### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

Related but distinct: - #26692 / PR #29207 — fixes unresolved `$ref` in OpenAPI MCP schemas; does **not** fix inline schemas where `items`, `enum`, etc. are stripped - PR #22952 — resolves `$ref` parameters at parse time; does not change `build_input_schema` field copying

---

### What happened?

When LiteLLM registers MCP tools from an OpenAPI spec, `build_input_schema()` in `litellm/proxy/_experimental/mcp_server/openapi_to_mcp_generator.py` only copies **`type`** and **`description`** from each parameter's JSON Schema. All other schema keywords are discarded — including `items`, `enum`, `format`, `default`, nested `properties`, etc.

For query/path parameters defined as an array of strings (common OpenAPI pattern for repeatable query params), the OpenAPI spec is correct:

```json { "name": "domain", "in": "query", "required": true, "schema": { "type": "array", "items": { "type": "string" } } } ```

LiteLLM registers the MCP tool with:

```json { "domain": { "type": "array", "description": "..." } } ```

**Expected:** the full reso…