mirror of
https://github.com/czlonkowski/n8n-mcp.git
synced 2026-03-23 19:03:07 +00:00
feat: Add Session Lifecycle Events and Retry Policy (Phase 3 + 4)
Implements Phase 3 (Session Lifecycle Events - REQ-4) and Phase 4 (Retry Policy - REQ-7) for v2.19.0 session persistence feature. Phase 3 - Session Lifecycle Events (REQ-4): - Added 5 lifecycle event callbacks: onSessionCreated, onSessionRestored, onSessionAccessed, onSessionExpired, onSessionDeleted - Fire-and-forget pattern: non-blocking, errors don't affect operations - Supports both sync and async handlers - Events emitted at 5 key lifecycle points Phase 4 - Retry Policy (REQ-7): - Configurable retry logic with sessionRestorationRetries and sessionRestorationRetryDelay - Overall timeout applies to ALL retry attempts combined - Timeout errors are never retried (already took too long) - Smart error handling with comprehensive logging Features: - Backward compatible: all new options are optional with sensible defaults - Type-safe interfaces with comprehensive JSDoc documentation - Security: session ID validation before restoration attempts - Performance: non-blocking events, efficient retry logic - Observability: structured logging at all critical points Files modified: - src/types/session-restoration.ts: Added SessionLifecycleEvents interface and retry options - src/http-server-single-session.ts: Added emitEvent() and restoreSessionWithRetry() methods - src/mcp-engine.ts: Added sessionEvents and retry options to EngineOptions - CHANGELOG.md: Comprehensive v2.19.0 release documentation Tests: - 34 unit tests passing (14 lifecycle events + 20 retry policy) - Integration tests created for combined behavior - Code reviewed and approved (9.3/10 rating) - MCP server tested and verified working 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
This commit is contained in:
czlonkowski
@@ -25,7 +25,7 @@ import {
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STANDARD_PROTOCOL_VERSION
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} from './utils/protocol-version';
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import { InstanceContext, validateInstanceContext } from './types/instance-context';
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import { SessionRestoreHook, SessionState } from './types/session-restoration';
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import { SessionRestoreHook, SessionState, SessionLifecycleEvents } from './types/session-restoration';
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dotenv.config();
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@@ -90,10 +90,20 @@ export class SingleSessionHTTPServer {
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private onSessionNotFound?: SessionRestoreHook;
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private sessionRestorationTimeout: number;
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// Session lifecycle events (Phase 3 - v2.19.0)
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private sessionEvents?: SessionLifecycleEvents;
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// Retry policy (Phase 4 - v2.19.0)
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private sessionRestorationRetries: number;
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private sessionRestorationRetryDelay: number;
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constructor(options: {
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sessionTimeout?: number;
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onSessionNotFound?: SessionRestoreHook;
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sessionRestorationTimeout?: number;
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sessionEvents?: SessionLifecycleEvents;
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sessionRestorationRetries?: number;
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sessionRestorationRetryDelay?: number;
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} = {}) {
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// Validate environment on construction
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this.validateEnvironment();
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@@ -102,6 +112,13 @@ export class SingleSessionHTTPServer {
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this.onSessionNotFound = options.onSessionNotFound;
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this.sessionRestorationTimeout = options.sessionRestorationTimeout || 5000; // 5 seconds default
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// Lifecycle events configuration
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this.sessionEvents = options.sessionEvents;
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// Retry policy configuration
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this.sessionRestorationRetries = options.sessionRestorationRetries ?? 0; // Default: no retries
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this.sessionRestorationRetryDelay = options.sessionRestorationRetryDelay || 100; // Default: 100ms
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// Override session timeout if provided
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if (options.sessionTimeout) {
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this.sessionTimeout = options.sessionTimeout;
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@@ -177,6 +194,15 @@ export class SingleSessionHTTPServer {
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// Remove expired sessions
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for (const sessionId of expiredSessions) {
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// Phase 3: Emit onSessionExpired event BEFORE removal (REQ-4)
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// Fire-and-forget: don't await or block cleanup
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this.emitEvent('onSessionExpired', sessionId).catch(err => {
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logger.error('Failed to emit onSessionExpired event (non-blocking)', {
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sessionId,
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error: err instanceof Error ? err.message : String(err)
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});
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});
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this.removeSession(sessionId, 'expired');
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}
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@@ -313,6 +339,16 @@ export class SingleSessionHTTPServer {
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private updateSessionAccess(sessionId: string): void {
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if (this.sessionMetadata[sessionId]) {
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this.sessionMetadata[sessionId].lastAccess = new Date();
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// Phase 3: Emit onSessionAccessed event (REQ-4)
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// Fire-and-forget: don't await or block request processing
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// IMPORTANT: This fires on EVERY request - implement throttling in your handler!
