MCP tool `file-download-batch-exports-create` has a top-level `anyOf` input_schema → breaks Anthropic API clients (Claude Desktop/Code)

Summary

The MCP tool file-download-batch-exports-create exposes an inputSchema whose root is an anyOf. The Anthropic Messages API rejects any tool input_schema that uses oneOf/allOf/anyOf at the top level, so this one tool breaks the entire PostHog MCP integration for Anthropic-API-backed clients (Claude Desktop, Claude Code).

Impact

Because clients send all connected tools in a single tools array, one invalid schema fails the whole request — not just calls to this tool. Every model turn 400s with:

API Error: 400 tools.N.custom.input_schema: input_schema does not support oneOf, allOf, or anyOf at the top level

In Claude Code specifically, this breaks all built-in subagents (Explore/general-purpose/Plan) that eager-load connector tools — they can't start at all. The only user-side workaround is manually blocking this single tool in connector settings. Verified against the live tool catalog on 2026-05-28: file-download-batch-exports-create is the only PostHog MCP tool with a top-level union (every sibling has an {"type":"object"} root and works fine).

Root cause

In services/mcp/src/tools/generated/batch_exports.ts:

const FileDownloadBatchExportsCreateSchema = FileDownloadBatchExportsCreateBody   // union → anyOf at root
// vs the sibling, which is object-rooted:
const FileDownloadBatchExportsRetrieveSchema = FileDownloadBatchExportsRetrieveParams.omit({ project_id: true })

FileDownloadBatchExportsCreateBody is a union type, which zod-to-json-schema renders as a top-level anyOf. (Source: products/batch_exports/mcp/tools.yaml → generated batch_exports.ts.)

Suggested fix

Guarantee that every MCP tool inputSchema has a {"type":"object"} root. For a union request body, wrap the union under a single object property, e.g.:

{ "type": "object", "properties": { "body": { "anyOf": [ ... ] } }, "required": ["body"] }

(Nested anyOf is accepted by the Anthropic API — only the top level is rejected.) A generator-level guard that wraps/flags any top-level non-object schema for MCP inputSchema would prevent this whole class of breakage.

Environment

• Client: Claude Desktop / Claude Code (Anthropic Messages API)
• Observed: 2026-05-28

Start with services/mcp/src/tools/generated/batch_exports.ts and compare the create schema with the object-rooted retrieve schema. Trace the generator input in products/batch_exports/mcp/tools.yaml and identify where MCP input schemas are emitted. Done means this tool has an object root with the union nested beneath it, without breaking the generated tool definition.