The bug was one line of code. It cost a customer 7 days of waiting.

I run a small shop that sells Claude Code skill packs. When someone buys, a Python script polls Stripe for new charges and sends the product zip via Resend. Simple enough.

Here's what the original delivery loop looked like:

for charge in charges : if charge . id in processed : continue try : send_delivery_email ( to_email , zip_filename , charge . id ) except Exception as e : log . error ( " Delivery error: %s " , e )

processed . add ( charge . id ) # BUG: runs even if delivery failed save_state ( state )

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Can you see it?

processed.add(charge.id) is outside the try/except. It runs regardless of whether the delivery succeeded or failed. If Resend returned a 500, if the zip file was missing, if there was a network timeout — the charge gets marked as processed anyway.

The next poll run? Skipped. Silently. No retry. No alert.…