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/Cargo.lock

@@ -1166,8 +1166,6 @@ dependencies = [
  "codex-rmcp-client",
  "codex-stdio-to-uds",
  "codex-tui",
- "codex-tui2",
- "codex-utils-absolute-path",
  "codex-utils-cargo-bin",
  "codex-windows-sandbox",
  "libc",
@@ -1811,81 +1809,6 @@ dependencies = [
  "winsplit",
 ]
 
-[[package]]
-name = "codex-tui2"
-version = "0.0.0"
-dependencies = [
- "anyhow",
- "arboard",
- "assert_matches",
- "async-stream",
- "base64",
- "chrono",
- "clap",
- "codex-ansi-escape",
- "codex-app-server-protocol",
- "codex-arg0",
- "codex-backend-client",
- "codex-cli",
- "codex-common",
- "codex-core",
- "codex-feedback",
- "codex-file-search",
- "codex-login",
- "codex-otel",
- "codex-protocol",
- "codex-tui",
- "codex-utils-absolute-path",
- "codex-utils-cargo-bin",
- "codex-utils-pty",
- "codex-windows-sandbox",
- "color-eyre",
- "crossterm",
- "derive_more 2.1.1",
- "diffy",
- "dirs",
- "dunce",
- "image",
- "insta",
- "itertools 0.14.0",
- "lazy_static",
- "libc",
- "mcp-types",
- "pathdiff",
- "pretty_assertions",
- "pulldown-cmark",
- "rand 0.9.2",
- "ratatui",
- "ratatui-core",
- "ratatui-macros",
- "regex-lite",
- "reqwest",
- "serde",
- "serde_json",
- "serial_test",
- "shlex",
- "strum 0.27.2",
- "strum_macros 0.27.2",
- "supports-color 3.0.2",
- "tempfile",
- "textwrap 0.16.2",
- "tokio",
- "tokio-stream",
- "tokio-util",
- "toml 0.9.5",
- "tracing",
- "tracing-appender",
- "tracing-subscriber",
- "tree-sitter-bash",
- "tree-sitter-highlight",
- "tui-scrollbar",
- "unicode-segmentation",
- "unicode-width 0.2.1",
- "url",
- "uuid",
- "vt100",
-]
-
 [[package]]
 name = "codex-utils-absolute-path"
 version = "0.0.0"
@@ -2048,20 +1971,6 @@ dependencies = [
  "static_assertions",
 ]
 
-[[package]]
-name = "compact_str"
-version = "0.9.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3fdb1325a1cece981e8a296ab8f0f9b63ae357bd0784a9faaf548cc7b480707a"
-dependencies = [
- "castaway",
- "cfg-if",
- "itoa",
- "rustversion",
- "ryu",
- "static_assertions",
-]
-
 [[package]]
 name = "concurrent-queue"
 version = "2.5.0"
@@ -2648,15 +2557,6 @@ version = "0.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fea41bba32d969b513997752735605054bc0dfa92b4c56bf1189f2e174be7a10"
 
-[[package]]
-name = "document-features"
-version = "0.2.12"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d4b8a88685455ed29a21542a33abd9cb6510b6b129abadabdcef0f4c55bc8f61"
-dependencies = [
- "litrs",
-]
-
 [[package]]
 name = "dotenvy"
 version = "0.15.7"
@@ -3988,16 +3888,6 @@ dependencies = [
  "wasm-bindgen",
 ]
 
-[[package]]
-name = "kasuari"
-version = "0.4.11"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8fe90c1150662e858c7d5f945089b7517b0a80d8bf7ba4b1b5ffc984e7230a5b"
-dependencies = [
- "hashbrown 0.16.0",
- "thiserror 2.0.17",
-]
-
 [[package]]
 name = "keyring"
 version = "3.6.3"
@@ -4143,12 +4033,6 @@ version = "0.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "241eaef5fd12c88705a01fc1066c48c4b36e0dd4377dcdc7ec3942cea7a69956"
 
-[[package]]
-name = "litrs"
-version = "1.0.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "11d3d7f243d5c5a8b9bb5d6dd2b1602c0cb0b9db1621bafc7ed66e35ff9fe092"
-
 [[package]]
 name = "local-waker"
 version = "0.1.4"
@@ -5488,7 +5372,7 @@ source = "git+https://github.com/nornagon/ratatui?branch=nornagon-v0.29.0-patch#
 dependencies = [
  "bitflags 2.10.0",
  "cassowary",
- "compact_str 0.8.1",
+ "compact_str",
  "crossterm",
  "indoc",
  "instability",
@@ -5497,27 +5381,7 @@ dependencies = [
  "paste",
  "strum 0.26.3",
  "unicode-segmentation",
- "unicode-truncate 1.1.0",
- "unicode-width 0.2.1",
-]
-
-[[package]]
-name = "ratatui-core"
-version = "0.1.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5ef8dea09a92caaf73bff7adb70b76162e5937524058a7e5bff37869cbbec293"
-dependencies = [
- "bitflags 2.10.0",
- "compact_str 0.9.0",
- "hashbrown 0.16.0",
- "indoc",
- "itertools 0.14.0",
- "kasuari",
- "lru 0.16.3",
- "strum 0.27.2",
- "thiserror 2.0.17",
- "unicode-segmentation",
- "unicode-truncate 2.0.0",
+ "unicode-truncate",
  "unicode-width 0.2.1",
 ]
 
@@ -6684,9 +6548,6 @@ name = "strum"
 version = "0.27.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "af23d6f6c1a224baef9d3f61e287d2761385a5b88fdab4eb4c6f11aeb54c4bcf"
-dependencies = [
- "strum_macros 0.27.2",
-]
 
 [[package]]
 name = "strum_macros"
@@ -7549,16 +7410,6 @@ dependencies = [
  "termcolor",
 ]
 
-[[package]]
-name = "tui-scrollbar"
-version = "0.2.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0e4267311b5c7999a996ea94939b6d2b1b44a9e5cc11e76cbbb6dcca4c281df4"
-dependencies = [
- "document-features",
- "ratatui-core",
-]
-
 [[package]]
 name = "tungstenite"
 version = "0.28.0"
@@ -7644,17 +7495,6 @@ dependencies = [
  "unicode-width 0.1.14",
 ]
 
-[[package]]
-name = "unicode-truncate"
-version = "2.0.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8fbf03860ff438702f3910ca5f28f8dac63c1c11e7efb5012b8b175493606330"
-dependencies = [
- "itertools 0.13.0",
- "unicode-segmentation",
- "unicode-width 0.2.1",
-]
-
 [[package]]
 name = "unicode-width"
 version = "0.1.14"