fix(waking_check): guard wake-prefix check against empty message chain

[he-yufeng]

问题

WakingCheckStage 在群聊里检查 wake-prefix 时，会无条件地访问 messages[0]：

for wake_prefix in wake_prefixes:
    if event.message_str.startswith(wake_prefix):
        if (
            not event.is_private_chat()
            and isinstance(messages[0], At)   # messages 为空时 IndexError
            ...

当 messages = event.get_messages() 为空列表时，这里会抛 IndexError: list index out of range。两种常见触发：

• wake_prefix 配成了空字符串 ""（让机器人对任何消息都唤醒），此时 message_str.startswith("") 恒为真；
• 平台适配器给出的消息带有文本（message_str）但消息段列表为空（例如某些转发 / 系统类负载）。

只要同时满足「群聊 + message_str 命中 wake_prefix + 消息段为空」，唤醒检查就会崩在 messages[0]。

修复

在 isinstance(messages[0], At) 前加一个 and messages 短路：消息段为空时不是「@ 了别人」，应当正常唤醒，而不是崩溃。改动只有一行，其余分支行为不变。

测试

新增 tests/unit/test_waking_check_stage.py，覆盖空 wake-prefix 和非空 wake-prefix 两种情况下消息段为空的场景。两个用例在改动前都会因 messages[0] 抛 IndexError，改动后通过；tests/unit/test_astr_message_event.py（78 个）保持全绿。

python -m pytest tests/unit/test_waking_check_stage.py -q   # 2 passed

Summary by Sourcery

Prevent group wake-prefix checking from crashing on events with an empty message chain.

Bug Fixes:

• Guard wake-prefix @-mention checks against empty message lists to avoid IndexError in group chats.

Tests:

• Add unit tests covering wake-prefix handling when the message text is present but the message component list is empty for both empty and non-empty prefixes.

[sourcery-ai]

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[gemini-code-assist]

Code Review

This pull request adds a safety check to ensure that the messages list is not empty before attempting to access its first element in WakingCheckStage.process. This prevents potential IndexError crashes when processing events with empty message chains. Additionally, corresponding unit tests have been introduced to verify this fix. I have no further feedback to provide.

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