fix: parse JSON string messages in send_message_to_user

[whatevertogo]

Fixes #7961

CronJob-triggered send_message_to_user calls can receive messages as a JSON string when some providers serialize a multiline message array inside the tool arguments. The tool previously rejected that value before building the message chain.

Modifications / 改动点

• Parse messages with json.loads() when the value arrives as a string, then keep the existing list/object validation path.

• Add regression coverage for JSON-string message arrays, multiline text preservation, and invalid JSON strings.

• This is NOT a breaking change. / 这不是一个破坏性变更。

Screenshots or Test Results / 运行截图或测试结果

uv run pytest tests/unit/test_message_tools.py
# 9 passed

uv run ruff check astrbot/core/tools/message_tools.py tests/unit/test_message_tools.py
# All checks passed!

uv run ruff format --check astrbot/core/tools/message_tools.py tests/unit/test_message_tools.py
# 2 files already formatted

---

Checklist / 检查清单

• If there are new features added in the PR, I have discussed it with the authors through issues/emails, etc. / 如果 PR 中有新加入的功能，已经通过 Issue / 邮件等方式和作者讨论过。
• My changes have been well-tested, and "Verification Steps" and "Screenshots" have been provided above. / 我的更改经过了良好的测试，并已在上方提供了“验证步骤”和“运行截图”。
• I have ensured that no new dependencies are introduced, OR if new dependencies are introduced, they have been added to the appropriate locations in requirements.txt and pyproject.toml. / 我确保没有引入新依赖库，或者引入了新依赖库的同时将其添加到 requirements.txt 和 pyproject.toml 文件相应位置。
• My changes do not introduce malicious code. / 我的更改没有引入恶意代码。

Summary by Sourcery

Handle JSON-string message payloads in send_message_to_user and add regression tests for this behavior.

Bug Fixes:

• Allow send_message_to_user to accept messages provided as a JSON string by deserializing them before validation, while still rejecting empty or invalid payloads.

Tests:

• Add tests covering JSON-string message arrays, preservation of multiline text after parsing, and error handling for invalid JSON strings.

[gemini-code-assist]

Code Review

This pull request implements a recovery mechanism for the messages parameter in message_tools.py, allowing it to handle JSON-serialized strings produced by certain LLMs. Corresponding unit tests were added to ensure robustness against valid and invalid JSON inputs. Feedback focuses on refining the exception handling by removing a redundant TypeError and improving code style by moving a local import in the test suite to the top of the file to comply with PEP 8.

[sourcery-ai]

Hey - I've found 1 issue

Prompt for AI Agents

Please address the comments from this code review:

## Individual Comments

### Comment 1
<location path="astrbot/core/tools/message_tools.py" line_range="138-142" />
<code_context>
+        # Some LLMs (e.g. MiniMax) may serialize the array value as a JSON string
+        # when the text contains newlines. Try to recover.
+        # https://github.com/AstrBotDevs/AstrBot/issues/7961
+        if isinstance(messages, str):
+            try:
+                messages = json.loads(messages)
+            except (json.JSONDecodeError, TypeError):
+                pass
         if not isinstance(messages, list) or not messages:
</code_context>
<issue_to_address>
**suggestion (bug_risk):** Consider simplifying the exception handling to only catch JSONDecodeError.

Because of the preceding `isinstance(messages, str)` check, `json.loads(messages)` should not legitimately raise `TypeError`; the realistic failure is `json.JSONDecodeError`. Restricting the `except` to `json.JSONDecodeError` clarifies the intent and avoids silently hiding unexpected `TypeError`s.

```suggestion
        if isinstance(messages, str):
            try:
                messages = json.loads(messages)
            except json.JSONDecodeError:
                pass
```
</issue_to_address>

---

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[Copilot]

Pull request overview

This PR fixes send_message_to_user handling when messages arrives as a JSON-encoded string (not a list) in CronJob-triggered tool calls, restoring compatibility with providers that serialize multiline arrays as strings.

Changes:

• Parse messages with json.loads() when messages is a str, then proceed with existing validation/construction logic.
• Add unit tests covering JSON-string message arrays, multiline newline preservation, and invalid JSON-string inputs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
astrbot/core/tools/message_tools.py	Adds JSON-string parsing fallback for messages before list validation.
tests/unit/test_message_tools.py	Adds regression tests for JSON-string messages behavior and newline preservation.