audit: 2026-05-30 full-codebase audit — report, issues, docs, runbooks

Full-codebase-audit 2026-05-30 outputs:
- Audit report: 09 - Audits/Full Codebase Audit - 2026-05-30.md
- 81 issue files ISSUE-055..135 (decisions + 1 skipped no-brainer).
- Scanner docs from scratch (was zero): architecture, data model, API ref, payment
  flow, operations runbook + repo README.
- Doc-sync updates across API reference, data models, flows, design system.
- Secret Rotation Runbook (08 - Operations) for the exposed credentials.
- Reusable workflow guide (07 - Development) + .claude/workflows/full-codebase-audit.js.

Issues remain status:open intentionally — the code fixes are uncommitted-then-committed
working-tree changes per repo and aren't "resolved" until merged/deployed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Issues/ISSUE-078-scanner-idempotency-path-ignores-mismatched-parameters.md

@@ -0,0 +1,38 @@
+---
+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