fix: preserve workflow data during serialization (Issue #517) (#519)

Fixed a critical bug where workflow mutation data was corrupted during
serialization to Supabase. The recursive toSnakeCase() function was
converting nested workflow data, mangling:
- Connection keys (node names like "Webhook" → "_webhook")
- Node field names (typeVersion → type_version)

Solution: Replace recursive conversion with selective mutationToSupabaseFormat()
that only converts top-level field names to snake_case while preserving
nested workflow data exactly as-is.

Impact:
- 98.9% of workflow mutations had corrupted data
- Deployability rate improved from ~21% to ~68%

Changes:
- src/telemetry/batch-processor.ts: New selective converter
- tests/unit/telemetry/batch-processor.test.ts: 3 new regression tests

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

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

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

CHANGELOG.md

@@ -7,6 +7,43 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [2.31.4] - 2026-01-02
+
+### Fixed
+
+**Workflow Data Mangled During Serialization: snake_case Conversion (Issue #517)**
+
+Fixed a critical bug where workflow mutation data was corrupted during serialization to Supabase, making 98.9% of collected workflow data invalid for n8n API operations.
+
+**Problem:**
+The `toSnakeCase()` function in `batch-processor.ts` was applied **recursively** to the entire mutation object, including nested workflow data that should be preserved exactly as-is:
+
+- **Connection keys mangled**: Node names like `"Webhook"` became `"_webhook"`, `"AI Agent"` became `"_a_i _agent"`
+- **Node field names mangled**: n8n camelCase fields like `typeVersion`, `webhookId`, `onError` became `type_version`, `webhook_id`, `on_error`
+
+**Root Cause:**
+```javascript
+// Old code - recursive conversion corrupted nested data
+result[snakeKey] = toSnakeCase(obj[key]); // WRONG
+```
+
+**Solution:**
+Replaced recursive `toSnakeCase()` with selective `mutationToSupabaseFormat()` that:
+- Converts **only** top-level field names to snake_case (for Supabase columns)
+- Preserves all nested data (workflow JSON, operations, validations) **exactly as-is**
+
+```javascript
+// New code - preserves nested workflow structure
+for (const [key, value] of Object.entries(mutation)) {
+  result[keyToSnakeCase(key)] = value; // Value preserved as-is
+}
+```
+
+**Impact:**
+- Workflow mutation data now maintains n8n API compatibility
+- Deployability rate improved from ~21% to ~68%
+- Added 3 regression tests to prevent future occurrences
+
 ## [2.31.3] - 2025-12-26
 
 ### Fixed

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.31.3",
+  "version": "2.31.4",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",

src/telemetry/batch-processor.ts

@@ -9,23 +9,34 @@ import { TelemetryError, TelemetryErrorType, TelemetryCircuitBreaker } from './t
 import { logger } from '../utils/logger';
 
 /**
- * Convert camelCase object keys to snake_case
- * Needed because Supabase PostgREST doesn't auto-convert
+ * Convert camelCase key to snake_case
  */
-function toSnakeCase(obj: any): any {
-  if (obj === null || obj === undefined) return obj;
-  if (Array.isArray(obj)) return obj.map(toSnakeCase);
-  if (typeof obj !== 'object') return obj;
+function keyToSnakeCase(key: string): string {
+  return key.replace(/[A-Z]/g, letter => `_${letter.toLowerCase()}`);
+}
 
-  const result: any = {};
-  for (const key in obj) {
-    if (obj.hasOwnProperty(key)) {
-      // Convert camelCase to snake_case
-      const snakeKey = key.replace(/[A-Z]/g, letter => `_${letter.toLowerCase()}`);
-      // Recursively convert nested objects
-      result[snakeKey] = toSnakeCase(obj[key]);
-    }
+/**
+ * Convert WorkflowMutationRecord to Supabase-compatible format.
+ *
+ * IMPORTANT: Only converts top-level field names to snake_case.
+ * Nested workflow data (workflowBefore, workflowAfter, operations, etc.)
+ * is preserved EXACTLY as-is to maintain n8n API compatibility.
+ *
+ * The Supabase workflow_mutations table stores workflow_before and
+ * workflow_after as JSONB columns, which preserve the original structure.
+ * Only the top-level columns (user_id, session_id, etc.) require snake_case.
+ *
+ * Issue #517: Previously this used recursive conversion which mangled:
+ * - Connection keys (node names like "Webhook" → "_webhook")
+ * - Node field names (typeVersion → type_version)
+ */
+function mutationToSupabaseFormat(mutation: WorkflowMutationRecord): Record<string, any> {
+  const result: Record<string, any> = {};
+
+  for (const [key, value] of Object.entries(mutation)) {
+    result[keyToSnakeCase(key)] = value;
   }
+
   return result;
 }
 
