+        self.queued_lines.is_empty()
     }
-    pub(crate) fn enqueue(&mut self, lines: Vec<ratatui::text::Line<'static>>) {
-        self.streamer.enqueue(lines)
+    pub(crate) fn enqueue(&mut self, lines: Vec<Line<'static>>) {
+        self.queued_lines.extend(lines);
     }
 }