prevent doubles

agent.md

@@ -132,7 +132,7 @@ On mobile (< 620 px): scan input goes full-width on its own row; user dropdown a
 
 ## Key behaviours
 - **On load**: cookie credentials restored → GET webhook fires → dropdown populated → scan input auto-focused
-- **Enter key**: trims input, POSTs to webhook, prepends result row, clears + re-focuses input
+- **Enter key**: trims input → **duplicate check** → POSTs to webhook, prepends result row, clears + re-focuses input
 - **Clear button**: empties the table, clears the scan input, resets the scan counter
 - **No user selected**: red toast + highlighted dropdown; does not submit
 - **401 on any request**: modal prompts for credentials (pre-filled from cookie), saves to cookie, retries original call
@@ -140,6 +140,15 @@ On mobile (< 620 px): scan input goes full-width on its own row; user dropdown a
 - **Network error**: dismissing error banner; input selected so user can retry
 - **Dropdown error state**: tapping/focusing the dropdown while it shows an error re-triggers `loadUsers()`
 - **NDJSON/array/object**: `parseJson()` normalises all response formats from n8n
+- **Duplicate scan**: `isDuplicate(code)` queries `.col-code` cells in the live table before every POST; if found, shows a warning toast and skips the webhook call entirely
+
+## Table columns (DOM)
+| Visible | Header | CSS class | Content |
+|---------|--------|-----------|---------|
+| ✓ | Country | — | `item.country` wrapped in teal badge |
+| ✓ | Name | `name-cell` | `item.name` |
+| ✓ | Tag | — | `item.producttag` in monospace pill |
+| ✗ | Code | `col-code` | Raw scanned code (`display:none`), used for duplicate detection |
 
 ## How to run
 Open `index.html` directly in a browser (`file://`) — no server needed for local use.