[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/core/src/session/turn.rs

@@ -18,7 +18,6 @@ use crate::compact_remote_v2::run_inline_remote_auto_compact_task as run_inline_
 use crate::connectors;
 use crate::context::ContextualUserFragment;
 use crate::feedback_tags;
-use crate::goals::GoalRuntimeEvent;
 use crate::hook_runtime::inspect_pending_input;
 use crate::hook_runtime::record_additional_contexts;
 use crate::hook_runtime::record_pending_input;
@@ -151,15 +150,6 @@ pub(crate) async fn run_turn(
         let error = err.to_codex_protocol_error();
         sess.emit_turn_error_lifecycle(turn_context.as_ref(), error.clone())
             .await;
-        if error == CodexErrorInfo::UsageLimitExceeded
-            && let Err(err) = sess
-                .goal_runtime_apply(GoalRuntimeEvent::UsageLimitReached {
-                    turn_context: turn_context.as_ref(),
-                })
-                .await
-        {
-            warn!("failed to usage-limit active goal after usage-limit error: {err}");
-        }
         error!("Failed to run pre-sampling compact");
         return None;
     }
@@ -294,17 +284,6 @@ pub(crate) async fn run_turn(
                         let error = err.to_codex_protocol_error();
                         sess.emit_turn_error_lifecycle(turn_context.as_ref(), error.clone())
                             .await;
-                        if error == CodexErrorInfo::UsageLimitExceeded
-                            && let Err(err) = sess
-                                .goal_runtime_apply(GoalRuntimeEvent::UsageLimitReached {
-                                    turn_context: turn_context.as_ref(),
-                                })
-                                .await
-                        {
-                            warn!(
-                                "failed to usage-limit active goal after usage-limit error: {err}"
-                            );
-                        }
                         return None;
                     }
                     can_drain_pending_input = !model_needs_follow_up;
@@ -390,15 +369,6 @@ pub(crate) async fn run_turn(
                 let error = e.to_codex_protocol_error();
                 sess.emit_turn_error_lifecycle(turn_context.as_ref(), error.clone())
                     .await;
-                if error == CodexErrorInfo::UsageLimitExceeded
-                    && let Err(err) = sess
-                        .goal_runtime_apply(GoalRuntimeEvent::UsageLimitReached {
-                            turn_context: turn_context.as_ref(),
-                        })
-                        .await
-                {
-                    warn!("failed to usage-limit active goal after usage-limit error: {err}");
-                }
                 sess.track_turn_codex_error(turn_context.as_ref(), &e);
                 let event = EventMsg::Error(e.to_error_event(/*message_prefix*/ None));
                 sess.send_event(&turn_context, event).await;