feat: meter AI usage

docs/architecture/ai-career-assistant.md

@@ -55,10 +55,13 @@ master profile text ────────────┘        │
 overwritten. This is deliberately distinct from `AiWorkspaceNote` (a one-row-per-type *cache* for
 candidate-fit/focus-plan). History gives the user restore/reuse (re-surface a past result), compare
 (view two side by side), copy, and delete. `ResultJson` is `{ text, meta? }`; `Provider` records which
-provider produced it. Tenant-scoped (owner query filter), cascades with the application.
+provider produced it. Each row also stores input/output character counts and a conservative estimated
+token count (characters ÷ 4); the estimate is provider-neutral because the sidecar currently returns
+text rather than provider billing metadata. Tenant-scoped (owner query filter), cascades with the application.
 
 API (`AiWorkspaceController`, `/api/jobapplications/{id}/ai`): `GET modules` (+ current provider),
-`POST generate`, `GET history?module=`, `DELETE history/{id}`.
+`POST generate`, `GET history?module=`, `DELETE history/{id}`. `GET /api/ai/usage` returns current-month
+and all-time totals; the workspace displays the monthly calls and estimated tokens.
 
 ## Provider abstraction
 

docs/architecture/current.md

@@ -391,7 +391,7 @@ No structured sink (Seq/OTLP), no in-app log rotation, no ProblemDetails standar
 |---|---|---|
 | Medium | DataProtection keys recoverable from git history (`519c32e`, `955cae6`) | **Open — rotation required, needs an operator** |
 | Medium | **CORS: `Cors:Origins="*"` triggers `SetIsOriginAllowed(_ => true)` + `AllowCredentials()`** (`Program.cs:96-102`) — reflected-origin with cookies = session theft from any site. Not currently active (compose never sets `Cors__Origins`, so it defaults to `localhost:3000`), but it is one config value away. | **Open — landmine** |
-| Medium | No AI cost ceiling (no quota, no metering, unthrottled) | Open |
+| Medium | AI cost ceiling | Metering shipped in Phase 5; enforce quotas before open registration (Phase 7). |
 | Low | No CAPTCHA (rate limiting only) | Open — blocks public signup |
 | Low | Unbounded storage: attachments, CV artifacts, extraction runs, base64 avatars | Open |
 | Low | Backup / DPAPI is Windows-oriented — verify behaviour on Linux prod | Unverified |