Claude for Excel (Mac) does not recognize structuredContent

### What happened?

Prior to ~7/30, Claude for Excel appeared to accept structuredContent MCP responses, but past that date we are seeing MCP tool calls made via the Excel plugin universally return empty-array response data unless a content response field is provided as fallback for backwards compatibility.

Note that this is **not** the case for claude.ai overall, which continues to properly handle structuredContent. This looks like it's specific to the Office plugin, and FWIW I have only confirmed the behavior in Office for Mac (have not tested Office online or Windows desktop versions).

### What did you expect to happen?

StructuredContent responses would be handled as previously and as observed in claude.ai generally.

### Steps to reproduce

1. Install Claude for Excel plugin (Mac)
2. Connect to an MCP server which returns only structuredContent responses
3. Observe that all tool calls return empty data

### Area

Tool Discovery / Invocation

### MCP Server (if applicable)

_No response_

### Error messages or logs

```shell

```

### Additional context

_No response_