A cadence cap on the local-API whole-guest backup route (R-973, unreleased)

Each successful run prunes its tier, so a compromised controller calling POST /backup in a loop
pushed out every pre-compromise restore point. A tier with a cadence of at most 24 h now allows 3
successful runs per rolling 24 h (night, a press, the next night); a longer tier 1 per
max(cadence - 24 h, cadence/2), 6 days for the weekly off-site tier. Only successes count. A
refusal is a 429, a WARN, saved, and for 24 h a critical host-report status that the hub turns
into its existing operator-only agent_capability_degraded event. The success history and the
refusal are kept in the R-894 state file, so a restart does not reset the cap. No sudoers change.
Tests TestBackupCap_* and the state, status and wiring tests, red-proved.

CHANGELOG.md

@@ -36,6 +36,25 @@ Committed, not released — the release and its vouch are the operator's.
   `deferUpload: false` → „json mode must defer the upload"; the `Upload:` line removed → „has no Upload". **Residual:**
   the customer's typed-back check after the claim is browser-only, so „confirmed" here means „claimed" — a customer
   who opens the code and closes the page without writing it down has replaced the package.
+- **R-973 — the local-API whole-guest backup route has a cadence cap.** Every successful run prunes its tier, so a
+  compromised controller calling `POST /backup` in a loop pushed out every pre-compromise restore point (local
+  keep-last 3; off-site via ep0's keep-last 2). Now (`internal/localapi/backup_cap.go`): a tier whose cadence is ≤ 24 h
+  allows **3 successful runs per rolling 24 h** (the `07` §6 day: the night run, a „Mentés most" press, and the next
+  night, which since R-899 still runs and can land inside the same 24 h — so a press never costs the night); a longer
+  tier allows **1 per max(cadence − 24 h, cadence/2)** — 6 days for the 7-day off-site tier, which the controller only
+  runs when due and the button never targets. Only successes count (a failed run prunes nothing). A refusal answers
+  **429** with the next allowed time, is logged at WARN, is saved, and for 24 h raises the CRITICAL host-report status
+  `localapi:backup-cadence-cap` — the hub's existing operator-only `agent_capability_degraded` event, **no hub change**.
+  **The cap survives an agent restart:** `BackupSuccessState` (the R-894 file) now also keeps the newest 8 success
+  times and the last refusal per tier and guest (additive JSON fields; a pre-R-973 file counts its one known
+  success). Tests `TestBackupCap_*` (an off-site flood keeps a pre-compromise copy for 5+ days; a local flood runs 3
+  a day; the scheduled day is never refused; restart; failures; the operator signal) + `TestBackupCadenceCap`,
+  `TestBackupSuccessState_R973_*`, `TestBackupCapStatus_*`, `TestR973_CapRefusalIsWiredIntoTheReport`. Red-proved:
+  the cap disabled → „the off-site tier lost every pre-compromise copy: 10 runs"; the disk history ignored → „after a
+  restart the 4th run in a day was allowed"; the wiring line removed → „never binds backupCapRefusal". **Limits, stated:**
+  with keep-last 3 the local tier's three points can still be replaced within one day (3 per day is the schedule's own
+  pace plus one press); the hub's event text reads „agent privileged capability degraded" (the type is generic). No
+  sudoers or bundle change.
 
 ## v0.159.2 — the orphan thin check runs only after a failed backup (R-1012 follow-up) (2026-10-18)
 

CONTEXT.md

@@ -1,5 +1,17 @@
 # CONTEXT — felhom-agent working state
 
+> **2026-10-18 (night) — UNRELEASED on main: R-1093, R-978, R-973** (release + vouch: the operator's). R-1093 an empty
+> partition is blank (lsblk's PTTYPE on a partition is the parent's; set aside only on a clean blkid exit 0 with a
+> matching `PART_ENTRY_SCHEME`; an unparsable lsblk is unprobed). R-978 the escrow package reaches the hub only at the
+> claim (ceremony output v2, `PendingUpload`; `EscrowCeremonyConfig.Upload`). R-973 the `POST /backup` cadence cap.
+> **Decision (decided by CC unattended — operator may reverse): the cap's numbers.** Q: how many whole-guest runs may
+> the guest ask for? Options: (a) 2 per 24 h on the daily tier — keeps one local point older than a day, but refuses
+> the NIGHT after a press (R-899's night can fall inside the same 24 h); (b) 3 per 24 h + 1 per 6 days on the weekly
+> tier — the schedule never refused, a second press in a day refused, the local tier still replaceable in a day;
+> (c) none — status quo. Chose (b): the off-site tier is the one `07` §8 row 10 relies on and it is fully protected
+> for ~6 days; the local half's real fix is a time-bucketed prune (keep-daily), which is a retention change for the
+> operator. No sudoers or bundle change in any of the three.
+
 > **2026-10-17 — v0.159.1 RELEASED (0.159.0 superseded, do not vouch).** Go 1.27.2; R-1124 a decommissioned drive that is
 > gone is forgotten (`ForgetRetiredDrives`, root verb `unit-forget`); R-1012 the read-only `felhom-thin-check` names an
 > orphan thin device in a failed backup's text; the signed decommission prunes the guest-bind record. Bundle adds a path →

