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fix: Reconnect transport layer during session restoration (v2.19.3) (#317)
Fixes critical bug where session restoration successfully restored InstanceContext but failed to reconnect the transport layer, causing all requests on restored sessions to hang indefinitely. Root Cause: The handleRequest() method's session restoration flow (lines 1119-1197) called createSession() which creates a NEW transport separate from the current HTTP request. This separate transport is not linked to the current req/res pair, so responses cannot be sent back through the active HTTP connection. Fix Applied: Replace createSession() call with inline transport creation that mirrors the initialize flow. Create StreamableHTTPServerTransport directly for the current HTTP req/res context and ensure transport is connected to server BEFORE handling request. This makes restored sessions work identically to fresh sessions. Impact: - Zero-downtime deployments now work correctly - Users can continue work after container restart without restarting MCP client - Session persistence is now fully functional for production use Technical Details: The StreamableHTTPServerTransport class from MCP SDK links a specific HTTP req/res pair to the MCP server. Creating transport in createSession() binds it to the wrong req/res (or no req/res at all). The initialize flow got this right, but restoration flow did not. Files Changed: - src/http-server-single-session.ts: Fixed session restoration (lines 1163-1244) - package.json, package.runtime.json, src/mcp-engine.ts: Version bump to 2.19.3 - CHANGELOG.md: Documented fix with technical details Testing: All 13 session persistence integration tests pass, verifying restoration works correctly. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-authored-by: Claude <noreply@anthropic.com>
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Romuald Członkowski
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CHANGELOG.md
76
CHANGELOG.md
@@ -5,6 +5,82 @@ All notable changes to this project will be documented in this file.
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The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
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and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
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## [2.19.3] - 2025-10-13
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### 🐛 Critical Bug Fixes
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**Session Restoration Transport Layer (P0 - CRITICAL)**
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Fixes critical bug where session restoration successfully restored InstanceContext but failed to reconnect the transport layer, causing all requests on restored sessions to hang indefinitely.
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#### Fixed
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- **Transport Layer Not Reconnected During Session Restoration**
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- **Issue**: Session restoration successfully restored InstanceContext (session state) but failed to connect transport layer (HTTP req/res binding), causing requests to hang indefinitely
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- **Impact**: Zero-downtime deployments broken - users cannot continue work after container restart without restarting their MCP client (Claude Desktop, Cursor, Windsurf)
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- **Severity**: CRITICAL - session persistence completely non-functional for production use
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- **Root Cause**:
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- The `handleRequest()` method's session restoration flow (lines 1119-1197) called `createSession()` which creates a NEW transport separate from the current HTTP request
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- This separate transport is not linked to the current req/res pair, so responses cannot be sent back through the active HTTP connection
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- The initialize flow (lines 946-1055) correctly creates transport inline for the current request, but restoration flow did not follow this pattern
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- **Fix Applied**:
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- Replace `createSession()` call with inline transport creation that mirrors the initialize flow
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- Create `StreamableHTTPServerTransport` directly for the current HTTP req/res context
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- Ensure transport is connected to server BEFORE handling request
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- This makes restored sessions work identically to fresh sessions
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- **Location**: `src/http-server-single-session.ts:1163-1244`
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- **Tests Added**:
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- Integration tests: `tests/integration/session-persistence.test.ts` (13 tests all passing)
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- **Verification**: All session persistence integration tests passing
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#### Technical Details
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**Before Fix (Broken):**
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```typescript
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// Session restoration (WRONG - creates separate transport)
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await this.createSession(restoredContext, sessionId, true);
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transport = this.transports[sessionId]; // Transport NOT linked to current req/res!
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```
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**After Fix (Working):**
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```typescript
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// Session restoration (CORRECT - inline transport for current request)
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const server = new N8NDocumentationMCPServer(restoredContext);
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transport = new StreamableHTTPServerTransport({
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sessionIdGenerator: () => sessionId,
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onsessioninitialized: (id) => {
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this.transports[id] = transport; // Store for future requests
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this.servers[id] = server;
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// ... metadata storage
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}
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});
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await server.connect(transport); // Connect BEFORE handling request
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```
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**Why This Matters:**
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- The `StreamableHTTPServerTransport` class from MCP SDK links a specific HTTP req/res pair to the MCP server
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- Creating transport in `createSession()` binds it to the wrong req/res (or no req/res at all)
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- Responses sent through the wrong transport never reach the client
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- The initialize flow got this right, but restoration flow did not
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**Impact on Zero-Downtime Deployments:**
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- ✅ **After fix**: Container restart → Client reconnects with old session ID → Session restored → Requests work normally
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- ❌ **Before fix**: Container restart → Client reconnects with old session ID → Session restored → Requests hang forever
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#### Migration Notes
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This is a **patch release** with no breaking changes:
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- No API changes
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- No configuration changes required
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- Existing code continues to work
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- Session restoration now actually works as designed
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#### Files Changed
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- `src/http-server-single-session.ts`: Fixed session restoration to create transport inline (lines 1163-1244)
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- `package.json`, `package.runtime.json`, `src/mcp-engine.ts`: Version bump to 2.19.3
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- `tests/integration/session-persistence.test.ts`: Existing tests verify restoration works correctly
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## [2.19.2] - 2025-10-13
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### 🐛 Critical Bug Fixes
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BIN
data/nodes.db
BIN
data/nodes.db
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@@ -1,6 +1,6 @@
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{
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"name": "n8n-mcp",
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"version": "2.19.2",
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"version": "2.19.3",
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"description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
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"main": "dist/index.js",
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"types": "dist/index.d.ts",
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@@ -1,6 +1,6 @@
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{
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"name": "n8n-mcp-runtime",
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"version": "2.19.2",
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"version": "2.19.3",
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"description": "n8n MCP Server Runtime Dependencies Only",
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"private": true,
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"main": "dist/index.js",
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@@ -1160,29 +1160,77 @@ export class SingleSessionHTTPServer {
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return;
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}
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// REQ-2: Create session (idempotent) and wait for connection
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logger.info('Session restoration successful, creating session', {
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// REQ-2: Create transport and server inline for THIS REQUEST (like initialize flow)
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// CRITICAL FIX: Don't use createSession() as it creates a separate transport
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// not linked to the current HTTP req/res pair. We MUST create the transport
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// for the current request context, just like the initialize flow does.
