Register the transcript v2 feature flag (#40554)

## What changed

- Add the under-development `transcript_v2` feature for the interactive
  transcript composer and turn-selection UI.
- Keep it disabled by default and expose it through the configuration schema
  and `codex features enable transcript_v2`.

## Testing

- Verify explicit configuration overrides and CLI persistence for the new
  feature.

GitOrigin-RevId: 138ab7851621c066e8121cc3eb6cd4e7299f9c31

codex-rs/cli/tests/features.rs

@@ -133,15 +133,19 @@ fn strict_config_is_not_supported_for_cloud_command() -> Result<()> {
 async fn features_enable_writes_feature_flag_to_config() -> Result<()> {
     let codex_home = TempDir::new()?;
 
-    let mut cmd = codex_command(codex_home.path())?;
-    cmd.args(["features", "enable", "unified_exec"])
-        .assert()
-        .success()
-        .stdout(contains("Enabled feature `unified_exec` in config.toml."));
+    for feature in ["unified_exec", "transcript_v2"] {
+        let mut cmd = codex_command(codex_home.path())?;
+        cmd.args(["features", "enable", feature])
+            .assert()
+            .success()
+            .stdout(contains(format!(
+                "Enabled feature `{feature}` in config.toml."
+            )));
 
-    let config = std::fs::read_to_string(codex_home.path().join("config.toml"))?;
-    assert!(config.contains("[features]"));
-    assert!(config.contains("unified_exec = true"));
+        let config = std::fs::read_to_string(codex_home.path().join("config.toml"))?;
+        assert!(config.contains("[features]"));
+        assert!(config.contains(&format!("{feature} = true")));
+    }
 
     Ok(())
 }

codex-rs/core/config.schema.json

@@ -931,6 +931,9 @@
             "tool_suggest": {
               "type": "boolean"
             },
+            "transcript_v2": {
+              "type": "boolean"
+            },
             "tui_app_server": {
               "type": "boolean"
             },
@@ -5934,6 +5937,9 @@
         "tool_suggest": {
           "type": "boolean"
         },
+        "transcript_v2": {
+          "type": "boolean"
+        },
         "tui_app_server": {
           "type": "boolean"
         },

codex-rs/features/src/lib.rs

@@ -88,6 +88,8 @@ impl Stage {
 /// Unique features toggled via configuration.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub enum Feature {
+    /// Enable the interactive transcript composer and turn-selection UI.
+    TranscriptV2,
     // Stable.
     /// Enable the default shell tool.
     ShellTool,
@@ -834,6 +836,12 @@ pub struct FeatureSpec {
 }
 
 pub const FEATURES: &[FeatureSpec] = &[
+    FeatureSpec {
+        id: Feature::TranscriptV2,
+        key: "transcript_v2",
+        stage: Stage::UnderDevelopment,
+        default_enabled: false,
+    },
     // Stable features.
     FeatureSpec {
         id: Feature::GhostCommit,

codex-rs/features/src/tests.rs

@@ -14,6 +14,15 @@ use std::collections::BTreeMap;
 use toml::Table;
 use toml::Value as TomlValue;
 
+#[test]
+fn transcript_v2_resolves_explicit_config_overrides() {
+    let mut features = Features::with_defaults();
+    for enabled in [false, true, false] {
+        features.apply_map(&BTreeMap::from([("transcript_v2".to_string(), enabled)]));
+        assert_eq!(features.enabled(Feature::TranscriptV2), enabled);
+    }
+}
+
 #[test]
 fn under_development_features_are_disabled_by_default() {
     for spec in crate::FEATURES {