Merge pull request #661: feat(config): timestamped config backups with a configurable folder and retention

Conflicts in CLAUDE.md, README.md, docs/api-reference.md and
src/web/server.ts were additions beside #662's Copilot quota read and
#666's keep-warm sections; both sides kept.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/api-reference.md

@@ -1171,6 +1171,21 @@ Claude Code reports the main conversation's prompt-cache state on its statusline
 
 `status` is `{ enabled, idleCompactionOff, state, nextCheckAt?, reason?, nudges, lastNudgeAt?, budgetEndsAt? }` (`idleCompactionOff`: whether the session's current launch carries that opt-out; `budgetEndsAt` only while `enabled`) with `state` one of `off`, `armed` (waiting for the due time), `waiting` (due, deferred by a guard named in `reason`), `nudged` (sent, waiting for the next cache report) or `stopped` (`reason` says why). Two SSE events carry changes: `session:promptCache` (`{ sessionId, ...promptCache }`) and `session:keepWarm` (`{ sessionId, ...status }`), both change-only. The keep-alive turn's `hook:stop` and `hook:idle_prompt` broadcasts carry `acknowledgedReason: "cache keep-alive"`, no push is sent for them and the run summary does not record them; an idle approval already pending stays as it was (only a person spends its alert). Its `session:working` and `session:idle` broadcasts carry `keepAlive: true`.
 
+## Config backups
+
+Timestamped snapshots of the files that hold what a user has customized (`src/config-backup.ts`). On by default; a snapshot is taken at startup and whenever the tracked files' content changes (checked every 5 minutes), so there is one entry per real change. All four routes are admin only in multi-user mode (`403`), because the files include credentials. Responses carry file names and sizes; only the diff returns values, and never a credential's.
+
+Tracked files (a fixed list, relative to the data dir): `settings.json`, `clis.json`, `custom-model-hosts.json`, `webhook.json`, `intents.json`, `linked-cases.json`, `remote-hosts.json`, `remote-cases.json`, `docker-hosts.json`, `docker-cases.json`, `webviews.json`, `push-keys.json`, `users.json`, `.env`. Session state (`state.json`, which also holds cron jobs and respawn presets), logs, the hook secret and caches are not.
+
+Settings (synced, in `settings.json`): `configBackupEnabled` (absent = on), `configBackupDir` (absolute path, `~` expanded; empty = `<data dir>/backups/config`), `configBackupKeepCount` (2–500, default 20), `configBackupKeepDays` (0–3650, default 30; `0` = no age limit). A key absent from `settings.json` means the retention the newest backup in the folder recorded, and the default only when none did. Retention only ever deletes snapshot folders Codeman made there, and never the newest one. Each snapshot is a `0700` folder named `cfg-YYYYMMDD-HHMMSS` (server local time; `-2`, `-3`… on a same-second collision) holding the tracked files under their own names plus a `manifest.json` (`id`, `createdAt`, `reason` of `startup`/`auto`/`manual`/`pre-restore`, `appVersion`, the change-check `hash`, an `origin` id, the `keepCount` and `keepDays` in force, and a SHA-256 and size per file), all `0600`. A snapshot is never dated earlier than the instance's newest one, so a clock that read ahead once does not make every later pass write a copy. All four routes answer `503 OPERATION_FAILED` when a custom folder does not respond, and diff and restore answer `409` for a symlinked or group/world-accessible backup as well as a checksum mismatch. Only folders with that name and a valid manifest are listed, restored or pruned. Full guide: `docs/wiki/Config-Backups.md`.
+
+| Method | Path                                 | Body | Notes                                                                                                                                                                                                                                                                                                                                                                                                                  |
+| ------ | ------------------------------------ | ---- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `GET`  | `/api/config-backups`                | none | `settings` in effect, `dir`, `defaultDir`, `tracked[]` and `backups[]` (`id`, `createdAt`, `reason`, `appVersion`, `files[]`, `bytes`), newest first.                                                                                                                                                                                                                                                                  |
+| `POST` | `/api/config-backups`                | none | Snapshot now, even if nothing changed (`reason: manual`), then apply retention. `status` is `created` or `empty` (nothing tracked exists yet); `removed[]` lists the ids retention deleted. `503` when a custom folder does not answer.                                                                                                                                                                                                                                                                         |
+| `GET`  | `/api/config-backups/diff?from=&to=` | none | What differs between two states: `from`/`to` are a backup id or `current` (the running config; the default for `to`). `files[]` (`name`, `status` `added`/`removed`/`changed`/`unchanged`, `changes[]` of `path`, `kind`, `before`/`after`, `truncated`, `detail`) and `changed`. Credential values are never returned (`redacted: true`). `400` without `from`; `404` unknown id; `409` if a file fails its checksum. |
+| `POST` | `/api/config-backups/:id/restore`    | none | Put a snapshot's files back, atomically, after a `pre-restore` snapshot of the current ones (none when nothing changed since the newest backup). `404` unknown id; `409 CONFLICT` if a file fails its checksum (nothing changed). Returns `restored[]`, `untouched[]` (tracked files present now that the backup did not hold; left as they are), `safetySnapshot` (the `pre-restore` id, or the newest backup's when nothing had changed since it) and `restartRequired[]` (files the running server only reads at start: `.env`, `push-keys.json`, `settings.json`). A file that cannot be written (a full disk, a directory in its place) does not stop the others: the answer is then `500 OPERATION_FAILED` with the same fields in `data` plus `failed[]` (`name`, `error`); the files listed in `restored[]` are the backup's and are reloaded like a full restore.                                                                                                                                                              |
+
 ## Webhook notifications
 
 Posts the Web Push events to ntfy, Slack, Discord or a generic JSON URL (Settings → Notifications). Off by default. The webhook URL is a bearer secret (anyone holding a Slack/Discord URL can post as it), so it lives in `~/.codeman/webhook.json` (0600), is **never returned**, and is kept out of `settings.json`. All three routes answer `403` for a non-admin in multi-user mode.