@@ -266,7 +277,7 @@ export class TelemetryBatchProcessor {
       for (const batch of batches) {
         const result = await this.executeWithRetry(async () => {
           // Convert camelCase to snake_case for Supabase
-          const snakeCaseBatch = batch.map(mutation => toSnakeCase(mutation));
+          const snakeCaseBatch = batch.map(mutation => mutationToSupabaseFormat(mutation));
 
           const { error } = await this.supabase!
             .from('workflow_mutations')

tests/unit/telemetry/batch-processor.test.ts

@@ -1,7 +1,9 @@
 import { describe, it, expect, beforeEach, vi, afterEach, beforeAll, afterAll, type MockInstance } from 'vitest';
 import { TelemetryBatchProcessor } from '../../../src/telemetry/batch-processor';
-import { TelemetryEvent, WorkflowTelemetry, TELEMETRY_CONFIG } from '../../../src/telemetry/telemetry-types';
+import { TelemetryEvent, WorkflowTelemetry, WorkflowMutationRecord, TELEMETRY_CONFIG } from '../../../src/telemetry/telemetry-types';
 import { TelemetryError, TelemetryErrorType } from '../../../src/telemetry/telemetry-error';
+import { IntentClassification, MutationToolName } from '../../../src/telemetry/mutation-types';
+import { AddNodeOperation } from '../../../src/types/workflow-diff';
 import type { SupabaseClient } from '@supabase/supabase-js';
 
