From ec9f0e5f2db1e3ed2132f327656a38c540e5daa1 Mon Sep 17 00:00:00 2001
From: Josh Siviour <mrk@mulgadc.com>
Date: Thu, 9 Jul 2026 16:49:31 +1000
Subject: [PATCH] fix(eks,ebs): EKS multi-node create-cluster + EBS/instance
 lifecycle hardening (#487)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

* feat(ec2,ebs): harden volume attach/detach + instance lifecycle state machine

Batch of related EBS/instance-lifecycle correctness fixes verified together.

- u94vs: add compare-and-swap (casUpdate/casPut via nats KV Update revision)
  to the multi-writer lifecycle KV sites (WriteTerminatedInstance,
  WriteStoppedInstance, WriteClusterShutdown); make the teardown-reaper
  read-modify-write atomic via a merge callback so retries never re-run
  cleaner side effects.
- yi2ed: add ClaimStoppedInstance, a revision-checked delete-as-claim on the
  stopped bucket performed before Allocate/Insert/Run, so a forwarded start
  and a local fallback cannot double-start one instance onto the same volume.
- siv-473: make AttachVolume idempotent — return attached success when the
  volume is already attached to the requesting instance; a conflicting
  requested device returns InvalidParameterValue.
- siv-462: reconnect now re-asserts in-use for all attached volumes (boot and
  non-boot data volumes), not just boot, so a daemon restart no longer leaves
  stateful-pod data volumes split-brain; EFI pflash is skipped.
- 9w2mv: wait for the QMP DEVICE_DELETED event (bounded) before blockdev-del
  instead of a blind sleep, so a slow guest unplug no longer exhausts retries.
- soyah: poll (50ms) instead of fixed 1s sleeps in KillProcess and the
  viperblockd nbdkit confirm-running path, cutting volume-lifecycle latency.
- siv-481: a cross-node start forward that times out now falls back to a local
  start; this is safe because the yi2ed claim is the single serialization point.

* fix(eks): create per-account and leader KV buckets with cluster replica count

The EKS per-account KV bucket and the leader lease bucket were created at
Replicas=1 and never upgraded, since they're created lazily after
upgradeJetStreamReplicas runs at startup. On multi-node clusters this leaves
their single-replica Raft group transiently leaderless during formation,
causing KV timeouts that surface as a deterministic 503 on ListClusters.

Thread clusterSize through GetOrCreateAccountBucket/InitLeaderBucket (backed
by a new utils.GetOrCreateKVBucketWithReplicas) so both buckets are created
at max(clusterSize,1) replicas, matching every other node-count-scaled
JetStream stream.
---
 spinifex/daemon/daemon.go                     |  37 +-
 spinifex/daemon/daemon_handlers_instance.go   |  31 +-
 .../daemon_handlers_instance_tags_test.go     |   9 +
 .../daemon/daemon_handlers_instance_test.go   | 107 ++++++
 spinifex/daemon/daemon_handlers_volume.go     |  20 +
 .../daemon/daemon_handlers_volume_test.go     | 228 ++++++++++++
 spinifex/daemon/daemon_test.go                |  12 +-
 spinifex/daemon/eks_deps.go                   |   3 +
 spinifex/daemon/jetstream.go                  | 255 ++++++++++++-
 spinifex/daemon/jetstream_test.go             | 198 ++++++++++
 spinifex/daemon/vm_adapters.go                |   9 +
 spinifex/gateway/oidc_discovery_test.go       |   2 +-
 spinifex/handlers/ec2/instance/service.go     |   5 +
 .../handlers/ec2/instance/service_impl.go     |  48 ++-
 .../ec2/instance/service_impl_test.go         | 193 +++++++++-
 spinifex/handlers/eks/addon_installer.go      |  12 +-
 .../eks/addon_status_reconciler_test.go       |   2 +-
 spinifex/handlers/eks/addons.go               |   2 +-
 spinifex/handlers/eks/addons_test.go          |   2 +-
 .../eks/cluster_reconciler_state_test.go      |   4 +-
 .../handlers/eks/cluster_reconciler_test.go   |   8 +-
 spinifex/handlers/eks/cluster_state_test.go   |   2 +-
 spinifex/handlers/eks/delete_cluster_test.go  |   2 +-
 spinifex/handlers/eks/eks_billable_reaper.go  |   2 +-
 spinifex/handlers/eks/nats_bootstrap_test.go  |   4 +-
 spinifex/handlers/eks/nodegroup.go            |   2 +-
 spinifex/handlers/eks/nodegroup_test.go       |   2 +-
 .../handlers/eks/recovery_directive_test.go   |   4 +-
 spinifex/handlers/eks/service_impl.go         |  21 +-
 spinifex/handlers/eks/service_impl_test.go    |   6 +-
 spinifex/handlers/eks/store.go                |  29 +-
 spinifex/handlers/eks/store_test.go           |  40 +-
 .../sts/assume_role_with_web_identity_test.go |   4 +-
 spinifex/handlers/sts/oidc_jwks_test.go       |   4 +-
 spinifex/services/viperblockd/viperblockd.go  |  34 +-
 spinifex/utils/account.go                     |  15 +-
 spinifex/utils/account_test.go                |  45 +++
 spinifex/utils/process.go                     |  49 +--
 spinifex/utils/process_test.go                |  78 ++++
 spinifex/vm/errors.go                         |   7 +
 spinifex/vm/lifecycle.go                      |  21 +-
 spinifex/vm/manager.go                        |  13 +-
 spinifex/vm/manager_deps_test.go              |  29 ++
 spinifex/vm/restore.go                        |   7 +-
 spinifex/vm/restore_test.go                   |  12 +-
 spinifex/vm/shutdown_test.go                  |  14 +-
 spinifex/vm/state_store.go                    |  12 +
 spinifex/vm/teardown.go                       |  11 +-
 spinifex/vm/teardown_reaper.go                |  57 ++-
 spinifex/vm/volumes.go                        |  78 +++-
 spinifex/vm/volumes_test.go                   | 350 ++++++++++++++++++
 51 files changed, 1939 insertions(+), 202 deletions(-)
 create mode 100644 spinifex/utils/process_test.go

diff --git a/spinifex/daemon/daemon.go b/spinifex/daemon/daemon.go
index 43d8e446b..08f9fa720 100644
--- a/spinifex/daemon/daemon.go
+++ b/spinifex/daemon/daemon.go
@@ -175,9 +175,15 @@ type Daemon struct {
 	// initJetStream succeeds.
 	stateStore vm.StateStore
 
-	// Delay after QMP device_del before blockdev-del (default 1s, 0 in tests)
+	// Delay after QMP device_del before blockdev-del (default 1s, 0 in tests).
+	// Only used as a fallback when deviceDeletedTimeout is 0.
 	detachDelay time.Duration
 
+	// deviceDeletedTimeout bounds how long DetachVolume waits for QEMU's
+	// DEVICE_DELETED event after device_del before falling back to the
+	// blockdev-del retry loop (default 15s, 0 disables the wait in tests).
+	deviceDeletedTimeout time.Duration
+
 	// NATS connect retry options (nil uses defaults: 5min max, 500ms initial delay)
 	natsRetryOpts []utils.RetryOption
 
@@ -701,20 +707,21 @@ func NewDaemon(cfg *config.ClusterConfig) (*Daemon, error) {
 	}
 
 	d := &Daemon{
-		node:               cfg.Node,
-		clusterConfig:      cfg,
-		config:             &nodeCfg,
-		resourceMgr:        rm,
-		gpuProbe:           gpuProbe,
-		gpuManager:         gpuMgr,
-		ctx:                ctx,
-		cancel:             cancel,
-		vmMgr:              vm.NewManager(),
-		natsSubscriptions:  make(map[string]*nats.Subscription),
-		startTime:          time.Now(),
-		detachDelay:        1 * time.Second,
-		requireNATSTimeout: 30 * time.Second,
-		exitFunc:           os.Exit,
+		node:                 cfg.Node,
+		clusterConfig:        cfg,
+		config:               &nodeCfg,
+		resourceMgr:          rm,
+		gpuProbe:             gpuProbe,
+		gpuManager:           gpuMgr,
+		ctx:                  ctx,
+		cancel:               cancel,
+		vmMgr:                vm.NewManager(),
+		natsSubscriptions:    make(map[string]*nats.Subscription),
+		startTime:            time.Now(),
+		detachDelay:          1 * time.Second,
+		deviceDeletedTimeout: 15 * time.Second,
+		requireNATSTimeout:   30 * time.Second,
+		exitFunc:             os.Exit,
 	}
 	// Initialise peersReachable true so the first probe tick never fires a
 	// spurious reconcileOnHeal at startup. Mode() still requires natsConnected
diff --git a/spinifex/daemon/daemon_handlers_instance.go b/spinifex/daemon/daemon_handlers_instance.go
index 19b7507a6..0077ce543 100644
--- a/spinifex/daemon/daemon_handlers_instance.go
+++ b/spinifex/daemon/daemon_handlers_instance.go
@@ -25,11 +25,9 @@ import (
 
 // startStoppedForwardTimeout bounds the wait for ec2.start.{nodeId} to respond.
 // StartStoppedInstance does volume rehydrate + QEMU launch + QMP handshake,
-// which can take 10-20s on a cold start. Match the awsgw upstream 30s budget
-// so a slow-but-alive target node never trips the fallback path — falling back
-// while the target is still launching causes a duplicate Run that collides on
-// the deterministic tap name (TUNSETIFF: Device or resource busy).
-const startStoppedForwardTimeout = 30 * time.Second
+// which can take 10-20s on a cold start. Match the awsgw upstream 30s budget.
+// A var (not const) so tests can shrink it instead of sleeping real seconds.
+var startStoppedForwardTimeout = 30 * time.Second
 
 // handleSetInstanceTags applies a create-tags/delete-tags mutation to a running
 // instance: central store first, then the record under the manager lock, so a
@@ -477,14 +475,11 @@ func (d *Daemon) handleEC2DescribeInstanceStatus(msg *nats.Msg) {
 
 // handleEC2StartStoppedInstance handles the generic ec2.start queue-group topic.
 // It reads the stopped instance's LastNode from shared KV and forwards the
-// request to ec2.start.{lastNode} when the instance last ran on a different
-// node. This keeps instances on their original node so the per-node resource
-// manager sees the correct allocation. Local fallback fires only when the
-// targeted node has no active subscriber (ErrNoResponders — node down or not
-// yet recovered) or returns InsufficientInstanceCapacity. A timeout from a
-// reachable-but-slow target is surfaced as ServerInternal so the caller can
-// retry; falling back in that case races the still-running launch on the
-// target and collides on the deterministic tap name.
+// request to ec2.start.{lastNode} to keep instances on their original node.
+// Local fallback fires on any forward failure — no responders, capacity, or
+// timeout — because StartStoppedInstance's ClaimStoppedInstance call is the
+// single cluster-wide serialization point, so a losing racer bails out
+// cleanly instead of double-starting.
 func (d *Daemon) handleEC2StartStoppedInstance(msg *nats.Msg) {
 	// Peek at the instance ID without full unmarshal — we only need it for the
 	// LastNode lookup. The full unmarshal happens inside StartStoppedInstance.
@@ -532,13 +527,11 @@ func (d *Daemon) handleEC2StartStoppedInstance(msg *nats.Msg) {
 			slog.Warn("ec2.start: original node has no subscriber, starting locally",
 				"instanceId", peek.InstanceID, "lastNode", lastNode, "err", err)
 		} else {
-			// Timeout or other transport error from a node whose subscription
-			// did exist. Do NOT fall back — the target may still be launching
-			// the VM, and a duplicate Run here would collide on tap setup.
-			slog.Error("ec2.start: forward to original node failed, not falling back",
+			// Timeout or other transport error — e.g. lastNode crashed without
+			// a clean NATS disconnect, so no ErrNoResponders fires. The atomic
+			// claim in StartStoppedInstance makes a local retry safe either way.
+			slog.Warn("ec2.start: forward to original node failed, attempting local start",
 				"instanceId", peek.InstanceID, "lastNode", lastNode, "err", err)
-			respondWithError(msg, awserrors.ErrorServerInternal)
-			return
 		}
 	}
 
diff --git a/spinifex/daemon/daemon_handlers_instance_tags_test.go b/spinifex/daemon/daemon_handlers_instance_tags_test.go
index 3aafd98da..234edc290 100644
--- a/spinifex/daemon/daemon_handlers_instance_tags_test.go
+++ b/spinifex/daemon/daemon_handlers_instance_tags_test.go
@@ -52,6 +52,15 @@ func (m *memStoppedStore) DeleteStoppedInstance(id string) error {
 	return nil
 }
 
+func (m *memStoppedStore) ClaimStoppedInstance(id string) (*vm.VM, error) {
+	v, ok := m.instances[id]
+	if !ok {
+		return nil, vm.ErrStoppedInstanceClaimed
+	}
+	delete(m.instances, id)
+	return v, nil
+}
+
 func (m *memStoppedStore) WriteTerminatedInstance(string, *vm.VM) error { return nil }
 
 // tagTestDaemon returns a test daemon with an in-memory central tag store, an
diff --git a/spinifex/daemon/daemon_handlers_instance_test.go b/spinifex/daemon/daemon_handlers_instance_test.go
index 989d191bd..e3bf3376a 100644
--- a/spinifex/daemon/daemon_handlers_instance_test.go
+++ b/spinifex/daemon/daemon_handlers_instance_test.go
@@ -44,6 +44,8 @@ type fakeStateStore struct {
 	deleteStoppedFailFirst bool
 	deleteStoppedAttempts  int
 
+	claimStoppedErr error
+
 	terminated         map[string]*vm.VM
 	writeTerminatedErr error
 	listTerminatedErr  error
@@ -104,6 +106,23 @@ func (f *fakeStateStore) DeleteStoppedInstance(id string) error {
 	return nil
 }
 
+// ClaimStoppedInstance mimics the real atomic-delete claim for tests: under
+// the store lock, remove and return the entry, or claimStoppedErr /
+// vm.ErrStoppedInstanceClaimed if it is already gone or a test forced an error.
+func (f *fakeStateStore) ClaimStoppedInstance(id string) (*vm.VM, error) {
+	if f.claimStoppedErr != nil {
+		return nil, f.claimStoppedErr
+	}
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	v, ok := f.stopped[id]
+	if !ok {
+		return nil, vm.ErrStoppedInstanceClaimed
+	}
+	delete(f.stopped, id)
+	return v, nil
+}
+
 func (f *fakeStateStore) ListStoppedInstances() ([]*vm.VM, error) {
 	if f.listStoppedErr != nil {
 		return nil, f.listStoppedErr
@@ -147,6 +166,19 @@ func (f *fakeStateStore) DeleteTerminatedInstance(id string) error {
 	return nil
 }
 
+// UpdateTerminatedInstance mimics the real CAS semantics for tests: mutate
+// runs under the store lock against the stored value.
+func (f *fakeStateStore) UpdateTerminatedInstance(id string, mutate func(*vm.VM)) (*vm.VM, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	v, ok := f.terminated[id]
+	if !ok {
+		return nil, errors.New("terminated instance not found")
+	}
+	mutate(v)
+	return v, nil
+}
+
 var _ vm.StateStore = (*fakeStateStore)(nil)
 
