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/cli/src/main.rs

@@ -26,7 +26,6 @@ use codex_tui::AppExitInfo;
 use codex_tui::Cli as TuiCli;
 use codex_tui::ExitReason;
 use codex_tui::update_action::UpdateAction;
-use codex_tui2 as tui2;
 use owo_colors::OwoColorize;
 use std::io::IsTerminal;
 use std::path::PathBuf;
@@ -40,14 +39,8 @@ use crate::mcp_cmd::McpCli;
 
 use codex_core::config::Config;
 use codex_core::config::ConfigOverrides;
-use codex_core::config::find_codex_home;
-use codex_core::config::load_config_as_toml_with_cli_overrides;
-use codex_core::features::Feature;
-use codex_core::features::FeatureOverrides;
-use codex_core::features::Features;
 use codex_core::features::is_known_feature_key;
 use codex_core::terminal::TerminalName;
-use codex_utils_absolute_path::AbsolutePathBuf;
 
 /// Codex CLI
 ///
@@ -727,8 +720,6 @@ fn prepend_config_flags(
         .splice(0..0, cli_config_overrides.raw_overrides);
 }
 
-/// Run the interactive Codex TUI, dispatching to either the legacy implementation or the
-/// experimental TUI v2 shim based on feature flags resolved from config.
 async fn run_interactive_tui(
     mut interactive: TuiCli,
     codex_linux_sandbox_exe: Option<PathBuf>,
@@ -756,12 +747,7 @@ async fn run_interactive_tui(
         }
     }
 
-    if is_tui2_enabled(&interactive).await? {
-        let result = tui2::run_main(interactive.into(), codex_linux_sandbox_exe).await?;
-        Ok(result.into())
-    } else {
-        codex_tui::run_main(interactive, codex_linux_sandbox_exe).await
-    }
+    codex_tui::run_main(interactive, codex_linux_sandbox_exe).await
 }
 
 fn confirm(prompt: &str) -> std::io::Result<bool> {
@@ -773,32 +759,6 @@ fn confirm(prompt: &str) -> std::io::Result<bool> {
     Ok(answer.eq_ignore_ascii_case("y") || answer.eq_ignore_ascii_case("yes"))
 }
 
-/// Returns `Ok(true)` when the resolved configuration enables the `tui2` feature flag.
-///
-/// This performs a lightweight config load (honoring the same precedence as the lower-level TUI
-/// bootstrap: `$CODEX_HOME`, config.toml, profile, and CLI `-c` overrides) solely to decide which
-/// TUI frontend to launch. The full configuration is still loaded later by the interactive TUI.
-async fn is_tui2_enabled(cli: &TuiCli) -> std::io::Result<bool> {
-    let raw_overrides = cli.config_overrides.raw_overrides.clone();
-    let overrides_cli = codex_common::CliConfigOverrides { raw_overrides };
-    let cli_kv_overrides = overrides_cli
-        .parse_overrides()
-        .map_err(|e| std::io::Error::new(std::io::ErrorKind::InvalidInput, e))?;
-
-    let codex_home = find_codex_home()?;
-    let cwd = cli.cwd.clone();
-    let config_cwd = match cwd.as_deref() {
-        Some(path) => AbsolutePathBuf::from_absolute_path(path)?,
-        None => AbsolutePathBuf::current_dir()?,
-    };
-    let config_toml =
-        load_config_as_toml_with_cli_overrides(&codex_home, &config_cwd, cli_kv_overrides).await?;
-    let config_profile = config_toml.get_config_profile(cli.config_profile.clone())?;
-    let overrides = FeatureOverrides::default();
-    let features = Features::from_config(&config_toml, &config_profile, overrides);
-    Ok(features.enabled(Feature::Tui2))
-}
-
 /// Build the final `TuiCli` for a `codex resume` invocation.
 fn finalize_resume_interactive(
     mut interactive: TuiCli,