[2 of 2] Finish moving goal runtime to extension (#26548)

## Stack

1. [#26547](https://github.com/openai/codex/pull/26547) - [1 of 2] Align
goal extension with core behavior
2. [#26548](https://github.com/openai/codex/pull/26548) - [2 of 2] Move
goal runtime to extension

## Why

This PR completes the switch of the goal behavior to the
extension-backed runtime and removes the old core goal implementation.

## What Changed

- Installs the goal extension for app-server `ThreadManager` sessions.
- Routes app-server thread goal `get`, `set`, and `clear` through
`GoalService`.
- Uses thread-idle lifecycle emission after goal resume and snapshot
ordering so the extension can decide whether to continue the goal.
- Forwards extension goal updates through a FIFO async app-server
notification path so backpressure does not drop them or reorder updates.
- Keeps review turns from enabling goal runtime behavior.
- Plans extension tools before dynamic tools so built-in goal tool names
keep their old precedence when goals are enabled.
- Removes the old core goal runtime, core goal tool handlers, and core
goal tool specs.
- Updates tests that were coupled to the core-owned goal runtime while
leaving the legacy `<goal_context>` compatibility path in core for old
threads.
- Removes the stale cargo-shear ignore now that `codex-goal-extension`
is used by the workspace.
- Keeps realtime event matching exhaustive after removing the old
goal-specific realtime text path.


## Validation

- Ran manual `/goal` runs in TUI. Validated time accounting matched
wall-clock time and goal lifecycle state transitions.

codex-rs/app-server/src/message_processor.rs

@@ -70,6 +70,7 @@ use codex_core::ThreadManager;
 use codex_core::config::Config;
 use codex_exec_server::EnvironmentManager;
 use codex_feedback::CodexFeedback;
+use codex_goal_extension::GoalService;
 use codex_login::AuthManager;
 use codex_login::auth::ExternalAuth;
 use codex_login::auth::ExternalAuthRefreshContext;
@@ -305,6 +306,7 @@ impl MessageProcessor {
         // resumed, or forked threads to a different persistence backend/root.
         let thread_store = codex_core::thread_store_from_config(config.as_ref(), state_db.clone());
         let environment_manager_for_requests = Arc::clone(&environment_manager);
+        let goal_service = Arc::new(GoalService::new());
         let thread_manager = Arc::new_cyclic(|thread_manager| {
             ThreadManager::new(
                 config.as_ref(),
@@ -313,8 +315,11 @@ impl MessageProcessor {
                 environment_manager,
                 thread_extensions(
                     guardian_agent_spawner(thread_manager.clone()),
-                    app_server_extension_event_sink(outgoing.clone()),
+                    app_server_extension_event_sink(outgoing.clone(), thread_state_manager.clone()),
                     auth_manager.clone(),
+                    state_db.clone(),
+                    thread_manager.clone(),
+                    Arc::clone(&goal_service),
                 ),
                 Some(analytics_events_client.clone()),
                 Arc::clone(&thread_store),
@@ -416,6 +421,7 @@ impl MessageProcessor {
             Arc::clone(&config),
             thread_state_manager.clone(),
             state_db.clone(),
+            Arc::clone(&goal_service),
         );
         let thread_processor = ThreadRequestProcessor::new(
             auth_manager.clone(),