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this.emitEvent('onSessionAccessed', sessionId).catch(err => {
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logger.error('Failed to emit onSessionAccessed event (non-blocking)', {
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sessionId,
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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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@@ -382,6 +418,133 @@ export class SingleSessionHTTPServer {
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});
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}
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/**
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* Emit a session lifecycle event (Phase 3 - REQ-4)
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* Errors in event handlers are logged but don't break session operations
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*
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* @param eventName - The event to emit
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* @param args - Arguments to pass to the event handler
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* @since 2.19.0
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*/
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private async emitEvent(
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eventName: keyof SessionLifecycleEvents,
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...args: [string, InstanceContext?]
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): Promise<void> {
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const handler = this.sessionEvents?.[eventName] as (((...args: any[]) => void | Promise<void>) | undefined);
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if (!handler) return;
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try {
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// Support both sync and async handlers
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await Promise.resolve(handler(...args));
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} catch (error) {
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logger.error(`Session event handler failed: ${eventName}`, {
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error: error instanceof Error ? error.message : String(error),
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sessionId: args[0] // First arg is always sessionId
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});
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// DON'T THROW - event failures shouldn't break session operations
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}
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}
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/**
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* Restore session with retry policy (Phase 4 - REQ-7)
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*
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* Attempts to restore a session using the onSessionNotFound hook,
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* with configurable retry logic for transient failures.
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*
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* Timeout applies to ALL attempts combined (not per attempt).
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* Timeout errors are never retried.
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*
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* @param sessionId - Session ID to restore
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* @returns Restored instance context or null
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* @throws TimeoutError if overall timeout exceeded
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* @throws Error from hook if all retry attempts failed
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* @since 2.19.0
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*/
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private async restoreSessionWithRetry(sessionId: string): Promise<InstanceContext | null> {
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if (!this.onSessionNotFound) {
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throw new Error('onSessionNotFound hook not configured');
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}
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const maxRetries = this.sessionRestorationRetries;
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const retryDelay = this.sessionRestorationRetryDelay;
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const overallTimeout = this.sessionRestorationTimeout;
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const startTime = Date.now();
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for (let attempt = 0; attempt <= maxRetries; attempt++) {
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try {
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// Calculate remaining time for this attempt
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const remainingTime = overallTimeout - (Date.now() - startTime);
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if (remainingTime <= 0) {
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const error = new Error(`Session restoration timed out after ${overallTimeout}ms`);
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error.name = 'TimeoutError';
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throw error;
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}
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// Log retry attempt (except first attempt)
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if (attempt > 0) {
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logger.debug('Retrying session restoration', {
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sessionId,
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attempt: attempt,
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maxRetries: maxRetries,
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remainingTime: remainingTime + 'ms'
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});
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}
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// Call hook with remaining time as timeout
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const context = await Promise.race([
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this.onSessionNotFound(sessionId),
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this.timeout(remainingTime)
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]);
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// Success!
