docs: Syncro invoice verification pattern (lesson from false alarm)

Created memory entry documenting correct way to verify ticket-invoice linkage
in Syncro API after 2026-04-30 incident where faulty verification script
falsely claimed 31 tickets had no invoices (actually 29 had invoices properly,
2 were correctly Non-Billable).

Key lessons:
- List endpoint does NOT return ticket_id or line_items
- Must query individual invoices for full data
- Invoice numbers are strings, not integers
- Use ticket ID (internal), not ticket number (user-visible)

Added to memory index for future GrepAI semantic search.

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

.claude/memory/MEMORY.md

@@ -1,6 +1,7 @@
 # Memory Index
 
 ## Reference
+- [Syncro API — Invoice Verification Pattern](syncro_invoice_verification_pattern.md) - **CRITICAL:** List endpoint (/invoices?customer_id=X) does NOT return ticket linkage. Must query individual invoices (/invoices/{number}) to get ticket_id field. Invoice numbers are strings. Use ticket ID (not number) for comparison. Real case: falsely reported 31 tickets had no invoices (actually 29 had invoices, 2 were Non-Billable).
 - [Approval Workflow: Tools vs Projects](approval-workflow-tools-vs-projects.md) - General tools (remediation-tool, onboard scripts, MSP utilities): Howard can modify OR Claude can execute with Howard/Mike approval. Projects (GuruRMM, etc.): require Mike approval, features→roadmap, bugs→bug list.
 - [Community Forum (Flarum)](reference_community_forum.md) - Flarum forum at community.azcomputerguru.com, API access, database, posting workflow
 - [Radio Show Website](reference_radio_website.md) - Astro static site at radio.azcomputerguru.com on IX server