fix(update): an unlistable jobs directory refuses; the rowless-agent hint names its server (Issue #72, review R2, R3)

R2: glob() hid a listing error, so an unreadable .mam/jobs (or MAM_JOBS_DIR,
or another row's jobs dir) counted as empty and the update installed over an
open job. Records are now listed with os.listdir; a directory that cannot be
listed, or stat'ed, is a blocker with its path.

R3: a discovered agent with no row was told to run stop with --session only;
stop then looked on the workspace's server, not the one the agent was found
on. The hint now carries --herdr-session <server>, quoted.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.agents/skills/multi-agent-mux-update/SKILL.md

@@ -22,7 +22,7 @@ bash .agents/skills/multi-agent-mux-update/scripts/update.sh --yes
 |---|---|
 | Where | An installed workspace only (`.mam_deploy/remove.sh` present). A git checkout updates with `git pull`. |
 | Confirmation | `[y/N]` prompt; without a terminal `-y`/`--yes` is required. There is no force option. |
-| Refused when | a running registry row, a live herdr agent whose cwd is in the workspace (any running server), an open job (unreadable job JSON included, `dry_run` excluded), a live loop marker, `.mam/monitor.lock` held by a monitor the skills did not start, or another update. The calling agent (its herdr server + pane, row and one running job) is not counted. Each refusal lists the cleanup; nothing is changed. |
+| Refused when | a running registry row, a live herdr agent whose cwd is in the workspace (any running server), an open job (an unreadable job JSON or jobs directory included, `dry_run` excluded), a live loop marker, `.mam/monitor.lock` held by a monitor the skills did not start, or another update. The calling agent (its herdr server + pane, row and one running job) is not counted. Each refusal lists the cleanup; nothing is changed. |
 | During the update | create, resume, `run_loop.sh`, delegate submit, stop and orc-onboard refuse (`.mam/update-in-progress`, `.mam/update-admission.lock`). |
 | Monitor | stopped first, started again afterwards only if it ran (`MAM_NO_SUBSCRIBER_DAEMON=1`: not started). |
 | Install | the installer at `MAM_INSTALLER_URL` (default: Gitea `main`) runs in place; `.mam` is kept. On failure `.agents/`, `.mam_deploy/`, root files, `.venv`, the installer's `.mam` files and the registry are restored from `.mam/update-backup/`. |