 // daemonWithFakeStateStore returns a daemon wired with an in-memory NATS
@@ -257,6 +289,81 @@ func TestHandleEC2StartStoppedInstance_InstanceTypeUnknown(t *testing.T) {
 	assert.Equal(t, awserrors.ErrorInsufficientInstanceCapacity, decodeError(t, reply.Data)["Code"])
 }
 
+// withShortForwardTimeout shrinks startStoppedForwardTimeout for the duration
+// of a test so a forced forward timeout doesn't cost real wall-clock seconds.
+func withShortForwardTimeout(t *testing.T, d time.Duration) {
+	t.Helper()
+	orig := startStoppedForwardTimeout
+	startStoppedForwardTimeout = d
+	t.Cleanup(func() { startStoppedForwardTimeout = orig })
+}
+
+// TestHandleEC2StartStoppedInstance_ForwardTimeoutFallsBackLocally pins
+// siv-481: a forward to LastNode that times out (as opposed to an immediate
+// ErrNoResponders) must still fall back to a local start attempt instead of
+// surfacing a bare ServerInternal. The target subscriber below is alive but
+// silent, so nats: timeout is the only error the forward can produce — proof
+// that the fallback path, not ErrNoResponders handling, is what fires here.
+// An unresolvable instance type turns "local start was attempted" into a
+// distinct, assertable response code (InsufficientInstanceCapacity) instead
+// of colliding with the old no-fallback ServerInternal response.
+func TestHandleEC2StartStoppedInstance_ForwardTimeoutFallsBackLocally(t *testing.T) {
+	withShortForwardTimeout(t, 50*time.Millisecond)
+
+	store := newFakeStateStore()
+	v := stoppedVMFixture("i-timeout-fallback", testAccountID)
+	v.InstanceType = "definitely.not.a.real.type"
+	v.LastNode = "node-other"
+	store.stopped[v.ID] = v
+	d := daemonWithFakeStateStore(t, store)
+
+	// Simulate a live-but-unresponsive original node: subscribed, so no
+	// ErrNoResponders, but it never replies, so the forward times out.
+	silentSub, err := d.natsConn.Subscribe("ec2.start.node-other", func(*nats.Msg) {})
+	require.NoError(t, err)
+	t.Cleanup(func() { _ = silentSub.Unsubscribe() })
+
+	body, _ := json.Marshal(handlers_ec2_instance.StartStoppedInstanceInput{InstanceID: v.ID})
+	reply := requestHandler(t, d.natsConn, "ec2.start.test5", d.handleEC2StartStoppedInstance, testAccountID, body)
+	assert.Equal(t, awserrors.ErrorInsufficientInstanceCapacity, decodeError(t, reply.Data)["Code"],
+		"a forward timeout must fall back to a local start attempt, not a bare ServerInternal")
+}
+
+// TestHandleEC2StartStoppedInstance_ForwardTimeoutAfterRemoteClaim_NoDoubleStart
+// pins the other half of siv-481: if the forward times out on the caller's
+// side AFTER the original node already won the atomic claim (removed the
+// record from shared KV) and kept working, the caller's local fallback must
+// not double-start the instance. It should observe the record already gone
+// and fail cleanly, and must never insert a second copy into its own vmMgr.
+func TestHandleEC2StartStoppedInstance_ForwardTimeoutAfterRemoteClaim_NoDoubleStart(t *testing.T) {
+	withShortForwardTimeout(t, 50*time.Millisecond)
+
+	store := newFakeStateStore()
+	v := stoppedVMFixture("i-race-claim", testAccountID)
+	v.LastNode = "node-other"
+	store.stopped[v.ID] = v
+	d := daemonWithFakeStateStore(t, store)
+
+	// Simulate the original node winning the claim (atomically removing the
+	// shared-KV record, as StartStoppedInstance's ClaimStoppedInstance does)
+	// but never replying — e.g. still mid-launch when the caller's forward
+	// budget expires.
+	claimingSub, err := d.natsConn.Subscribe("ec2.start.node-other", func(*nats.Msg) {
+		_, claimErr := store.ClaimStoppedInstance(v.ID)
+		assert.NoError(t, claimErr)
+	})
+	require.NoError(t, err)
+	t.Cleanup(func() { _ = claimingSub.Unsubscribe() })
+
+	body, _ := json.Marshal(handlers_ec2_instance.StartStoppedInstanceInput{InstanceID: v.ID})
+	reply := requestHandler(t, d.natsConn, "ec2.start.test6", d.handleEC2StartStoppedInstance, testAccountID, body)
+
+	assert.Equal(t, awserrors.ErrorInvalidInstanceIDNotFound, decodeError(t, reply.Data)["Code"],
+		"local fallback must see the record already claimed and fail without double-starting")
+	_, found := d.vmMgr.Get(v.ID)
+	assert.False(t, found, "local fallback must not insert a second running copy of an already-claimed instance")
+}
+
 // --- handleEC2TerminateStoppedInstance ---
 
 func TestHandleEC2TerminateStoppedInstance_LoadError(t *testing.T) {
diff --git a/spinifex/daemon/daemon_handlers_volume.go b/spinifex/daemon/daemon_handlers_volume.go
index e803d0a05..0ee731bd3 100644
--- a/spinifex/daemon/daemon_handlers_volume.go
+++ b/spinifex/daemon/daemon_handlers_volume.go
@@ -59,6 +59,26 @@ func (d *Daemon) handleAttachVolume(ctx context.Context, msg *nats.Msg, command
 	}
 
 	if volCfg.VolumeMetadata.State != "available" {
+		if volCfg.VolumeMetadata.AttachedInstance == command.ID {
+			if command.AttachVolumeData.Device != "" &&
+				command.AttachVolumeData.Device != volCfg.VolumeMetadata.DeviceName {
+				slog.ErrorContext(ctx, "AttachVolume: requested device conflicts with existing attachment",
+					"volumeId", volumeID, "instanceId", command.ID,
+					"requestedDevice", command.AttachVolumeData.Device,
+					"attachedDevice", volCfg.VolumeMetadata.DeviceName)
+				respondWithError(msg, attachDetachErrorCode(vm.ErrVolumeDeviceMismatch))
+				return
+			}
+
+			// Volume is already attached to this instance (e.g. a CSI
+			// ControllerPublishVolume retry after a slow first attach).
+			// Treat as an idempotent success instead of VolumeInUse.
+			slog.InfoContext(ctx, "AttachVolume: volume already attached to requesting instance, returning idempotent success",
+				"volumeId", volumeID, "instanceId", command.ID, "device", volCfg.VolumeMetadata.DeviceName)
+			d.respondWithVolumeAttachment(msg, volumeID, command.ID, volCfg.VolumeMetadata.DeviceName, "attached")
+			return
+		}
+
 		slog.ErrorContext(ctx, "AttachVolume: volume not available",
 			"volumeId", volumeID, "state", volCfg.VolumeMetadata.State)
 		respondWithError(msg, awserrors.ErrorVolumeInUse)
diff --git a/spinifex/daemon/daemon_handlers_volume_test.go b/spinifex/daemon/daemon_handlers_volume_test.go
index a06a87439..9068baf01 100644
--- a/spinifex/daemon/daemon_handlers_volume_test.go
+++ b/spinifex/daemon/daemon_handlers_volume_test.go
@@ -1,13 +1,25 @@
 package daemon
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
+	"strings"
 	"testing"
+	"time"
+
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/service/ec2"
+	awss3 "github.com/aws/aws-sdk-go/service/s3"
 
 	"github.com/mulgadc/spinifex/spinifex/awserrors"
+	"github.com/mulgadc/spinifex/spinifex/objectstore"
+	"github.com/mulgadc/spinifex/spinifex/qmp"
+	"github.com/mulgadc/spinifex/spinifex/types"
 	"github.com/mulgadc/spinifex/spinifex/vm"
+	"github.com/mulgadc/viperblock/viperblock"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 // TestAttachDetachErrorCode locks down the manager-error → AWS-API-code
@@ -86,3 +98,219 @@ func TestAttachDetachErrorCode(t *testing.T) {
 		})
 	}
 }
+
+// seedVolumeConfig writes a minimal VolumeConfig to config.json, matching
+// the seeding pattern used by the handleAttachVolume tests in
+// daemon_handlers_test.go.
+func seedVolumeConfig(t *testing.T, store *objectstore.MemoryObjectStore, volumeID string, meta viperblock.VolumeMetadata) {
+	t.Helper()
+	wrapper := struct {
+		VolumeConfig viperblock.VolumeConfig `json:"VolumeConfig"`
+	}{
+		VolumeConfig: viperblock.VolumeConfig{VolumeMetadata: meta},
+	}
+	data, err := json.Marshal(wrapper)
+	require.NoError(t, err)
+	_, err = store.PutObject(t.Context(), &awss3.PutObjectInput{
+		Bucket: aws.String("test-bucket"),
+		Key:    aws.String(volumeID + "/config.json"),
+		Body:   strings.NewReader(string(data)),
+	})
+	require.NoError(t, err)
+}
+
+// TestAttachVolume_IdempotentSameInstance verifies that re-attaching a
+// volume already attached to the requesting instance (e.g. a CSI
+// ControllerPublishVolume retry after a slow first attach) short-circuits
+// to an idempotent "attached" success instead of VolumeInUse, and does not
+// invoke vm.Manager.AttachVolume (the fake QMPClient on the seeded instance
+// has no live socket, so a real AttachVolume call would fail rather than
+// silently succeed with the pre-existing device).
+func TestAttachVolume_IdempotentSameInstance(t *testing.T) {
+	tests := []struct {
+		name            string
+		requestedDevice string
+	}{
+		{name: "no device specified", requestedDevice: ""},
+		{name: "device matches existing attachment", requestedDevice: "/dev/sdf"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			daemon, store := createFullTestDaemonWithStore(t, sharedNATSURL)
+
+			instanceID := "i-attach-idempotent-" + strings.ReplaceAll(tt.name, " ", "-")
+			volumeID := "vol-idempotent-" + strings.ReplaceAll(tt.name, " ", "-")
+
+			instance := &vm.VM{
+				ID:           instanceID,
+				Status:       vm.StateRunning,
+				AccountID:    testAccountID,
+				InstanceType: getTestInstanceType(t),
+				Instance:     &ec2.Instance{},
+				QMPClient:    &qmp.QMPClient{},
+			}
+			daemon.vmMgr.Insert(instance)
+
+			seedVolumeConfig(t, store, volumeID, viperblock.VolumeMetadata{
+				VolumeID:         volumeID,
+				SizeGiB:          10,
+				State:            "in-use",
+				TenantID:         testAccountID,
+				AttachedInstance: instanceID,
+				DeviceName:       "/dev/sdf",
+			})
+
+			sub, err := daemon.natsConn.Subscribe(
+				fmt.Sprintf("ec2.cmd.%s", instanceID),
+				daemon.handleEC2Events,
+			)
+			require.NoError(t, err)
+			defer sub.Unsubscribe()
+
+			command := types.EC2InstanceCommand{
+				ID: instanceID,
+				Attributes: types.EC2CommandAttributes{
+					AttachVolume: true,
+				},
+				AttachVolumeData: &types.AttachVolumeData{
+					VolumeID: volumeID,
+					Device:   tt.requestedDevice,
+				},
+			}
+			cmdData, err := json.Marshal(command)
+			require.NoError(t, err)
+
+			resp, err := natsRequest(daemon.natsConn,
+				fmt.Sprintf("ec2.cmd.%s", instanceID),
+				cmdData,
+				5*time.Second,
+			)
+			require.NoError(t, err)
+
+			var attachment ec2.VolumeAttachment
+			require.NoError(t, json.Unmarshal(resp.Data, &attachment))
+
+			assert.Equal(t, volumeID, *attachment.VolumeId)
+			assert.Equal(t, instanceID, *attachment.InstanceId)
+			assert.Equal(t, "/dev/sdf", *attachment.Device)
+			assert.Equal(t, "attached", *attachment.State)
+		})
+	}
+}
+
+// TestAttachVolume_InUseDifferentInstance is a regression test locking down
+// that a volume attached to a DIFFERENT instance than the requester still
+// returns VolumeInUse unchanged, distinguishing it from the same-instance
+// idempotent short-circuit.
+func TestAttachVolume_InUseDifferentInstance(t *testing.T) {
+	daemon, store := createFullTestDaemonWithStore(t, sharedNATSURL)
+
+	instanceID := "i-attach-vol-other-instance"
+	otherInstanceID := "i-already-attached-elsewhere"
+	volumeID := "vol-in-use-other-instance"
+
+	instance := &vm.VM{
+		ID:           instanceID,
+		Status:       vm.StateRunning,
+		AccountID:    testAccountID,
+		InstanceType: getTestInstanceType(t),
+		Instance:     &ec2.Instance{},
+		QMPClient:    &qmp.QMPClient{},
+	}
+	daemon.vmMgr.Insert(instance)
+
+	seedVolumeConfig(t, store, volumeID, viperblock.VolumeMetadata{
+		VolumeID:         volumeID,
+		SizeGiB:          10,
+		State:            "in-use",
+		TenantID:         testAccountID,
+		AttachedInstance: otherInstanceID,
+		DeviceName:       "/dev/sdf",
+	})
+
+	sub, err := daemon.natsConn.Subscribe(
+		fmt.Sprintf("ec2.cmd.%s", instanceID),
+		daemon.handleEC2Events,
+	)
+	require.NoError(t, err)
+	defer sub.Unsubscribe()
+
+	command := types.EC2InstanceCommand{
+		ID: instanceID,
+		Attributes: types.EC2CommandAttributes{
+			AttachVolume: true,
+		},
+		AttachVolumeData: &types.AttachVolumeData{
+			VolumeID: volumeID,
+		},
+	}
+	cmdData, err := json.Marshal(command)
+	require.NoError(t, err)
+
+	resp, err := natsRequest(daemon.natsConn,
+		fmt.Sprintf("ec2.cmd.%s", instanceID),
+		cmdData,
+		5*time.Second,
+	)
+	require.NoError(t, err)
+	assert.Contains(t, string(resp.Data), "VolumeInUse")
+}
+
+// TestAttachVolume_IdempotentSameInstance_DeviceMismatch verifies that a
+// same-instance re-attach requesting a DIFFERENT device than the one
+// already attached is treated as a real CSI conflict (InvalidParameterValue
+// via vm.ErrVolumeDeviceMismatch), not silently echoed back or accepted.
+func TestAttachVolume_IdempotentSameInstance_DeviceMismatch(t *testing.T) {
+	daemon, store := createFullTestDaemonWithStore(t, sharedNATSURL)
+
+	instanceID := "i-attach-device-mismatch"
+	volumeID := "vol-device-mismatch"
+
+	instance := &vm.VM{
+		ID:           instanceID,
+		Status:       vm.StateRunning,
+		AccountID:    testAccountID,
+		InstanceType: getTestInstanceType(t),
+		Instance:     &ec2.Instance{},
+		QMPClient:    &qmp.QMPClient{},
+	}
+	daemon.vmMgr.Insert(instance)
+
+	seedVolumeConfig(t, store, volumeID, viperblock.VolumeMetadata{
+		VolumeID:         volumeID,
+		SizeGiB:          10,
+		State:            "in-use",
+		TenantID:         testAccountID,
+		AttachedInstance: instanceID,
+		DeviceName:       "/dev/sdf",
+	})
+
+	sub, err := daemon.natsConn.Subscribe(
+		fmt.Sprintf("ec2.cmd.%s", instanceID),
+		daemon.handleEC2Events,
+	)
+	require.NoError(t, err)
+	defer sub.Unsubscribe()
+
+	command := types.EC2InstanceCommand{
+		ID: instanceID,
+		Attributes: types.EC2CommandAttributes{
+			AttachVolume: true,
+		},
+		AttachVolumeData: &types.AttachVolumeData{
+			VolumeID: volumeID,
+			Device:   "/dev/sdg",
+		},
+	}
+	cmdData, err := json.Marshal(command)
+	require.NoError(t, err)
+
+	resp, err := natsRequest(daemon.natsConn,
+		fmt.Sprintf("ec2.cmd.%s", instanceID),
+		cmdData,
+		5*time.Second,
+	)
+	require.NoError(t, err)
+	assert.Contains(t, string(resp.Data), awserrors.ErrorInvalidParameterValue)
+}
diff --git a/spinifex/daemon/daemon_test.go b/spinifex/daemon/daemon_test.go
index 89fd232ba..6a440f9f4 100644
--- a/spinifex/daemon/daemon_test.go
+++ b/spinifex/daemon/daemon_test.go
@@ -119,7 +119,8 @@ func createTestDaemon(t *testing.T, natsURL string) *Daemon {
 	require.NoError(t, err, "Failed to connect to NATS")
 
 	daemon.natsConn = nc
-	daemon.detachDelay = 0 // Skip sleep in tests
+	daemon.detachDelay = 0          // Skip sleep in tests
+	daemon.deviceDeletedTimeout = 0 // Skip DEVICE_DELETED wait in tests
 
