Tool title and inputSchema: what to expose when not provided? #224

See #223 (comment) for discussion.

The spec and Chromium implementation always expose the RegisteredTool#title member to JavaScript as a string (empty when not provided), never undefined (see https://crrev.com/c/7742044). We liked this because then the shape of the API is "simple" and the developer doesn't have to reason about what undefined vs "" means. The downside is that we break from MCP, where an MCP client will observe tool.title is undefined if the server doesn't provide it.

Perhaps we should treat title like inputSchema, and expose both as undefined when not provided. Although it's worth noting that this is a different kind of break from MCP, where inputSchema is required there but not in WebMCP.

/cc @beaufortfrancois @liady