fix: v2.7.3 — Update now restarts through our own service unit, member panes stay live on a dev server, a start refuses a missing folder

- self-restart: a server in our unit's cgroup (/agenthub.service, system
  or user) restarts via `systemctl restart --no-block` (sudo -n for the
  system unit), our launchd job by exiting into KeepAlive. The detached
  restart-helper replacement held the port while Restart=always started
  the unit every 3 s (v2.7.2 on the S3 box: 240+ restarts, MainPID 0).
- run-as.mayHaveTmux: only ENOENT means "no tmux". A dev server in server
  mode without CAP_DAC_READ_SEARCH got EACCES on a member's 0700
  .agenthub/tmux, dropped the member from the list and ended their runs
  within seconds — the real cause of `401 not a live pane's token`.
- tmux: a member's list is re-asked every 5 s, not 1 s (one sudo + three
  auth.log lines each).
- POST /api/lanes/:id/start: 409 ENOCWD for a folder that no longer
  exists (the pane started in the account's home otherwise).
- Settings: Remote sources only for staff (a developer got a 403).
- scripts/test-server.js drops every inherited AGENTHUB_* (pane env).
Tests: self-restart.test.js, server-s3-panes (mayHaveTmux), lanes-api
(ENOCWD); touched suites 771 + client pages 191, tsc -b.

docs/SERVER-MODE.md

@@ -801,7 +801,26 @@ agenthub users provision alice      # the Linux account only (a user made before
   v2.7.2 on it leaves any run and workspace under the users root (read from
   `/etc/agenthub/server.conf`) alone; a build older than v2.7.2 marks their
   runs interrupted or abandoned within seconds, and the proxy gateway then
-  refuses those panes (`401 not a live pane's token`).
+  refuses those panes (`401 not a live pane's token`). A dev server that DOES
+  run in server mode (it read `AGENTHUB_MODE=server` from
+  `~/.config/agenthub/settings.env`) but lacks the unit's
+  `CAP_DAC_READ_SEARCH` cannot stat a member's 0700 `.agenthub/tmux`; from
+  v2.7.3 on that `EACCES` counts as "maybe running" and the member's list is
+  asked through sudo, never read as "no panes".
+- **Update now** under the system unit restarts through
+  `sudo -n systemctl restart --no-block agenthub.service` (from v2.7.3). An
+  older build started a detached replacement instead, which kept the port
+  while `Restart=always` started the unit every few seconds, each start exiting
+  "already running" — `systemctl status agenthub.service` shows
+  `activating (auto-restart)` with `MainPID` 0. Recover with
+  `kill -TERM <pid of the server on the port>`; the unit then starts on the
+  new code.
+- A member's tmux list is re-asked at most every 5 s (one `sudo` each, which
+  writes three `auth.log` lines); a pane the dashboard starts or stops shows at
+  once, one that exits on its own within those 5 s.
+- Claude Code does not carry a folder's trust down from the member's home
+  (which provisioning trusts): a member answers "Trust this folder" once per
+  workspace, in the terminal.
 
 ### Undo and uninstall