fix: AI node connection validation in partial workflow updates (#357) (#358)

* fix: AI node connection validation in partial workflow updates (#357)

Fix critical validation issue where n8n_update_partial_workflow incorrectly
required 'main' connections for AI nodes that exclusively use AI-specific
connection types (ai_languageModel, ai_memory, ai_embedding, ai_vectorStore, ai_tool).

Problem:
- Workflows containing AI nodes could not be updated via n8n_update_partial_workflow
- Validation incorrectly expected ALL nodes to have 'main' connections
- AI nodes only have AI-specific connection types, never 'main'

Root Cause:
- Zod schema in src/services/n8n-validation.ts defined 'main' as required field
- Schema didn't support AI-specific connection types

Fixed:
- Made 'main' connection optional in Zod schema
- Added support for all AI connection types: ai_tool, ai_languageModel, ai_memory,
  ai_embedding, ai_vectorStore
- Created comprehensive test suite (13 tests) covering all AI connection scenarios
- Updated documentation to clarify AI nodes don't require 'main' connections

Testing:
- All 13 new integration tests passing
- Tested with actual workflow 019Vrw56aROeEzVj from issue #357
- Zero breaking changes (making required fields optional is always safe)

Files Changed:
- src/services/n8n-validation.ts - Fixed Zod schema
- tests/integration/workflow-diff/ai-node-connection-validation.test.ts - New test suite
- src/mcp/tool-docs/workflow_management/n8n-update-partial-workflow.ts - Updated docs
- package.json - Version bump to 2.21.1
- CHANGELOG.md - Comprehensive release notes

Closes #357

🤖 Generated with Claude Code (https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

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

* fix: Add missing id parameter in test file and JSDoc comment

Address code review feedback from PR #358:
- Add 'id' field to all applyDiff calls in test file (fixes TypeScript errors)
- Add JSDoc comment explaining why 'main' is optional in schema
- Ensures TypeScript compilation succeeds

Changes:
- tests/integration/workflow-diff/ai-node-connection-validation.test.ts:
  Added id parameter to all 13 test cases
- src/services/n8n-validation.ts:
  Added JSDoc explaining optional main connections

Testing:
- npm run typecheck: PASS ✅
- npm run build: PASS ✅
- All 13 tests: PASS ✅

🤖 Generated with Claude Code (https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/services/n8n-validation.ts

@@ -24,17 +24,31 @@ export const workflowNodeSchema = z.object({
   executeOnce: z.boolean().optional(),
 });
 
+// Connection array schema used by all connection types
+const connectionArraySchema = z.array(
+  z.array(
+    z.object({
+      node: z.string(),
+      type: z.string(),
+      index: z.number(),
+    })
+  )
+);
+
+/**
+ * Workflow connection schema supporting all connection types.
+ * Note: 'main' is optional because AI nodes exclusively use AI-specific
+ * connection types (ai_languageModel, ai_memory, etc.) without main connections.
+ */
 export const workflowConnectionSchema = z.record(
   z.object({
-    main: z.array(
-      z.array(
-        z.object({
-          node: z.string(),
-          type: z.string(),
-          index: z.number(),
-        })
-      )
-    ),
+    main: connectionArraySchema.optional(),
+    error: connectionArraySchema.optional(),
+    ai_tool: connectionArraySchema.optional(),
+    ai_languageModel: connectionArraySchema.optional(),
+    ai_memory: connectionArraySchema.optional(),
+    ai_embedding: connectionArraySchema.optional(),
+    ai_vectorStore: connectionArraySchema.optional(),
   })
 );