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/session-management.test.ts

@@ -73,10 +73,11 @@ describe('MCP Session Management', { timeout: 15000 }, () => {
       const serverInfo = await client.getServerVersion();
       expect(serverInfo).toBeDefined();
       expect(serverInfo?.name).toBe('n8n-documentation-mcp');
-      
-      // Check capabilities if they exist
-      if (serverInfo?.capabilities) {
-        expect(serverInfo.capabilities).toHaveProperty('tools');
+
+      // Check capabilities via the dedicated method
+      const capabilities = client.getServerCapabilities();
+      if (capabilities) {
+        expect(capabilities).toHaveProperty('tools');
       }
       
       // Clean up - ensure proper order
@@ -340,9 +341,9 @@ describe('MCP Session Management', { timeout: 15000 }, () => {
     it('should handle different client versions', async () => {
       const mcpServer = new TestableN8NMCPServer();
       await mcpServer.initialize();
-      
-      const clients = [];
 
+      // MCP SDK 1.27+ enforces single-connection per Server instance,
+      // so we test each version sequentially rather than concurrently.
       for (const version of ['1.0.0', '1.1.0', '2.0.0']) {
         const [serverTransport, clientTransport] = InMemoryTransport.createLinkedPair();
         await mcpServer.connectToTransport(serverTransport);
@@ -353,21 +354,14 @@ describe('MCP Session Management', { timeout: 15000 }, () => {
         }, {});
 
         await client.connect(clientTransport);
-        clients.push(client);
+
+        const info = await client.getServerVersion();
+        expect(info!.name).toBe('n8n-documentation-mcp');
+
+        await client.close();
+        await new Promise(resolve => setTimeout(resolve, 50));
       }
 
-      // All versions should work
-      const responses = await Promise.all(
-        clients.map(client => client.getServerVersion())
-      );
-
-      responses.forEach(info => {
-        expect(info!.name).toBe('n8n-documentation-mcp');
-      });
-      
-      // Clean up
-      await Promise.all(clients.map(client => client.close()));
-      await new Promise(resolve => setTimeout(resolve, 100)); // Give time for all clients to fully close
       await mcpServer.close();
     });
   });