REUSE.md

@@ -174,6 +174,7 @@
 | `capability` store-grant probe (`storeGrantStatuses` / `storeGrantVerdict` / `Client.Permissions`) | cmd/felhom-agent/main.go, internal/proxmox/query.go | *"may the agent READ this backup tier?"*, one `capability.Status` per configured tier | R-185. **Never infer permission from an empty content listing** — `{"data":[]}` is what a FORBIDDEN tier and a NEWBORN tier both return, and that ambiguity hid an unreadable host tier on both demo boxes. Ask `/access/permissions` **as the agent's own token** (root always says yes). **The ungranted answer is not empty and not a 403** — it carries the privileges inherited from the box-wide `/` grant, so test for **`Datastore.AllocateSpace`** specifically; path-presence or `Datastore.Audit` reports a blinded storage healthy. Probed set comes from `BackupTiers()`, never a fixed list. Critical except the `local` fallback. Composes AROUND the sudo prober (the `poolReadStatus` precedent); `Status`'s wire shape is untouched so the hub alert is free. Unreachable PVE ⇒ degraded, never ok. |
 | `backup.RestoreTestState` | internal/backup/restoretest_state.go | `RecordSuccess(target,archive,tier,verified,t)` / `ProvenArchive(target)` / `ProvenRestoreTests(ctx)` / `LastSuccess(target)` / `OldestFirst(targets)` | Per-tier restore-test PROOF state, persisted (atomic tmp+rename) — **which archive** was proven, and when (R-86) | **Credit ONLY on success** — a permanently failing tier must keep sorting first, or it looks freshly proven and stops being retried. Ties break on target id: without it, two tiers proven in the same second rotate by Go's randomised map order. **This one NEEDS persistence unlike R-84** — R-84 had ground truth to consult (the archive is still on the storage); a restore-test destroys its scratch and leaves no artifact. **R-86: the ARCHIVE is the state, the time is metadata** — a time alone cannot answer "have we proven THIS archive", which is the due-check's whole question. A pre-R-86 file (bare RFC3339 per target) keeps its time and yields NO proven archive, so each tier is due once after the upgrade; reading a legacy time as proof of the current archive would invent a guarantee. **R-189: it is also the REPORTABLE half of the restore-test signal.** The in-memory `backup.Store` holds only this process's latest run, and under per-archive due-ness the agent will not re-test a proven archive — so a proof lost to a restart is not repeated for a whole archive generation (observed live: a passing 14.5 GB offsite restore reached no host-report). `ProvenRestoreTests` renders the stored proofs as `hub.RestoreTest` entries and the collector merges them; a record missing the archive or the tier is NOT emitted, because an unproven tier reading as proven is worse than the defect. **Only successes are stored, deliberately:** a success suppresses future work, a failure causes it. |
 | `backup.BackupSuccessState` | internal/backup/backup_state.go | `RecordBackupSuccess(target, b)` / `LastKnownSuccess(target, vmid)` | Newest SUCCESSFUL backup per tier+guest, persisted (atomic tmp+rename) — the due-check's fallback when the tier's storage cannot be read after a restart (R-894) | **Read ONLY when the storage cannot be read** — a storage that answers is the ground truth (R-84), and an archive absent there must make the tier due even when this file remembers one. A saved copy older than the cadence still reads due. Only successes are written. |
+| localapi backup cadence cap (R-973) | internal/localapi/backup_cap.go | `backupCadenceCap(cadence)`, `Server.capRefuses`, `Server.BackupCapRefusal()` | POST /backup refuses (429) a run the `07` §6 schedule would never ask for: ≤24 h tier → 3 successes per rolling 24 h; longer tier → 1 per max(cadence−24 h, cadence/2) | Counts SUCCESSES only, from this process AND `BackupSuccessState.RecentBackupSuccesses` (so a restart does not reset it); refusals saved (`RecordBackupRefusal`) and raised for 24 h as the CRITICAL host-report status `localapi:backup-cadence-cap` (`backupCapStatus` in main) → the hub's existing `agent_capability_degraded`. Tests `TestBackupCap_*`. |
 | `hub.ProvenRestoreTestReporter` + `Collector.SetProvenRestoreTests` | internal/hub/collect.go | the DURABLE restore-test source, merged with the in-memory one | R-189. Merge rule: **one entry per tier, newest by `TestedAt` wins** — a fresh failure beats a stored success (the failure is the news, and it lives nowhere else), a stored success beats a stale in-memory entry after a restart, and a tier never appears twice (the hub would read two tests). An unparseable timestamp counts as OLDER, so a malformed entry cannot displace a good one. **The wiring is pinned by an AST test** — the method this replaced (`RestoreTestState.Snapshot`) carried a doc comment naming a host-report gauge and had no caller for weeks. |
 | `backup.SpecBuilder` / `backup.TierPicker` / `(*BackupRunner).PickSettledRestoreCandidateOn` | internal/backup/schedule.go, runner.go | `func(ctx,archive) RestoreTestSpec`; `func(ctx,target,notAfter) (archive,landed,error)` | The per-run restore-test spec + per-tier **settled** candidate lookup (R-85, widened by R-86) | The spec is built **PER RUN**, never frozen at construction — the pre-R-85 immediately-invoked value made the offsite tier unschedulable AND went stale on any config change. `SourceTier` comes from **the archive**, never the configured target (the v0.100.0 rule). A tier with no archive returns `("", zero, nil)` — **`""` is NOT an error**, or every fresh box looks broken for its first week. **R-86: `notAfter` is the settle cutoff** (zero = no cutoff, which is what keeps `PickRestoreCandidateOn` a one-line call into it), and the picker now skips entries failing `archivePlausiblyComplete` — under per-archive due-ness an incomplete phantom would be picked forever, fail forever, never earn proof, and make the tier due at EVERY evaluation. |
 | `localapi.BackupTier` + `normalizeBackupTiers` / `config.BackupConfig.BackupTiers` | internal/localapi/backup_tiers.go, internal/config/config.go | `normalizeBackupTiers(tiers, legacy, cadence) []BackupTier`; `BackupTiers() ([]BackupTier, []string)` | THE R-82 multi-tier resolution — one runner per tier, primary first | **The untargeted local-API contract is FROZEN**: no `?target=` ⇒ primary tier ⇒ pre-R-82 response BYTES (Target is `omitempty` and stays empty). Never default a missing cadence — reject it and log the warning at ERROR. Never share one retention knob between tiers. Jobs are keyed by (vmid,target). |