 	// Initialize services (needed for handler tests).
 	// jsManager is nil here; pass a nil literal to keep the StoppedInstanceStore
@@ -133,10 +134,11 @@ func createTestDaemon(t *testing.T, natsURL string) *Daemon {
 	// AttachVolume / DetachVolume manager methods enough plumbing to drive
 	// ebs.mount/unmount over NATS using the test's connection.
 	daemon.vmMgr.SetDeps(vm.Deps{
-		NodeID:             daemon.node,
-		VolumeMounter:      newVolumeMounterAdapter(daemon.natsConn, daemon.node, daemon.volumeService),
-		VolumeStateUpdater: daemon.volumeService,
-		DetachDelay:        daemon.detachDelay,
+		NodeID:               daemon.node,
+		VolumeMounter:        newVolumeMounterAdapter(daemon.natsConn, daemon.node, daemon.volumeService),
+		VolumeStateUpdater:   daemon.volumeService,
+		DetachDelay:          daemon.detachDelay,
+		DeviceDeletedTimeout: daemon.deviceDeletedTimeout,
 	})
 
 	t.Cleanup(func() {
diff --git a/spinifex/daemon/eks_deps.go b/spinifex/daemon/eks_deps.go
index 9989b9072..f6f7cd6d5 100644
--- a/spinifex/daemon/eks_deps.go
+++ b/spinifex/daemon/eks_deps.go
@@ -57,8 +57,10 @@ func (d *Daemon) buildEKSServiceDeps() handlers_eks.EKSServiceDeps {
 	}
 
 	internalSuffix := ""
+	clusterSize := 1
 	if d.clusterConfig != nil {
 		internalSuffix = d.clusterConfig.AWS.InternalSuffix
+		clusterSize = len(d.clusterConfig.Nodes)
 	}
 
 	gatewayCA := ""
@@ -78,6 +80,7 @@ func (d *Daemon) buildEKSServiceDeps() handlers_eks.EKSServiceDeps {
 		GatewayBaseURL:   d.resolveGatewayBaseURL(),
 		Region:           d.config.Region,
 		HolderID:         d.node,
+		ClusterSize:      clusterSize,
 		InternalSuffix:   internalSuffix,
 		SystemGatewayURL: d.resolveSystemGatewayBaseURL(),
 		SystemAccessKey:  d.config.Predastore.AccessKey,
diff --git a/spinifex/daemon/jetstream.go b/spinifex/daemon/jetstream.go
index 340136bc8..c249ca109 100644
--- a/spinifex/daemon/jetstream.go
+++ b/spinifex/daemon/jetstream.go
@@ -252,6 +252,146 @@ func (m *JetStreamManager) recoverTerminatedKVBucket() (nats.KeyValue, error) {
 	}, &m.terminatedKV, TerminatedInstanceBucketVersion)
 }
 
+// maxCASRetries bounds the optimistic-concurrency retry loop in casUpdate.
+// A conflict this many times in a row means sustained write contention on
+// the key, not a single overlapping update — callers should surface an error.
+const maxCASRetries = 5
+
+// isRevisionConflict reports whether err is the nats.go "wrong last
+// sequence" error that KeyValue.Update/Create return when the key's
+// revision no longer matches what the caller expected, i.e. a concurrent
+// writer won the race. nats.go surfaces this as nats.ErrKeyExists for both
+// Update (stale revision) and Create (key already present).
+func isRevisionConflict(err error) bool {
+	return errors.Is(err, nats.ErrKeyExists)
+}
+
+// casUpdate performs an optimistic-concurrency read-modify-write against kv:
+// Get the current entry (or start from a zero value when absent and
+// createIfAbsent is set), apply mutate to the decoded value, then commit via
+// Update/Create using the observed revision. A concurrent writer that changes
+// the key between Get and Update/Create is detected via a revision conflict
+// and retried, bounded by maxCASRetries.
+func casUpdate[T any](kv nats.KeyValue, key string, mutate func(*T), createIfAbsent bool) (*T, error) {
+	var lastErr error
+	for range maxCASRetries {
+		var value T
+		var revision uint64
+
+		entry, err := kv.Get(key)
+		switch {
+		case err == nil:
+			if uerr := json.Unmarshal(entry.Value(), &value); uerr != nil {
+				return nil, uerr
+			}
+			revision = entry.Revision()
+		case errors.Is(err, nats.ErrKeyNotFound) && createIfAbsent:
+			revision = 0
+		default:
+			return nil, err
+		}
+
+		mutate(&value)
+
+		data, merr := json.Marshal(&value)
+		if merr != nil {
+			return nil, merr
+		}
+
+		if revision == 0 {
+			_, err = kv.Create(key, data)
+		} else {
+			_, err = kv.Update(key, data, revision)
+		}
+		if err == nil {
+			return &value, nil
+		}
+		if isRevisionConflict(err) {
+			lastErr = err
+			continue
+		}
+		return nil, err
+	}
+	return nil, fmt.Errorf("CAS update exhausted %d retries for key %s: %w", maxCASRetries, key, lastErr)
+}
+
+// casPut writes data to key under kv using optimistic concurrency: it reads
+// the current revision (or treats the key as absent, using Create, when
+// createIfAbsent is set) then commits via Update/Create, retrying on a
+// revision conflict up to maxCASRetries. This is the "replace wholesale"
+// counterpart to casUpdate, for values (like vm.VM, which embeds a
+// sync.Mutex) that cannot be safely decoded into and copied out of a shared
+// struct value.
+func casPut(kv nats.KeyValue, key string, data []byte, createIfAbsent bool) error {
+	var lastErr error
+	for range maxCASRetries {
+		var revision uint64
+
+		entry, err := kv.Get(key)
+		switch {
+		case err == nil:
+			revision = entry.Revision()
+		case errors.Is(err, nats.ErrKeyNotFound) && createIfAbsent:
+			revision = 0
+		default:
+			return err
+		}
+
+		if revision == 0 {
+			_, err = kv.Create(key, data)
+		} else {
+			_, err = kv.Update(key, data, revision)
+		}
+		if err == nil {
+			return nil
+		}
+		if isRevisionConflict(err) {
+			lastErr = err
+			continue
+		}
+		return err
+	}
+	return fmt.Errorf("CAS put exhausted %d retries for key %s: %w", maxCASRetries, key, lastErr)
+}
+
+// casClaim atomically removes key from kv, decoding its current value into T
+// first — the delete-side counterpart to casPut/casUpdate. It is the
+// primitive an exclusive "claim" is built on: at most one caller can ever
+// observe a successful delete for a given revision, so at most one caller
+// gets back a non-nil value. A concurrent writer that changes the key
+// between Get and Delete (another claim, or an unrelated update) is
+// detected via a revision conflict and retried, bounded by maxCASRetries,
+// so a losing racer only fails outright when the key is truly gone
+// (notFound) or retries are exhausted.
+func casClaim[T any](kv nats.KeyValue, key string) (value *T, notFound bool, err error) {
+	var lastErr error
+	for range maxCASRetries {
+		entry, gerr := kv.Get(key)
+		if gerr != nil {
+			if errors.Is(gerr, nats.ErrKeyNotFound) {
+				return nil, true, nil
+			}
+			return nil, false, gerr
+		}
+
+		var v T
+		if uerr := json.Unmarshal(entry.Value(), &v); uerr != nil {
+			return nil, false, uerr
+		}
+
+		if derr := kv.Delete(key, nats.LastRevision(entry.Revision())); derr != nil {
+			if isRevisionConflict(derr) {
+				lastErr = derr
+				continue
+			}
+			return nil, false, derr
+		}
+
+		return &v, false, nil
+	}
+	return nil, false, fmt.Errorf("CAS claim exhausted %d retries for key %s: %w", maxCASRetries, key, lastErr)
+}
+
 // Heartbeat represents a daemon's periodic health status published to cluster KV.
 //
 // AvailableVCPU / AvailableMem are observability-only (host - allocated,
@@ -313,19 +453,31 @@ type ClusterShutdownState struct {
 	NodesAcked map[string]string `json:"nodes_acked"`
 }
 
-// WriteClusterShutdown writes the cluster shutdown state to KV.
+// WriteClusterShutdown writes the cluster shutdown state to KV, replacing
+// any existing value. Uses CAS internally (bounded retry) so a write racing
+// a concurrent update is detected and retried rather than silently applied
+// out of order.
 func (m *JetStreamManager) WriteClusterShutdown(state *ClusterShutdownState) error {
 	if m.clusterKV == nil {
 		return errors.New("cluster state KV not initialized")
 	}
-	data, err := json.Marshal(state)
-	if err != nil {
-		return err
-	}
-	_, err = m.clusterKV.Put("cluster.shutdown", data)
+	_, err := casUpdate(m.clusterKV, "cluster.shutdown", func(s *ClusterShutdownState) {
+		*s = *state
+	}, true)
 	return err
 }
 
+// UpdateClusterShutdown atomically applies mutate to the current cluster
+// shutdown state (e.g. merging a node's ack into NodesAcked) and writes it
+// back with optimistic concurrency, retrying on a concurrent writer's
+// revision conflict. Returns nats.ErrKeyNotFound if no shutdown is in progress.
+func (m *JetStreamManager) UpdateClusterShutdown(mutate func(*ClusterShutdownState)) (*ClusterShutdownState, error) {
+	if m.clusterKV == nil {
+		return nil, errors.New("cluster state KV not initialized")
+	}
+	return casUpdate(m.clusterKV, "cluster.shutdown", mutate, false)
+}
+
 // ReadClusterShutdown reads the cluster shutdown state from KV.
 func (m *JetStreamManager) ReadClusterShutdown() (*ClusterShutdownState, error) {
 	if m.clusterKV == nil {
@@ -628,7 +780,12 @@ func (m *JetStreamManager) UpdateReplicas(newReplicas int) error {
 	return nil
 }
 
-// WriteStoppedInstance writes a stopped instance to the shared KV store.
+// WriteStoppedInstance writes a stopped instance to the shared KV store,
+// replacing any existing record for instanceID. Uses CAS internally (bounded
+// retry) so a write racing a concurrent update is detected and retried
+// rather than silently overwriting it out of order. This is the substrate
+// callers that read-modify-write a stopped instance (e.g. tag/attribute
+// mutations) build on.
 func (m *JetStreamManager) WriteStoppedInstance(instanceID string, instance *vm.VM) error {
 	if m.kv == nil {
 		return errors.New("KV bucket not initialized")
@@ -640,7 +797,7 @@ func (m *JetStreamManager) WriteStoppedInstance(instanceID string, instance *vm.
 	}
 
 	key := StoppedInstancePrefix + instanceID
-	_, err = m.kv.Put(key, jsonData)
+	err = casPut(m.kv, key, jsonData, true)
 	if err != nil {
 		if isStreamUnavailable(err) {
 			slog.Warn("KV stream unavailable, attempting recovery", "operation", "WriteStoppedInstance", "key", key, "err", err)
@@ -648,7 +805,7 @@ func (m *JetStreamManager) WriteStoppedInstance(instanceID string, instance *vm.
 			if recoverErr != nil {
 				return err
 			}
-			if _, retryErr := kv.Put(key, jsonData); retryErr != nil {
+			if retryErr := casPut(kv, key, jsonData, true); retryErr != nil {
 				return retryErr
 			}
 			slog.Debug("Wrote stopped instance to JetStream KV (after recovery)", "key", key, "instanceId", instanceID)
@@ -731,6 +888,45 @@ func (m *JetStreamManager) DeleteStoppedInstance(instanceID string) error {
 	return nil
 }
 
+// ClaimStoppedInstance atomically removes instanceID's record from the
+// shared KV store and returns the VM it held, so that at most one caller
+// across the cluster can ever win a race to (re)launch the same stopped
+// instance. It is the first step of StartStoppedInstance, replacing the
+// unguarded Load+Delete pair that previously let two callers both observe
+// the instance as claimable. A losing racer (this node's local fallback
+// racing a forwarded call, two nodes racing the same forwarded call, or a
+// retry after the instance was already claimed) gets vm.ErrStoppedInstanceClaimed
+// instead of a VM and must not proceed to allocate resources or launch qemu.
+func (m *JetStreamManager) ClaimStoppedInstance(instanceID string) (*vm.VM, error) {
+	if m.kv == nil {
+		return nil, errors.New("KV bucket not initialized")
+	}
+
+	key := StoppedInstancePrefix + instanceID
+	instance, notFound, err := casClaim[vm.VM](m.kv, key)
+	if err != nil {
+		if isStreamUnavailable(err) {
+			slog.Warn("KV stream unavailable, attempting recovery", "operation", "ClaimStoppedInstance", "key", key, "err", err)
+			kv, recoverErr := m.recoverKVBucket()
+			if recoverErr != nil {
+				return nil, err
+			}
+			instance, notFound, err = casClaim[vm.VM](kv, key)
+			if err != nil {
+				return nil, err
+			}
+		} else {
+			return nil, err
+		}
+	}
+	if notFound {
+		return nil, vm.ErrStoppedInstanceClaimed
+	}
+
+	slog.Debug("Claimed stopped instance from JetStream KV", "key", key, "instanceId", instanceID)
+	return instance, nil
+}
+
 // ListStoppedInstances returns all stopped instances from the shared KV store.
 func (m *JetStreamManager) ListStoppedInstances() ([]*vm.VM, error) {
 	if m.kv == nil {
@@ -791,8 +987,14 @@ func (m *JetStreamManager) ListStoppedInstances() ([]*vm.VM, error) {
 	return instances, nil
 }
 