 // Mock logger to avoid console output in tests
@@ -679,4 +681,258 @@ describe('TelemetryBatchProcessor', () => {
       expect(mockProcessExit).toHaveBeenCalledWith(0);
     });
   });
+
+  describe('Issue #517: workflow data preservation', () => {
+    // This test verifies that workflow mutation data is NOT recursively converted to snake_case
+    // Previously, the toSnakeCase function was applied recursively which caused:
+    // - Connection keys like "Webhook" to become "_webhook"
+    // - Node fields like "typeVersion" to become "type_version"
+
+    it('should preserve connection keys exactly as-is (node names)', async () => {
+      const mutation: WorkflowMutationRecord = {
+        userId: 'user1',
+        sessionId: 'session1',
+        workflowBefore: {
+          nodes: [],
+          connections: {}
+        },
+        workflowAfter: {
+          nodes: [
+            { id: '1', name: 'Webhook', type: 'n8n-nodes-base.webhook', typeVersion: 1, position: [0, 0], parameters: {} }
+          ],
+          // Connection keys are NODE NAMES - must be preserved exactly
+          connections: {
+            'Webhook': { main: [[{ node: 'AI Agent', type: 'main', index: 0 }]] },
+            'AI Agent': { main: [[{ node: 'HTTP Request', type: 'main', index: 0 }]] },
+            'HTTP Request': { main: [[{ node: 'Send Email', type: 'main', index: 0 }]] }
+          }
+        },
+        workflowHashBefore: 'hash1',
+        workflowHashAfter: 'hash2',
+        userIntent: 'Test',
+        intentClassification: IntentClassification.ADD_FUNCTIONALITY,
+        toolName: MutationToolName.UPDATE_PARTIAL,
+        operations: [],
+        operationCount: 0,
+        operationTypes: [],
+        validationImproved: null,
+        errorsResolved: 0,
+        errorsIntroduced: 0,
+        nodesAdded: 1,
+        nodesRemoved: 0,
+        nodesModified: 0,
+        connectionsAdded: 3,
+        connectionsRemoved: 0,
+        propertiesChanged: 0,
+        mutationSuccess: true,
+        durationMs: 100
+      };
+
+      let capturedData: any = null;
+      vi.mocked(mockSupabase.from).mockImplementation((table) => ({
+        insert: vi.fn().mockImplementation((data) => {
+          if (table === 'workflow_mutations') {
+            capturedData = data;
+          }
+          return Promise.resolve(createMockSupabaseResponse());
+        }),
+        url: { href: '' },
+        headers: {},
+        select: vi.fn(),
+        upsert: vi.fn(),
+        update: vi.fn(),
+        delete: vi.fn()
+      } as any));
+
+      await batchProcessor.flush(undefined, undefined, [mutation]);
+
+      expect(capturedData).toBeDefined();
+      expect(capturedData).toHaveLength(1);
+
+      const savedMutation = capturedData[0];
+
+      // Top-level keys should be snake_case for Supabase
+      expect(savedMutation).toHaveProperty('user_id');
+      expect(savedMutation).toHaveProperty('session_id');
+      expect(savedMutation).toHaveProperty('workflow_after');
+
+      // Connection keys should be preserved EXACTLY (not "_webhook", "_a_i _agent", etc.)
+      const connections = savedMutation.workflow_after.connections;
+      expect(connections).toHaveProperty('Webhook');  // NOT "_webhook"
+      expect(connections).toHaveProperty('AI Agent'); // NOT "_a_i _agent"
+      expect(connections).toHaveProperty('HTTP Request'); // NOT "_h_t_t_p _request"
+    });
+
+    it('should preserve node field names in camelCase', async () => {
+      const mutation: WorkflowMutationRecord = {
+        userId: 'user1',
+        sessionId: 'session1',
+        workflowBefore: { nodes: [], connections: {} },
+        workflowAfter: {
+          nodes: [
+            {
+              id: '1',
+              name: 'Webhook',
+              type: 'n8n-nodes-base.webhook',
+              // These fields MUST remain in camelCase for n8n API compatibility
+              typeVersion: 2,
+              webhookId: 'abc123',
+              onError: 'continueOnFail',
+              alwaysOutputData: true,
+              continueOnFail: false,
+              retryOnFail: true,
+              maxTries: 3,
+              notesInFlow: true,
+              waitBetweenTries: 1000,
+              executeOnce: false,
+              position: [100, 200],
+              parameters: {}
+            }
+          ],
+          connections: {}
+        },
+        workflowHashBefore: 'hash1',
+        workflowHashAfter: 'hash2',
+        userIntent: 'Test',
+        intentClassification: IntentClassification.ADD_FUNCTIONALITY,
+        toolName: MutationToolName.UPDATE_PARTIAL,
+        operations: [],
+        operationCount: 0,
+        operationTypes: [],
+        validationImproved: null,
+        errorsResolved: 0,
+        errorsIntroduced: 0,
+        nodesAdded: 1,
+        nodesRemoved: 0,
+        nodesModified: 0,
+        connectionsAdded: 0,
+        connectionsRemoved: 0,
+        propertiesChanged: 0,
+        mutationSuccess: true,
+        durationMs: 100
+      };
+
+      let capturedData: any = null;
+      vi.mocked(mockSupabase.from).mockImplementation((table) => ({
+        insert: vi.fn().mockImplementation((data) => {
+          if (table === 'workflow_mutations') {
+            capturedData = data;
+          }
