refactor: migrate delegate_task to task tool with metadata fixes

- Rename delegate_task tool to task across codebase (100 files)
- Update model references: claude-opus-4-6 → 4-5, gpt-5.3-codex → 5.2-codex
- Add tool-metadata-store to restore metadata overwritten by fromPlugin()
- Add session ID polling for BackgroundManager task sessions
- Await async ctx.metadata() calls in tool executors
- Add ses_ prefix guard to getMessageDir for performance
- Harden BackgroundManager with idle deferral and error handling
- Fix duplicate task key in sisyphus-junior test object literals
- Fix unawaited showOutputToUser in ast_grep_replace
- Fix background=true → run_in_background=true in ultrawork prompt
- Fix duplicate task/task references in docs and comments

src/tools/task/task-list.ts

@@ -70,7 +70,7 @@ Returns summary format: id, subject, status, owner, blockedBy (not full descript
 
        return JSON.stringify({
          tasks: summaries,
-         reminder: "1 task = 1 delegate_task. Maximize parallel execution by running independent tasks (tasks with empty blockedBy) concurrently."
+         reminder: "1 task = 1 task. Maximize parallel execution by running independent tasks (tasks with empty blockedBy) concurrently."
        })
     },
   })