TUI: enforce core boundary (#17399)

Problem: The TUI still depended on `codex-core` directly in a number of
places, and we had no enforcement from keeping this problem from getting
worse.

Solution: Route TUI core access through
`codex-app-server-client::legacy_core`, add CI enforcement for that
boundary, and re-export this legacy bridge inside the TUI as
`crate::legacy_core` so the remaining call sites stay readable. There is
no functional change in this PR — just changes to import targets.

Over time, we can whittle away at the remaining symbols in this legacy
namespace with the eventual goal of removing them all. In the meantime,
this linter rule will prevent us from inadvertently importing new
symbols from core.

codex-rs/app-server-client/src/lib.rs

@@ -56,6 +56,90 @@ use tracing::warn;
 pub use crate::remote::RemoteAppServerClient;
 pub use crate::remote::RemoteAppServerConnectArgs;
 
+/// Transitional access to core-only embedded app-server types.
+///
+/// New TUI behavior should prefer the app-server protocol methods. This
+/// module exists so clients can remove a direct `codex-core` dependency
+/// while legacy startup/config paths are migrated to RPCs.
+pub mod legacy_core {
+    pub use codex_core::Cursor;
+    pub use codex_core::DEFAULT_PROJECT_DOC_FILENAME;
+    pub use codex_core::INTERACTIVE_SESSION_SOURCES;
+    pub use codex_core::LOCAL_PROJECT_DOC_FILENAME;
+    pub use codex_core::McpManager;
+    pub use codex_core::PLUGIN_TEXT_MENTION_SIGIL;
+    pub use codex_core::RolloutRecorder;
+    pub use codex_core::TOOL_MENTION_SIGIL;
+    pub use codex_core::ThreadItem;
+    pub use codex_core::ThreadSortKey;
+    pub use codex_core::ThreadsPage;
+    pub use codex_core::append_message_history_entry;
+    pub use codex_core::check_execpolicy_for_warnings;
+    pub use codex_core::discover_project_doc_paths;
+    pub use codex_core::find_thread_meta_by_name_str;
+    pub use codex_core::find_thread_name_by_id;
+    pub use codex_core::find_thread_names_by_ids;
+    pub use codex_core::format_exec_policy_error_with_source;
+    pub use codex_core::grant_read_root_non_elevated;
+    pub use codex_core::lookup_message_history_entry;
+    pub use codex_core::message_history_metadata;
+    pub use codex_core::path_utils;
+    pub use codex_core::read_session_meta_line;
+    pub use codex_core::web_search_detail;
+
+    pub mod config {
+        pub use codex_core::config::*;
+
+        pub mod edit {
+            pub use codex_core::config::edit::*;
+        }
+    }
+
+    pub mod config_loader {
+        pub use codex_core::config_loader::*;
+    }
+
+    pub mod connectors {
+        pub use codex_core::connectors::*;
+    }
+
+    pub mod otel_init {
+        pub use codex_core::otel_init::*;
+    }
+
+    pub mod personality_migration {
+        pub use codex_core::personality_migration::*;
+    }
+
+    pub mod plugins {
+        pub use codex_core::plugins::*;
+    }
+
+    pub mod review_format {
+        pub use codex_core::review_format::*;
+    }
+
+    pub mod review_prompts {
+        pub use codex_core::review_prompts::*;
+    }
+
+    pub mod skills {
+        pub use codex_core::skills::*;
+    }
+
+    pub mod test_support {
+        pub use codex_core::test_support::*;
+    }
+
+    pub mod util {
+        pub use codex_core::util::*;
+    }
+
+    pub mod windows_sandbox {
+        pub use codex_core::windows_sandbox::*;
+    }
+}
+
 const SHUTDOWN_TIMEOUT: Duration = Duration::from_secs(5);
 
 /// Raw app-server request result for typed in-process requests.