Support multiple managed environments (#18401)

## Summary
- refactor EnvironmentManager to own keyed environments with
default/local lookup helpers
- keep remote exec-server client creation lazy until exec/fs use
- preserve disabled agent environment access separately from internal
local environment access

## Validation
- not run (per Codex worktree instruction to avoid tests/builds unless
requested)

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/src/codex_delegate.rs

@@ -4,7 +4,6 @@ use std::sync::Arc;
 use async_channel::Receiver;
 use async_channel::Sender;
 use codex_async_utils::OrCancelExt;
-use codex_exec_server::EnvironmentManager;
 use codex_protocol::protocol::ApplyPatchApprovalRequestEvent;
 use codex_protocol::protocol::Event;
 use codex_protocol::protocol::EventMsg;
@@ -78,9 +77,7 @@ pub(crate) async fn run_codex_thread_interactive(
         config,
         auth_manager,
         models_manager,
-        environment_manager: Arc::new(EnvironmentManager::from_environment(
-            parent_ctx.environment.as_deref(),
-        )),
+        environment_manager: Arc::clone(&parent_session.services.environment_manager),
         skills_manager: Arc::clone(&parent_session.services.skills_manager),
         plugins_manager: Arc::clone(&parent_session.services.plugins_manager),
         mcp_manager: Arc::clone(&parent_session.services.mcp_manager),