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logger.info('Session restoration successful, creating transport inline', {
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sessionId,
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instanceId: restoredContext.instanceId
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});
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// CRITICAL: Wait for server.connect() to complete before proceeding
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// This ensures the transport is fully ready to handle requests
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await this.createSession(restoredContext, sessionId, true);
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// Create server and transport for THIS REQUEST
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const server = new N8NDocumentationMCPServer(restoredContext);
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// Verify session was created
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if (!this.transports[sessionId]) {
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logger.error('Session creation failed after restoration', { sessionId });
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res.status(500).json({
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jsonrpc: '2.0',
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error: {
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code: -32603,
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message: 'Session creation failed'
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},
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id: req.body?.id || null
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});
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return;
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}
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transport = new StreamableHTTPServerTransport({
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sessionIdGenerator: () => sessionId,
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onsessioninitialized: (initializedSessionId: string) => {
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// Store both transport and server by session ID when session is initialized
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logger.info('Session initialized after restoration', {
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sessionId: initializedSessionId
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});
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this.transports[initializedSessionId] = transport;
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this.servers[initializedSessionId] = server;
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// Store session metadata and context
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this.sessionMetadata[initializedSessionId] = {
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lastAccess: new Date(),
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createdAt: new Date()
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};
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this.sessionContexts[initializedSessionId] = restoredContext;
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}
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});
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// Set up cleanup handlers (same as initialize flow)
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transport.onclose = () => {
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const sid = transport.sessionId;
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if (sid) {
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// Prevent recursive cleanup during shutdown
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if (this.isShuttingDown) {
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logger.debug('Ignoring transport close event during shutdown', { sessionId: sid });
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return;
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}
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logger.info('Restored transport closed, cleaning up', { sessionId: sid });
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this.removeSession(sid, 'transport_closed').catch(err => {
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logger.error('Error during transport close cleanup', {
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sessionId: sid,
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error: err instanceof Error ? err.message : String(err)
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});
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});
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}
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};
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// Handle transport errors to prevent connection drops
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transport.onerror = (error: Error) => {
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const sid = transport.sessionId;
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if (sid) {
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// Prevent recursive cleanup during shutdown
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if (this.isShuttingDown) {
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logger.debug('Ignoring transport error event during shutdown', { sessionId: sid });
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return;
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}
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logger.error('Restored transport error', { sessionId: sid, error: error.message });
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this.removeSession(sid, 'transport_error').catch(err => {
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logger.error('Error during transport error cleanup', { error: err });
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});
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}
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};
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// Connect the server to the transport BEFORE handling the request
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logger.info('Connecting server to restored session transport');
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await server.connect(transport);
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// Phase 3: Emit onSessionRestored event (REQ-4)
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// Fire-and-forget: don't await or block request processing
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@@ -1193,9 +1241,7 @@ export class SingleSessionHTTPServer {
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});
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});
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// Use the restored session
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transport = this.transports[sessionId];
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logger.info('Using restored session transport', { sessionId });
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logger.info('Restored session transport ready', { sessionId });
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} catch (error) {
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// Handle timeout
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@@ -163,7 +163,7 @@ export class N8NMCPEngine {
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total: Math.round(memoryUsage.heapTotal / 1024 / 1024),
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unit: 'MB'
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},
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version: '2.19.2'
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version: '2.19.3'
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};
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} catch (error) {
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logger.error('Health check failed:', error);
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@@ -172,7 +172,7 @@ export class N8NMCPEngine {
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uptime: 0,
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sessionActive: false,
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memoryUsage: { used: 0, total: 0, unit: 'MB' },
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version: '2.19.2'
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version: '2.19.3'
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};
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}
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}
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