Merging duplicate suppliers

The duplicate detector scans every supplier-typed contact on create / update and looks for matches against existing suppliers on three signals:

Signal	Confidence
Normalised name match (after stripping "Ltd", "Limited", "Plc" etc)	0.95
VAT number exact match	0.99
Sort code + account number exact match	0.99
Multiple of the above at once	up to 0.99

Hits surface as a banner on the Contacts page: "X possible duplicate suppliers".

Resolve a candidate

Click Resolve to open the side-by-side modal. For each flagged pair you see:

• Both contacts with their name, VAT, sort code, masked account number
• A confidence badge + match-kind explanation
• Three actions per pair

Action	Effect
Keep A	Merge B into A. Every invoice, expense, receipt, and bank-change-log entry referencing B is re-pointed to A. B is deleted.
Keep B	Same as above but in the opposite direction.
Not duplicates	Dismiss the suggestion. The pair stays as two distinct contacts; the candidate row is marked dismissed for audit.

What gets re-pointed during a merge

When you keep A and merge B in:

• fin_invoices.contact_id for every invoice / bill linked to B → re-pointed to A
• fin_supplier_bank_change_log.contact_id for every audit-log entry linked to B → re-pointed to A
• Any open duplicate candidates involving B → marked merged with the resolution noted
• B's contact-persons rows → deleted (A's persons remain)
• B's contact row → deleted

Historical bill PDFs continue to render the original supplier name because they're generated from the line data, not the live contact. The audit trail preserves the merge event.

When to dismiss

The detector is conservative but not infallible. Genuine reasons to dismiss:

• Two parent / subsidiary companies that share a VAT registration but bill separately
• Two suppliers using the same factoring service so the bank account looks identical
• Genuine namesakes with different VAT and different bank — the name match alone has 0.95 score but everything else differs