fix: use nullish coalescing to preserve zero values in MCP config defaults

- Replace logical OR (||) with nullish coalescing (??) in CLIMcpService
- Fixes bug where intentional zero values (timeout: 0, retryAttempts: 0, etc.) were overridden with defaults
- Add comprehensive test to verify zero values are preserved while undefined values get defaults
- Addresses code reviewer feedback about proper default value handling

Author: Eric Oliver

src/cli/services/CLIMcpService.ts

@@ -273,10 +273,10 @@ export class CLIMcpService implements ICLIMcpService {
 
 			return configFile.servers.map((server) => ({
 				...server,
-				timeout: server.timeout || this.defaults.timeout,
-				retryAttempts: server.retryAttempts || this.defaults.retryAttempts,
-				retryDelay: server.retryDelay || this.defaults.retryDelay,
-				healthCheckInterval: server.healthCheckInterval || this.defaults.healthCheckInterval,
+				timeout: server.timeout ?? this.defaults.timeout,
+				retryAttempts: server.retryAttempts ?? this.defaults.retryAttempts,
+				retryDelay: server.retryDelay ?? this.defaults.retryDelay,
+				healthCheckInterval: server.healthCheckInterval ?? this.defaults.healthCheckInterval,
 			}))
 		} catch (error) {
 			if (error.code === "ENOENT") {

src/cli/services/__tests__/CLIMcpService.test.ts

@@ -112,6 +112,55 @@ describe("CLIMcpService", () => {
 			// Should try home directory config
 			expect(mockFs.readFile).toHaveBeenCalledWith(path.join(os.homedir(), ".roo", "mcp-config.json"), "utf-8")
 		})
+		it("should preserve zero values and not replace them with defaults", async () => {
+			const mockConfig = {
+				version: "1.0.0",
+				servers: [
+					{
+						id: "test-server-zero-values",
+						name: "Test Server with Zero Values",
+						type: "stdio" as const,
+						enabled: true,
+						command: "test-command",
+						timeout: 0, // Intentionally set to 0
+						retryAttempts: 0, // Intentionally set to 0
+						retryDelay: 0, // Intentionally set to 0
+						healthCheckInterval: 0, // Intentionally set to 0
+					},
+					{
+						id: "test-server-undefined-values",
+						name: "Test Server with Undefined Values",
+						type: "stdio" as const,
+						enabled: true,
+						command: "test-command",
+						// No timeout, retryAttempts, retryDelay, healthCheckInterval - should use defaults
+					},
+				],
+				defaults: DEFAULT_MCP_CONFIG,
+			}
+
+			mockFs.readFile.mockResolvedValue(JSON.stringify(mockConfig))
+
+			const configs = await service.loadServerConfigs("/test/config.json")
+
+			expect(configs).toHaveLength(2)
+
+			// First server should preserve zero values
+			const zeroValueServer = configs[0]
+			expect(zeroValueServer.id).toBe("test-server-zero-values")
+			expect(zeroValueServer.timeout).toBe(0)
+			expect(zeroValueServer.retryAttempts).toBe(0)
+			expect(zeroValueServer.retryDelay).toBe(0)
+			expect(zeroValueServer.healthCheckInterval).toBe(0)
+
+			// Second server should use defaults for undefined values
+			const undefinedValueServer = configs[1]
+			expect(undefinedValueServer.id).toBe("test-server-undefined-values")
+			expect(undefinedValueServer.timeout).toBe(DEFAULT_MCP_CONFIG.timeout)
+			expect(undefinedValueServer.retryAttempts).toBe(DEFAULT_MCP_CONFIG.retryAttempts)
+			expect(undefinedValueServer.retryDelay).toBe(DEFAULT_MCP_CONFIG.retryDelay)
+			expect(undefinedValueServer.healthCheckInterval).toBe(DEFAULT_MCP_CONFIG.healthCheckInterval)
+		})
 	})
 
 	describe("validateServerConfig", () => {