cmd/felhom-agent/backup_cap_r973_test.go

@@ -0,0 +1,67 @@
+package main
+
+import (
+	"go/ast"
+	"strings"
+	"testing"
+	"time"
+
+	"gitea.dooplex.hu/admin/felhom-agent/internal/capability"
+)
+
+// R-973: a cadence-cap refusal becomes a CRITICAL degraded status — what the hub's existing
+// agent_capability_degraded event (operator-only) keys on — and clears when the refusal ages out.
+func TestBackupCapStatus_RefusalIsCriticalDegraded(t *testing.T) {
+	at := time.Date(2026, 10, 18, 3, 0, 0, 0, time.UTC)
+	s := backupCapStatus(func() (string, int, time.Time, bool) { return "felhom-pbs", 9201, at, true })
+	if !s.Critical || s.Status != capability.StatusDegraded || !strings.Contains(s.Reason, "9201") || !strings.Contains(s.Reason, "felhom-pbs") {
+		t.Fatalf("a refusal must raise a critical degraded status naming the guest and the tier: %+v", s)
+	}
+	if s := backupCapStatus(func() (string, int, time.Time, bool) { return "", 0, time.Time{}, false }); s.Status != capability.StatusOK || !s.Critical {
+		t.Fatalf("no refusal → ok (and still critical, so a later refusal alerts): %+v", s)
+	}
+	if s := backupCapStatus(nil); s.Status != capability.StatusOK {
+		t.Fatalf("no local API → ok: %+v", s)
+	}
+}
+
+// Wiring (the built-but-never-wired class): runDaemon's capability probe appends backupCapStatus, and the
+// late-bound source is set from the local API server.
+//
+// COMPANION RED-PROOF (observed 2026-10-18): delete `backupCapRefusal = localSrv.BackupCapRefusal` →
+// "runDaemon never binds backupCapRefusal to the local API server". Restored.
+func TestR973_CapRefusalIsWiredIntoTheReport(t *testing.T) {
+	_, f := parseMain(t)
+	var appended, bound bool
+	for _, d := range f.Decls {
+		fd, ok := d.(*ast.FuncDecl)
+		if !ok || fd.Name == nil || fd.Name.Name != "runDaemon" || fd.Body == nil {
+			continue
+		}
+		ast.Inspect(fd.Body, func(n ast.Node) bool {
+			switch x := n.(type) {
+			case *ast.CallExpr:
+				if id, ok := x.Fun.(*ast.Ident); ok && id.Name == "backupCapStatus" && len(x.Args) == 1 {
+					if a, ok := x.Args[0].(*ast.Ident); ok && a.Name == "backupCapRefusal" {
+						appended = true
+					}
+				}
+			case *ast.AssignStmt:
+				if len(x.Lhs) == 1 && len(x.Rhs) == 1 {
+					if l, ok := x.Lhs[0].(*ast.Ident); ok && l.Name == "backupCapRefusal" {
+						if sel, ok := x.Rhs[0].(*ast.SelectorExpr); ok && sel.Sel.Name == "BackupCapRefusal" {
+							bound = true
+						}
+					}
+				}
+			}
+			return true
+		})
+	}
+	if !appended {
+		t.Fatal("runDaemon's capability probe does not call backupCapStatus(backupCapRefusal)")
+	}
+	if !bound {
+		t.Fatal("runDaemon never binds backupCapRefusal to the local API server")
+	}
+}

cmd/felhom-agent/main.go

@@ -404,6 +404,31 @@ func (r *gateRemounter) Remount(ctx context.Context, t storage.KnownTarget) {
 // poolReadStatus probes the felhom-pool membership read (GET /pools/felhom) the stale-lock reaper's
 // ownership scoping depends on (v0.62.0, audit A1). Needs `Pool.Audit` at `/pool/felhom` — granted
 // by host-install v1.9.0; on an older ACL this reports degraded and the reaper fail-safes (skips).
+// backupCapStatusName is the host-report status the R-973 cadence cap raises.
+const backupCapStatusName = "localapi:backup-cadence-cap"
+
+// backupCapStatus turns the local-API backup cadence cap's newest refusal (R-973) into a CRITICAL
+// capability status: degraded for 24 h after a refusal, so the hub raises its operator-only
+// agent_capability_degraded event (no hub change). The Reason names the guest, the tier and the time, and
+// says what to do. nil source (local API off) → ok.
+func backupCapStatus(refusal func() (string, int, time.Time, bool)) capability.Status {
+	s := capability.Status{
+		Name:     backupCapStatusName,
+		Feature:  "whole-guest restore points: a guest asked for more whole-guest backups than its schedule allows, and the extra ones were refused (R-973)",
+		Critical: true,
+		Status:   capability.StatusOK,
+	}
+	if refusal == nil {
+		return s
+	}
+	if target, vmid, at, ok := refusal(); ok {
+		s.Status = capability.StatusDegraded
+		s.Reason = fmt.Sprintf("refused a whole-guest backup of guest %d on target %q at %s — more than the schedule allows; the guest's controller may be misbehaving or compromised: check the guest",
+			vmid, target, at.UTC().Format(time.RFC3339))
+	}
+	return s
+}
+
 func poolReadStatus(ctx context.Context, px *proxmox.Client) capability.Status {
 	s := capability.Status{
 		Name:     "pve:pool-read",
@@ -830,8 +855,13 @@ func runDaemon(cfg config.Config, logger *slog.Logger, logRing *applog.Ring) int
 		run: (&proxmox.ExecRunner{Mode: proxmox.RunnerMode(cfg.Privileged.Mode)}).Run,
 		log: logger,
 	}
+	// R-973: the local-API backup cadence cap's refusals ride the report as a CRITICAL status, so the hub's
+	// existing agent_capability_degraded event (operator-only) tells the operator. Late-bound like
+	// drConfigured: the local API server is built further down, before the loop starts.
+	var backupCapRefusal func() (string, int, time.Time, bool)
 	probeAll := func(ctx context.Context) []capability.Status {
 		out := append(capProber.Probe(ctx), poolReadStatus(ctx, px))
+		out = append(out, backupCapStatus(backupCapRefusal))
 		return append(out, storeGrantStatuses(ctx, px, cfg, grantRepairer)...)
 	}
 	// (The startup self-check log runs AFTER the pbsdr manager is wired below, so its snapshot
@@ -1209,6 +1239,7 @@ func runDaemon(cfg config.Config, logger *slog.Logger, logRing *applog.Ring) int
 	}
 	localSrv := buildLocalAPIServer(cfg, px, backupStore, heavyOps, observer, driveKnown, hostOps, gate, collector, client, intentRec, guestBindStore, formatJobStore, logRing, escrowCeremonyCfg, logger, &localTokens)
 	if localSrv != nil {
+		backupCapRefusal = localSrv.BackupCapRefusal // R-973
 		internalPlaceExec.SetEnsure(localSrv.EnsureInternalPlace)
 		// R-998 (doc 14): POST /host/poweroff — guest shutdown, then host power-off; guards in hostpoweroff.go.
 		pwMode := proxmox.RunnerMode(cfg.Privileged.Mode)

internal/backup/backup_state.go

@@ -39,13 +39,25 @@ type savedSuccess struct {
 	target string
 	vmid   int
 	at     time.Time
+	// recent (R-973) holds the start times of the newest successes (at most maxRecentSuccesses, newest
+	// last) — what the local-API backup cadence cap counts, so an agent restart does not reset the cap.
+	recent []time.Time
+	// refusedAt (R-973) is the newest time the cap refused a backup of this guest on this tier.
+	refusedAt time.Time
 }
 
