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/tui/src/bottom_pane/chat_composer.rs

@@ -192,12 +192,12 @@ use crate::bottom_pane::textarea::TextAreaState;
 use crate::clipboard_paste::normalize_pasted_path;
 use crate::clipboard_paste::pasted_image_format;
 use crate::history_cell;
+use crate::legacy_core::plugins::PluginCapabilitySummary;
+use crate::legacy_core::skills::model::SkillMetadata;
 use crate::tui::FrameRequester;
 use crate::ui_consts::LIVE_PREFIX_COLS;
 use codex_chatgpt::connectors;
 use codex_chatgpt::connectors::AppInfo;
-use codex_core::plugins::PluginCapabilitySummary;
-use codex_core::skills::model::SkillMetadata;
 use codex_file_search::FileMatch;
 use std::cell::RefCell;
 use std::collections::HashMap;
@@ -3241,7 +3241,7 @@ impl ChatComposer {
                 }
                 let display_name = connectors::connector_display_label(connector);
                 let description = Some(Self::connector_brief_description(connector));
-                let slug = codex_core::connectors::connector_mention_slug(connector);
+                let slug = crate::legacy_core::connectors::connector_mention_slug(connector);
                 let search_terms = vec![display_name.clone(), connector.id.clone(), slug.clone()];
                 let connector_id = connector.id.as_str();
                 mentions.push(MentionItem {
@@ -4830,7 +4830,7 @@ mod tests {
             name: "google-calendar:availability".to_string(),
             description: "Find availability and plan event changes".to_string(),
             short_description: None,
-            interface: Some(codex_core::skills::model::SkillInterface {
+            interface: Some(crate::legacy_core::skills::model::SkillInterface {
                 display_name: Some("Google Calendar".to_string()),
                 short_description: None,
                 icon_small: None,
@@ -4852,7 +4852,7 @@ mod tests {
             ),
             has_skills: true,
             mcp_server_names: vec!["google-calendar".to_string()],
-            app_connector_ids: vec![codex_core::plugins::AppConnectorId(
+            app_connector_ids: vec![crate::legacy_core::plugins::AppConnectorId(
                 "google_calendar".to_string(),
             )],
         }]));
@@ -4907,7 +4907,7 @@ mod tests {
                     ),
                     has_skills: true,
                     mcp_server_names: vec!["sample".to_string()],
-                    app_connector_ids: vec![codex_core::plugins::AppConnectorId(
+                    app_connector_ids: vec![crate::legacy_core::plugins::AppConnectorId(
                         "calendar".to_string(),
                     )],
                 }]));
@@ -4928,7 +4928,7 @@ mod tests {
                     name: "google-calendar-skill".to_string(),
                     description: "Find availability and plan event changes".to_string(),
                     short_description: None,
-                    interface: Some(codex_core::skills::model::SkillInterface {
+                    interface: Some(crate::legacy_core::skills::model::SkillInterface {
                         display_name: Some("Google Calendar".to_string()),
                         short_description: None,
                         icon_small: None,

codex-rs/tui/src/bottom_pane/mod.rs

@@ -22,13 +22,13 @@ use crate::bottom_pane::pending_thread_approvals::PendingThreadApprovals;
 use crate::bottom_pane::unified_exec_footer::UnifiedExecFooter;
 use crate::key_hint;
 use crate::key_hint::KeyBinding;
+use crate::legacy_core::plugins::PluginCapabilitySummary;
+use crate::legacy_core::skills::model::SkillMetadata;
 use crate::render::renderable::FlexRenderable;
 use crate::render::renderable::Renderable;
 use crate::render::renderable::RenderableItem;
 use crate::tui::FrameRequester;
 use bottom_pane_view::BottomPaneView;
-use codex_core::plugins::PluginCapabilitySummary;
-use codex_core::skills::model::SkillMetadata;
 use codex_features::Features;
 use codex_file_search::FileMatch;
 use codex_protocol::request_user_input::RequestUserInputEvent;