feat(api): tag each error with a ref and count errors by service

Every structured error carries a short ref, appended to its message and logged with the request; /api/dashboard/status gains per-service error counts. Gzip now compresses in place.

docs/dev/rest-api/dashboard.md

@@ -43,7 +43,7 @@ All are `GET`.
 
 | Path | Returns |
 |------|---------|
-| `/api/dashboard/status` | Version, `code_hash`, bind host and port, `mode` (`full`, `api_only`, `remote_only`), uptime, `requests_total`, `requests_rejected` (401s), `requests_by_key` (label → count), configured service count (the same services as `/api/dashboard/services`), session count, `max_sessions` (`null` when the operator configured no limit), `session_ttl`, job counts by status. The service count includes services that failed to import - use `/api/dashboard/services` for the number that loaded. |
+| `/api/dashboard/status` | Version, `code_hash`, bind host and port, `mode` (`full`, `api_only`, `remote_only`), uptime, `requests_total`, `requests_rejected` (401s), `requests_by_key` (label → count), `errors` (error counts by service tag, then by `error_code`), configured service count (the same services as `/api/dashboard/services`), session count, `max_sessions` (`null` when the operator configured no limit), `session_ttl`, job counts by status. The service count includes services that failed to import - use `/api/dashboard/services` for the number that loaded. |
 | `/api/dashboard/sessions` | Every live remote session: `id`, `owner` (username or masked key), `creator_ip`, `service`, `title_id`, `titles`, `tracks`, `title` (the display name of the title the client is on: the last one it asked tracks for, else the first resolved title), `auth_status`, `auth_error`, `server_account` (the server profile lent to the remote session, else `null`), `server_cdm` (`false` when the client's own device licenses the remote session), `server_cdm_max_height` (the tallest video the server CDM licenses live, else `null`), `client`, `actions`, `created_at` and `last_accessed` (ISO 8601) with `created_ts` and `last_accessed_ts` (Unix epoch, the same clock as log `ts`), `age_seconds`, `idle_seconds`, `log_seq`. `client` is whatever the remote client sent as `client` in its session create request. The CLI sends `version`, `code_hash` (the commit the client runs, `null` when its source cannot be read), `platform` and `argv`. `argv` is the command line the user ran: proxy and URL userinfo, secret query parameters and credential values become `***`, home and install paths shorten as in the logs, and the line is cut at 3000 characters. An older client sends less or nothing and the field is `{}`. `log_seq` is the last sequence number in the remote session's service log - poll `/api/dashboard/sessions/{id}/logs` when it changes. `actions` is the session's request log, newest last, capped at 500: `ts`, `method`, `action` (`titles`, `tracks`, `segments`, `license`, `prompt`, …), `query`, `status`, `ms`, `bytes_in`, `bytes_out`. |
 | `/api/dashboard/jobs` | Every download job with full detail, regardless of owner. Empty in `--remote-only` mode. |
 | `/api/dashboard/logs` | `{"seq": N, "records": [...]}`: the last 1000 log records. `?since=<seq>` returns only newer records; `?level=WARNING` sets the minimum level; `?logger=serve` keeps one logger and its children (`aiohttp.access` is the noisiest). `ts` is a Unix epoch in seconds. |
@@ -54,6 +54,11 @@ All are `GET`.
 | `/api/dashboard/health` | Preflight: whether this instance could finish a download. Cached 30 seconds. |
 | `/api/dashboard/events` | Server-Sent Events stream. With `?since=<seq>` it returns `{"seq", "stats", "events": [...]}` instead: every event after `seq` (the server keeps the last 20000, log records included, so a poll every few seconds is safe even under a busy access log) as one JSON burst, so a UI that polls every few seconds still sees a remote session that opened and closed in between. |
 
+`errors` counts every structured error response since the server started, for example
+`{"EXAMPLE": {"SERVICE_ERROR": 4}, "-": {"SESSION_NOT_FOUND": 1}}`. The service is the one of
+the remote session, else the `service` field of the JSON body. `-` holds an error with no
+installed service. Each error also logs its [`ref`](errors.md#find-an-error-from-its-ref).
+
 `requests_rejected` counts 401 responses; those never appear in `requests_by_key`. The
 label is the `username` from the `users` entry when one is set, else the first four
 characters of the API key.