feat: add error mode for execution debugging with AI suggestions (#505)

* feat: add error mode for execution debugging with AI suggestions

Add a new `mode='error'` option to n8n_executions action=get that's optimized
for AI agents debugging workflow failures. This mode provides intelligent
error extraction with 80-99% token savings compared to `mode='full'`.

Key features:
- Error Analysis: Extracts error message, type, node name, and parameters
- Upstream Context: Samples input data from upstream node (configurable limit)
- Execution Path: Shows node execution sequence from trigger to error
- AI Suggestions: Pattern-based fix suggestions for common errors
- Workflow Fetch: Optionally fetches workflow for accurate upstream detection

New parameters for mode='error':
- errorItemsLimit (default: 2) - Sample items from upstream node
- includeStackTrace (default: false) - Full vs truncated stack trace
- includeExecutionPath (default: true) - Include node execution path
- fetchWorkflow (default: true) - Fetch workflow for upstream detection

Token efficiency:
- 11 items: ~11KB full vs ~3KB error (73% savings)
- 1001 items: ~354KB full vs ~3KB error (99% savings)

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* fix: add security hardening to error-execution-processor

- Add prototype pollution protection (block __proto__, constructor, prototype)
- Expand sensitive data patterns (20+ patterns including JWT, OAuth, certificates)
- Create recursive sanitizeData function for deep object sanitization
- Apply sanitization to both nodeParameters and upstream sampleItems
- Add comprehensive unit tests (42 tests, 96% coverage)

Security improvements address code review findings:
- Critical: Prototype pollution protection
- Warning: Expanded sensitive data filtering
- Warning: Nested data sanitization

Concieved by Romuald Członkowski - www.aiadvisors.pl/en

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Romuald Członkowski <romualdczlonkowski@MacBook-Pro-Romuald.local>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

src/types/n8n-api.ts

@@ -321,7 +321,7 @@ export interface McpToolResponse {
 }
 
 // Execution Filtering Types
-export type ExecutionMode = 'preview' | 'summary' | 'filtered' | 'full';
+export type ExecutionMode = 'preview' | 'summary' | 'filtered' | 'full' | 'error';
 
 export interface ExecutionPreview {
   totalNodes: number;
@@ -354,6 +354,10 @@ export interface ExecutionFilterOptions {
   itemsLimit?: number;
   includeInputData?: boolean;
   fieldsToInclude?: string[];
+  // Error mode specific options
+  errorItemsLimit?: number;       // Sample items from upstream node (default: 2)
+  includeStackTrace?: boolean;    // Include full stack trace (default: false)
+  includeExecutionPath?: boolean; // Include execution path to error (default: true)
 }
 
 export interface FilteredExecutionResponse {
@@ -381,6 +385,9 @@ export interface FilteredExecutionResponse {
 
   // Error information
   error?: Record<string, unknown>;
+
+  // Error mode specific (mode='error')
+  errorInfo?: ErrorAnalysis;
 }
 
 export interface FilteredNodeData {
@@ -398,4 +405,51 @@ export interface FilteredNodeData {
       truncated: boolean;
     };
   };
+}
+
+// Error Mode Types
+export interface ErrorAnalysis {
+  // Primary error information
+  primaryError: {
+    message: string;
+    errorType: string;  // NodeOperationError, NodeApiError, etc.
+    nodeName: string;
+    nodeType: string;
+    nodeId?: string;
+    nodeParameters?: Record<string, unknown>;  // Relevant params only (no secrets)
+    stackTrace?: string;  // Truncated by default
+  };
+
+  // Upstream context (input to error node)
+  upstreamContext?: {
+    nodeName: string;
+    nodeType: string;
+    itemCount: number;
+    sampleItems: unknown[];  // Configurable limit, default 2
+    dataStructure: Record<string, unknown>;
+  };
+
+  // Execution path leading to error (from trigger to error)
+  executionPath?: Array<{
+    nodeName: string;
+    status: 'success' | 'error' | 'skipped';
+    itemCount: number;
+    executionTime?: number;
+  }>;
+
+  // Additional errors (if workflow had multiple failures)
+  additionalErrors?: Array<{
+    nodeName: string;
+    message: string;
+  }>;
+
+  // AI-friendly suggestions
+  suggestions?: ErrorSuggestion[];
+}
+
+export interface ErrorSuggestion {
+  type: 'fix' | 'investigate' | 'workaround';
+  title: string;
+  description: string;
+  confidence: 'high' | 'medium' | 'low';
 }