test: fix failing test and add comprehensive version extraction test coverage

Address code review feedback from PR #285:

1. Fix Failing Test (CRITICAL)
   - Updated test from baseDescription.defaultVersion to description.defaultVersion
   - Added test to verify baseDescription is correctly ignored (legacy bug)

2. Add Missing Test Coverage (HIGH PRIORITY)
   - Test currentVersion priority over description.defaultVersion
   - Test currentVersion = 0 edge case (version 0 should be valid)
   - All 34 tests now passing

3. Enhanced Documentation
   - Added comprehensive JSDoc for extractVersion() explaining priority chain
   - Enhanced validation comments explaining why typeVersion must run before langchain skip
   - Clarified that parameter validation (not typeVersion) is skipped for langchain nodes

Test Results:
- ✅ 34/34 tests passing
- ✅ Version extraction priority chain validated
- ✅ Edge cases covered (version 0, missing properties)
- ✅ Legacy bug prevention tested

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

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

src/parsers/node-parser.ts

@@ -134,6 +134,24 @@ export class NodeParser {
            description.name?.toLowerCase().includes('webhook');
   }
   
+  /**
+   * Extracts the version from a node class.
+   *
+   * Priority Chain:
+   * 1. Instance currentVersion (VersionedNodeType's computed property)
+   * 2. Instance description.defaultVersion (explicit default)
+   * 3. Instance nodeVersions (fallback to max available version)
+   * 4. Description version array (legacy nodes)
+   * 5. Description version scalar (simple versioning)
+   * 6. Class-level properties (if instantiation fails)
+   * 7. Default to "1"
+   *
+   * Critical Fix (v2.17.4): Removed check for non-existent instance.baseDescription.defaultVersion
+   * which caused AI Agent to incorrectly return version "3" instead of "2.2"
+   *
+   * @param nodeClass - The node class or instance to extract version from
+   * @returns The version as a string
+   */
   private extractVersion(nodeClass: any): string {
     // Check instance properties first
     try {

src/services/workflow-validator.ts

@@ -445,7 +445,9 @@ export class WorkflowValidator {
         }
 
         // Validate typeVersion for ALL versioned nodes (including langchain nodes)
-        // This validation runs BEFORE the langchain skip to ensure typeVersion is checked
+        // CRITICAL: This MUST run BEFORE the langchain skip below!
+        // Otherwise, langchain nodes with invalid typeVersion (e.g., 99999) would pass validation
+        // but fail at runtime in n8n. This was the bug fixed in v2.17.4.
         if (nodeInfo.isVersioned) {
           // Check if typeVersion is missing
           if (!node.typeVersion) {
@@ -485,9 +487,9 @@ export class WorkflowValidator {
           }
         }
 
-        // Skip parameter validation for langchain nodes
+        // Skip PARAMETER validation for langchain nodes (but NOT typeVersion validation above!)
-        // They have dedicated AI-specific validators in validateAISpecificNodes()
+        // Langchain nodes have dedicated AI-specific validators in validateAISpecificNodes()
-        // This prevents parameter validation conflicts and ensures proper AI validation
+        // which handle their unique parameter structures (AI connections, tool ports, etc.)
         if (normalizedType.startsWith('nodes-langchain.')) {
           continue;
         }

tests/unit/parsers/node-parser.test.ts

@@ -286,20 +286,64 @@ describe('NodeParser', () => {
   });
 
   describe('version extraction', () => {
-    it('should extract version from baseDescription.defaultVersion', () => {
+    it('should prioritize currentVersion over description.defaultVersion', () => {
       const NodeClass = class {
-        baseDescription = {
+        currentVersion = 2.2;  // Should be returned
+        description = {
+          name: 'AI Agent',
+          displayName: 'AI Agent',
+          defaultVersion: 3  // Should be ignored when currentVersion exists
+        };
+      };
+
+      const result = parser.parse(NodeClass, 'n8n-nodes-base');
+
+      expect(result.version).toBe('2.2');
+    });
+
+    it('should extract version from description.defaultVersion', () => {
+      const NodeClass = class {
+        description = {
           name: 'test',
           displayName: 'Test',
           defaultVersion: 3
         };
       };
-      
+
       const result = parser.parse(NodeClass, 'n8n-nodes-base');
-      
+
       expect(result.version).toBe('3');
     });
 
+    it('should handle currentVersion = 0 correctly', () => {
+      const NodeClass = class {
+        currentVersion = 0;  // Edge case: version 0 should be valid
+        description = {
+          name: 'test',
+          displayName: 'Test',
+          defaultVersion: 5  // Should be ignored
+        };
+      };
+
+      const result = parser.parse(NodeClass, 'n8n-nodes-base');
+
+      expect(result.version).toBe('0');
+    });
+
+    it('should NOT extract version from non-existent baseDescription (legacy bug)', () => {
+      const NodeClass = class {
+        baseDescription = {  // This property doesn't exist on VersionedNodeType!
+          name: 'test',
+          displayName: 'Test',
+          defaultVersion: 3
+        };
+      };
+
+      const result = parser.parse(NodeClass, 'n8n-nodes-base');
+
+      expect(result.version).toBe('1');  // Should fallback to default
+    });
+
     it('should extract version from nodeVersions keys', () => {
       const NodeClass = class {
         description = { name: 'test', displayName: 'Test' };