feat(tui): retire the tui2 experiment (#9640)

## Summary
- Retire the experimental TUI2 implementation and its feature flag.
- Remove TUI2-only config/schema/docs so the CLI stays on the
terminal-native path.
- Keep docs aligned with the legacy TUI while we focus on redraw-based
improvements.

## Customer impact
- Retires the TUI2 experiment and keeps Codex on the proven
terminal-native UI while we invest in redraw-based improvements to the
existing experience.

## Migration / compatibility
- If you previously set tui2-related options in config.toml, they are
now ignored and Codex continues using the existing terminal-native TUI
(no action required).

## Context
- What worked: a transcript-owned viewport delivered excellent resize
rewrap and high-fidelity copy (especially for code).
- Why stop: making that experience feel fully native across the
environment matrix (terminal emulator, OS, input modality, multiplexer,
font/theme, alt-screen behavior) creates a combinatorial explosion of
edge cases.
- What next: we are focusing on redraw-based improvements to the
existing terminal-native TUI so scrolling, selection, and copy remain
native while resize/redraw correctness improves.

## Testing
- just write-config-schema
- just fmt
- cargo clippy --fix --all-features --tests --allow-dirty --allow-no-vcs
-p codex-core
- cargo clippy --fix --all-features --tests --allow-dirty --allow-no-vcs
-p codex-cli
- cargo check
- cargo test -p codex-core
- cargo test -p codex-cli

codex-rs/core/src/config/mod.rs

@@ -13,7 +13,6 @@ use crate::config::types::OtelConfigToml;
 use crate::config::types::OtelExporterKind;
 use crate::config::types::Personality;
 use crate::config::types::SandboxWorkspaceWrite;
-use crate::config::types::ScrollInputMode;
 use crate::config::types::ShellEnvironmentPolicy;
 use crate::config::types::ShellEnvironmentPolicyToml;
 use crate::config::types::SkillsConfig;
@@ -200,58 +199,6 @@ pub struct Config {
     /// Show startup tooltips in the TUI welcome screen.
     pub show_tooltips: bool,
 
