fix: throw ProtocolError as JSON-RPC error for tool not found

Per MCP spec, calling a nonexistent tool should return a JSON-RPC Error
(code -32602), not a JSON-RPC Result with isError: true.

Previously, only UrlElicitationRequired errors were re-thrown; all other
ProtocolErrors (including tool/disabled checks) were swallowed and wrapped
in a CallToolResult. Now all ProtocolErrors propagate as JSON-RPC errors,
which is the correct behavior per the specification.

Fixes #1510

Author: User

packages/server/src/server/mcp.ts

@@ -213,8 +213,9 @@ export class McpServer {
                 await this.validateToolOutput(tool, result, request.params.name);
                 return result;
             } catch (error) {
-                if (error instanceof ProtocolError && error.code === ProtocolErrorCode.UrlElicitationRequired) {
-                    throw error; // Return the error to the caller without wrapping in CallToolResult
+                if (error instanceof ProtocolError) {
+                    // Protocol errors should be returned as JSON-RPC errors, not wrapped in CallToolResult
+                    throw error;
                 }
                 return this.createToolError(error instanceof Error ? error.message : String(error));
             }

test/integration/test/server/mcp.test.ts

@@ -1837,25 +1837,17 @@ describe('Zod v4', () => {
 
             await Promise.all([client.connect(clientTransport), mcpServer.server.connect(serverTransport)]);
 
-            const result = await client.request(
-                {
-                    method: 'tools/call',
-                    params: {
-                        name: 'nonexistent-tool'
-                    }
-                },
-                CallToolResultSchema
-            );
-
-            expect(result.isError).toBe(true);
-            expect(result.content).toEqual(
-                expect.arrayContaining([
+            await expect(
+                client.request(
                     {
-                        type: 'text',
-                        text: expect.stringContaining('Tool nonexistent-tool not found')
-                    }
-                ])
-            );
+                        method: 'tools/call',
+                        params: {
+                            name: 'nonexistent-tool'
+                        }
+                    },
+                    CallToolResultSchema
+                )
+            ).rejects.toThrow(/Tool nonexistent-tool not found/);
         });
 
         /***