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-097-backend-validtransitions-map-missing-in-negotiation-key.md

@@ -0,0 +1,38 @@
+---
+issue: 097
+title: "Backend: validTransitions map missing 'in_negotiation' key"
+severity: medium
+domain: Marketplace
+labels: [bug, backend, state-machine]
+status: open
+created: 2026-05-30
+source: Full Codebase Audit 2026-05-30
+---
+
+# Backend: validTransitions map missing 'in_negotiation' key
+
+**Severity:** medium
+**Domain:** Marketplace
+**Labels:** bug, backend, state-machine
+
+## Description
+
+`marketplaceController.ts:544-555` defines a `validTransitions` map for PurchaseRequest status transitions but has no entry for `'in_negotiation'`. A PurchaseRequest in the `in_negotiation` state cannot transition to any other state via this validator.
+
+## Options
+
+1. Add `'in_negotiation'` with its allowed next statuses (e.g. `payment`, `cancelled`).
+2. Treat missing key as 'allow same-tier transitions' default.
+3. Derive transitions from `STATUS_PROGRESSION_ORDER` instead of a hand-maintained map.
+
+## Recommendation
+
+Add an explicit `'in_negotiation'` entry with the correct next statuses. Requires product/state-machine confirmation of valid transitions.
+
+## Affected Files
+
+- `backend/src/services/marketplace/marketplaceController.ts:544-555`
+
+## References
+
+- [Full Codebase Audit 2026-05-30](../09%20-%20Audits/Full%20Codebase%20Audit%20-%202026-05-30.md) — DEC-35