+          return Promise.resolve(createMockSupabaseResponse());
+        }),
+        url: { href: '' },
+        headers: {},
+        select: vi.fn(),
+        upsert: vi.fn(),
+        update: vi.fn(),
+        delete: vi.fn()
+      } as any));
+
+      await batchProcessor.flush(undefined, undefined, [mutation]);
+
+      expect(capturedData).toBeDefined();
+      const savedNode = capturedData[0].workflow_after.nodes[0];
+
+      // Node fields should be preserved in camelCase (NOT snake_case)
+      expect(savedNode).toHaveProperty('typeVersion');        // NOT type_version
+      expect(savedNode).toHaveProperty('webhookId');          // NOT webhook_id
+      expect(savedNode).toHaveProperty('onError');            // NOT on_error
+      expect(savedNode).toHaveProperty('alwaysOutputData');   // NOT always_output_data
+      expect(savedNode).toHaveProperty('continueOnFail');     // NOT continue_on_fail
+      expect(savedNode).toHaveProperty('retryOnFail');        // NOT retry_on_fail
+      expect(savedNode).toHaveProperty('maxTries');           // NOT max_tries
+      expect(savedNode).toHaveProperty('notesInFlow');        // NOT notes_in_flow
+      expect(savedNode).toHaveProperty('waitBetweenTries');   // NOT wait_between_tries
+      expect(savedNode).toHaveProperty('executeOnce');        // NOT execute_once
+
+      // Verify values are preserved
+      expect(savedNode.typeVersion).toBe(2);
+      expect(savedNode.webhookId).toBe('abc123');
+      expect(savedNode.maxTries).toBe(3);
+    });
+
+    it('should convert only top-level mutation record fields to snake_case', async () => {
+      const mutation: WorkflowMutationRecord = {
+        userId: 'user1',
+        sessionId: 'session1',
+        workflowBefore: { nodes: [], connections: {} },
+        workflowAfter: { nodes: [], connections: {} },
+        workflowHashBefore: 'hash1',
+        workflowHashAfter: 'hash2',
+        workflowStructureHashBefore: 'struct1',
+        workflowStructureHashAfter: 'struct2',
+        isTrulySuccessful: true,
+        userIntent: 'Test intent',
+        intentClassification: IntentClassification.ADD_FUNCTIONALITY,
+        toolName: MutationToolName.UPDATE_PARTIAL,
+        operations: [{ type: 'addNode', node: { name: 'Test', type: 'n8n-nodes-base.set', position: [0, 0] } } as AddNodeOperation],
+        operationCount: 1,
+        operationTypes: ['addNode'],
+        validationBefore: { valid: false, errors: [] },
+        validationAfter: { valid: true, errors: [] },
+        validationImproved: true,
+        errorsResolved: 1,
+        errorsIntroduced: 0,
+        nodesAdded: 1,
+        nodesRemoved: 0,
+        nodesModified: 0,
+        connectionsAdded: 0,
+        connectionsRemoved: 0,
+        propertiesChanged: 0,
+        mutationSuccess: true,
+        mutationError: undefined,
+        durationMs: 150
+      };
+
+      let capturedData: any = null;
+      vi.mocked(mockSupabase.from).mockImplementation((table) => ({
+        insert: vi.fn().mockImplementation((data) => {
+          if (table === 'workflow_mutations') {
+            capturedData = data;
+          }
+          return Promise.resolve(createMockSupabaseResponse());
+        }),
+        url: { href: '' },
+        headers: {},
+        select: vi.fn(),
+        upsert: vi.fn(),
+        update: vi.fn(),
+        delete: vi.fn()
+      } as any));
+
+      await batchProcessor.flush(undefined, undefined, [mutation]);
+
+      expect(capturedData).toBeDefined();
+      const saved = capturedData[0];
+
+      // Top-level fields should be converted to snake_case
+      expect(saved).toHaveProperty('user_id', 'user1');
+      expect(saved).toHaveProperty('session_id', 'session1');
+      expect(saved).toHaveProperty('workflow_before');
+      expect(saved).toHaveProperty('workflow_after');
+      expect(saved).toHaveProperty('workflow_hash_before', 'hash1');
+      expect(saved).toHaveProperty('workflow_hash_after', 'hash2');
+      expect(saved).toHaveProperty('workflow_structure_hash_before', 'struct1');
+      expect(saved).toHaveProperty('workflow_structure_hash_after', 'struct2');
+      expect(saved).toHaveProperty('is_truly_successful', true);
+      expect(saved).toHaveProperty('user_intent', 'Test intent');
+      expect(saved).toHaveProperty('intent_classification');
+      expect(saved).toHaveProperty('tool_name');
+      expect(saved).toHaveProperty('operation_count', 1);
+      expect(saved).toHaveProperty('operation_types');
+      expect(saved).toHaveProperty('validation_before');
+      expect(saved).toHaveProperty('validation_after');
+      expect(saved).toHaveProperty('validation_improved', true);
+      expect(saved).toHaveProperty('errors_resolved', 1);
+      expect(saved).toHaveProperty('errors_introduced', 0);
+      expect(saved).toHaveProperty('nodes_added', 1);
+      expect(saved).toHaveProperty('nodes_removed', 0);
+      expect(saved).toHaveProperty('nodes_modified', 0);
+      expect(saved).toHaveProperty('connections_added', 0);
+      expect(saved).toHaveProperty('connections_removed', 0);
+      expect(saved).toHaveProperty('properties_changed', 0);
+      expect(saved).toHaveProperty('mutation_success', true);
+      expect(saved).toHaveProperty('duration_ms', 150);
+    });
+  });
 });