-// WriteTerminatedInstance writes a terminated instance to the terminated KV bucket.
-// The entry will auto-expire after the bucket's TTL (1 hour).
+// WriteTerminatedInstance writes a terminated instance to the terminated KV
+// bucket, replacing any existing record for instanceID. The entry will
+// auto-expire after the bucket's TTL (1 hour). Uses CAS internally (bounded
+// retry) so a write racing a concurrent update (e.g. the teardown reaper
+// advancing the Teardown map) is detected and retried rather than silently
+// overwriting it out of order. Callers that need to merge into the current
+// record instead of replacing it wholesale should use
+// UpdateTerminatedInstance.
 func (m *JetStreamManager) WriteTerminatedInstance(instanceID string, instance *vm.VM) error {
 	if m.terminatedKV == nil {
 		return errors.New("terminated instance KV bucket not initialized")
@@ -804,7 +1006,7 @@ func (m *JetStreamManager) WriteTerminatedInstance(instanceID string, instance *
 	}
 
 	key := TerminatedInstancePrefix + instanceID
-	_, err = m.terminatedKV.Put(key, jsonData)
+	err = casPut(m.terminatedKV, key, jsonData, true)
 	if err != nil {
 		if isStreamUnavailable(err) {
 			slog.Warn("KV stream unavailable, attempting recovery", "operation", "WriteTerminatedInstance", "key", key, "err", err)
@@ -812,7 +1014,7 @@ func (m *JetStreamManager) WriteTerminatedInstance(instanceID string, instance *
 			if recoverErr != nil {
 				return err
 			}
-			if _, retryErr := kv.Put(key, jsonData); retryErr != nil {
+			if retryErr := casPut(kv, key, jsonData, true); retryErr != nil {
 				return retryErr
 			}
 			slog.Debug("Wrote terminated instance to JetStream KV (after recovery)", "key", key, "instanceId", instanceID)
@@ -825,6 +1027,33 @@ func (m *JetStreamManager) WriteTerminatedInstance(instanceID string, instance *
 	return nil
 }
 
+// UpdateTerminatedInstance atomically applies mutate to the current
+// KV-stored terminated record for instanceID and writes it back using
+// optimistic concurrency (CAS), retrying on a concurrent writer's revision
+// conflict. Used by the teardown reaper to merge per-dependent Teardown
+// progress without clobbering marks written by a concurrent update to the
+// same record. Returns nats.ErrKeyNotFound if no record exists yet.
+func (m *JetStreamManager) UpdateTerminatedInstance(instanceID string, mutate func(*vm.VM)) (*vm.VM, error) {
+	if m.terminatedKV == nil {
+		return nil, errors.New("terminated instance KV bucket not initialized")
+	}
+
+	key := TerminatedInstancePrefix + instanceID
+	updated, err := casUpdate(m.terminatedKV, key, mutate, false)
+	if err != nil {
+		if isStreamUnavailable(err) {
+			slog.Warn("KV stream unavailable, attempting recovery", "operation", "UpdateTerminatedInstance", "key", key, "err", err)
+			kv, recoverErr := m.recoverTerminatedKVBucket()
+			if recoverErr != nil {
+				return nil, err
+			}
+			return casUpdate(kv, key, mutate, false)
+		}
+		return nil, err
+	}
+	return updated, nil
+}
+
 // ListTerminatedInstances returns all terminated instances from the terminated KV bucket.
 func (m *JetStreamManager) ListTerminatedInstances() ([]*vm.VM, error) {
 	if m.terminatedKV == nil {
diff --git a/spinifex/daemon/jetstream_test.go b/spinifex/daemon/jetstream_test.go
index 924a3cc22..c7f64e52b 100644
--- a/spinifex/daemon/jetstream_test.go
+++ b/spinifex/daemon/jetstream_test.go
@@ -456,6 +456,103 @@ func TestJetStreamManager_DeleteStoppedInstance(t *testing.T) {
 	require.NoError(t, err)
 }
 
+// TestJetStreamManager_ClaimStoppedInstance_HappyPath verifies a claim
+// atomically removes the record and hands back the VM it held.
+func TestJetStreamManager_ClaimStoppedInstance_HappyPath(t *testing.T) {
+	nc, err := nats.Connect(sharedJSNATSURL)
+	require.NoError(t, err)
+	defer nc.Close()
+
+	jsm, err := NewJetStreamManager(nc, 1)
+	require.NoError(t, err)
+	require.NoError(t, jsm.InitKVBucket())
+
+	testVM := &vm.VM{ID: "i-claim-happy", Status: vm.StateStopped, InstanceType: "t3.micro"}
+	require.NoError(t, jsm.WriteStoppedInstance(testVM.ID, testVM))
+
+	claimed, err := jsm.ClaimStoppedInstance(testVM.ID)
+	require.NoError(t, err)
+	require.NotNil(t, claimed)
+	assert.Equal(t, testVM.ID, claimed.ID)
+	assert.Equal(t, "t3.micro", claimed.InstanceType)
+
+	// The claim must have removed the record — a second claim, or a plain
+	// Load, must both observe it gone.
+	loaded, err := jsm.LoadStoppedInstance(testVM.ID)
+	require.NoError(t, err)
+	assert.Nil(t, loaded, "a successful claim must remove the record")
+}
+
+// TestJetStreamManager_ClaimStoppedInstance_NotFound verifies claiming an id
+// with no record returns vm.ErrStoppedInstanceClaimed rather than a bare
+// nats not-found error, so callers can map it directly to the API error.
+func TestJetStreamManager_ClaimStoppedInstance_NotFound(t *testing.T) {
+	nc, err := nats.Connect(sharedJSNATSURL)
+	require.NoError(t, err)
+	defer nc.Close()
+
+	jsm, err := NewJetStreamManager(nc, 1)
+	require.NoError(t, err)
+	require.NoError(t, jsm.InitKVBucket())
+
+	_, err = jsm.ClaimStoppedInstance("i-does-not-exist")
+	assert.ErrorIs(t, err, vm.ErrStoppedInstanceClaimed)
+}
+
+// TestJetStreamManager_ClaimStoppedInstance_ConcurrentClaim is the
+// lower-level regression test for the double-start bug: it fires N
+// concurrent ClaimStoppedInstance calls at the same key against a real
+// JetStream KV bucket and asserts exactly one succeeds — proving the
+// nats.LastRevision-guarded Delete this claim is built on is a genuine
+// mutual-exclusion primitive under real NATS wire semantics, not just at
+// the fake/mock layer exercised by the handlers-level test.
+func TestJetStreamManager_ClaimStoppedInstance_ConcurrentClaim(t *testing.T) {
+	nc, err := nats.Connect(sharedJSNATSURL)
+	require.NoError(t, err)
+	defer nc.Close()
+
+	jsm, err := NewJetStreamManager(nc, 1)
+	require.NoError(t, err)
+	require.NoError(t, jsm.InitKVBucket())
+
+	testVM := &vm.VM{ID: "i-claim-race", Status: vm.StateStopped, InstanceType: "t3.micro"}
+	require.NoError(t, jsm.WriteStoppedInstance(testVM.ID, testVM))
+
+	const n = 8
+	results := make([]*vm.VM, n)
+	errs := make([]error, n)
+	var wg sync.WaitGroup
+	wg.Add(n)
+	for i := range n {
+		go func(i int) {
+			defer wg.Done()
+			results[i], errs[i] = jsm.ClaimStoppedInstance(testVM.ID)
+		}(i)
+	}
+	wg.Wait()
+
+	var won, lost int
+	for i := range n {
+		switch {
+		case errs[i] == nil:
+			won++
+			require.NotNil(t, results[i])
+			assert.Equal(t, testVM.ID, results[i].ID)
+		case errors.Is(errs[i], vm.ErrStoppedInstanceClaimed):
+			lost++
+		default:
+			t.Fatalf("unexpected error from ClaimStoppedInstance: %v", errs[i])
+		}
+	}
+
+	assert.Equal(t, 1, won, "exactly one concurrent claim must succeed")
+	assert.Equal(t, n-1, lost, "every other concurrent claim must lose with ErrStoppedInstanceClaimed")
+
+	loaded, err := jsm.LoadStoppedInstance(testVM.ID)
+	require.NoError(t, err)
+	assert.Nil(t, loaded, "the winning claim must have removed the record")
+}
+
 // TestJetStreamManager_ListStoppedInstances tests listing multiple stopped instances
 func TestJetStreamManager_ListStoppedInstances(t *testing.T) {
 	nc, err := nats.Connect(sharedJSNATSURL)
@@ -1113,6 +1210,107 @@ func TestJetStreamManager_TerminatedInstance_KVNotInitialized(t *testing.T) {
 	assert.Error(t, err)
 }
 
+// --- CAS conflict-retry tests ---
+
+// TestJetStreamManager_UpdateTerminatedInstance_ConflictRetry locks the CAS
+// contract for the multi-writer Teardown map: a concurrent writer that lands
+// between UpdateTerminatedInstance's Get and Update must be detected via a
+// revision conflict and retried, and BOTH updates — the injected concurrent
+// one and the retried one — must land, none silently dropped.
+func TestJetStreamManager_UpdateTerminatedInstance_ConflictRetry(t *testing.T) {
+	nc, err := nats.Connect(sharedJSNATSURL)
+	require.NoError(t, err)
+	defer nc.Close()
+
+	jsm, err := NewJetStreamManager(nc, 1)
+	require.NoError(t, err)
+	require.NoError(t, jsm.InitTerminatedInstanceBucket())
+
+	testVM := &vm.VM{ID: "i-cas-conflict", Teardown: map[string]string{"volumes": "pending", "gpu": "pending"}}
+	require.NoError(t, jsm.WriteTerminatedInstance(testVM.ID, testVM))
+	defer func() { _ = jsm.DeleteTerminatedInstance(testVM.ID) }()
+
+	var attempts int
+	var injectOnce sync.Once
+	updated, err := jsm.UpdateTerminatedInstance(testVM.ID, func(v *vm.VM) {
+		attempts++
+		if v.Teardown == nil {
+			v.Teardown = map[string]string{}
+		}
+		v.Teardown["gpu"] = "done"
+
+		// Simulate a concurrent writer landing between our Get and Update on
+		// the first attempt only, forcing exactly one revision conflict.
+		injectOnce.Do(func() {
+			_, cerr := jsm.UpdateTerminatedInstance(testVM.ID, func(cv *vm.VM) {
+				if cv.Teardown == nil {
+					cv.Teardown = map[string]string{}
+				}
+				cv.Teardown["volumes"] = "done"
+			})
+			require.NoError(t, cerr)
+		})
+	})
+	require.NoError(t, err, "the retried Update must eventually succeed against the fresh revision")
+	require.NotNil(t, updated)
+	assert.Equal(t, 2, attempts, "the injected concurrent write must force exactly one retry")
+	assert.Equal(t, "done", updated.Teardown["gpu"])
+
+	loaded, err := jsm.LoadTerminatedInstance(testVM.ID)
+	require.NoError(t, err)
+	require.NotNil(t, loaded)
+	assert.Equal(t, "done", loaded.Teardown["volumes"], "the concurrent writer's update must survive, not be clobbered")
+	assert.Equal(t, "done", loaded.Teardown["gpu"], "the retried update must also land")
+}
+
+// TestJetStreamManager_UpdateTerminatedInstance_NotFound verifies
+// UpdateTerminatedInstance surfaces a clear error rather than silently
+// creating a record when there is nothing to merge into.
+func TestJetStreamManager_UpdateTerminatedInstance_NotFound(t *testing.T) {
+	nc, err := nats.Connect(sharedJSNATSURL)
+	require.NoError(t, err)
+	defer nc.Close()
+
+	jsm, err := NewJetStreamManager(nc, 1)
+	require.NoError(t, err)
+	require.NoError(t, jsm.InitTerminatedInstanceBucket())
+
+	_, err = jsm.UpdateTerminatedInstance("i-does-not-exist", func(v *vm.VM) {})
+	assert.ErrorIs(t, err, nats.ErrKeyNotFound)
+}
+
+// TestJetStreamManager_WriteStoppedInstance_OverwritesConcurrentValue verifies
+// WriteStoppedInstance's CAS write still succeeds and lands the caller's full
+// snapshot even when a concurrent writer changed the key first — the
+// conflict-retry loop must not surface a spurious error for the common,
+// non-merging "replace wholesale" write path.
+func TestJetStreamManager_WriteStoppedInstance_OverwritesConcurrentValue(t *testing.T) {
+	nc, err := nats.Connect(sharedJSNATSURL)
+	require.NoError(t, err)
+	defer nc.Close()
+
+	jsm, err := NewJetStreamManager(nc, 1)
+	require.NoError(t, err)
+	require.NoError(t, jsm.InitKVBucket())
+
+	first := &vm.VM{ID: "i-stopped-cas", InstanceType: "t3.micro"}
+	require.NoError(t, jsm.WriteStoppedInstance(first.ID, first))
+	defer func() { _ = jsm.DeleteStoppedInstance(first.ID) }()
+
+	// A concurrent writer changes the record between the caller's decision to
+	// write and WriteStoppedInstance's internal Get.
+	concurrent := &vm.VM{ID: "i-stopped-cas", InstanceType: "t3.small"}
+	require.NoError(t, jsm.WriteStoppedInstance(concurrent.ID, concurrent))
+
+	final := &vm.VM{ID: "i-stopped-cas", InstanceType: "t3.large"}
+	require.NoError(t, jsm.WriteStoppedInstance(final.ID, final))
+
+	loaded, err := jsm.LoadStoppedInstance(final.ID)
+	require.NoError(t, err)
+	require.NotNil(t, loaded)
+	assert.Equal(t, "t3.large", loaded.InstanceType)
+}
+
 // --- Terminated KV bucket recovery tests ---
 
 // deleteTerminatedInstanceBucket deletes the underlying JetStream stream for the terminated-instances KV bucket.
diff --git a/spinifex/daemon/vm_adapters.go b/spinifex/daemon/vm_adapters.go
index 99fc397ee..fbbea414f 100644
--- a/spinifex/daemon/vm_adapters.go
+++ b/spinifex/daemon/vm_adapters.go
@@ -52,6 +52,10 @@ func (a *stateStoreAdapter) DeleteStoppedInstance(id string) error {
 	return a.js.DeleteStoppedInstance(id)
 }
 
+func (a *stateStoreAdapter) ClaimStoppedInstance(id string) (*vm.VM, error) {
+	return a.js.ClaimStoppedInstance(id)
+}
+
 func (a *stateStoreAdapter) ListStoppedInstances() ([]*vm.VM, error) {
 	return a.js.ListStoppedInstances()
 }
@@ -60,6 +64,10 @@ func (a *stateStoreAdapter) WriteTerminatedInstance(id string, v *vm.VM) error {
 	return a.js.WriteTerminatedInstance(id, v)
 }
 
+func (a *stateStoreAdapter) UpdateTerminatedInstance(id string, mutate func(*vm.VM)) (*vm.VM, error) {
+	return a.js.UpdateTerminatedInstance(id, mutate)
+}
+
 func (a *stateStoreAdapter) ListTerminatedInstances() ([]*vm.VM, error) {
 	return a.js.ListTerminatedInstances()
 }
@@ -550,6 +558,7 @@ func (d *Daemon) buildVMManagerDeps() vm.Deps {
 		DevNetworking:              d.config.Daemon.DevNetworking,
 		BindHost:                   d.config.Host,
 		DetachDelay:                d.detachDelay,
+		DeviceDeletedTimeout:       d.deviceDeletedTimeout,
 		ConsumeCleanShutdownMarker: d.consumeCleanShutdownMarker(),
 	}
 }
diff --git a/spinifex/gateway/oidc_discovery_test.go b/spinifex/gateway/oidc_discovery_test.go
index a8203ed81..1d375aa21 100644
--- a/spinifex/gateway/oidc_discovery_test.go
+++ b/spinifex/gateway/oidc_discovery_test.go
@@ -22,7 +22,7 @@ func seedDiscoveryCluster(t *testing.T) http.Handler {
 	t.Helper()
 	_, nc, js := testutil.StartTestJetStream(t)
 