-// backupSuccessJSON is one entry on disk.
+// maxRecentSuccesses bounds the per-tier success history kept for the cadence cap (R-973). The cap
+// allows at most 3 runs in a window, so 8 is ample.
+const maxRecentSuccesses = 8
+
+// backupSuccessJSON is one entry on disk. Recent and LastRefusedAt are additive (R-973): a file written
+// before them reads as "no history", and an older agent ignores them.
 type backupSuccessJSON struct {
-	Target    string `json:"target"`
-	VMID      int    `json:"vmid"`
-	StartedAt string `json:"started_at"`
+	Target        string   `json:"target"`
+	VMID          int      `json:"vmid"`
+	StartedAt     string   `json:"started_at"`
+	Recent        []string `json:"recent,omitempty"`
+	LastRefusedAt string   `json:"last_refused_at,omitempty"`
 }
 
 func backupStateKey(target string, vmid int) string { return target + "/" + strconv.Itoa(vmid) }
@@ -67,7 +79,19 @@ func NewBackupSuccessState(path string) *BackupSuccessState {
 		if perr != nil {
 			continue // one unreadable entry must not lose the others
 		}
-		s.last[backupStateKey(e.Target, e.VMID)] = savedSuccess{target: e.Target, vmid: e.VMID, at: t.UTC()}
+		ss := savedSuccess{target: e.Target, vmid: e.VMID, at: t.UTC()}
+		for _, r := range e.Recent {
+			if rt, rerr := time.Parse(time.RFC3339, r); rerr == nil {
+				ss.recent = append(ss.recent, rt.UTC())
+			}
+		}
+		if len(ss.recent) == 0 {
+			ss.recent = []time.Time{ss.at} // a pre-R-973 file: its one known success counts
+		}
+		if rt, rerr := time.Parse(time.RFC3339, e.LastRefusedAt); rerr == nil {
+			ss.refusedAt = rt.UTC()
+		}
+		s.last[backupStateKey(e.Target, e.VMID)] = ss
 	}
 	return s
 }
@@ -85,13 +109,72 @@ func (s *BackupSuccessState) RecordBackupSuccess(target string, b hub.Backup) er
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	k := backupStateKey(target, b.VMID)
-	if old, ok := s.last[k]; ok && !t.After(old.at) {
+	old, had := s.last[k]
+	if had && !t.After(old.at) {
 		return nil
 	}
-	s.last[k] = savedSuccess{target: target, vmid: b.VMID, at: t.UTC()}
+	ss := savedSuccess{target: target, vmid: b.VMID, at: t.UTC(), refusedAt: old.refusedAt}
+	ss.recent = append(append([]time.Time(nil), old.recent...), t.UTC())
+	if len(ss.recent) > maxRecentSuccesses {
+		ss.recent = ss.recent[len(ss.recent)-maxRecentSuccesses:]
+	}
+	s.last[k] = ss
 	return s.saveLocked()
 }
 
+// RecentBackupSuccesses returns the saved success start times for this tier and guest that are not
+// older than since (R-973 — the cadence cap's restart-proof count).
+func (s *BackupSuccessState) RecentBackupSuccesses(target string, vmid int, since time.Time) []time.Time {
+	if s == nil {
+		return nil
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	var out []time.Time
+	for _, t := range s.last[backupStateKey(target, vmid)].recent {
+		if !t.Before(since) {
+			out = append(out, t)
+		}
+	}
+	return out
+}
+
+// RecordBackupRefusal saves that the cadence cap refused a backup of this guest on this tier at at
+// (R-973), so the operator signal it raises survives an agent restart.
+func (s *BackupSuccessState) RecordBackupRefusal(target string, vmid int, at time.Time) error {
+	if s == nil {
+		return nil
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	k := backupStateKey(target, vmid)
+	ss, ok := s.last[k]
+	if !ok {
+		return nil // nothing to cap against without a success; the cap never refuses then
+	}
+	if !at.After(ss.refusedAt) {
+		return nil
+	}
+	ss.refusedAt = at.UTC()
+	s.last[k] = ss
+	return s.saveLocked()
+}
+
+// LastBackupRefusal returns the newest saved cadence-cap refusal across every tier and guest.
+func (s *BackupSuccessState) LastBackupRefusal() (target string, vmid int, at time.Time, ok bool) {
+	if s == nil {
+		return "", 0, time.Time{}, false
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	for _, e := range s.last {
+		if !e.refusedAt.IsZero() && e.refusedAt.After(at) {
+			target, vmid, at, ok = e.target, e.vmid, e.refusedAt, true
+		}
+	}
+	return target, vmid, at, ok
+}
+
 // LastKnownSuccess returns the newest saved success for this tier and guest (ok=false = none on file).
 func (s *BackupSuccessState) LastKnownSuccess(target string, vmid int) (time.Time, bool) {
 	if s == nil {
@@ -129,7 +212,14 @@ func (s *BackupSuccessState) KnownBackupSuccesses() []hub.Backup {
 func (s *BackupSuccessState) saveLocked() error {
 	entries := make([]backupSuccessJSON, 0, len(s.last))
 	for _, e := range s.last {
-		entries = append(entries, backupSuccessJSON{Target: e.target, VMID: e.vmid, StartedAt: e.at.Format(time.RFC3339)})
+		j := backupSuccessJSON{Target: e.target, VMID: e.vmid, StartedAt: e.at.Format(time.RFC3339)}
+		for _, r := range e.recent {
+			j.Recent = append(j.Recent, r.Format(time.RFC3339))
+		}
+		if !e.refusedAt.IsZero() {
+			j.LastRefusedAt = e.refusedAt.Format(time.RFC3339)
+		}
+		entries = append(entries, j)
 	}
 	// Deterministic file content (Go's map order is random).
 	sort.Slice(entries, func(i, j int) bool {

