Stream model responses (#1810)

Stream models thoughts and responses instead of waiting for the whole
thing to come through. Very rough right now, but I'm making the risk call to push through.

codex-rs/tui/tests/vt100_live_commit.rs

@@ -0,0 +1,101 @@
+#![cfg(feature = "vt100-tests")]
+
+use ratatui::backend::TestBackend;
+use ratatui::layout::Rect;
+use ratatui::text::Line;
+
+#[test]
+fn live_001_commit_on_overflow() {
+    let backend = TestBackend::new(20, 6);
+    let mut term = match codex_tui::custom_terminal::Terminal::with_options(backend) {
+        Ok(t) => t,
+        Err(e) => panic!("failed to construct terminal: {e}"),
+    };
+    let area = Rect::new(0, 5, 20, 1);
+    term.set_viewport_area(area);
+
+    // Build 5 explicit rows at width 20.
+    let mut rb = codex_tui::live_wrap::RowBuilder::new(20);
+    rb.push_fragment("one\n");
+    rb.push_fragment("two\n");
+    rb.push_fragment("three\n");
+    rb.push_fragment("four\n");
+    rb.push_fragment("five\n");
+
+    // Keep the last 3 in the live ring; commit the first 2.
+    let commit_rows = rb.drain_commit_ready(3);
+    let lines: Vec<Line<'static>> = commit_rows
+        .into_iter()
+        .map(|r| Line::from(r.text))
+        .collect();
+
+    let mut buf: Vec<u8> = Vec::new();
+    codex_tui::insert_history::insert_history_lines_to_writer(&mut term, &mut buf, lines);
+
+    let mut parser = vt100::Parser::new(6, 20, 0);
+    parser.process(&buf);
+    let screen = parser.screen();
+
+    // The words "one" and "two" should appear above the viewport.
+    let mut joined = String::new();
+    for row in 0..6 {
+        for col in 0..20 {
+            if let Some(cell) = screen.cell(row, col) {
+                if let Some(ch) = cell.contents().chars().next() {
+                    joined.push(ch);
+                } else {
+                    joined.push(' ');
+                }
+            }
+        }
+        joined.push('\n');
+    }
+    assert!(
+        joined.contains("one"),
+        "expected committed 'one' to be visible\n{joined}"
+    );
+    assert!(
+        joined.contains("two"),
+        "expected committed 'two' to be visible\n{joined}"
+    );
+    // The last three (three,four,five) remain in the live ring, not committed here.
+}
+
+#[test]
+fn live_002_pre_scroll_and_commit() {
+    let backend = TestBackend::new(20, 6);
+    let mut term = match codex_tui::custom_terminal::Terminal::with_options(backend) {
+        Ok(t) => t,
+        Err(e) => panic!("failed to construct terminal: {e}"),
+    };
+    // Viewport not at bottom: y=3
+    let area = Rect::new(0, 3, 20, 1);
+    term.set_viewport_area(area);
+
+    let mut rb = codex_tui::live_wrap::RowBuilder::new(20);
+    rb.push_fragment("alpha\n");
+    rb.push_fragment("beta\n");
+    rb.push_fragment("gamma\n");
+    rb.push_fragment("delta\n");
+
+    // Keep 3, commit 1.
+    let commit_rows = rb.drain_commit_ready(3);
+    let lines: Vec<Line<'static>> = commit_rows
+        .into_iter()
+        .map(|r| Line::from(r.text))
+        .collect();
+
+    let mut buf: Vec<u8> = Vec::new();
+    codex_tui::insert_history::insert_history_lines_to_writer(&mut term, &mut buf, lines);
+    let s = String::from_utf8_lossy(&buf);
+
+    // Expect a SetScrollRegion to [area.top()+1 .. screen_height] and a cursor move to top of that region.
+    assert!(
+        s.contains("\u{1b}[4;6r"),
+        "expected pre-scroll region 4..6, got: {s:?}"
+    );
+    assert!(
+        s.contains("\u{1b}[4;1H"),
+        "expected cursor CUP 4;1H, got: {s:?}"
+    );
+}