fix(tool): let TaskList and TaskGet report read-only so explore mode allows them - #3579

Fixes #3567.

AgentScope Version

2.0.12dev (main @ 2f8c029)

Description

TaskList and TaskGet only read the task list, but they inherit is_read_only: bool = False from _TaskToolBase (src/agentscope/tool/_task/_task_tool_base.py:23). EXPLORE (plan) mode decides entirely through check_read_only (src/agentscope/permission/_engine.py:683), so both tools fall through to the deny fallback — while the toolkit keeps advertising them as planning tools ("Planning tools — always on.", app/_service/_toolkit.py:142) and the agent prompts the model to call them ("Use TaskList to view them...", agent/_agent.py:1548-1553). Net effect: in plan mode the agent is told to use tools it is not allowed to call. #3567 has the details and a no-network repro.

Changes — declare is_read_only: bool = True on TaskList and TaskGet, matching how Read and SkillViewer already mark themselves (_builtin/_read.py:126, _builtin/_skill.py:54). The base class default stays False since TaskCreate / TaskUpdate mutate state.

How to test

Regression cases added to the existing tests/permission_mode_test.py (EXPLORE suite):

• test_explore_task_readers_allow — fails on main (<PermissionBehavior.DENY> != <PermissionBehavior.ALLOW> : TaskList should be allowed in EXPLORE), passes with this fix;
• test_explore_task_writers_deny — pins that TaskCreate / TaskUpdate stay denied, guarding against overcorrecting.

python -m pytest tests/permission_mode_test.py tests/permission_engine_test.py tests/task_tool_test.py tests/toolkit_task_test.py
# 75 passed.

Checklist

• An issue has been created for this PR
• I have read the CONTRIBUTING.md
• Docstrings are in Google style
• Related documentation has been updated (e.g. links, examples, etc.) in documentation repository
• Code is ready for review