fix: raise session timeout default, fix VS Code MCP compatibility (#674)

* fix: raise session timeout default and fix VS Code MCP compatibility (#626, #600, #611)

- #626: Raise SESSION_TIMEOUT_MINUTES default from 5 to 30 minutes.
  Complex editing sessions easily exceed 5 min between LLM calls.

- #600: Add z.preprocess(tryParseJson, ...) to operations parameter
  in n8n_update_partial_workflow. VS Code extension sends arrays as
  JSON strings.

- #611: Strip undefined values from tool args via JSON round-trip
  before Zod validation. VS Code sends explicit undefined which
  Zod's .optional() rejects.

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refactor: deduplicate tryParseJson — export from handlers-n8n-manager

tryParseJson was duplicated in handlers-workflow-diff.ts. Now imported
from handlers-n8n-manager.ts where it was already defined. Updated
test mock to use importOriginal so the real function is available.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/http-server-single-session.ts

@@ -107,11 +107,10 @@ export class SingleSessionHTTPServer {
   private session: Session | null = null;  // Keep for SSE compatibility
   private consoleManager = new ConsoleManager();
   private expressServer: any;
-  // Session timeout reduced from 30 minutes to 5 minutes for faster cleanup
-  // Configurable via SESSION_TIMEOUT_MINUTES environment variable
-  // This prevents memory buildup from stale sessions
+  // Session timeout — configurable via SESSION_TIMEOUT_MINUTES environment variable
+  // Default 30 minutes: balances memory cleanup with real editing sessions (#626)
   private sessionTimeout = parseInt(
-    process.env.SESSION_TIMEOUT_MINUTES || '5', 10
+    process.env.SESSION_TIMEOUT_MINUTES || '30', 10
   ) * 60 * 1000;
   private authToken: string | null = null;
   private cleanupTimer: NodeJS.Timeout | null = null;

src/mcp/handlers-n8n-manager.ts

@@ -2731,7 +2731,7 @@ const updateTableSchema = tableIdSchema.extend({
 
 // MCP transports may serialize JSON objects/arrays as strings.
 // Parse them back, but return the original value on failure so Zod reports a proper type error.
-function tryParseJson(val: unknown): unknown {
+export function tryParseJson(val: unknown): unknown {
   if (typeof val !== 'string') return val;
   try { return JSON.parse(val); } catch { return val; }
 }

src/mcp/handlers-workflow-diff.ts

@@ -7,7 +7,7 @@ import { z } from 'zod';
 import { McpToolResponse } from '../types/n8n-api';
 import { WorkflowDiffRequest, WorkflowDiffOperation, WorkflowDiffValidationError } from '../types/workflow-diff';
 import { WorkflowDiffEngine } from '../services/workflow-diff-engine';
-import { getN8nApiClient } from './handlers-n8n-manager';
+import { getN8nApiClient, tryParseJson } from './handlers-n8n-manager';
 import { N8nApiError, getUserFriendlyErrorMessage } from '../utils/n8n-errors';
 import { logger } from '../utils/logger';
 import { InstanceContext } from '../types/instance-context';
@@ -39,7 +39,7 @@ const NODE_TARGETING_OPERATIONS = new Set([
 // Zod schema for the diff request
 const workflowDiffSchema = z.object({
   id: z.string(),
-  operations: z.array(z.object({
+  operations: z.preprocess(tryParseJson, z.array(z.object({
     type: z.string(),
     description: z.string().optional(),
     // Node operations
@@ -87,7 +87,7 @@ const workflowDiffSchema = z.object({
       }
     }
     return op;
-  })),
+  }))),
   validateOnly: z.boolean().optional(),
   continueOnError: z.boolean().optional(),
   createBackup: z.boolean().optional(),

src/mcp/server.ts

@@ -748,6 +748,13 @@ export class N8NDocumentationMCPServer {
       // tool's inputSchema as the source of truth.
       processedArgs = this.coerceStringifiedJsonParams(name, processedArgs);
 
+      // Strip undefined values from args (#611) — VS Code extension sends
+      // explicit undefined values which Zod's .optional() rejects.
+      // Removing them makes Zod treat them as missing (which .optional() allows).
+      if (processedArgs) {
+        processedArgs = JSON.parse(JSON.stringify(processedArgs));
+      }
+
       try {
         logger.debug(`Executing tool: ${name}`, { args: processedArgs });
         const startTime = Date.now();