-	kv, err := handlers_eks.GetOrCreateAccountBucket(js, testDiscAccount)
+	kv, err := handlers_eks.GetOrCreateAccountBucket(js, testDiscAccount, 1)
 	if err != nil {
 		t.Fatalf("account bucket: %v", err)
 	}
diff --git a/spinifex/handlers/ec2/instance/service.go b/spinifex/handlers/ec2/instance/service.go
index 82dfa469a..f69ccbcd3 100644
--- a/spinifex/handlers/ec2/instance/service.go
+++ b/spinifex/handlers/ec2/instance/service.go
@@ -86,6 +86,11 @@ type StoppedInstanceStore interface {
 	WriteStoppedInstance(instanceID string, instance *vm.VM) error
 	DeleteStoppedInstance(instanceID string) error
 	WriteTerminatedInstance(instanceID string, instance *vm.VM) error
+	// ClaimStoppedInstance atomically removes instanceID's record and
+	// returns the VM it held, so at most one caller can ever win a race to
+	// (re)launch the same stopped instance. Returns vm.ErrStoppedInstanceClaimed
+	// if a concurrent caller already claimed (or otherwise removed) the record.
+	ClaimStoppedInstance(instanceID string) (*vm.VM, error)
 }
 
 // InstanceTagWriter projects an instance record's full tag set into the
diff --git a/spinifex/handlers/ec2/instance/service_impl.go b/spinifex/handlers/ec2/instance/service_impl.go
index 20dec201d..aee44496e 100644
--- a/spinifex/handlers/ec2/instance/service_impl.go
+++ b/spinifex/handlers/ec2/instance/service_impl.go
@@ -2161,6 +2161,25 @@ func (s *InstanceServiceImpl) StartStoppedInstance(ctx context.Context, input *S
 		return nil, errors.New(awserrors.ErrorInvalidInstanceIDNotFound)
 	}
 
+	// Atomic claim: at most one caller across the cluster can win this race
+	// — a forwarded call and this node's local fallback, or two nodes
+	// racing the same forwarded call, both pass the checks above, but only
+	// one succeeds here. The loser must not touch resourceMgr/vmMgr at
+	// all, closing the double-start-onto-the-same-volume race. This also
+	// replaces the plain Load used above as the record of truth going
+	// forward: `instance` is reassigned to the freshest claimed value.
+	instance, err = s.stoppedStore.ClaimStoppedInstance(input.InstanceID)
+	if err != nil {
+		if errors.Is(err, vm.ErrStoppedInstanceClaimed) {
+			slog.WarnContext(ctx, "StartStoppedInstance: lost race to claim stopped instance",
+				"instanceId", input.InstanceID)
+			return nil, errors.New(awserrors.ErrorIncorrectInstanceState)
+		}
+		slog.ErrorContext(ctx, "StartStoppedInstance: failed to claim stopped instance",
+			"instanceId", input.InstanceID, "err", err)
+		return nil, errors.New(awserrors.ErrorServerInternal)
+	}
+
 	// Reset node-local fields that are stale after cross-node migration.
 	instance.ResetNodeLocalState()
 
@@ -2168,10 +2187,12 @@ func (s *InstanceServiceImpl) StartStoppedInstance(ctx context.Context, input *S
 	if !ok {
 		slog.ErrorContext(ctx, "StartStoppedInstance: instance type not available on this node",
 			"instanceId", input.InstanceID, "instanceType", instance.InstanceType)
+		s.restoreClaimedStoppedInstance(ctx, instance)
 		return nil, errors.New(awserrors.ErrorInsufficientInstanceCapacity)
 	}
 	if err := s.resourceMgr.Allocate(instanceType); err != nil {
 		slog.ErrorContext(ctx, "StartStoppedInstance: failed to allocate resources", "instanceId", input.InstanceID, "err", err)
+		s.restoreClaimedStoppedInstance(ctx, instance)
 		return nil, errors.New(awserrors.ErrorInsufficientInstanceCapacity)
 	}
 
@@ -2188,6 +2209,7 @@ func (s *InstanceServiceImpl) StartStoppedInstance(ctx context.Context, input *S
 			slog.ErrorContext(ctx, "StartStoppedInstance: GPU claim failed", "instanceId", input.InstanceID, "err", gpuErr)
 			s.resourceMgr.Deallocate(instanceType)
 			s.vmMgr.Delete(instance.ID)
+			s.restoreClaimedStoppedInstance(ctx, instance)
 			return nil, errors.New(awserrors.ErrorInsufficientInstanceCapacity)
 		}
 		instance.GPUAttachments = []gpu.GPUAttachment{*att}
@@ -2206,27 +2228,31 @@ func (s *InstanceServiceImpl) StartStoppedInstance(ctx context.Context, input *S
 		}
 		s.resourceMgr.Deallocate(instanceType)
 		s.vmMgr.Delete(instance.ID)
+		s.restoreClaimedStoppedInstance(ctx, instance)
 		return nil, errors.New(awserrors.ErrorServerInternal)
 	}
 
 	// Discover actual guest device names via QMP query-block.
 	s.vmMgr.UpdateGuestDeviceNames(instance)
 
-	// Remove from shared KV now that it's running locally. Retry once on failure —
-	// a stale KV entry risks duplicate starts.
-	if err := s.stoppedStore.DeleteStoppedInstance(input.InstanceID); err != nil {
-		slog.WarnContext(ctx, "StartStoppedInstance: first KV delete failed, retrying",
-			"instanceId", input.InstanceID, "err", err)
-		if retryErr := s.stoppedStore.DeleteStoppedInstance(input.InstanceID); retryErr != nil {
-			slog.ErrorContext(ctx, "StartStoppedInstance: KV delete failed after retry, instance is running locally but stale entry remains in shared KV",
-				"instanceId", input.InstanceID, "err", retryErr)
-		}
-	}
-
 	slog.InfoContext(ctx, "Started stopped instance from shared KV", "instanceId", instance.ID)
 	return &StartStoppedInstanceOutput{Status: "running", InstanceID: instance.ID}, nil
 }
 
+// restoreClaimedStoppedInstance writes instance back to the shared
+// stopped-instance store after a downstream failure that follows a
+// successful ClaimStoppedInstance (which already removed it), so the claim
+// does not silently lose the instance. Best-effort: the caller already has
+// an error to return, so a restore failure is logged, not surfaced — the
+// instance is still safely stopped in the local vm.Manager's view (it was
+// never inserted, or was removed again above).
+func (s *InstanceServiceImpl) restoreClaimedStoppedInstance(ctx context.Context, instance *vm.VM) {
+	if err := s.stoppedStore.WriteStoppedInstance(instance.ID, instance); err != nil {
+		slog.ErrorContext(ctx, "StartStoppedInstance: failed to restore claimed instance to shared KV after downstream failure",
+			"instanceId", instance.ID, "err", err)
+	}
+}
+
 // TerminateStoppedInstance terminates a stopped instance: deletes its volumes,
 // releases its public IP and ENI, and moves it to the terminated KV bucket.
 func (s *InstanceServiceImpl) TerminateStoppedInstance(ctx context.Context, input *TerminateStoppedInstanceInput, accountID string) (*TerminateStoppedInstanceOutput, error) {
diff --git a/spinifex/handlers/ec2/instance/service_impl_test.go b/spinifex/handlers/ec2/instance/service_impl_test.go
index 51f3e2c95..7c99c5f20 100644
--- a/spinifex/handlers/ec2/instance/service_impl_test.go
+++ b/spinifex/handlers/ec2/instance/service_impl_test.go
@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -516,6 +517,9 @@ func TestParseVolumeParams_Io1WithIops(t *testing.T) {
 // --- Describe* coverage -----------------------------------------------------
 
 type fakeResourceCapacityProvider struct {
+	// mu guards the mutating fields below so concurrent-claim tests can
+	// call Allocate/Deallocate from multiple goroutines race-free.
+	mu             sync.Mutex
 	types          []*ec2.InstanceTypeInfo
 	supportedTypes []*ec2.InstanceTypeInfo
 	gotShowCap     bool
@@ -552,6 +556,8 @@ func (f *fakeResourceCapacityProvider) GetSupportedInstanceTypeInfos() []*ec2.In
 }
 
 func (f *fakeResourceCapacityProvider) Allocate(it *ec2.InstanceTypeInfo) error {
+	f.mu.Lock()
+	defer f.mu.Unlock()
 	if f.allocateErr != nil {
 		return f.allocateErr
 	}
@@ -560,6 +566,8 @@ func (f *fakeResourceCapacityProvider) Allocate(it *ec2.InstanceTypeInfo) error
 }
 
 func (f *fakeResourceCapacityProvider) Deallocate(it *ec2.InstanceTypeInfo) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
 	f.deallocated = append(f.deallocated, it)
 }
 
@@ -594,6 +602,7 @@ func (f *fakeResourceCapacityProvider) InstanceTypes() map[string]*ec2.InstanceT
 }
 
 type fakeStoppedStore struct {
+	mu              sync.Mutex
 	stopped         []*vm.VM
 	terminated      []*vm.VM
 	loadByID        map[string]*vm.VM
@@ -608,12 +617,22 @@ type fakeStoppedStore struct {
 	deleteErr       error
 	deleteFailFirst bool
 	deleteAttempts  int
+
+	// claimedStopped / claimErr drive ClaimStoppedInstance, the atomic
+	// claim used by StartStoppedInstance. Claiming removes the entry from
+	// loadByID (mirroring the real KV delete-as-claim), guarded by mu so
+	// concurrent StartStoppedInstance callers race exactly like production.
+	claimedStopped []string
+	claimErr       error
+	claimAttempts  int
 }
 
 func (f *fakeStoppedStore) LoadStoppedInstance(id string) (*vm.VM, error) {
 	if f.loadErr != nil {
 		return nil, f.loadErr
 	}
+	f.mu.Lock()
+	defer f.mu.Unlock()
 	if v, ok := f.loadByID[id]; ok {
 		return v, nil
 	}
@@ -623,18 +642,24 @@ func (f *fakeStoppedStore) ListStoppedInstances() ([]*vm.VM, error) {
 	if f.listErr != nil {
 		return nil, f.listErr
 	}
+	f.mu.Lock()
+	defer f.mu.Unlock()
 	return f.stopped, nil
 }
 func (f *fakeStoppedStore) ListTerminatedInstances() ([]*vm.VM, error) {
 	if f.listTermErr != nil {
 		return nil, f.listTermErr
 	}
+	f.mu.Lock()
+	defer f.mu.Unlock()
 	return f.terminated, nil
 }
 func (f *fakeStoppedStore) WriteStoppedInstance(id string, instance *vm.VM) error {
 	if f.writeErr != nil {
 		return f.writeErr
 	}
+	f.mu.Lock()
+	defer f.mu.Unlock()
 	if f.wroteStopped == nil {
 		f.wroteStopped = make(map[string]*vm.VM)
 	}
@@ -645,6 +670,8 @@ func (f *fakeStoppedStore) WriteTerminatedInstance(id string, instance *vm.VM) e
 	if f.writeTermErr != nil {
 		return f.writeTermErr
 	}
+	f.mu.Lock()
+	defer f.mu.Unlock()
 	if f.wroteTerminated == nil {
 		f.wroteTerminated = make(map[string]*vm.VM)
 	}
@@ -652,18 +679,44 @@ func (f *fakeStoppedStore) WriteTerminatedInstance(id string, instance *vm.VM) e
 	return nil
 }
 func (f *fakeStoppedStore) DeleteStoppedInstance(id string) error {
+	f.mu.Lock()
 	f.deleteAttempts++
-	if f.deleteFailFirst && f.deleteAttempts == 1 {
+	attempt := f.deleteAttempts
+	f.mu.Unlock()
+	if f.deleteFailFirst && attempt == 1 {
 		return errors.New("transient delete failure")
 	}
 	if f.deleteErr != nil {
 		return f.deleteErr
 	}
+	f.mu.Lock()
+	defer f.mu.Unlock()
 	f.deletedStopped = append(f.deletedStopped, id)
 	return nil
 }
 func (f *fakeStoppedStore) DeleteTerminatedInstance(string) error { return nil }
 
+// ClaimStoppedInstance mimics the real atomic delete-as-claim: under the
+// store lock, remove and return loadByID[id], or vm.ErrStoppedInstanceClaimed
+// if it is already gone — mirroring the real KV's "revision conflict or
+// not-found" outcome for a losing racer. The lock makes this genuinely
+// exclusive under concurrent callers, matching the production guarantee.
+func (f *fakeStoppedStore) ClaimStoppedInstance(id string) (*vm.VM, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.claimAttempts++
+	if f.claimErr != nil {
+		return nil, f.claimErr
+	}
+	v, ok := f.loadByID[id]
+	if !ok {
+		return nil, vm.ErrStoppedInstanceClaimed
+	}
+	delete(f.loadByID, id)
+	f.claimedStopped = append(f.claimedStopped, id)
+	return v, nil
+}
+
 func TestDescribeInstanceTypes_NilResourceMgr(t *testing.T) {
 	svc := &InstanceServiceImpl{}
 	_, err := svc.DescribeInstanceTypes(context.Background(), &ec2.DescribeInstanceTypesInput{}, "")
@@ -1942,6 +1995,12 @@ func TestStartStoppedInstance_InstanceTypeUnknown(t *testing.T) {
 	require.Error(t, err)
 	assert.Equal(t, awserrors.ErrorInsufficientInstanceCapacity, err.Error())
 	assert.Empty(t, prov.allocated, "no allocation should occur for unknown type")
+
+	// The claim removed the entry from KV before the instance-type check;
+	// the rollback must write it back so the instance is not lost.
+	assert.Contains(t, store.claimedStopped, id, "claim must run before the instance-type check")
+	require.NotNil(t, store.wroteStopped[id], "claimed instance must be restored to KV after a downstream failure")
+	assert.Equal(t, vm.StateStopped, store.wroteStopped[id].Status)
 }
 
 func TestStartStoppedInstance_AllocateFails(t *testing.T) {
@@ -1964,6 +2023,12 @@ func TestStartStoppedInstance_AllocateFails(t *testing.T) {
 	_, err := svc.StartStoppedInstance(context.Background(), &StartStoppedInstanceInput{InstanceID: id}, "acc")
 	require.Error(t, err)
 	assert.Equal(t, awserrors.ErrorInsufficientInstanceCapacity, err.Error())
+
+	// A failed Allocate must not leave the instance stranded — it was
+	// already claimed (removed from KV) by this point, so it must be
+	// restored.
+	require.NotNil(t, store.wroteStopped[id], "claimed instance must be restored to KV after Allocate failure")
+	assert.Equal(t, vm.StateStopped, store.wroteStopped[id].Status)
 }
 
