feat(core): normalize nullable unions in Google tool schemas

[SunmiJJW]

Modifications / 改动点

This PR improves Google/Gemini tool schema conversion for common nullable JSON Schema unions.

本 PR 改进 Google/Gemini 工具 schema 转换，对常见 nullable JSON Schema union 做兼容归一化。

• Collapse nullable anyOf / oneOf forms such as [{type: string}, {type: null}] into a typed schema with nullable: true.
• Mark type: ["string", "null"] schemas as nullable: true while keeping the selected non-null type.
• Preserve supported metadata such as description and enum.
• Avoid forwarding unsupported default values in the converted Google schema.
• Add focused regression tests in tests/unit/test_tool_google_schema.py.
• 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

Verification:

python -m pytest tests\unit\test_tool_google_schema.py -q
...                                                                      [100%]
3 passed in 0.51s

python -m ruff check astrbot\core\agent\tool.py tests\unit\test_tool_google_schema.py
All checks passed!

python -m ruff format --check astrbot\core\agent\tool.py tests\unit\test_tool_google_schema.py
2 files already formatted

git diff --check
# no whitespace errors

Smoke output for a nullable recency enum:

{'type': 'string', 'enum': ['day', 'week', 'month', 'year'], 'nullable': True, 'description': 'Optional recency filter'}

Duplicate check:

gh pr list --repo AstrBotDevs/AstrBot --state open --limit 100 --json number,title,files,url
# One open PR (#8617) also touches astrbot/core/agent/tool.py, but only adds a FunctionTool permission field.
# It does not modify ToolSet.google_schema() or tests/unit/test_tool_google_schema.py.

Checklist / 检查清单

• 😊 No user-facing feature is added; this checklist item is N/A.
  / 未新增面向用户的功能；此项不适用。

• 👀 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

Normalize nullable union types when converting JSON Schemas to Google/Gemini tool schemas.

Enhancements:

• Collapse nullable anyOf/oneOf unions that combine a single non-null type with null into a nullable typed schema while preserving supported metadata.
• Treat schemas with type lists that include "null" as nullable while keeping the non-null type in the converted schema.
• Centralize and reuse logic for propagating only supported fields from source schemas into converted Google schemas, avoiding unsupported defaults.

Tests:

• Add regression tests covering nullable anyOf unions and type lists including null in Google tool schema conversion.

[gemini-code-assist]

Code Review

This pull request enhances the Google schema conversion logic in astrbot/core/agent/tool.py to handle anyOf and oneOf unions by collapsing them into a single nullable type when they contain only one non-null branch. It also marks list types containing "null" as nullable and adds corresponding unit tests. The reviewer suggested a code improvement to simplify the union collapsing logic and support single-element unions without null branches.

Important

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[gemini-code-assist]

We can simplify the condition and also support collapsing single-element anyOf/oneOf arrays (e.g., [{"type": "string"}]) by checking len(non_null_branches) == 1 and conditionally setting nullable only if there are other (null) branches in the union. Since Gemini does not support anyOf/oneOf at all, collapsing single-element unions to their underlying type is always a safe and beneficial normalization.

Suggested change

	if len(non_null_branches) == 1 and len(non_null_branches) < len(
	converted_branches
	):
	result = non_null_branches[0].copy()
	result["nullable"] = True
	apply_supported_fields(result, schema)
	return result
	if len(non_null_branches) == 1:
	result = non_null_branches[0].copy()
	if len(converted_branches) > 1:
	result["nullable"] = True
	apply_supported_fields(result, schema)
	return result

[sourcery-ai]

Hey - I've left some high level feedback:

• In the anyOf/oneOf handling, non-dict branches are silently dropped (if isinstance(item, dict)); if the source schema ever includes literal values or refs there, you may want to preserve those branches unchanged rather than omitting them to avoid losing parts of the schema.
• The new nullable-collapse logic only treats branches with type == "null" as the null case; if you expect schemas that encode nullability differently (e.g., via enum: [null, ...] or $ref to a null type), consider whether those should also be normalized for consistency.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In the anyOf/oneOf handling, non-dict branches are silently dropped (`if isinstance(item, dict)`); if the source schema ever includes literal values or refs there, you may want to preserve those branches unchanged rather than omitting them to avoid losing parts of the schema.
- The new nullable-collapse logic only treats branches with `type == "null"` as the null case; if you expect schemas that encode nullability differently (e.g., via `enum: [null, ...]` or `$ref` to a null type), consider whether those should also be normalized for consistency.

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