internal/backup/backup_state_test.go

@@ -74,3 +74,40 @@ func TestBackupSuccessState_KnownBackupSuccessesSurviveAReopen(t *testing.T) {
 		t.Fatal("uncovered_volumes must marshal as [], not null")
 	}
 }
+
+// R-973: the cadence cap's history and refusals survive a reopen; the history is bounded; a file
+// written before R-973 counts its one known success (never "no history" for a tier that has a copy).
+func TestBackupSuccessState_R973_RecentHistoryAndRefusalSurviveAReopen(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "backup-success-state.json")
+	s := NewBackupSuccessState(path)
+	base := time.Date(2026, 10, 18, 2, 30, 0, 0, time.UTC)
+	for i := 0; i < 10; i++ {
+		at := base.Add(time.Duration(i) * time.Hour)
+		if err := s.RecordBackupSuccess("local", hub.Backup{VMID: 9201, Success: true, StartedAt: at.Format(time.RFC3339)}); err != nil {
+			t.Fatal(err)
+		}
+	}
+	refused := base.Add(11 * time.Hour)
+	if err := s.RecordBackupRefusal("local", 9201, refused); err != nil {
+		t.Fatal(err)
+	}
+	r := NewBackupSuccessState(path)
+	all := r.RecentBackupSuccesses("local", 9201, time.Time{})
+	if len(all) != maxRecentSuccesses || !all[len(all)-1].Equal(base.Add(9*time.Hour)) {
+		t.Fatalf("recent history after a reopen: %v (want the newest %d, ending at +9h)", all, maxRecentSuccesses)
+	}
+	if got := r.RecentBackupSuccesses("local", 9201, base.Add(7*time.Hour)); len(got) != 3 {
+		t.Fatalf("successes since +7h: %d, want 3", len(got))
+	}
+	if tg, vm, at, ok := r.LastBackupRefusal(); !ok || tg != "local" || vm != 9201 || !at.Equal(refused) {
+		t.Fatalf("refusal after a reopen: %q %d %v %v", tg, vm, at, ok)
+	}
+
+	old := filepath.Join(t.TempDir(), "old.json")
+	if err := os.WriteFile(old, []byte(`[{"target":"felhom-pbs","vmid":9201,"started_at":"2026-10-17T03:00:00Z"}]`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if got := NewBackupSuccessState(old).RecentBackupSuccesses("felhom-pbs", 9201, time.Time{}); len(got) != 1 {
+		t.Fatalf("a pre-R-973 file must count its one success: %v", got)
+	}
+}

internal/localapi/backup_cap.go

@@ -0,0 +1,146 @@
+package localapi
+
+import (
+	"fmt"
+	"net/http"
+	"sort"
+	"time"
+
+	"gitea.dooplex.hu/admin/felhom-agent/internal/hub"
+)
+
+// The whole-guest backup cadence cap (R-973, security review 2026-10-12).
+//
+// POST /backup is reachable from inside the guest, and every successful run prunes the tier
+// (`--prune-backups keep-last=N` on a local tier; ep0's server-side keep-last 2 on the off-site tier). So
+// a compromised controller calling it in a loop pushed every pre-compromise whole-guest restore point out
+// within minutes — the threat `07` §8 row 10 counts the off-site tier as the answer to. The agent now
+// refuses a run that the schedule in `07` §6 would never ask for:
+//
+//   - a tier whose cadence is at most 24 h (the local tier): at most 3 successful runs in any rolling
+//     24 h. The schedule is one night run; a „Mentés most" press makes a LOCAL copy and, since R-899, the
+//     night still takes its own after it, which can land inside the same 24 h as the previous night (the
+//     window opens anywhere in [W+2h, W+6h)). So a normal day needs at most 3: two nights plus one press.
+//     A second press inside 24 h is refused — the margin is spent on the night, which must never be refused
+//     because of the household's presses.
+//   - a longer tier (the 7-day off-site tier): at most 1 successful run per max(cadence − 24 h, cadence/2)
+//     — 6 days for 7 days. The controller asks /backup/due first and runs only when the newest copy is older
+//     than the cadence, and the button never targets this tier (`07` §6, controller v0.301.0), so a
+//     legitimate run never comes sooner; 24 h of slack absorbs clock and archive-time differences.
+//
+// Only SUCCESSES count — a failed run prunes nothing and must stay retryable. The count survives an agent
+// restart: it reads the success history saved on disk (LastKnownBackupStore, the R-894 file) as well as
+// this process's own record. A refusal answers 429, is logged at WARN, is saved, and raises the operator
+// signal BackupCapRefusal feeds (a critical capability in the host report → the hub's existing
+// `agent_capability_degraded` event, operator-only). Pinned by TestBackupCap_* (backup_cap_test.go).
+
+// backupCapRefusalHold is how long one refusal keeps the operator signal raised.
+const backupCapRefusalHold = 24 * time.Hour
+
+// backupCadenceCap returns the rolling window and the most successful runs allowed in it for a tier.
+func backupCadenceCap(cadence time.Duration) (window time.Duration, max int) {
+	if cadence <= 0 {
+		cadence = defaultBackupCadence
+	}
+	if cadence <= 24*time.Hour {
+		return 24 * time.Hour, 3
+	}
+	w := cadence - 24*time.Hour
+	if w < cadence/2 {
+		w = cadence / 2
+	}
+	return w, 1
+}
+
+// recentCapRuns returns the start times of the successful runs on this tier for this guest inside the
+// window ending now — this process's record and the saved one, each counted once. Caller holds no lock.
+func (s *Server) recentCapRuns(key backupJobKey, since time.Time) []time.Time {
+	seen := map[int64]bool{}
+	var out []time.Time
+	add := func(t time.Time) {
+		if t.Before(since) || seen[t.Unix()] {
+			return
+		}
+		seen[t.Unix()] = true
+		out = append(out, t)
+	}
+	s.capMu.Lock()
+	for _, t := range s.capRuns[key] {
+		add(t)
+	}
+	s.capMu.Unlock()
+	if s.lastKnown != nil {
+		for _, t := range s.lastKnown.RecentBackupSuccesses(key.target, key.vmid, since) {
+			add(t)
+		}
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].Before(out[j]) })
+	return out
+}
+
+// recordCapRun notes a successful run for the cap (the saved half is written by RecordBackupSuccess).
+func (s *Server) recordCapRun(key backupJobKey, b hub.Backup) {
+	t, err := time.Parse(time.RFC3339, b.StartedAt)
+	if err != nil {
+		t = s.now()
+	}
+	s.capMu.Lock()
+	defer s.capMu.Unlock()
+	if s.capRuns == nil {
+		s.capRuns = map[backupJobKey][]time.Time{}
+	}
+	runs := append(s.capRuns[key], t.UTC())
+	if len(runs) > 8 {
+		runs = runs[len(runs)-8:]
+	}
+	s.capRuns[key] = runs
+}
+
+// capRefuses applies the cap to a new run request. It writes the 429 and returns true when refused.
+func (s *Server) capRefuses(w http.ResponseWriter, key backupJobKey, tier BackupTier) bool {
+	window, max := backupCadenceCap(tier.Cadence)
+	now := s.now()
+	runs := s.recentCapRuns(key, now.Add(-window))
+	if len(runs) < max {
+		return false
+	}
+	next := runs[len(runs)-max].Add(window)
+	s.capMu.Lock()
+	s.capRefusal = capRefusal{target: key.target, vmid: key.vmid, at: now.UTC()}
+	s.capMu.Unlock()
+	if s.lastKnown != nil {
+		if err := s.lastKnown.RecordBackupRefusal(key.target, key.vmid, now); err != nil {
+			s.logger.Warn("local-api: could not save the backup refusal on disk (R-973)", "vmid", key.vmid, "target", key.target, "err", err)
+		}
+	}
+	s.logger.Warn("local-api: backup REFUSED — more whole-guest backups than the schedule allows (R-973 cadence cap; check the guest)",
+		"vmid", key.vmid, "target", key.target, "runs_in_window", len(runs), "allowed", max,
+		"window_h", int(window.Hours()), "next_allowed", next.UTC().Format(time.RFC3339))
+	writeStatus(w, http.StatusTooManyRequests, false, nil, fmt.Sprintf(
+		"too many whole-guest backups on target %q: %d successful in the last %d h, the schedule allows %d — refused (the next one is allowed after %s)",
+		key.target, len(runs), int(window.Hours()), max, next.UTC().Format(time.RFC3339)))
+	return true
+}
+
+type capRefusal struct {
+	target string
+	vmid   int
+	at     time.Time
+}
+
+// BackupCapRefusal reports the newest cadence-cap refusal still inside the 24 h hold (this process's or
+// the saved one) — the source of the operator signal in the host report (R-973). ok=false = none.
+func (s *Server) BackupCapRefusal() (target string, vmid int, at time.Time, ok bool) {
+	s.capMu.Lock()
+	r := s.capRefusal
+	s.capMu.Unlock()
+	if s.lastKnown != nil {
+		if t, v, a, found := s.lastKnown.LastBackupRefusal(); found && a.After(r.at) {
+			r = capRefusal{target: t, vmid: v, at: a}
+		}
+	}
+	if r.at.IsZero() || s.now().Sub(r.at) > backupCapRefusalHold {
+		return "", 0, time.Time{}, false
+	}
+	return r.target, r.vmid, r.at, true
+}