 // GPU claim failure must roll back the resource allocation and remove the VM
@@ -1998,6 +2063,132 @@ func TestStartStoppedInstance_GPUClaimFailureRollsBack(t *testing.T) {
 	_, stillInMgr := mgr.Get(id)
 	assert.False(t, stillInMgr, "GPU claim failure must remove the VM from the manager map")
 	assert.Empty(t, store.deletedStopped, "stopped-KV entry must remain on rollback")
+
+	// The atomic claim removed the entry from KV before Allocate/GPU-claim
+	// ran; the rollback must write it back so it is not lost.
+	require.NotNil(t, store.wroteStopped[id], "claimed instance must be restored to KV after GPU claim failure")
+	assert.Equal(t, vm.StateStopped, store.wroteStopped[id].Status)
+}
+
+// TestStartStoppedInstance_ClaimConflict proves a lost claim race is
+// reported as ErrorIncorrectInstanceState and never reaches Allocate/Insert.
+func TestStartStoppedInstance_ClaimConflict(t *testing.T) {
+	id := "i-claim-conflict"
+	itype := "t3.micro"
+	store := &fakeStoppedStore{
+		loadByID: map[string]*vm.VM{
+			id: {ID: id, Status: vm.StateStopped, AccountID: "acc", InstanceType: itype},
+		},
+		claimErr: vm.ErrStoppedInstanceClaimed,
+	}
+	prov := &fakeResourceCapacityProvider{
+		instanceTypes: map[string]*ec2.InstanceTypeInfo{itype: {InstanceType: aws.String(itype)}},
+	}
+	svc := &InstanceServiceImpl{
+		stoppedStore: store,
+		resourceMgr:  prov,
+		vmMgr:        vm.NewManager(),
+	}
+
+	_, err := svc.StartStoppedInstance(context.Background(), &StartStoppedInstanceInput{InstanceID: id}, "acc")
+	require.Error(t, err)
+	assert.Equal(t, awserrors.ErrorIncorrectInstanceState, err.Error())
+	assert.Empty(t, prov.allocated, "a lost claim race must never reach Allocate")
+}
+
+// raceVolumeMounter is a no-op vm.VolumeMounter that lets vmMgr.Run proceed
+// past the mount step in the concurrent-claim race test below, so Run
+// reaches vm.Manager's (deliberately unwired) InstanceTypeResolver check and
+// fails fast and deterministically without touching a real qemu process.
+type raceVolumeMounter struct{}
+
+func (raceVolumeMounter) Mount(*vm.VM) error                   { return nil }
+func (raceVolumeMounter) Unmount(*vm.VM) error                 { return nil }
+func (raceVolumeMounter) MountOne(*spxtypes.EBSRequest) error  { return nil }
+func (raceVolumeMounter) UnmountOne(spxtypes.EBSRequest) error { return nil }
+
+// TestStartStoppedInstance_ConcurrentClaimRace is the regression test for
+// the double-start bug this claim closes: two nodes (or a forwarded call
+// racing a local fallback) could both observe the same stopped instance as
+// claimable and both launch it onto the same viperblock volume. It fires two
+// concurrent StartStoppedInstance calls at the same stopped instance id and
+// asserts the atomic claim lets exactly one of them proceed past it —
+// reaching resourceMgr.Allocate / vmMgr.Insert / vmMgr.Run — while the other
+// loses the race and never touches resourceMgr or vmMgr at all.
+//
+// The loser's error code depends on exactly when it lost: if it loses the
+// atomic ClaimStoppedInstance call itself, it gets ErrorIncorrectInstanceState;
+// if the winner's claim already completed before the loser's preliminary
+// (non-atomic, pre-claim) LoadStoppedInstance validation ran, the loser sees
+// the record as already gone and gets ErrorInvalidInstanceIDNotFound instead.
+// Both are safe, non-destructive outcomes — the property under test is that
+// exactly one caller ever reaches past the claim, not which of the two
+// equally-valid error codes the loser receives.
+//
+// The winner's vmMgr.Run is wired to fail fast (no InstanceTypeResolver) so
+// the test stays deterministic without exec'ing a real qemu process; that
+// failure also exercises restoreClaimedStoppedInstance, so this test doubles
+// as coverage that a downstream failure after a successful claim does not
+// lose the instance.
+func TestStartStoppedInstance_ConcurrentClaimRace(t *testing.T) {
+	t.Setenv("XDG_RUNTIME_DIR", t.TempDir())
+
+	id := "i-race"
+	itype := "t3.micro"
+	store := &fakeStoppedStore{loadByID: map[string]*vm.VM{
+		id: {ID: id, Status: vm.StateStopped, AccountID: "acc", InstanceType: itype},
+	}}
+	prov := &fakeResourceCapacityProvider{
+		instanceTypes: map[string]*ec2.InstanceTypeInfo{itype: {InstanceType: aws.String(itype)}},
+	}
+	mgr := vm.NewManagerWithDeps(vm.Deps{VolumeMounter: raceVolumeMounter{}})
+	svc := &InstanceServiceImpl{
+		stoppedStore: store,
+		resourceMgr:  prov,
+		vmMgr:        mgr,
+	}
+
+	const n = 2
+	errs := make([]error, n)
+	var wg sync.WaitGroup
+	wg.Add(n)
+	for i := range n {
+		go func(i int) {
+			defer wg.Done()
+			_, err := svc.StartStoppedInstance(context.Background(), &StartStoppedInstanceInput{InstanceID: id}, "acc")
+			errs[i] = err
+		}(i)
+	}
+	wg.Wait()
+
+	var conflicted, winnerFailed int
+	for _, err := range errs {
+		require.Error(t, err, "vmMgr.Run is wired to fail fast — no caller should succeed end-to-end")
+		switch err.Error() {
+		case awserrors.ErrorIncorrectInstanceState, awserrors.ErrorInvalidInstanceIDNotFound:
+			conflicted++
+		case awserrors.ErrorServerInternal:
+			winnerFailed++
+		default:
+			t.Fatalf("unexpected error: %v", err)
+		}
+	}
+
+	assert.Equal(t, 1, conflicted, "exactly one caller must lose the claim race")
+	assert.Equal(t, 1, winnerFailed, "exactly one caller must win the claim and proceed to vmMgr.Run")
+
+	assert.Len(t, prov.allocated, 1, "only the claim winner may reach resourceMgr.Allocate")
+	// Exactly one caller ever wins the atomic claim, regardless of whether
+	// the loser lost at the claim itself or earlier at the preliminary Load
+	// (see comment above) — it may not always attempt the claim at all.
+	assert.Len(t, store.claimedStopped, 1, "the atomic claim must succeed exactly once")
+	assert.GreaterOrEqual(t, store.claimAttempts, 1, "the winner must have attempted the claim")
+
+	require.NotNil(t, store.wroteStopped[id], "the winner's downstream Run failure must restore the instance to KV")
+	assert.Equal(t, vm.StateStopped, store.wroteStopped[id].Status)
+
+	_, stillInMgr := mgr.Get(id)
+	assert.False(t, stillInMgr, "a failed Run must not leave the VM in the manager map")
 }
 
 // --- PrepareRunInstances / ec2.cmd dispatch tests ---------------------------
diff --git a/spinifex/handlers/eks/addon_installer.go b/spinifex/handlers/eks/addon_installer.go
index 732e2705b..f48257eef 100644
--- a/spinifex/handlers/eks/addon_installer.go
+++ b/spinifex/handlers/eks/addon_installer.go
@@ -35,14 +35,16 @@ type StagedAddonManifest struct {
 // The VM-side delivery slice applies it via the K3s auto-deploy dir; until then
 // the add-on sits CREATING.
 type stagingInstaller struct {
-	nc *nats.Conn
+	nc          *nats.Conn
+	clusterSize int
 }
 
 var _ AddonInstaller = (*stagingInstaller)(nil)
 
-// newStagingInstaller returns a stagingInstaller bound to the daemon NATS connection.
-func newStagingInstaller(nc *nats.Conn) *stagingInstaller {
-	return &stagingInstaller{nc: nc}
+// newStagingInstaller returns a stagingInstaller bound to the daemon NATS
+// connection, using clusterSize as the per-account bucket's replica count.
+func newStagingInstaller(nc *nats.Conn, clusterSize int) *stagingInstaller {
+	return &stagingInstaller{nc: nc, clusterSize: clusterSize}
 }
 
 func (i *stagingInstaller) acctKV(accountID string) (nats.KeyValue, error) {
@@ -53,7 +55,7 @@ func (i *stagingInstaller) acctKV(accountID string) (nats.KeyValue, error) {
 	if err != nil {
 		return nil, fmt.Errorf("jetstream: %w", err)
 	}
-	return GetOrCreateAccountBucket(js, accountID)
+	return GetOrCreateAccountBucket(js, accountID, max(i.clusterSize, 1))
 }
 
 func (i *stagingInstaller) Install(accountID, cluster string, rec *AddonRecord) error {
diff --git a/spinifex/handlers/eks/addon_status_reconciler_test.go b/spinifex/handlers/eks/addon_status_reconciler_test.go
index df6c93c98..a51672d05 100644
--- a/spinifex/handlers/eks/addon_status_reconciler_test.go
+++ b/spinifex/handlers/eks/addon_status_reconciler_test.go
@@ -14,7 +14,7 @@ func acctKVForTest(t *testing.T, svc *EKSServiceImpl) nats.KeyValue {
 	t.Helper()
 	js, err := svc.deps.NATSConn.JetStream()
 	require.NoError(t, err)
-	kv, err := GetOrCreateAccountBucket(js, testAccountID)
+	kv, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 	return kv
 }
diff --git a/spinifex/handlers/eks/addons.go b/spinifex/handlers/eks/addons.go
index 27f2576ca..ec3dc2ef0 100644
--- a/spinifex/handlers/eks/addons.go
+++ b/spinifex/handlers/eks/addons.go
@@ -329,7 +329,7 @@ func (s *EKSServiceImpl) addonInstaller() AddonInstaller {
 	if s.deps.AddonInstaller != nil {
 		return s.deps.AddonInstaller
 	}
-	return newStagingInstaller(s.deps.NATSConn)
+	return newStagingInstaller(s.deps.NATSConn, s.deps.ClusterSize)
 }
 
 // markAddonFailed best-effort flips a record to CREATE_FAILED with the error reason.
diff --git a/spinifex/handlers/eks/addons_test.go b/spinifex/handlers/eks/addons_test.go
index db2490880..a5f0f315b 100644
--- a/spinifex/handlers/eks/addons_test.go
+++ b/spinifex/handlers/eks/addons_test.go
@@ -243,7 +243,7 @@ func TestStagingInstaller_StagesManifest(t *testing.T) {
 
 	js, err := svc.deps.NATSConn.JetStream()
 	require.NoError(t, err)
-	kv, err := GetOrCreateAccountBucket(js, testAccountID)
+	kv, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 	entry, err := kv.Get(AddonManifestKey("c1", albController))
 	require.NoError(t, err, "installer must stage a manifest for VM-side delivery")
diff --git a/spinifex/handlers/eks/cluster_reconciler_state_test.go b/spinifex/handlers/eks/cluster_reconciler_state_test.go
index b70de9ca3..d959f0427 100644
--- a/spinifex/handlers/eks/cluster_reconciler_state_test.go
+++ b/spinifex/handlers/eks/cluster_reconciler_state_test.go
@@ -19,9 +19,9 @@ import (
 func newStateReconcilerHarness(t *testing.T, opts ...ReconcilerOption) (*ClusterReconciler, *nats.Conn, nats.KeyValue) {
 	t.Helper()
 	_, nc, js := testutil.StartTestJetStream(t)
-	leaderKV, err := InitLeaderBucket(js)
+	leaderKV, err := InitLeaderBucket(js, 1)
 	require.NoError(t, err)
-	acctKV, err := GetOrCreateAccountBucket(js, testAccountID)
+	acctKV, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 	require.NoError(t, PutClusterMeta(acctKV, sampleClusterMeta("alpha")))
 
diff --git a/spinifex/handlers/eks/cluster_reconciler_test.go b/spinifex/handlers/eks/cluster_reconciler_test.go
index f327e5571..bc2b397a4 100644
--- a/spinifex/handlers/eks/cluster_reconciler_test.go
+++ b/spinifex/handlers/eks/cluster_reconciler_test.go
@@ -48,9 +48,9 @@ func (s *stubHTTPDoer) setResponse(status int, err error) {
 func newReconcilerHarness(t *testing.T, healthURL string, opts ...ReconcilerOption) (*ClusterReconciler, nats.KeyValue, nats.KeyValue) {
 	t.Helper()
 	_, _, js := testutil.StartTestJetStream(t)
-	leaderKV, err := InitLeaderBucket(js)
+	leaderKV, err := InitLeaderBucket(js, 1)
 	require.NoError(t, err)
-	acctKV, err := GetOrCreateAccountBucket(js, testAccountID)
+	acctKV, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 	require.NoError(t, PutClusterMeta(acctKV, sampleClusterMeta("alpha")))
 
@@ -61,9 +61,9 @@ func newReconcilerHarness(t *testing.T, healthURL string, opts ...ReconcilerOpti
 
 func TestNewClusterReconciler_EmptyInputsRejected(t *testing.T) {
 	_, _, js := testutil.StartTestJetStream(t)
-	leaderKV, err := InitLeaderBucket(js)
+	leaderKV, err := InitLeaderBucket(js, 1)
 	require.NoError(t, err)
-	acctKV, err := GetOrCreateAccountBucket(js, testAccountID)
+	acctKV, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 
 	_, err = NewClusterReconciler(nil, acctKV, testAccountID, "alpha", "h", "")
diff --git a/spinifex/handlers/eks/cluster_state_test.go b/spinifex/handlers/eks/cluster_state_test.go
index d25d2ca52..f01f5f47a 100644
--- a/spinifex/handlers/eks/cluster_state_test.go
+++ b/spinifex/handlers/eks/cluster_state_test.go
@@ -15,7 +15,7 @@ import (
 func newClusterStateTestKV(t *testing.T) nats.KeyValue {
 	t.Helper()
 	_, _, js := testutil.StartTestJetStream(t)
-	kv, err := GetOrCreateAccountBucket(js, testAccountID)
+	kv, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 	return kv
 }
diff --git a/spinifex/handlers/eks/delete_cluster_test.go b/spinifex/handlers/eks/delete_cluster_test.go
index e55a61a58..34332b57b 100644
--- a/spinifex/handlers/eks/delete_cluster_test.go
+++ b/spinifex/handlers/eks/delete_cluster_test.go
@@ -57,7 +57,7 @@ type eksServiceFixture struct {
 func newEKSServiceFixture(t *testing.T) *eksServiceFixture {
 	t.Helper()
 	_, nc, js := testutil.StartTestJetStream(t)
-	kv, err := GetOrCreateAccountBucket(js, testAccountID)
+	kv, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 
 	nlb := newFakeNLBProvisioner()
diff --git a/spinifex/handlers/eks/eks_billable_reaper.go b/spinifex/handlers/eks/eks_billable_reaper.go
index 0081e67a0..0392a7071 100644
--- a/spinifex/handlers/eks/eks_billable_reaper.go
+++ b/spinifex/handlers/eks/eks_billable_reaper.go
@@ -68,7 +68,7 @@ func (r *EKSBillableReaper) Sweep(ctx context.Context) (int, error) {
 			continue // ENI gone or untagged: cannot confirm orphan-hood, never reap
 		}
 
