[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_context.rs

@@ -91,7 +91,6 @@ pub struct TurnContext {
     pub(crate) shell_environment_policy: ShellEnvironmentPolicy,
     pub(crate) available_models: Vec<ModelPreset>,
     pub(crate) unified_exec_shell_mode: UnifiedExecShellMode,
-    pub(crate) goal_tools_supported: bool,
     pub features: ManagedFeatures,
     pub(crate) ghost_snapshot: GhostSnapshotConfig,
     pub(crate) final_output_json_schema: Option<Value>,
@@ -170,10 +169,6 @@ impl TurnContext {
         ToolEnvironmentMode::from_count(self.environments.turn_environments.len())
     }
 
-    pub(crate) fn goal_tools_enabled(&self) -> bool {
-        self.goal_tools_supported && self.features.get().enabled(Feature::Goals)
-    }
-
     pub(crate) async fn with_model(
         &self,
         model: String,
@@ -264,7 +259,6 @@ impl TurnContext {
             shell_environment_policy: self.shell_environment_policy.clone(),
             available_models,
             unified_exec_shell_mode: self.unified_exec_shell_mode.clone(),
-            goal_tools_supported: self.goal_tools_supported,
             features,
             ghost_snapshot: self.ghost_snapshot.clone(),
             final_output_json_schema: self.final_output_json_schema.clone(),
@@ -477,7 +471,6 @@ impl Session {
         cwd: AbsolutePathBuf,
         sub_id: String,
         skills_outcome: Arc<SkillLoadOutcome>,
-        goal_tools_supported: bool,
     ) -> TurnContext {
         let reasoning_effort = session_configuration.collaboration_mode.reasoning_effort();
         let reasoning_summary = session_configuration
@@ -568,7 +561,6 @@ impl Session {
             shell_environment_policy: per_turn_config.permissions.shell_environment_policy.clone(),
             available_models,
             unified_exec_shell_mode,
-            goal_tools_supported,
             features: per_turn_config.features.clone(),
             ghost_snapshot: per_turn_config.ghost_snapshot.clone(),
             final_output_json_schema: None,
@@ -781,7 +773,6 @@ impl Session {
                 .skills_for_config(&skills_input, fs)
                 .await,
         );
-        let goal_tools_supported = !per_turn_config.ephemeral && self.state_db().is_some();
         let mut turn_context: TurnContext = Self::make_turn_context(
             self.thread_id(),
             self.session_id(),
@@ -810,7 +801,6 @@ impl Session {
             cwd,
             sub_id,
             skills_outcome,
-            goal_tools_supported,
         );
         turn_context.realtime_active = self.conversation.running_state().await.is_some();