v0.335.0: no app stop for a tier the agent will refuse because its host is busy (host_busy pre-check, R-921)

CHANGELOG.md

@@ -1,3 +1,22 @@
+## v0.335.0 — no app stop for an off-site tier the agent will refuse because its host is busy (R-921) (2026-10-19)
+
+**MinAgent: 0.158.1** — the floor's, carried. The new check needs the agent's `host_busy` answer (felhom-agent,
+Unreleased on 2026-10-19, `56aabc7`); an agent without it keeps the old order, so no agent is required. No golden
+(`09` §3 decision 250). Task: the evening/night brief of 2026-10-19, Part 1 (operator answer: „add one field").
+
+- **Check first, stop second — now for the agent's host-wide gate too (R-921).** Measured 2026-10-08 on demo-hp: the
+  night OS step held the agent's heavy-operation gate, the controller stopped all 15 apps for the off-site tier, the
+  agent refused (409), the apps came back a minute later with no copy. Before it stops any app the loop now reads
+  `host_busy` on `GET /backup/status` (`agentapi.HostBusy`, `quiesce.HostBusyProber`, wired in `main.go` with a
+  compile-time pin). Held → no app is stopped, no backup is asked for, and each due tier gets the verdict a 409 gets
+  (contention: skipped for 15 minutes, one „BLOCKED" alarm after 3 hours, no failure breaker). Free, an older agent, a
+  failed read → the old order (stop, ask, resume at once on 409). The window's own tier in flight attaches to its job
+  as before. **The race stays:** the check is a read, not a reservation — a gate taken between the read and the start
+  costs one short stop, resumed at once (pinned since 0.305.0 by `TestR921_BusyRefusalResumesAtOnce`). Tests
+  `TestR921_NoStopWhileTheHostIsBusy` (red-proved: without the branch, 3 apps stopped and the start refused),
+  `TestR921_HostBusySkipsStillAlarmAfterTheCeiling`, `TestR921_HostBusyOtherAnswersKeepTheOldOrder` (4 rows),
+  `TestHostBusy_ReadsTheAgentsGate` (the wire shape; an agent without the field is „not known", never „free").
+
 ## v0.334.0 — a live box refreshes its config with its own key (box-config, R-1159, operator decision D19) (2026-10-19)
 
 **MinAgent: 0.158.1** — the floor's, carried; no agent change. No golden (`09` §3 decision 250). Needs hub ≥ 0.161.0