-		acctKV, err := GetOrCreateAccountBucket(js, clusterAccount)
+		acctKV, err := GetOrCreateAccountBucket(js, clusterAccount, max(r.svc.deps.ClusterSize, 1))
 		if err != nil {
 			slog.WarnContext(ctx, "eks-billable: account bucket lookup failed", "account", clusterAccount, "err", err)
 			continue
diff --git a/spinifex/handlers/eks/nats_bootstrap_test.go b/spinifex/handlers/eks/nats_bootstrap_test.go
index 51518e3bc..060f13c15 100644
--- a/spinifex/handlers/eks/nats_bootstrap_test.go
+++ b/spinifex/handlers/eks/nats_bootstrap_test.go
@@ -37,7 +37,7 @@ type natsBootstrapHarness struct {
 func newBootstrapHarness(t *testing.T) *natsBootstrapHarness {
 	t.Helper()
 	_, nc, js := testutil.StartTestJetStream(t)
-	kv, err := GetOrCreateAccountBucket(js, testAccountID)
+	kv, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 
 	require.NoError(t, PutClusterMeta(kv, sampleClusterMeta(bootstrapTestCluster)))
@@ -82,7 +82,7 @@ func (h *natsBootstrapHarness) waitSubsBound(base, want int) {
 
 func TestNewNATSBootstrap_RejectsBadInputs(t *testing.T) {
 	_, nc, js := testutil.StartTestJetStream(t)
-	kv, err := GetOrCreateAccountBucket(js, testAccountID)
+	kv, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 
 	_, err = NewNATSBootstrap(nil, kv, bootstrapTestMasterKey, testAccountID, "alpha")
diff --git a/spinifex/handlers/eks/nodegroup.go b/spinifex/handlers/eks/nodegroup.go
index f504d37e8..12c2e19f5 100644
--- a/spinifex/handlers/eks/nodegroup.go
+++ b/spinifex/handlers/eks/nodegroup.go
@@ -163,7 +163,7 @@ func (s *EKSServiceImpl) nodegroupAcctKV(accountID string) (nats.KeyValue, error
 	if err != nil {
 		return nil, fmt.Errorf("jetstream: %w", err)
 	}
-	acctKV, err := GetOrCreateAccountBucket(js, accountID)
+	acctKV, err := GetOrCreateAccountBucket(js, accountID, max(s.deps.ClusterSize, 1))
 	if err != nil {
 		return nil, fmt.Errorf("get account bucket: %w", err)
 	}
diff --git a/spinifex/handlers/eks/nodegroup_test.go b/spinifex/handlers/eks/nodegroup_test.go
index 3cdce6540..1820179a2 100644
--- a/spinifex/handlers/eks/nodegroup_test.go
+++ b/spinifex/handlers/eks/nodegroup_test.go
@@ -175,7 +175,7 @@ func TestReclaimOrphanedNodegroups_TerminatesStrandedWorkers(t *testing.T) {
 
 func TestNodegroupRecord_CRUDRoundTrip(t *testing.T) {
 	_, _, js := testutil.StartTestJetStream(t)
-	kv, err := GetOrCreateAccountBucket(js, testAccountID)
+	kv, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 
 	rec := &NodegroupRecord{
diff --git a/spinifex/handlers/eks/recovery_directive_test.go b/spinifex/handlers/eks/recovery_directive_test.go
index 7d1122c61..c0f99a664 100644
--- a/spinifex/handlers/eks/recovery_directive_test.go
+++ b/spinifex/handlers/eks/recovery_directive_test.go
@@ -12,7 +12,7 @@ import (
 
 func TestLoadRecoveryDirective_AbsentIsZeroNone(t *testing.T) {
 	_, _, js := testutil.StartTestJetStream(t)
-	acctKV, err := GetOrCreateAccountBucket(js, testAccountID)
+	acctKV, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 
 	d, err := LoadRecoveryDirective(acctKV, "alpha", "i-missing")
@@ -23,7 +23,7 @@ func TestLoadRecoveryDirective_AbsentIsZeroNone(t *testing.T) {
 
 func TestStoreRecoveryDirective_EpochIncrements(t *testing.T) {
 	_, _, js := testutil.StartTestJetStream(t)
-	acctKV, err := GetOrCreateAccountBucket(js, testAccountID)
+	acctKV, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 
 	first, err := StoreRecoveryDirective(acctKV, "alpha", "i-0", RecoveryActionClusterReset, "")
diff --git a/spinifex/handlers/eks/service_impl.go b/spinifex/handlers/eks/service_impl.go
index 5e79e27f2..d875fee33 100644
--- a/spinifex/handlers/eks/service_impl.go
+++ b/spinifex/handlers/eks/service_impl.go
@@ -44,6 +44,11 @@ type EKSServiceDeps struct {
 	Region         string
 	HolderID       string
 
+	// ClusterSize is the daemon's node count, used as the JetStream replica
+	// count for the lazily-created per-account and leader KV buckets so they
+	// match the cluster's other R3 streams instead of staying stuck at R1.
+	ClusterSize int
+
 	// InternalSuffix is the AWS-parity internal DNS suffix (e.g. spinifex.internal)
 	// used to compose the worker's ECR registry host.
 	InternalSuffix string
@@ -244,7 +249,7 @@ func NewEKSServiceImpl(deps EKSServiceDeps) (*EKSServiceImpl, error) {
 	if err != nil {
 		return nil, fmt.Errorf("failed to get JetStream context: %w", err)
 	}
-	leaderKV, err := InitLeaderBucket(js)
+	leaderKV, err := InitLeaderBucket(js, max(deps.ClusterSize, 1))
 	if err != nil {
 		return nil, err
 	}
@@ -417,7 +422,7 @@ func (s *EKSServiceImpl) CreateCluster(ctx context.Context, input *eks.CreateClu
 	if err != nil {
 		return nil, logCreateErr(name, accountID, "jetstream", err)
 	}
-	acctKV, err := GetOrCreateAccountBucket(js, accountID)
+	acctKV, err := GetOrCreateAccountBucket(js, accountID, max(s.deps.ClusterSize, 1))
 	if err != nil {
 		return nil, logCreateErr(name, accountID, "get account bucket", err)
 	}
@@ -843,7 +848,7 @@ func (s *EKSServiceImpl) DescribeCluster(ctx context.Context, input *eks.Describ
 	if err != nil {
 		return nil, fmt.Errorf("jetstream: %w", err)
 	}
-	acctKV, err := GetOrCreateAccountBucket(js, accountID)
+	acctKV, err := GetOrCreateAccountBucket(js, accountID, max(s.deps.ClusterSize, 1))
 	if err != nil {
 		return nil, fmt.Errorf("get account bucket: %w", err)
 	}
@@ -862,7 +867,7 @@ func (s *EKSServiceImpl) ListClusters(ctx context.Context, input *eks.ListCluste
 	if err != nil {
 		return nil, eksReadUnavailableOr(err, "jetstream")
 	}
-	acctKV, err := GetOrCreateAccountBucket(js, accountID)
+	acctKV, err := GetOrCreateAccountBucket(js, accountID, max(s.deps.ClusterSize, 1))
 	if err != nil {
 		return nil, eksReadUnavailableOr(err, "get account bucket")
 	}
@@ -909,7 +914,7 @@ func (s *EKSServiceImpl) DeleteCluster(ctx context.Context, input *eks.DeleteClu
 	if err != nil {
 		return nil, fmt.Errorf("jetstream: %w", err)
 	}
-	acctKV, err := GetOrCreateAccountBucket(js, accountID)
+	acctKV, err := GetOrCreateAccountBucket(js, accountID, max(s.deps.ClusterSize, 1))
 	if err != nil {
 		return nil, fmt.Errorf("get account bucket: %w", err)
 	}
@@ -1296,7 +1301,7 @@ func (s *EKSServiceImpl) acctKVForCluster(accountID, cluster string) (nats.KeyVa
 	if err != nil {
 		return nil, fmt.Errorf("jetstream: %w", err)
 	}
-	acctKV, err := GetOrCreateAccountBucket(js, accountID)
+	acctKV, err := GetOrCreateAccountBucket(js, accountID, max(s.deps.ClusterSize, 1))
 	if err != nil {
 		return nil, fmt.Errorf("get account bucket: %w", err)
 	}
@@ -1758,7 +1763,7 @@ func (s *EKSServiceImpl) accountBucket(accountID string) (nats.KeyValue, error)
 	if err != nil {
 		return nil, fmt.Errorf("jetstream: %w", err)
 	}
-	return GetOrCreateAccountBucket(js, accountID)
+	return GetOrCreateAccountBucket(js, accountID, max(s.deps.ClusterSize, 1))
 }
 
 // clusterNameFromARN extracts the cluster name from an EKS cluster ARN
@@ -1931,7 +1936,7 @@ func (s *EKSServiceImpl) spawnReconciler(accountID, clusterName string, _ *Clust
 		slog.Error("spawnReconciler: jetstream", "err", err)
 		return
 	}
-	acctKV, err := GetOrCreateAccountBucket(js, accountID)
+	acctKV, err := GetOrCreateAccountBucket(js, accountID, max(s.deps.ClusterSize, 1))
 	if err != nil {
 		slog.Error("spawnReconciler: account bucket", "err", err)
 		return
diff --git a/spinifex/handlers/eks/service_impl_test.go b/spinifex/handlers/eks/service_impl_test.go
index 5c090cc37..95e375c62 100644
--- a/spinifex/handlers/eks/service_impl_test.go
+++ b/spinifex/handlers/eks/service_impl_test.go
@@ -195,7 +195,7 @@ func seedTestCluster(t *testing.T, svc *EKSServiceImpl, cluster string) {
 	t.Helper()
 	js, err := svc.deps.NATSConn.JetStream()
 	require.NoError(t, err)
-	kv, err := GetOrCreateAccountBucket(js, testAccountID)
+	kv, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 	require.NoError(t, PutClusterMeta(kv, &ClusterMeta{Name: cluster, Status: ClusterStatusActive}))
 }
@@ -374,7 +374,7 @@ func TestEKSServiceImpl_ClusterTagRoundTrip(t *testing.T) {
 	svc := setupTestService(t)
 	js, err := svc.deps.NATSConn.JetStream()
 	require.NoError(t, err)
-	kv, err := GetOrCreateAccountBucket(js, testAccountID)
+	kv, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 
 	const arn = "arn:aws:eks:us-east-1:111122223333:cluster/c1"
@@ -417,7 +417,7 @@ func TestEKSServiceImpl_NodegroupTagRoundTrip(t *testing.T) {
 	svc := setupTestService(t)
 	js, err := svc.deps.NATSConn.JetStream()
 	require.NoError(t, err)
-	kv, err := GetOrCreateAccountBucket(js, testAccountID)
+	kv, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 
 	const arn = "arn:aws:eks:us-east-1:111122223333:nodegroup/c1/ng1/abc123"
diff --git a/spinifex/handlers/eks/store.go b/spinifex/handlers/eks/store.go
index ce501cfe5..292b5c302 100644
--- a/spinifex/handlers/eks/store.go
+++ b/spinifex/handlers/eks/store.go
@@ -181,11 +181,12 @@ func AccountBucketName(accountID string) string {
 }
 
 // GetOrCreateAccountBucket returns the per-account KV bucket for accountID,
-// creating it on first use. Idempotent: subsequent calls with the same
-// accountID return the existing handle.
-func GetOrCreateAccountBucket(js nats.JetStreamContext, accountID string) (nats.KeyValue, error) {
+// creating it on first use at the given replica count (clamped to a minimum
+// of 1). Idempotent: subsequent calls with the same accountID return the
+// existing handle.
+func GetOrCreateAccountBucket(js nats.JetStreamContext, accountID string, replicas int) (nats.KeyValue, error) {
 	bucket := AccountBucketName(accountID)
-	kv, err := utils.GetOrCreateKVBucket(js, bucket, KVBucketEKSAccountHistory)
+	kv, err := utils.GetOrCreateKVBucketWithReplicas(js, bucket, KVBucketEKSAccountHistory, replicas)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create EKS per-account KV bucket %s: %w", bucket, err)
 	}
@@ -196,16 +197,18 @@ func GetOrCreateAccountBucket(js nats.JetStreamContext, accountID string) (nats.
 }
 
 // InitLeaderBucket creates (or attaches to) the shared spinifex-eks-leader
-// bucket used for per-cluster reconciler leader-lease CAS locks. The bucket
-// is configured with History=1 and a 60s TTL so stale leases expire on their
-// own when a leader dies mid-cycle. utils.GetOrCreateKVBucket doesn't expose
-// a TTL knob, so this function takes the direct js.CreateKeyValue path and
-// falls back to js.KeyValue on already-exists.
-func InitLeaderBucket(js nats.JetStreamContext) (nats.KeyValue, error) {
+// bucket used for per-cluster reconciler leader-lease CAS locks, at the given
+// replica count (clamped to a minimum of 1). The bucket is configured with
+// History=1 and a 60s TTL so stale leases expire on their own when a leader
+// dies mid-cycle. utils.GetOrCreateKVBucketWithReplicas doesn't expose a TTL
+// knob, so this function sets Replicas directly on its own js.CreateKeyValue
+// call and falls back to js.KeyValue on already-exists.
+func InitLeaderBucket(js nats.JetStreamContext, replicas int) (nats.KeyValue, error) {
 	kv, err := js.CreateKeyValue(&nats.KeyValueConfig{
-		Bucket:  KVBucketEKSLeader,
-		History: 1,
-		TTL:     KVBucketEKSLeaderTTL,
+		Bucket:   KVBucketEKSLeader,
+		History:  1,
+		TTL:      KVBucketEKSLeaderTTL,
+		Replicas: max(replicas, 1),
 	})
 	if err != nil {
 		kv, err = js.KeyValue(KVBucketEKSLeader)
diff --git a/spinifex/handlers/eks/store_test.go b/spinifex/handlers/eks/store_test.go
index 8432a6a88..26eefa652 100644
--- a/spinifex/handlers/eks/store_test.go
+++ b/spinifex/handlers/eks/store_test.go
@@ -13,11 +13,11 @@ const testAccountID = "111122223333"
 func TestGetOrCreateAccountBucket_Idempotent(t *testing.T) {
 	_, _, js := testutil.StartTestJetStream(t)
 
-	kv1, err := GetOrCreateAccountBucket(js, testAccountID)
+	kv1, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 	require.NotNil(t, kv1)
 
-	kv2, err := GetOrCreateAccountBucket(js, testAccountID)
+	kv2, err := GetOrCreateAccountBucket(js, testAccountID, 1)
 	require.NoError(t, err)
 	require.NotNil(t, kv2)
 
@@ -25,20 +25,52 @@ func TestGetOrCreateAccountBucket_Idempotent(t *testing.T) {
 	assert.Equal(t, kv1.Bucket(), kv2.Bucket())
 }
 
+// TestGetOrCreateAccountBucket_ReplicasClamped confirms the per-account
+// bucket is created with the requested replica count, clamped to a minimum
+// of 1. The embedded single-node test server rejects Replicas > 1
+// ("replicas > 1 not supported in non-clustered mode"), so only the clamping
+// path (replicas <= 0 -> 1) is exercisable end-to-end here; multi-node
+// replica counts are exercised live (see the associated bug doc).
+func TestGetOrCreateAccountBucket_ReplicasClamped(t *testing.T) {
+	_, _, js := testutil.StartTestJetStream(t)
+
+	kv, err := GetOrCreateAccountBucket(js, testAccountID, 0)
+	require.NoError(t, err)
+	require.NotNil(t, kv)
+
+	si, err := js.StreamInfo("KV_" + AccountBucketName(testAccountID))
+	require.NoError(t, err)
+	assert.Equal(t, 1, si.Config.Replicas)
+}
+
 func TestInitLeaderBucket_Idempotent(t *testing.T) {
 	_, _, js := testutil.StartTestJetStream(t)
 