internal/localapi/backup_cap_test.go

@@ -0,0 +1,293 @@
+package localapi
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+	"path/filepath"
+	"sync"
+	"testing"
+	"time"
+
+	"gitea.dooplex.hu/admin/felhom-agent/internal/backup"
+	"gitea.dooplex.hu/admin/felhom-agent/internal/hub"
+)
+
+// R-973 — the whole-guest backup cadence cap. A compromised controller calling POST /backup in a loop
+// pushed out every pre-compromise restore point: each success prunes the tier. These tests model the tier
+// the way Proxmox and ep0 keep it (keep-last N, pruned after each success) and ask what is LEFT.
+
+// keepLastTier is a whole-guest tier: every successful run adds an archive stamped with the clock and
+// prunes to keepLast, as vzdump's --prune-backups keep-last (local) and ep0's keep-last 2 (off-site) do.
+type keepLastTier struct {
+	mu       sync.Mutex
+	clock    *testClock
+	keepLast int
+	archives []time.Time
+	fail     bool
+	runs     int
+}
+
+func (k *keepLastTier) BackupWithSnapshotHook(_ context.Context, vmid int, _ func()) (hub.Backup, error) {
+	k.mu.Lock()
+	defer k.mu.Unlock()
+	k.runs++
+	now := k.clock.Now()
+	if k.fail {
+		return hub.Backup{VMID: vmid, StartedAt: now.Format(time.RFC3339)}, fmt.Errorf("vzdump failed")
+	}
+	k.archives = append(k.archives, now)
+	if len(k.archives) > k.keepLast {
+		k.archives = k.archives[len(k.archives)-k.keepLast:]
+	}
+	return hub.Backup{VMID: vmid, Success: true, Archive: "x", StartedAt: now.Format(time.RFC3339)}, nil
+}
+
+// oldestBefore reports whether the tier still holds an archive made before t (a pre-compromise point).
+func (k *keepLastTier) oldestBefore(t time.Time) bool {
+	k.mu.Lock()
+	defer k.mu.Unlock()
+	return len(k.archives) > 0 && k.archives[0].Before(t)
+}
+
+func (k *keepLastTier) count() (runs, kept int) {
+	k.mu.Lock()
+	defer k.mu.Unlock()
+	return k.runs, len(k.archives)
+}
+
+type testClock struct {
+	mu sync.Mutex
+	t  time.Time
+}
+
+func (c *testClock) Now() time.Time          { c.mu.Lock(); defer c.mu.Unlock(); return c.t }
+func (c *testClock) Advance(d time.Duration) { c.mu.Lock(); c.t = c.t.Add(d); c.mu.Unlock() }
+
+// capServer builds the two-tier box of `07` §6: local 24 h keep-last 3, off-site 7 d keep-last 2, the
+// success history on disk at path (a second capServer on the same path is an agent restart).
+func capServer(t *testing.T, path string, clock *testClock, local, offsite *keepLastTier) *Server {
+	t.Helper()
+	srv, err := NewServer(Options{
+		ListenAddr: "127.0.0.1:0", Guests: &fakeGuests{}, Backups: &fakeBackups{}, Store: &fakeStore{},
+		Storage: fakeStorage{targets: []hub.StorageTarget{{Name: "local"}, {Name: "felhom-pbs"}}},
+		Tokens:  staticTokens{"A": 8200},
+		BackupTiers: []BackupTier{
+			{TargetID: "local", Cadence: 24 * time.Hour, Primary: true, Service: local},
+			{TargetID: "felhom-pbs", Cadence: 7 * 24 * time.Hour, Service: offsite},
+		},
+		LastKnownBackups: backup.NewBackupSuccessState(path),
+		Logger:           slog.New(slog.NewTextHandler(io.Discard, nil)),
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	srv.baseCtx = context.Background()
+	srv.now = clock.Now
+	return srv
+}
+
+// runBackup POSTs one backup and waits for the job to end. Returns the HTTP status of the POST.
+func runBackup(t *testing.T, srv *Server, target string) int {
+	t.Helper()
+	rr := do(t, srv.Handler(), "POST", "/backup?target="+target, "A", "")
+	if rr.Code == http.StatusAccepted {
+		waitFor(t, func() bool {
+			srv.jobsMu.Lock()
+			defer srv.jobsMu.Unlock()
+			j := srv.jobs[backupJobKey{vmid: 8200, target: target}]
+			return j != nil && !backupInFlight(j.Phase)
+		})
+	}
+	return rr.Code
+}
+
+// The off-site tier — the one `07` §8 row 10 counts on against ransomware. Before the cap ten calls in a
+// row left ep0 holding only the attacker's two copies. Now ONE runs (the tier was due), the other nine
+// are refused, and the newest pre-compromise copy survives; five days of flooding later it still does.
+//
+// COMPANION RED-PROOF (observed 2026-10-18): make capRefuses always return false → this fails with
+// "the off-site tier lost every pre-compromise copy: 10 runs" . Restored.
+func TestBackupCap_OffsiteFloodKeepsAPreCompromiseCopy(t *testing.T) {
+	clock := &testClock{t: testNow}
+	local := &keepLastTier{clock: clock, keepLast: 3}
+	off := &keepLastTier{clock: clock, keepLast: 2}
+	path := filepath.Join(t.TempDir(), "backup-success-state.json")
+	srv := capServer(t, path, clock, local, off)
+
+	// The honest history: two weekly copies, the newest 7 days and 1 hour old (so the tier is due).
+	for _, age := range []time.Duration{14*24*time.Hour + time.Hour, 7*24*time.Hour + time.Hour} {
+		clock.t = testNow.Add(-age)
+		if code := runBackup(t, srv, "felhom-pbs"); code != http.StatusAccepted {
+			t.Fatalf("seeding the honest weekly copy: %d", code)
+		}
+	}
+	clock.t = testNow
+	compromise := testNow
+
+	refused := 0
+	for i := 0; i < 10; i++ {
+		if runBackup(t, srv, "felhom-pbs") == http.StatusTooManyRequests {
+			refused++
+		}
+		clock.Advance(time.Minute)
+	}
+	runs, _ := off.count()
+	if !off.oldestBefore(compromise) {
+		t.Fatalf("the off-site tier lost every pre-compromise copy: %d runs", runs-2)
+	}
+	if runs-2 != 1 || refused != 9 {
+		t.Fatalf("flood: %d runs, %d refused — want 1 run (the tier was due) and 9 refused", runs-2, refused)
+	}
+	for d := 0; d < 5; d++ { // five more days of flooding, every hour
+		for h := 0; h < 24; h++ {
+			clock.Advance(time.Hour)
+			if code := runBackup(t, srv, "felhom-pbs"); code != http.StatusTooManyRequests {
+				t.Fatalf("day %d hour %d: an off-site run was allowed %v after the last one", d, h, clock.Now().Sub(compromise))
+			}
+		}
+	}
+	if !off.oldestBefore(compromise) {
+		t.Fatal("five days of flooding pushed out the pre-compromise off-site copy")
+	}
+}
+
+// The local tier: a flood runs exactly 3 in a day (the schedule's own day: two nights + one press) and