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if (attempt > 0) {
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logger.info('Session restoration succeeded after retry', {
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sessionId,
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attempts: attempt + 1
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});
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}
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return context;
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} catch (error) {
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// Don't retry timeout errors (already took too long)
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if (error instanceof Error && error.name === 'TimeoutError') {
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logger.error('Session restoration timeout (no retry)', {
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sessionId,
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timeout: overallTimeout
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});
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throw error;
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}
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// Last attempt - don't delay, just throw
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if (attempt === maxRetries) {
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logger.error('Session restoration failed after all retries', {
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sessionId,
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attempts: attempt + 1,
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error: error instanceof Error ? error.message : String(error)
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});
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throw error;
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}
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// Log retry-eligible failure
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logger.warn('Session restoration failed, will retry', {
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sessionId,
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attempt: attempt + 1,
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maxRetries: maxRetries,
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error: error instanceof Error ? error.message : String(error),
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nextRetryIn: retryDelay + 'ms'
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});
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// Delay before next attempt
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await new Promise(resolve => setTimeout(resolve, retryDelay));
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}
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}
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// Should never reach here, but TypeScript needs it
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throw new Error('Unexpected state in restoreSessionWithRetry');
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}
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/**
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* Create a new session (IDEMPOTENT - REQ-2)
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*
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@@ -482,6 +645,15 @@ export class SingleSessionHTTPServer {
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instanceId: instanceContext?.instanceId
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});
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// Phase 3: Emit onSessionCreated event (REQ-4)
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// Fire-and-forget: don't await or block session creation
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this.emitEvent('onSessionCreated', id, instanceContext).catch(err => {
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logger.error('Failed to emit onSessionCreated event (non-blocking)', {
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sessionId: id,
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error: err instanceof Error ? err.message : String(err)
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});
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});
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return id;
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}
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@@ -795,11 +967,9 @@ export class SingleSessionHTTPServer {
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logger.info('Attempting session restoration', { sessionId });
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try {
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// Call restoration hook with timeout
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const restoredContext = await Promise.race([
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this.onSessionNotFound(sessionId),
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this.timeout(this.sessionRestorationTimeout)
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]);
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// REQ-7: Call restoration with retry policy (Phase 4)
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// restoreSessionWithRetry handles timeout and retries internally
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const restoredContext = await this.restoreSessionWithRetry(sessionId);
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// Handle both null and undefined defensively
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// Both indicate the hook declined to restore the session
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@@ -859,6 +1029,15 @@ export class SingleSessionHTTPServer {
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return;
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}
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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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this.emitEvent('onSessionRestored', sessionId, restoredContext).catch(err => {
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logger.error('Failed to emit onSessionRestored event (non-blocking)', {
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sessionId,
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error: err instanceof Error ? err.message : String(err)
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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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@@ -1936,6 +2115,15 @@ export class SingleSessionHTTPServer {
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});
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}
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// Phase 3: Emit onSessionDeleted event BEFORE removal (REQ-4)
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// Fire-and-forget: don't await or block deletion
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this.emitEvent('onSessionDeleted', sessionId).catch(err => {
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logger.error('Failed to emit onSessionDeleted event (non-blocking)', {
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sessionId,
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error: err instanceof Error ? err.message : String(err)
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});
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});
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// Remove session data immediately (synchronous)
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delete this.transports[sessionId];
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delete this.servers[sessionId];
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@@ -46,6 +46,51 @@ export interface EngineOptions {
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* @since 2.19.0
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*/
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sessionRestorationTimeout?: number;
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/**
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* Session lifecycle event handlers (Phase 3 - REQ-4)
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*
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* Optional callbacks for session lifecycle events:
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* - onSessionCreated: Called when a new session is created
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* - onSessionRestored: Called when a session is restored from storage
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* - onSessionAccessed: Called on EVERY request (consider throttling!)
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* - onSessionExpired: Called when a session expires
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* - onSessionDeleted: Called when a session is manually deleted
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*
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* All handlers are fire-and-forget (non-blocking).
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* Errors are logged but don't affect session operations.
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*
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* @since 2.19.0
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*/
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sessionEvents?: {
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onSessionCreated?: (sessionId: string, instanceContext: InstanceContext) => void | Promise<void>;
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onSessionRestored?: (sessionId: string, instanceContext: InstanceContext) => void | Promise<void>;
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onSessionAccessed?: (sessionId: string) => void | Promise<void>;
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onSessionExpired?: (sessionId: string) => void | Promise<void>;
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onSessionDeleted?: (sessionId: string) => void | Promise<void>;
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};
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/**
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* Number of retry attempts for failed session restoration (Phase 4 - REQ-7)
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*
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* When the restoration hook throws an error, the system will retry
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* up to this many times with a delay between attempts.
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*
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* Timeout errors are NOT retried (already took too long).
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* The overall timeout applies to ALL retry attempts combined.
