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/integration/mcp-protocol/protocol-compliance.test.ts

@@ -105,21 +105,14 @@ describe('MCP Protocol Compliance', () => {
 
   describe('Message Format Validation', () => {
     it('should reject messages without method', async () => {
-      // Test by sending raw message through transport
-      const [serverTransport, clientTransport] = InMemoryTransport.createLinkedPair();
-      const testClient = new Client({ name: 'test', version: '1.0.0' }, {});
-      
-      await mcpServer.connectToTransport(serverTransport);
-      await testClient.connect(clientTransport);
-
+      // MCP SDK 1.27+ enforces single-connection per Server instance,
+      // so use the existing client from beforeEach instead of a new one.
       try {
         // This should fail as MCP SDK validates method
-        await (testClient as any).request({ method: '', params: {} });
+        await (client as any).request({ method: '', params: {} });
         expect.fail('Should have thrown an error');
       } catch (error) {
         expect(error).toBeDefined();
-      } finally {
-        await testClient.close();
       }
     });
 
@@ -250,10 +243,15 @@ describe('MCP Protocol Compliance', () => {
 
   describe('Transport Layer', () => {
     it('should handle transport disconnection gracefully', async () => {
-      const [serverTransport, clientTransport] = InMemoryTransport.createLinkedPair();
-      const testClient = new Client({ name: 'test', version: '1.0.0' }, {});
+      // Use a dedicated server instance so we don't conflict with the
+      // shared mcpServer that beforeEach already connected a transport to.
+      const dedicatedServer = new TestableN8NMCPServer();
+      await dedicatedServer.initialize();
 
-      await mcpServer.connectToTransport(serverTransport);
+      const [serverTransport, clientTransport] = InMemoryTransport.createLinkedPair();
+      await dedicatedServer.connectToTransport(serverTransport);
+
+      const testClient = new Client({ name: 'test', version: '1.0.0' }, {});
       await testClient.connect(clientTransport);
 
       // Make a request
@@ -270,6 +268,8 @@ describe('MCP Protocol Compliance', () => {
       } catch (error) {
         expect(error).toBeDefined();
       }
+
+      await dedicatedServer.close();
     });
 
     it('should handle multiple sequential connections', async () => {