+// every further request is refused. Honest about the limit: with keep-last 3 those 3 replace the 3 kept
+// points — the cap slows a flush from minutes to a day; it cannot keep a point a 3-per-day pace prunes.
+func TestBackupCap_LocalFloodRunsAtMostThreeADay(t *testing.T) {
+	clock := &testClock{t: testNow}
+	local := &keepLastTier{clock: clock, keepLast: 3}
+	srv := capServer(t, filepath.Join(t.TempDir(), "s.json"), clock, local, &keepLastTier{clock: clock, keepLast: 2})
+	refused := 0
+	for i := 0; i < 20; i++ {
+		if runBackup(t, srv, "local") == http.StatusTooManyRequests {
+			refused++
+		}
+		clock.Advance(10 * time.Minute)
+	}
+	if runs, _ := local.count(); runs != 3 || refused != 17 {
+		t.Fatalf("local flood over ~3 h: %d runs, %d refused — want 3 and 17", runs, refused)
+	}
+	clock.Advance(24 * time.Hour) // a day later the window has moved on
+	if code := runBackup(t, srv, "local"); code != http.StatusAccepted {
+		t.Fatalf("a run a day later must be allowed: %d", code)
+	}
+}
+
+// The schedule itself is never refused: a night at W+6h, a press at 10:00, the next night at W+2h (all
+// three inside one rolling 24 h) run; a second press that day is refused; nights keep running after it.
+func TestBackupCap_TheScheduledDayIsNeverRefused(t *testing.T) {
+	day := time.Date(2026, 6, 10, 0, 0, 0, 0, time.UTC)
+	clock := &testClock{t: day.Add(8*time.Hour + 29*time.Minute)} // W=02:30 → W+6h ≈ 08:29
+	local := &keepLastTier{clock: clock, keepLast: 3}
+	srv := capServer(t, filepath.Join(t.TempDir(), "s.json"), clock, local, &keepLastTier{clock: clock, keepLast: 2})
+	steps := []struct {
+		at   time.Time
+		want int
+		what string
+	}{
+		{day.Add(8*time.Hour + 29*time.Minute), http.StatusAccepted, "night 1 at W+6h"},
+		{day.Add(10 * time.Hour), http.StatusAccepted, "a press at 10:00"},
+		{day.Add(24*time.Hour + 4*time.Hour + 30*time.Minute), http.StatusAccepted, "night 2 at W+2h (20 h later)"},
+		{day.Add(24*time.Hour + 7*time.Hour), http.StatusTooManyRequests, "a second press inside the same 24 h"},
+		{day.Add(48*time.Hour + 4*time.Hour + 30*time.Minute), http.StatusAccepted, "night 3"},
+	}
+	for _, s := range steps {
+		clock.t = s.at
+		if got := runBackup(t, srv, "local"); got != s.want {
+			t.Fatalf("%s: got %d, want %d", s.what, got, s.want)
+		}
+	}
+}
+
+// A restart must not reset the cap: the history is read back from disk.
+//
+// COMPANION RED-PROOF (observed 2026-10-18): make recentCapRuns ignore s.lastKnown → this fails with
+// "after a restart the 4th run in a day was allowed (got 202)". Restored.
+func TestBackupCap_SurvivesARestart(t *testing.T) {
+	clock := &testClock{t: testNow}
+	path := filepath.Join(t.TempDir(), "s.json")
+	local := &keepLastTier{clock: clock, keepLast: 3}
+	srv := capServer(t, path, clock, local, &keepLastTier{clock: clock, keepLast: 2})
+	for i := 0; i < 3; i++ {
+		if code := runBackup(t, srv, "local"); code != http.StatusAccepted {
+			t.Fatalf("run %d: %d", i+1, code)
+		}
+		clock.Advance(time.Minute)
+	}
+	srv2 := capServer(t, path, clock, local, &keepLastTier{clock: clock, keepLast: 2}) // the restart
+	if code := runBackup(t, srv2, "local"); code != http.StatusTooManyRequests {
+		t.Fatalf("after a restart the 4th run in a day was allowed (got %d)", code)
+	}
+}
+
+// Failed runs prune nothing and must stay retryable: they do not count.
+func TestBackupCap_FailuresDoNotCount(t *testing.T) {
+	clock := &testClock{t: testNow}
+	local := &keepLastTier{clock: clock, keepLast: 3, fail: true}
+	srv := capServer(t, filepath.Join(t.TempDir(), "s.json"), clock, local, &keepLastTier{clock: clock, keepLast: 2})
+	for i := 0; i < 6; i++ {
+		if code := runBackup(t, srv, "local"); code != http.StatusAccepted {
+			t.Fatalf("failed attempt %d was refused: %d", i+1, code)
+		}
+		clock.Advance(15 * time.Minute)
+	}
+	local.mu.Lock()
+	local.fail = false
+	local.mu.Unlock()
+	if code := runBackup(t, srv, "local"); code != http.StatusAccepted {
+		t.Fatalf("a success after six failures was refused: %d", code)
+	}
+}
+
+// A refusal raises the operator signal for 24 h, and the signal survives a restart.
+func TestBackupCap_RefusalRaisesTheOperatorSignal(t *testing.T) {
+	clock := &testClock{t: testNow}
+	path := filepath.Join(t.TempDir(), "s.json")
+	off := &keepLastTier{clock: clock, keepLast: 2}
+	srv := capServer(t, path, clock, &keepLastTier{clock: clock, keepLast: 3}, off)
+	if _, _, _, ok := srv.BackupCapRefusal(); ok {
+		t.Fatal("a fresh box must not raise the signal")
+	}
+	runBackup(t, srv, "felhom-pbs")
+	clock.Advance(time.Hour)
+	if code := runBackup(t, srv, "felhom-pbs"); code != http.StatusTooManyRequests {
+		t.Fatalf("second off-site run an hour later: %d, want 429", code)
+	}
+	target, vmid, at, ok := srv.BackupCapRefusal()
+	if !ok || target != "felhom-pbs" || vmid != 8200 || !at.Equal(clock.Now()) {
+		t.Fatalf("signal after a refusal: ok=%v target=%q vmid=%d at=%v", ok, target, vmid, at)
+	}
+	clock.Advance(23 * time.Hour)
+	srv2 := capServer(t, path, clock, &keepLastTier{clock: clock, keepLast: 3}, off) // a restart
+	if _, _, _, ok := srv2.BackupCapRefusal(); !ok {
+		t.Fatal("the signal did not survive a restart")
+	}
+	clock.Advance(2 * time.Hour)
+	if _, _, _, ok := srv2.BackupCapRefusal(); ok {
+		t.Fatal("the signal must clear 24 h after the last refusal")
+	}
+}
+
+func TestBackupCadenceCap(t *testing.T) {
+	cases := []struct {
+		cadence time.Duration
+		window  time.Duration
+		max     int
+	}{
+		{0, 24 * time.Hour, 3},
+		{24 * time.Hour, 24 * time.Hour, 3},
+		{12 * time.Hour, 24 * time.Hour, 3},
+		{7 * 24 * time.Hour, 6 * 24 * time.Hour, 1},
+		{36 * time.Hour, 18 * time.Hour, 1},
+		{30 * 24 * time.Hour, 29 * 24 * time.Hour, 1},
+	}
+	for _, c := range cases {
+		if w, m := backupCadenceCap(c.cadence); w != c.window || m != c.max {
+			t.Errorf("cadence %v: got %v/%d, want %v/%d", c.cadence, w, m, c.window, c.max)
+		}
+	}
+}

