[codex] Add interruptible sleep tool (#28429)

## Why

Models sometimes need to pause briefly while waiting for external work,
but using a shell command for that delay ties the wait to a process and
does not naturally resume when new turn input arrives.

## What changed

- add a built-in `sleep` tool behind the under-development `sleep_tool`
feature
- accept a bounded `duration_ms` argument, matching the millisecond
convention used by unified exec
- end the sleep early when either steered user input or mailbox input
arrives
- include elapsed wall-clock time in completed and interrupted outputs
- emit a dedicated core `SleepItem` through `item/started` and
`item/completed`
- expose the sleep item as app-server v2 `ThreadItem::Sleep` and retain
it in reconstructed thread history
- regenerate the configuration schema for the new feature flag
- regenerate app-server JSON and TypeScript schema fixtures

## Test plan

- `just test -p codex-core sleep_tool_follows_feature_gate`
- `just test -p codex-core any_new_input_interrupts_sleep`
- `just test -p codex-app-server-protocol`
- `just test -p codex-app-server
sleep_emits_started_and_completed_items`

codex-rs/core/src/tools/spec_plan.rs

@@ -22,6 +22,7 @@ use crate::tools::handlers::RequestPluginInstallHandler;
 use crate::tools::handlers::RequestUserInputHandler;
 use crate::tools::handlers::ShellCommandHandler;
 use crate::tools::handlers::ShellCommandHandlerOptions;
+use crate::tools::handlers::SleepHandler;
 use crate::tools::handlers::TestSyncHandler;
 use crate::tools::handlers::ToolSearchHandlerCache;
 use crate::tools::handlers::ViewImageHandler;
@@ -666,6 +667,10 @@ fn add_core_utility_tools(context: &CoreToolPlanContext<'_>, planned_tools: &mut
         planned_tools.add(GetContextRemainingHandler);
     }
 
+    if features.enabled(Feature::SleepTool) {
+        planned_tools.add(SleepHandler);
+    }
+
     if tool_suggest_enabled(turn_context)
         && let Some(discoverable_tools) =
             context.discoverable_tools.filter(|tools| !tools.is_empty())