Use step environment snapshots for subagent inheritance (#55331)

## What changed

- Remove `subagent_thread_environments` and the separate configured environment bindings. Spawned agents inherit the invoking step's environment snapshot.
- Retain environment selections across child eviction without retaining executor bindings. Reload V2 children against the parent's captured environments, requiring matching environment IDs, working directories, and workspace roots while preserving permission validation.

GitOrigin-RevId: d820c63ea20f5834ed88071d16c60683f2545406

codex-rs/features/src/lib.rs

@@ -232,8 +232,6 @@ pub enum Feature {
     ModelCatalogInContext,
     /// Inherit client-defined dynamic tools in fresh V2 subagents.
     MultiAgentV2DynamicTools,
-    /// Inherit configured thread environments instead of temporary turn selections.
-    SubagentThreadEnvironments,
     /// Use each subagent model's default context window and auto-compaction threshold.
     SubagentDefaultContextLimits,
     /// Keep sampling through reasoning and commentary boundaries when agent mail arrives.
@@ -1514,12 +1512,6 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::UnderDevelopment,
         default_enabled: false,
     },
-    FeatureSpec {
-        id: Feature::SubagentThreadEnvironments,
-        key: "subagent_thread_environments",
-        stage: Stage::UnderDevelopment,
-        default_enabled: false,
-    },
     FeatureSpec {
         id: Feature::SubagentDefaultContextLimits,
         key: "subagent_default_context_limits",