docs: Add Common Pitfall #79 - n8n undefined signalStrength field causing SHORT signal failures

.github/copilot-instructions.md

@@ -3182,6 +3182,75 @@ This section contains the **TOP 10 MOST CRITICAL** pitfalls that every AI agent
 
 📚 **Full Documentation:** `docs/COMMON_PITFALLS.md` (73 pitfalls with code examples, git commits, deployment dates)
 
+79. **CRITICAL: n8n Undefined Field Reference - SHORT Signals Failing (CRITICAL - Dec 12, 2025):**
+    - **Symptom:** SHORT signals stopped at Execute Trade1 node with error "JSON parameter needs to be valid JSON"
+    - **User Report:** "last short signal stopped in n8n at the execute trade 1 with the error JSON parameter needs to be valid JSON"
+    - **Financial Impact:** Part of $1,000+ losses - SHORT trades not executing in production
+    - **Root Cause:**
+      * File: `workflows/trading/Money_Machine.json` - Execute Trade1 node (id: 9902ecc4)
+      * Line ~430: jsonBody parameter included `"signalStrength": "{{ $('Parse Signal Enhanced').item.json.signalStrength }}"`
+      * Parse Signal Enhanced node DOES NOT extract or define signalStrength field
+      * Workflow tried to interpolate undefined variable → malformed JSON → validation error
+      * Orphaned reference: Field likely removed from parser in past update but not cleaned from downstream nodes
+    - **Parse Signal Enhanced Actual Output:**
+      * Extracts: symbol, direction, timeframe, atr, adx, rsi, volumeRatio, pricePosition, indicatorVersion
+      * Calculates: signalPrice (uses pricePosition value)
+      * Does NOT extract: signalStrength (field doesn't exist in code)
+    - **THE FIX (Dec 12, 2025):**
+      ```json
+      // BEFORE (line ~430 in Money_Machine.json):
+      "jsonBody": {
+        "symbol": "{{ $('Parse Signal Enhanced').item.json.symbol }}",
+        "direction": "{{ $('Parse Signal Enhanced').item.json.direction }}",
+        "signalStrength": "{{ $('Parse Signal Enhanced').item.json.signalStrength }}",  // ❌ UNDEFINED
+        ...
+      }
+      
+      // AFTER:
+      "jsonBody": {
+        "symbol": "{{ $('Parse Signal Enhanced').item.json.symbol }}",
+        "direction": "{{ $('Parse Signal Enhanced').item.json.direction }}",
+        // signalStrength removed entirely
+        ...
+      }
+      ```
+    - **Why This Broke SHORT Signals:**
+      * Execute Trade1 node sends HTTP POST to bot's /api/trading/execute endpoint
+      * Malformed JSON causes n8n to abort workflow execution
+      * Error appears at Execute Trade1 node, preventing API call from reaching bot
+      * Bot never receives signal → no trade opened → Position Manager never monitors
+      * User may not notice until checking n8n logs or missing expected positions
+    - **Manual Fix Required (n8n UI):**
+      * n8n workflows stored in n8n database, NOT in git-tracked JSON files
+      * Git fix updates source files but doesn't auto-update running workflows
+      * User must: Open https://flow.egonetix.de → Money Machine workflow → Execute Trade1 node → Remove signalStrength line → Save workflow
+      * Alternative: Import fixed Money_Machine.json via n8n UI
+    - **Files Changed:**
+      * workflows/trading/Money_Machine.json (line ~430 removed)
+    - **Verification Required:**
+      * Monitor next SHORT signal execution in n8n logs
+      * Confirm no "JSON parameter" error at Execute Trade1
+      * Verify trade executes successfully and Position Manager starts monitoring
+      * Check Telegram notification shows position opened
+    - **Prevention Rules:**
+      1. ALWAYS audit downstream nodes when removing fields from parser nodes
+      2. NEVER leave orphaned field references in n8n workflows
+      3. Test workflow changes with actual alert payload before deploying to production
+      4. Document all n8n workflow field dependencies (what depends on what)
+      5. Remember: n8n workflows require MANUAL UI update after JSON file changes
+      6. Add n8n workflow testing to deployment checklist
+    - **Red Flags Indicating This Bug:**
+      * Specific signal direction fails (SHORT) but other direction works (LONG)
+      * Error message: "JSON parameter needs to be valid JSON"
+      * Error occurs at Execute Trade node, not at Parse Signal or Check Risk
+      * n8n logs show workflow stops before bot API is called
+      * No corresponding error in bot container logs (bot never receives request)
+      * Check n8n node code for field references that don't exist in upstream output
+    - **Git commits:** 74b6103 "fix: Remove undefined signalStrength field from Execute Trade1 node" (Dec 12, 2025)
+    - **Deployment:** Git fixed, user must manually update n8n workflow via UI
+    - **Status:** ✅ JSON FILE FIXED - Awaiting manual n8n workflow update + production verification
+    - **See:** `/tmp/n8n_workflow_fix.md` for manual update instructions
+
 75. **CRITICAL: Wrong Year in SQL Queries - ALWAYS Use Current Year (CRITICAL - Dec 8, 2025):**
     - **Symptom:** Query returns 247 rows spanning months when expecting 5-6 recent trades
     - **Root Cause:** Database stores timestamps in 2024 format, AI agent queried '2024-12-07' instead of '2025-12-07'