-    /// Override the events-per-wheel-tick factor for TUI2 scroll normalization.
-    ///
-    /// This is the same `tui.scroll_events_per_tick` value from `config.toml`, plumbed through the
-    /// merged [`Config`] object (see [`Tui`]) so TUI2 can normalize scroll event density per
-    /// terminal.
-    pub tui_scroll_events_per_tick: Option<u16>,
-
-    /// Override the number of lines applied per wheel tick in TUI2.
-    ///
-    /// This is the same `tui.scroll_wheel_lines` value from `config.toml` (see [`Tui`]). TUI2
-    /// applies it to wheel-like scroll streams. Trackpad-like scrolling uses a separate
-    /// `tui.scroll_trackpad_lines` setting.
-    pub tui_scroll_wheel_lines: Option<u16>,
-
-    /// Override the number of lines per tick-equivalent used for trackpad scrolling in TUI2.
-    ///
-    /// This is the same `tui.scroll_trackpad_lines` value from `config.toml` (see [`Tui`]).
-    pub tui_scroll_trackpad_lines: Option<u16>,
-
-    /// Trackpad acceleration: approximate number of events required to gain +1x speed in TUI2.
-    ///
-    /// This is the same `tui.scroll_trackpad_accel_events` value from `config.toml` (see [`Tui`]).
-    pub tui_scroll_trackpad_accel_events: Option<u16>,
-
-    /// Trackpad acceleration: maximum multiplier applied to trackpad-like streams in TUI2.
-    ///
-    /// This is the same `tui.scroll_trackpad_accel_max` value from `config.toml` (see [`Tui`]).
-    pub tui_scroll_trackpad_accel_max: Option<u16>,
-
-    /// Control how TUI2 interprets mouse scroll input (wheel vs trackpad).
-    ///
-    /// This is the same `tui.scroll_mode` value from `config.toml` (see [`Tui`]).
-    pub tui_scroll_mode: ScrollInputMode,
-
-    /// Override the wheel tick detection threshold (ms) for TUI2 auto scroll mode.
-    ///
-    /// This is the same `tui.scroll_wheel_tick_detect_max_ms` value from `config.toml` (see
-    /// [`Tui`]).
-    pub tui_scroll_wheel_tick_detect_max_ms: Option<u64>,
-
-    /// Override the wheel-like end-of-stream threshold (ms) for TUI2 auto scroll mode.
-    ///
-    /// This is the same `tui.scroll_wheel_like_max_duration_ms` value from `config.toml` (see
-    /// [`Tui`]).
-    pub tui_scroll_wheel_like_max_duration_ms: Option<u64>,
-
-    /// Invert mouse scroll direction for TUI2.
-    ///
-    /// This is the same `tui.scroll_invert` value from `config.toml` (see [`Tui`]) and is applied
-    /// consistently to both mouse wheels and trackpads.
-    pub tui_scroll_invert: bool,
-
     /// Controls whether the TUI uses the terminal's alternate screen buffer.
     ///
     /// This is the same `tui.alternate_screen` value from `config.toml` (see [`Tui`]).
@@ -1613,27 +1560,6 @@ impl Config {
                 .unwrap_or_default(),
             animations: cfg.tui.as_ref().map(|t| t.animations).unwrap_or(true),
             show_tooltips: cfg.tui.as_ref().map(|t| t.show_tooltips).unwrap_or(true),
-            tui_scroll_events_per_tick: cfg.tui.as_ref().and_then(|t| t.scroll_events_per_tick),
-            tui_scroll_wheel_lines: cfg.tui.as_ref().and_then(|t| t.scroll_wheel_lines),
-            tui_scroll_trackpad_lines: cfg.tui.as_ref().and_then(|t| t.scroll_trackpad_lines),
-            tui_scroll_trackpad_accel_events: cfg
-                .tui
-                .as_ref()
-                .and_then(|t| t.scroll_trackpad_accel_events),
-            tui_scroll_trackpad_accel_max: cfg
-                .tui
-                .as_ref()
-                .and_then(|t| t.scroll_trackpad_accel_max),
-            tui_scroll_mode: cfg.tui.as_ref().map(|t| t.scroll_mode).unwrap_or_default(),
-            tui_scroll_wheel_tick_detect_max_ms: cfg
-                .tui
-                .as_ref()
-                .and_then(|t| t.scroll_wheel_tick_detect_max_ms),
-            tui_scroll_wheel_like_max_duration_ms: cfg
-                .tui
-                .as_ref()
-                .and_then(|t| t.scroll_wheel_like_max_duration_ms),
-            tui_scroll_invert: cfg.tui.as_ref().map(|t| t.scroll_invert).unwrap_or(false),
             tui_alternate_screen: cfg
                 .tui
                 .as_ref()
@@ -1886,15 +1812,6 @@ persistence = "none"
                 notifications: Notifications::Enabled(true),
                 animations: true,
                 show_tooltips: true,
-                scroll_events_per_tick: None,
-                scroll_wheel_lines: None,
-                scroll_trackpad_lines: None,
-                scroll_trackpad_accel_events: None,
-                scroll_trackpad_accel_max: None,
-                scroll_mode: ScrollInputMode::Auto,
-                scroll_wheel_tick_detect_max_ms: None,
-                scroll_wheel_like_max_duration_ms: None,
-                scroll_invert: false,
                 alternate_screen: AltScreenMode::Auto,
             }
         );
@@ -3782,15 +3699,6 @@ model_verbosity = "high"
                 show_tooltips: true,
                 analytics_enabled: Some(true),
                 feedback_enabled: true,
-                tui_scroll_events_per_tick: None,
-                tui_scroll_wheel_lines: None,
-                tui_scroll_trackpad_lines: None,
-                tui_scroll_trackpad_accel_events: None,
-                tui_scroll_trackpad_accel_max: None,
-                tui_scroll_mode: ScrollInputMode::Auto,
-                tui_scroll_wheel_tick_detect_max_ms: None,
-                tui_scroll_wheel_like_max_duration_ms: None,
-                tui_scroll_invert: false,
                 tui_alternate_screen: AltScreenMode::Auto,
                 otel: OtelConfig::default(),
             },
@@ -3871,15 +3779,6 @@ model_verbosity = "high"
             show_tooltips: true,
             analytics_enabled: Some(true),
             feedback_enabled: true,
-            tui_scroll_events_per_tick: None,
-            tui_scroll_wheel_lines: None,
-            tui_scroll_trackpad_lines: None,
-            tui_scroll_trackpad_accel_events: None,
-            tui_scroll_trackpad_accel_max: None,
-            tui_scroll_mode: ScrollInputMode::Auto,
-            tui_scroll_wheel_tick_detect_max_ms: None,
-            tui_scroll_wheel_like_max_duration_ms: None,
-            tui_scroll_invert: false,
             tui_alternate_screen: AltScreenMode::Auto,
             otel: OtelConfig::default(),
         };
@@ -3975,15 +3874,6 @@ model_verbosity = "high"
             show_tooltips: true,
             analytics_enabled: Some(false),
             feedback_enabled: true,
-            tui_scroll_events_per_tick: None,
-            tui_scroll_wheel_lines: None,
-            tui_scroll_trackpad_lines: None,
-            tui_scroll_trackpad_accel_events: None,
-            tui_scroll_trackpad_accel_max: None,
-            tui_scroll_mode: ScrollInputMode::Auto,
-            tui_scroll_wheel_tick_detect_max_ms: None,
-            tui_scroll_wheel_like_max_duration_ms: None,
-            tui_scroll_invert: false,
             tui_alternate_screen: AltScreenMode::Auto,
             otel: OtelConfig::default(),
         };
@@ -4065,15 +3955,6 @@ model_verbosity = "high"
             show_tooltips: true,
             analytics_enabled: Some(true),
             feedback_enabled: true,
-            tui_scroll_events_per_tick: None,
-            tui_scroll_wheel_lines: None,
-            tui_scroll_trackpad_lines: None,
-            tui_scroll_trackpad_accel_events: None,
-            tui_scroll_trackpad_accel_max: None,
-            tui_scroll_mode: ScrollInputMode::Auto,
-            tui_scroll_wheel_tick_detect_max_ms: None,
-            tui_scroll_wheel_like_max_duration_ms: None,
-            tui_scroll_invert: false,
             tui_alternate_screen: AltScreenMode::Auto,
             otel: OtelConfig::default(),
         };