fix: ensure tool inputSchema includes type: "object" for non-object Zod schemas

z.toJSONSchema() on z.discriminatedUnion() produces { oneOf: [...] }
without a top-level type field. The MCP protocol requires
inputSchema.type === "object" (spec.types.ts), so clients that
validate the tools/list response reject discriminated union schemas.

Since discriminated unions are always unions of object types (each
variant shares a discriminator key), type: "object" is semantically
correct at the top level. Spreading it before the schema output
is a no-op for z.object() (already has type) and adds the required
field for unions, intersections, etc.

Fixes: #1643

Author: MayCXC

packages/server/src/server/mcp.ts

@@ -147,7 +147,7 @@ export class McpServer {
                             title: tool.title,
                             description: tool.description,
                             inputSchema: tool.inputSchema
-                                ? (schemaToJson(tool.inputSchema, { io: 'input' }) as Tool['inputSchema'])
+                                ? ({ type: 'object' as const, ...schemaToJson(tool.inputSchema, { io: 'input' }) } as Tool['inputSchema'])
                                 : EMPTY_OBJECT_JSON_SCHEMA,
                             annotations: tool.annotations,
                             execution: tool.execution,