---
issue: 078
title: "Scanner: idempotency path ignores mismatched parameters — silent collision"
severity: high
domain: Scanner
labels: [bug, scanner, idempotency]
status: open
created: 2026-05-30
source: Full Codebase Audit 2026-05-30
---

# Scanner: idempotency path ignores mismatched parameters — silent collision

**Severity:** high
**Domain:** Scanner
**Labels:** bug, scanner, idempotency

## Description

`scanner/api.go:191` returns the existing intent when an `intentId` collision is detected, but does not compare the stored parameters to the incoming request. If a caller reuses an `intentId` with different `amount`, `tokenAddress`, or `callbackUrl`, the scanner silently returns the old intent and monitors the wrong payment parameters.

## Options

1. Return `409 Conflict` if stored params differ from request.
2. Return existing intent only if params match; else error.
3. Treat any reuse as conflict regardless of params.

## Recommendation

Compare stored vs incoming params and return `409 Conflict` on mismatch (return existing only on exact match). Changes API contract.

## Affected Files

- `scanner/api.go:191`

## References

- [Full Codebase Audit 2026-05-30](../09%20-%20Audits/Full%20Codebase%20Audit%20-%202026-05-30.md) — DEC-62