fix(provider): drop top-level schema composition for Anthropic MCP tools

[vrutkovs]

Issue for this PR

Closes #37916

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Applies the same approach as in #32489 to Anthropic models.

How did you verify your code works?

• bun test test/provider/transform.test.ts --timeout 30000
• bun run typecheck
• Push hook also ran bun turbo typecheck successfully
• Manual verification via nix install

Screenshots / recordings

Non-UI change

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[TomasEkeli]

Dropping the keywords fixes the API error but leaves some tools undocumented to the model. The real-world case that led me here is the hosted Notion MCP, whose notion-create-attachment tool has a pure top-level anyOf: three branches and no top-level properties at all (makenotion/notion-mcp-server#340). After the drop the model sees {"type": "object"} and has to guess every argument.

Suggestion: merge the branches instead of dropping them.

• properties: union across branches (first definition wins on collision)
• required: intersection for anyOf/oneOf, union for allOf
• append the valid combinations to the description, e.g. Exactly one of these parameter combinations must be provided: filename + content; or filename + source_url; or source_file_id.

I run this as a local sanitizing proxy today and the merged schema works well with Anthropic models; the description line is enough for the model to pick a valid branch. I can send the merge logic as a follow-up if this PR wants to stay minimal.

[vrutkovs]

merge the branches instead of dropping them

Iiuc this needs to be applied to every provider as well? That would be a change of scope in this PR, so I'd prefer this to be implemented in a separate PR

[TomasEkeli]

Totally valid.