fix: resolve multiple n8n_update_partial_workflow bugs (#635)

* fix: use correct MCP SDK API for server capabilities in test

getServerVersion() returns Implementation (name/version only), not the
full init result. Use client.getServerCapabilities() instead to access
server capabilities, fixing the CI typecheck failure.

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

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

* fix: resolve multiple n8n_update_partial_workflow bugs (#592, #599, #610, #623, #624, #625, #629, #630, #633)

Phase 1 - Data loss prevention:
- Add missing unary operators (empty, notEmpty, exists, notExists) to sanitizer (#592)
- Preserve positional empty arrays in connections during removeNode/cleanStale (#610)
- Scope sanitization to modified nodes only, preventing unrelated node corruption
- Add empty body {} to activate/deactivate POST calls to fix 415 errors (#633)

Phase 2 - Error handling & response clarity:
- Serialize Zod errors to readable "path: message" strings (#630)
- Add saved:true/false field to all response paths (#625)
- Improve updateNode error hint with correct structure example (#623)
- Track removed node names for better removeConnection errors (#624)

Phase 3 - Connection & type fixes:
- Coerce sourceOutput/targetInput to String() consistently (#629)
- Accept numeric sourceOutput/targetInput at Zod schema level via transform

Phase 4 - Tag operations via dedicated API (#599):
- Track tags as tagsToAdd/tagsToRemove instead of mutating workflow.tags
- Orchestrate tag creation and association via listTags/createTag/updateWorkflowTags
- Reconcile conflicting add/remove for same tag (last operation wins)
- Tag failures produce warnings, not hard errors

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

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

* docs: add v2.37.0 changelog entry

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

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

* fix: resolve pre-existing integration test failures in CI

- Create new MCP Server instance per connection in test helpers (SDK 1.27+
  requires separate Protocol instance per connection)
- Normalize database paths with path.resolve() in shared-database singleton
  to prevent path mismatch errors across test files
- Add no-op catch handler to deferred initialization promise in server.ts
  to prevent unhandled rejection warnings
- Properly call mcpServer.shutdown() in test helper close() to release
  shared database references

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

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

---------

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

tests/unit/services/workflow-diff-engine.test.ts

@@ -424,7 +424,7 @@ describe('WorkflowDiffEngine', () => {
 
       expect(result.success).toBe(false);
       expect(result.errors![0].message).toContain('Missing required parameter \'updates\'');
-      expect(result.errors![0].message).toContain('Example:');
+      expect(result.errors![0].message).toContain('Correct structure:');
     });
   });
 
@@ -1898,16 +1898,15 @@ describe('WorkflowDiffEngine', () => {
       };
 
       const result = await diffEngine.applyDiff(baseWorkflow, request);
-      
+
       expect(result.success).toBe(true);
-      expect(result.workflow!.tags).toContain('production');
-      expect(result.workflow!.tags).toHaveLength(3);
+      expect(result.tagsToAdd).toContain('production');
     });
 
     it('should not add duplicate tags', async () => {
       const operation: AddTagOperation = {
         type: 'addTag',
-        tag: 'test' // Already exists
+        tag: 'test' // Already exists in workflow but tagsToAdd tracks it for API
       };
 
       const request: WorkflowDiffRequest = {
@@ -1916,9 +1915,10 @@ describe('WorkflowDiffEngine', () => {
       };
 
       const result = await diffEngine.applyDiff(baseWorkflow, request);
-      
+
       expect(result.success).toBe(true);
-      expect(result.workflow!.tags).toHaveLength(2); // No change
+      // Tags are now tracked for dedicated API call, not modified on workflow
+      expect(result.tagsToAdd).toEqual(['test']);
     });
 
     it('should create tags array if not exists', async () => {
@@ -1935,10 +1935,9 @@ describe('WorkflowDiffEngine', () => {
       };
 
       const result = await diffEngine.applyDiff(baseWorkflow, request);
-      
+
       expect(result.success).toBe(true);
-      expect(result.workflow!.tags).toBeDefined();
-      expect(result.workflow!.tags).toEqual(['new-tag']);
+      expect(result.tagsToAdd).toEqual(['new-tag']);
     });
 
     it('should remove an existing tag', async () => {
@@ -1953,10 +1952,9 @@ describe('WorkflowDiffEngine', () => {
       };
 
       const result = await diffEngine.applyDiff(baseWorkflow, request);
-      
+
       expect(result.success).toBe(true);
-      expect(result.workflow!.tags).not.toContain('test');
-      expect(result.workflow!.tags).toHaveLength(1);
+      expect(result.tagsToRemove).toContain('test');
     });
 
     it('should handle removing non-existent tag gracefully', async () => {
@@ -1971,9 +1969,11 @@ describe('WorkflowDiffEngine', () => {
       };
 
       const result = await diffEngine.applyDiff(baseWorkflow, request);
-      
+
       expect(result.success).toBe(true);
-      expect(result.workflow!.tags).toHaveLength(2); // No change
+      expect(result.tagsToRemove).toEqual(['non-existent']);
+      // workflow.tags unchanged since tags are now handled via dedicated API
+      expect(result.workflow!.tags).toHaveLength(2);
     });
   });
 
@@ -2509,7 +2509,7 @@ describe('WorkflowDiffEngine', () => {
         expect(result.failed).toEqual([1]); // Operation 1 failed
         expect(result.errors).toHaveLength(1);
         expect(result.workflow.name).toBe('New Workflow Name');
-        expect(result.workflow.tags).toContain('production');
+        expect(result.tagsToAdd).toContain('production');
       });
 
       it('should return success false if all operations fail in continueOnError mode', async () => {
@@ -3356,7 +3356,7 @@ describe('WorkflowDiffEngine', () => {
         expect(result.failed).toContain(1); // replaceConnections with invalid node
         expect(result.applied).toContain(2); // removeConnection with ignoreErrors
         expect(result.applied).toContain(3); // addTag
-        expect(result.workflow.tags).toContain('final-tag');
+        expect(result.tagsToAdd).toContain('final-tag');
       });
     });
 
@@ -4610,7 +4610,7 @@ describe('WorkflowDiffEngine', () => {
       expect(result.success).toBe(true);
       expect(result.operationsApplied).toBe(3);
       expect(result.workflow!.name).toBe('Updated Workflow Name');
-      expect(result.workflow!.tags).toContain('production');
+      expect(result.tagsToAdd).toContain('production');
       expect(result.shouldActivate).toBe(true);
     });