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>

03 - API Reference/Authentication API.md

@@ -5,7 +5,7 @@ tags: [api, auth, reference]
 
 # Authentication API
 
-> **Last updated:** 2026-05-29 — aligned with code (see [Doc vs Code Audit Report](../09%20-%20Audits/Doc%20vs%20Code%20Audit%20Report%20-%202026-05-29.md))
+> **Last updated:** 2026-05-30 — Cloudflare Turnstile CAPTCHA added after 3 failed logins (commit `b8edbbf`)
 
 All endpoints are mounted under `/api/auth/*` in `backend/src/app.ts`. The routes file is [`backend/src/services/auth/authRoutes.ts`](../../backend/src/services/auth/authRoutes.ts) and the WebAuthn sub-routes are in [`passkeyRoutes.ts`](../../backend/src/services/auth/passkeyRoutes.ts). Controller logic lives in [`authController.ts`](../../backend/src/services/auth/authController.ts) and [`authService.ts`](../../backend/src/services/auth/authService.ts).
 
@@ -121,6 +121,12 @@ Two distinct identities are involved: a [[User]] (`models/User.ts`) and a [[Temp
 - `403` email not verified
 - `423` account locked (after repeated failures, tracked in Redis via `rateLimitService`)
 
+**Cloudflare Turnstile CAPTCHA:** After **3 failed login attempts** from the same IP within 15 minutes the `captchaGate` middleware requires a valid `cf-turnstile-response` token in the request body. Responses when CAPTCHA is required but missing:
+```json
+{ "success": false, "captchaRequired": true, "message": "..." }
+```
+HTTP status: `429`. When `TURNSTILE_SECRET_KEY` is not set (local dev) the gate is skipped.
+
 **⚠️ Rate limiter behaviour:** The attempt counter increments on **every** attempt (before password validation), not only on failures. 5 total attempts within 15 minutes triggers lockout — a user burning 5 attempts with typos will be locked out even if they never had a valid password.
 
 **Side effects:**