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>

src/database/shared-database.ts

@@ -11,6 +11,7 @@
  * Issue: https://github.com/czlonkowski/n8n-mcp/issues/XXX
  */
 
+import path from 'path';
 import { DatabaseAdapter, createDatabaseAdapter } from './database-adapter';
 import { NodeRepository } from './node-repository';
 import { TemplateService } from '../templates/template-service';
@@ -43,21 +44,26 @@ let initializationPromise: Promise<SharedDatabaseState> | null = null;
  * @returns Shared database state with connection and services
  */
 export async function getSharedDatabase(dbPath: string): Promise<SharedDatabaseState> {
+  // Normalize to a canonical absolute path so that callers using different
+  // relative or join-based paths (e.g. "./data/nodes.db" vs an absolute path)
+  // resolve to the same string and do not trigger a false "different path" error.
+  const normalizedPath = dbPath === ':memory:' ? dbPath : path.resolve(dbPath);
+
   // If already initialized with the same path, increment ref count and return
-  if (sharedState && sharedState.initialized && sharedState.dbPath === dbPath) {
+  if (sharedState && sharedState.initialized && sharedState.dbPath === normalizedPath) {
     sharedState.refCount++;
     logger.debug('Reusing shared database connection', {
       refCount: sharedState.refCount,
-      dbPath
+      dbPath: normalizedPath
     });
     return sharedState;
   }
 
   // If already initialized with a DIFFERENT path, this is a configuration error
-  if (sharedState && sharedState.initialized && sharedState.dbPath !== dbPath) {
+  if (sharedState && sharedState.initialized && sharedState.dbPath !== normalizedPath) {
     logger.error('Attempted to initialize shared database with different path', {
       existingPath: sharedState.dbPath,
-      requestedPath: dbPath
+      requestedPath: normalizedPath
     });
     throw new Error(`Shared database already initialized with different path: ${sharedState.dbPath}`);
   }
@@ -69,7 +75,7 @@ export async function getSharedDatabase(dbPath: string): Promise<SharedDatabaseS
       state.refCount++;
       logger.debug('Reusing shared database (waited for init)', {
         refCount: state.refCount,
-        dbPath
+        dbPath: normalizedPath
       });
       return state;
     } catch (error) {
@@ -80,7 +86,7 @@ export async function getSharedDatabase(dbPath: string): Promise<SharedDatabaseS
   }
 
   // Start new initialization
-  initializationPromise = initializeSharedDatabase(dbPath);
+  initializationPromise = initializeSharedDatabase(normalizedPath);
 
   try {
     const state = await initializationPromise;