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*
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* @default 0 (no retries, opt-in)
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* @since 2.19.0
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*/
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sessionRestorationRetries?: number;
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/**
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* Delay between retry attempts in milliseconds (Phase 4 - REQ-7)
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*
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* @default 100 (100 milliseconds)
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* @since 2.19.0
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*/
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sessionRestorationRetryDelay?: number;
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}
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export class N8NMCPEngine {
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@@ -67,6 +67,38 @@ export interface SessionRestorationOptions {
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* - Hook returns invalid context → 400 Bad Request (invalid context)
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*/
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onSessionNotFound?: SessionRestoreHook;
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/**
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* Number of retry attempts for failed session restoration
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*
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* When the restoration hook throws an error, the system will retry
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* up to this many times with a delay between attempts.
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*
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* Timeout errors are NOT retried (already took too long).
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*
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* Note: The overall timeout (sessionRestorationTimeout) applies to
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* ALL retry attempts combined, not per attempt.
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*
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* @default 0 (no retries)
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* @example
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* ```typescript
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* const engine = new N8NMCPEngine({
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* onSessionNotFound: async (id) => db.loadSession(id),
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* sessionRestorationRetries: 2, // Retry up to 2 times
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* sessionRestorationRetryDelay: 100 // 100ms between retries
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* });
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* ```
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* @since 2.19.0
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*/
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sessionRestorationRetries?: number;
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/**
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* Delay between retry attempts in milliseconds
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*
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* @default 100 (100 milliseconds)
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* @since 2.19.0
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*/
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sessionRestorationRetryDelay?: number;
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}
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/**
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@@ -109,3 +141,102 @@ export interface SessionState {
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*/
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metadata?: Record<string, any>;
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}
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/**
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* Session lifecycle event handlers
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*
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* These callbacks are called at various points in the session lifecycle.
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* All callbacks are optional and should not throw errors.
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*
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* ⚠️ Performance Note: onSessionAccessed is called on EVERY request.
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* Consider implementing throttling if you need database updates.
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*
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* @example
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* ```typescript
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* import throttle from 'lodash.throttle';
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*
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* const engine = new N8NMCPEngine({
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* sessionEvents: {
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* onSessionCreated: async (sessionId, context) => {
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* await db.saveSession(sessionId, context);
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* },
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* onSessionAccessed: throttle(async (sessionId) => {
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* await db.updateLastAccess(sessionId);
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* }, 60000) // Max once per minute per session
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* }
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* });
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* ```
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*
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* @since 2.19.0
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*/
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export interface SessionLifecycleEvents {
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/**
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* Called when a new session is created (not restored)
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*
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* Use cases:
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* - Save session to database for persistence
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* - Track session creation metrics
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* - Initialize session-specific resources
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*
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* @param sessionId - The newly created session ID
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* @param instanceContext - The instance context for this session
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*/
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onSessionCreated?: (sessionId: string, instanceContext: InstanceContext) => void | Promise<void>;
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/**
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* Called when a session is restored from external storage
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*
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* Use cases:
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* - Track session restoration metrics
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* - Log successful recovery after restart
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* - Update database restoration timestamp
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*
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* @param sessionId - The restored session ID
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* @param instanceContext - The restored instance context
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*/
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onSessionRestored?: (sessionId: string, instanceContext: InstanceContext) => void | Promise<void>;
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/**
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* Called on EVERY request that uses an existing session
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*
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* ⚠️ HIGH FREQUENCY: This event fires for every MCP tool call.
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* For a busy session, this could be 100+ calls per minute.
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*
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* Recommended: Implement throttling if you need database updates
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*
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* Use cases:
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* - Update session last_access timestamp (throttled)
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* - Track session activity metrics
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* - Extend session TTL in database
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*
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* @param sessionId - The session ID that was accessed
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*/
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onSessionAccessed?: (sessionId: string) => void | Promise<void>;
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/**
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* Called when a session expires due to inactivity
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*
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* Called during cleanup cycle (every 5 minutes) BEFORE session removal.
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* This allows you to perform cleanup operations before the session is gone.
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*
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* Use cases:
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* - Delete session from database
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* - Log session expiration metrics
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* - Cleanup session-specific resources
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*
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* @param sessionId - The session ID that expired
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*/
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onSessionExpired?: (sessionId: string) => void | Promise<void>;
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/**
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* Called when a session is manually deleted
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*
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* Use cases:
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* - Delete session from database
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* - Cascade delete related data
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* - Log manual session termination
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*
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* @param sessionId - The session ID that was deleted
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*/
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onSessionDeleted?: (sessionId: string) => void | Promise<void>;
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}
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