Remove the legacy TUI split (#15922)

This is the part 1 of 2 PRs that will delete the `tui` /
`tui_app_server` split. This part simply deletes the existing `tui`
directory and marks the `tui_app_server` feature flag as removed. I left
the `tui_app_server` feature flag in place for now so its presence
doesn't result in an error. It is simply ignored.

Part 2 will rename the `tui_app_server` directory `tui`. I did this as
two parts to reduce visible code churn.

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

@@ -1,126 +0,0 @@
-//! Streaming primitives used by the TUI transcript pipeline.
-//!
-//! `StreamState` owns newline-gated markdown collection and a FIFO queue of committed render lines.
-//! Higher-level modules build on top of this state:
-//! - `controller` adapts queued lines into `HistoryCell` emission rules for message and plan streams.
-//! - `chunking` computes adaptive drain plans from queue pressure.
-//! - `commit_tick` binds policy decisions to concrete controller drains.
-//!
-//! The key invariant is queue ordering. All drains pop from the front, and enqueue records an
-//! arrival timestamp so policy code can reason about oldest queued age without peeking into text.
-
-use std::collections::VecDeque;
-use std::path::Path;
-use std::time::Duration;
-use std::time::Instant;
-
-use ratatui::text::Line;
-
-use crate::markdown_stream::MarkdownStreamCollector;
-pub(crate) mod chunking;
-pub(crate) mod commit_tick;
-pub(crate) mod controller;
-
-struct QueuedLine {
-    line: Line<'static>,
-    enqueued_at: Instant,
-}
-
-/// Holds in-flight markdown stream state and queued committed lines.
-pub(crate) struct StreamState {
-    pub(crate) collector: MarkdownStreamCollector,
-    queued_lines: VecDeque<QueuedLine>,
-    pub(crate) has_seen_delta: bool,
-}
-
-impl StreamState {
-    /// Create stream state whose markdown collector renders local file links relative to `cwd`.
-    ///
-    /// Controllers are expected to pass the session cwd here once and keep it stable for the
-    /// lifetime of the active stream.
-    pub(crate) fn new(width: Option<usize>, cwd: &Path) -> Self {
-        Self {
-            collector: MarkdownStreamCollector::new(width, cwd),
-            queued_lines: VecDeque::new(),
-            has_seen_delta: false,
-        }
-    }
-    /// Resets collector and queue state for the next stream lifecycle.
-    pub(crate) fn clear(&mut self) {
-        self.collector.clear();
-        self.queued_lines.clear();
-        self.has_seen_delta = false;
-    }
-    /// Drains one queued line from the front of the queue.
-    pub(crate) fn step(&mut self) -> Vec<Line<'static>> {
-        self.queued_lines
-            .pop_front()
-            .map(|queued| queued.line)
-            .into_iter()
-            .collect()
-    }
-    /// Drains up to `max_lines` queued lines from the front of the queue.
-    ///
-    /// Callers that pass very large values still get bounded behavior because this method clamps to
-    /// the currently available queue length.
-    pub(crate) fn drain_n(&mut self, max_lines: usize) -> Vec<Line<'static>> {
-        let end = max_lines.min(self.queued_lines.len());
-        self.queued_lines
-            .drain(..end)
-            .map(|queued| queued.line)
-            .collect()
-    }
-    /// Drains all queued lines from the front of the queue.
-    pub(crate) fn drain_all(&mut self) -> Vec<Line<'static>> {
-        self.queued_lines
-            .drain(..)
-            .map(|queued| queued.line)
-            .collect()
-    }
-    /// Returns whether no lines are queued for commit.
-    pub(crate) fn is_idle(&self) -> bool {
-        self.queued_lines.is_empty()
-    }
-    /// Returns the current queue depth.
-    pub(crate) fn queued_len(&self) -> usize {
-        self.queued_lines.len()
-    }
-    /// Returns the age of the oldest queued line.
-    pub(crate) fn oldest_queued_age(&self, now: Instant) -> Option<Duration> {
-        self.queued_lines
-            .front()
-            .map(|queued| now.saturating_duration_since(queued.enqueued_at))
-    }
-    /// Appends committed lines to the queue with a shared enqueue timestamp.
-    pub(crate) fn enqueue(&mut self, lines: Vec<Line<'static>>) {
-        let now = Instant::now();
-        self.queued_lines
-            .extend(lines.into_iter().map(|line| QueuedLine {
-                line,
-                enqueued_at: now,
-            }));
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use pretty_assertions::assert_eq;
-    use std::path::PathBuf;
-
-    fn test_cwd() -> PathBuf {
-        // These tests only need a stable absolute cwd; using temp_dir() avoids baking Unix- or
-        // Windows-specific root semantics into the fixtures.
-        std::env::temp_dir()
-    }
-
-    #[test]
-    fn drain_n_clamps_to_available_lines() {
-        let mut state = StreamState::new(None, &test_cwd());
-        state.enqueue(vec![Line::from("one")]);
-
-        let drained = state.drain_n(8);
-        assert_eq!(drained, vec![Line::from("one")]);
-        assert!(state.is_idle());
-    }
-}