internal/localapi/server.go

@@ -90,6 +90,10 @@ type BackupStore interface {
 type LastKnownBackupStore interface {
 	RecordBackupSuccess(target string, b hub.Backup) error
 	LastKnownSuccess(target string, vmid int) (time.Time, bool)
+	// R-973: the cadence cap's restart-proof history and its refusals.
+	RecentBackupSuccesses(target string, vmid int, since time.Time) []time.Time
+	RecordBackupRefusal(target string, vmid int, at time.Time) error
+	LastBackupRefusal() (target string, vmid int, at time.Time, ok bool)
 }
 
 // StorageView yields the host's observed storage targets (for mapping a mount's storage id →
@@ -302,6 +306,11 @@ type Server struct {
 	logger             *slog.Logger
 	now                func() time.Time
 
+	// R-973 cadence cap: this process's successful runs per tier+guest, and the newest refusal.
+	capMu      sync.Mutex
+	capRuns    map[backupJobKey][]time.Time
+	capRefusal capRefusal
+
 	disks           DiskOps           // slice 8C (optional)
 	diskGate        StorageGate       // slice 8C (optional)
 	guestList       GuestLister       // slice 8C (optional)
@@ -880,6 +889,12 @@ func (s *Server) handleBackup(w http.ResponseWriter, r *http.Request, vmid int)
 			"a backup is already in flight on target "+busyTarget+" (job "+busyJob+") — only one backup runs at a time per guest")
 		return
 	}
+	// R-973: the cadence cap (backup_cap.go). Checked under jobsMu, after the in-flight answers, so two
+	// requests cannot both pass it (only one run per guest is ever in flight).
+	if s.capRefuses(w, key, tier) {
+		s.jobsMu.Unlock()
+		return
+	}
 	// Job ids must be unique PER TIER, and by construction rather than by clock luck: two tiers
 	// started inside the same nanosecond (the weekly both-due night, or any injected clock) would
 	// otherwise collide and hand the second caller the first tier's id. The PRIMARY keeps the
@@ -943,6 +958,9 @@ func (s *Server) handleBackup(w http.ResponseWriter, r *http.Request, vmid int)
 			s.logger.Info("local-api: backup job complete", "vmid", vmid, "target", tier.TargetID, "job", jobID, "archive", b.Archive)
 		}
 		s.store.RecordBackup(b)
+		if b.Success {
+			s.recordCapRun(key, b) // R-973
+		}
 		if b.Success && s.lastKnown != nil {
 			if err := s.lastKnown.RecordBackupSuccess(tier.TargetID, b); err != nil {
 				// Not fatal: the backup exists. Only the fallback after a restart loses this copy.