-	kv1, err := InitLeaderBucket(js)
+	kv1, err := InitLeaderBucket(js, 1)
 	require.NoError(t, err)
 	require.NotNil(t, kv1)
 	assert.Equal(t, KVBucketEKSLeader, kv1.Bucket())
 
-	kv2, err := InitLeaderBucket(js)
+	kv2, err := InitLeaderBucket(js, 1)
 	require.NoError(t, err)
 	require.NotNil(t, kv2)
 	assert.Equal(t, KVBucketEKSLeader, kv2.Bucket())
 }
 
+// TestInitLeaderBucket_ReplicasClamped confirms the leader bucket is created
+// with the requested replica count, clamped to a minimum of 1.
+func TestInitLeaderBucket_ReplicasClamped(t *testing.T) {
+	_, _, js := testutil.StartTestJetStream(t)
+
+	kv, err := InitLeaderBucket(js, -1)
+	require.NoError(t, err)
+	require.NotNil(t, kv)
+
+	si, err := js.StreamInfo("KV_" + KVBucketEKSLeader)
+	require.NoError(t, err)
+	assert.Equal(t, 1, si.Config.Replicas)
+}
+
 func TestKeyPaths_MatchQ2Spec(t *testing.T) {
 	cases := []struct {
 		name string
diff --git a/spinifex/handlers/sts/assume_role_with_web_identity_test.go b/spinifex/handlers/sts/assume_role_with_web_identity_test.go
index 7fe14e925..fd3f3f5c9 100644
--- a/spinifex/handlers/sts/assume_role_with_web_identity_test.go
+++ b/spinifex/handlers/sts/assume_role_with_web_identity_test.go
@@ -62,7 +62,7 @@ func newWebIdentityFixture(t *testing.T, svc *STSServiceImpl, accountID string)
 	federatedARN := handlers_iam.OIDCProviderARN(accountID, issuerHostPath)
 
 	// Publish JWKS to the per-cluster EKS bucket.
-	kv, err := handlers_eks.GetOrCreateAccountBucket(svc.js, accountID)
+	kv, err := handlers_eks.GetOrCreateAccountBucket(svc.js, accountID, 1)
 	require.NoError(t, err)
 	raw, err := json.Marshal(jwks)
 	require.NoError(t, err)
@@ -352,7 +352,7 @@ func TestAssumeRoleWithWebIdentity_ProviderNotRegistered(t *testing.T) {
 	federatedARN := handlers_iam.OIDCProviderARN(testCallerAccountID, issuerHostPath)
 
 	// Publish JWKS — but skip the IAM provider registration.
-	kv, err := handlers_eks.GetOrCreateAccountBucket(svc.js, testCallerAccountID)
+	kv, err := handlers_eks.GetOrCreateAccountBucket(svc.js, testCallerAccountID, 1)
 	require.NoError(t, err)
 	jwks := &JWKS{Keys: []JWK{{
 		Kty: "EC", Crv: "P-256", Alg: "ES256", Use: "sig", Kid: kid,
diff --git a/spinifex/handlers/sts/oidc_jwks_test.go b/spinifex/handlers/sts/oidc_jwks_test.go
index c4ec3b5e4..752ee4d0a 100644
--- a/spinifex/handlers/sts/oidc_jwks_test.go
+++ b/spinifex/handlers/sts/oidc_jwks_test.go
@@ -79,7 +79,7 @@ func TestFetchClusterJWKS_NotFoundReturnsNil(t *testing.T) {
 func TestFetchClusterJWKS_RoundTrip(t *testing.T) {
 	_, _, js := testutil.StartTestJetStream(t)
 
-	kv, err := handlers_eks.GetOrCreateAccountBucket(js, "123456789012")
+	kv, err := handlers_eks.GetOrCreateAccountBucket(js, "123456789012", 1)
 	require.NoError(t, err)
 
 	want := &JWKS{Keys: []JWK{
@@ -102,7 +102,7 @@ func TestFetchClusterJWKS_RoundTrip(t *testing.T) {
 func TestFetchClusterJWKS_EmptyKeysIsError(t *testing.T) {
 	_, _, js := testutil.StartTestJetStream(t)
 
-	kv, err := handlers_eks.GetOrCreateAccountBucket(js, "123456789012")
+	kv, err := handlers_eks.GetOrCreateAccountBucket(js, "123456789012", 1)
 	require.NoError(t, err)
 
 	_, err = kv.Put(handlers_eks.OIDCJWKSKey("empty-cluster"), []byte(`{"keys":[]}`))
diff --git a/spinifex/services/viperblockd/viperblockd.go b/spinifex/services/viperblockd/viperblockd.go
index 351e07f57..26efb666c 100644
--- a/spinifex/services/viperblockd/viperblockd.go
+++ b/spinifex/services/viperblockd/viperblockd.go
@@ -885,20 +885,32 @@ func launchService(cfg *Config) (err error) {
 			return
 		}
 
-		// Wait for 1 second to confirm nbdkit is running
-		time.Sleep(1 * time.Second)
+		// Poll for up to 1 second to confirm nbdkit is running, checking every
+		// 50ms so a fast failure is detected quickly instead of always
+		// costing the full second. Any exit within that window means NBDKit
+		// failed to stay up.
+		const nbdkitConfirmPollInterval = 50 * time.Millisecond
+		const nbdkitConfirmDeadline = 1 * time.Second
+		confirmDeadline := time.Now().Add(nbdkitConfirmDeadline)
+		for {
+			select {
+			case exitErr := <-exitChan:
+				ebsResponse.Error = fmt.Sprintf("nbdkit exited unexpectedly (code=%d)", exitErr)
+				respondAndPublish(msg, nc, "ebs.mount.response", ebsResponse)
+				return
+			default:
+			}
 
-		// Any exit within the first second means NBDKit failed to stay up.
-		select {
-		case exitErr := <-exitChan:
-			ebsResponse.Error = fmt.Sprintf("nbdkit exited unexpectedly (code=%d)", exitErr)
-			respondAndPublish(msg, nc, "ebs.mount.response", ebsResponse)
-			return
-		default:
-			// nbdkit is still running after 1 second, which means it started successfully
-			slog.InfoContext(ctx, "NBDKit started successfully and is running")
+			if time.Now().After(confirmDeadline) {
+				break
+			}
+
+			time.Sleep(nbdkitConfirmPollInterval)
 		}
 
+		// nbdkit is still running after the poll window, which means it started successfully
+		slog.InfoContext(ctx, "NBDKit started successfully and is running")
+
 		// NBDKit creates the socket with its own umask (typically 0755).
 		// The daemon (different user, same group) needs write access to connect.
 		if nbdSocket != "" {
diff --git a/spinifex/utils/account.go b/spinifex/utils/account.go
index e904e54d3..b04e9ae18 100644
--- a/spinifex/utils/account.go
+++ b/spinifex/utils/account.go
@@ -69,11 +69,20 @@ func IsAccountID(s string) bool {
 	return true
 }
 
-// GetOrCreateKVBucket creates or retrieves a NATS KV bucket.
+// GetOrCreateKVBucket creates or retrieves a NATS KV bucket at Replicas=1.
 func GetOrCreateKVBucket(js nats.JetStreamContext, bucketName string, history int) (nats.KeyValue, error) {
+	return GetOrCreateKVBucketWithReplicas(js, bucketName, history, 1)
+}
+
+// GetOrCreateKVBucketWithReplicas creates or retrieves a NATS KV bucket at the
+// given replica count (clamped to a minimum of 1). The vendored nats.go
+// (v1.52.0) has no UpdateKeyValue to live-upgrade an existing under-replicated
+// bucket's replica count; existing buckets are upgraded on rebalance elsewhere.
+func GetOrCreateKVBucketWithReplicas(js nats.JetStreamContext, bucketName string, history int, replicas int) (nats.KeyValue, error) {
 	kv, err := js.CreateKeyValue(&nats.KeyValueConfig{
-		Bucket:  bucketName,
-		History: SafeIntToUint8(history),
+		Bucket:   bucketName,
+		History:  SafeIntToUint8(history),
+		Replicas: max(replicas, 1),
 	})
 	if err != nil {
 		kv, err = js.KeyValue(bucketName)
diff --git a/spinifex/utils/account_test.go b/spinifex/utils/account_test.go
index 5eb396031..4a089730a 100644
--- a/spinifex/utils/account_test.go
+++ b/spinifex/utils/account_test.go
@@ -106,6 +106,51 @@ func TestVersionStateMachine(t *testing.T) {
 	assert.Equal(t, "5", string(entry.Value()))
 }
 
+// streamReplicas returns the replica count of the JetStream stream backing a
+// KV bucket, so tests can assert on the config actually sent to the server.
+func streamReplicas(t *testing.T, js nats.JetStreamContext, bucket string) int {
+	t.Helper()
+	si, err := js.StreamInfo("KV_" + bucket)
+	require.NoError(t, err)
+	return si.Config.Replicas
+}
+
+func TestGetOrCreateKVBucket_CreatesAtReplicaOne(t *testing.T) {
+	_, js := startJSNATSServer(t)
+
+	kv, err := GetOrCreateKVBucket(js, "regression-bucket", 5)
+	require.NoError(t, err)
+	require.NotNil(t, kv)
+	assert.Equal(t, 1, streamReplicas(t, js, "regression-bucket"))
+}
+
+func TestGetOrCreateKVBucketWithReplicas_CreatesAtRequestedReplicas(t *testing.T) {
+	_, js := startJSNATSServer(t)
+
+	// The embedded single-node test server rejects Replicas > 1
+	// ("replicas > 1 not supported in non-clustered mode"), so the only
+	// replica count exercisable end-to-end here is 1; the clamping logic
+	// (max(replicas, 1)) is covered separately below.
+	kv, err := GetOrCreateKVBucketWithReplicas(js, "replicated-bucket", 5, 1)
+	require.NoError(t, err)
+	require.NotNil(t, kv)
+	assert.Equal(t, 1, streamReplicas(t, js, "replicated-bucket"))
+}
+
+func TestGetOrCreateKVBucketWithReplicas_ClampsBelowOne(t *testing.T) {
+	_, js := startJSNATSServer(t)
+
+	kv, err := GetOrCreateKVBucketWithReplicas(js, "clamped-zero", 1, 0)
+	require.NoError(t, err)
+	require.NotNil(t, kv)
+	assert.Equal(t, 1, streamReplicas(t, js, "clamped-zero"))
+
+	kv, err = GetOrCreateKVBucketWithReplicas(js, "clamped-negative", 1, -3)
+	require.NoError(t, err)
+	require.NotNil(t, kv)
+	assert.Equal(t, 1, streamReplicas(t, js, "clamped-negative"))
+}
+
 func TestDeleteKVBucketIfExists(t *testing.T) {
 	_, js := startJSNATSServer(t)
 
diff --git a/spinifex/utils/process.go b/spinifex/utils/process.go
index 734754967..fdd85a6b6 100644
--- a/spinifex/utils/process.go
+++ b/spinifex/utils/process.go
@@ -72,7 +72,22 @@ func ForceKillProcess(pid int, timeout time.Duration) error {
 	return WaitForProcessExit(pid, timeout)
 }
 
+// killProcessPollInterval and killProcessGracePeriod drive KillProcess's
+// liveness poll: check every pollInterval instead of blocking for the full
+// gracePeriod, so a process that dies quickly is detected almost immediately.
+const (
+	killProcessPollInterval = 50 * time.Millisecond
+	killProcessGracePeriod  = 120 * time.Second
+)
+
 func KillProcess(pid int) error {
+	return killProcessWithTiming(pid, killProcessPollInterval, killProcessGracePeriod)
+}
+
+// killProcessWithTiming implements KillProcess with an injectable poll
+// interval and grace period so tests can exercise the SIGKILL escalation
+// path without waiting out the full production grace period.
+func killProcessWithTiming(pid int, pollInterval, gracePeriod time.Duration) error {
 	process, err := os.FindProcess(pid)
 
 	if err != nil {
@@ -84,33 +99,25 @@ func KillProcess(pid int) error {
 		return err
 	}
 
-	checks := 0
+	deadline := time.Now().Add(gracePeriod)
 	for {
-		time.Sleep(1 * time.Second)
-		process, err = os.FindProcess(pid)
-
-		if err != nil {
-			return err
+		if !ProcessAlive(pid) {
+			return nil // process has terminated
 		}
 
-		err = process.Signal(syscall.Signal(0))
-
-		if err != nil {
-			break // Signal(0) error means process has terminated
-		}
-
-		checks++
-
-		if checks > 120 {
-			err = process.Kill() // SIGKILL after 120 s
-
+		if time.Now().After(deadline) {
+			process, err = os.FindProcess(pid)
 			if err != nil {
 				return err
 			}
 
-			break
-		}
-	}
+			if err := process.Kill(); err != nil { // SIGKILL after grace period
+				return err
+			}
 
-	return nil //nolint:nilerr // Signal(0) error means process exited — that's success
+			return nil
+		}
+
+		time.Sleep(pollInterval)
+	}
 }
diff --git a/spinifex/utils/process_test.go b/spinifex/utils/process_test.go
new file mode 100644
index 000000000..ccaec5c8b
--- /dev/null
+++ b/spinifex/utils/process_test.go
@@ -0,0 +1,78 @@
+package utils
+
+import (
+	"bufio"
+	"os/exec"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// KillProcess must poll for liveness instead of blindly sleeping, so a
+// process that dies quickly (nbdkit on unmount, in production) is reaped
+// in milliseconds rather than costing a fixed 1s+ per call.
+func TestKillProcessReturnsQuicklyWhenProcessExitsPromptly(t *testing.T) {
+	cmd := exec.Command("sleep", "60") // dies immediately on default SIGTERM
+	require.NoError(t, cmd.Start())
+	pid := cmd.Process.Pid
+	done := make(chan struct{})
+	go func() { _ = cmd.Wait(); close(done) }()
+
+	start := time.Now()
+	err := KillProcess(pid)
+	elapsed := time.Since(start)
+
+	require.NoError(t, err)
+	assert.Less(t, elapsed, 300*time.Millisecond,
+		"a process that dies promptly must be reaped well under the old fixed 1s sleep")
+	assert.False(t, ProcessAlive(pid))
+
+	select {
+	case <-done:
+	case <-time.After(2 * time.Second):
+		t.Fatal("process did not exit after KillProcess returned")
+	}
+}
+
+// The escalation-to-SIGKILL path must still be bounded, not hang forever,
+// when a process ignores SIGTERM. Uses a shortened grace period so the test
+// doesn't have to wait out the real (much longer) production grace period.
+func TestKillProcessEscalatesToSigkillWithinDeadline(t *testing.T) {
+	// Ignore SIGTERM so the process only dies via the SIGKILL escalation.
+	// The loop (rather than a single "sleep") stops the shell from exec-ing
+	// straight into sleep, which would silently drop the trap. Wait for the
+	// "ready" line so we never signal before the trap is installed.
+	cmd := exec.Command("sh", "-c", "trap '' TERM; echo ready; while true; do sleep 1; done")
+	stdout, err := cmd.StdoutPipe()
+	require.NoError(t, err)
+	require.NoError(t, cmd.Start())
+	pid := cmd.Process.Pid
+	done := make(chan struct{})
+	go func() { _ = cmd.Wait(); close(done) }()
+
+	scanner := bufio.NewScanner(stdout)
+	require.True(t, scanner.Scan(), "expected ready line from test process")
+	require.Equal(t, "ready", scanner.Text())
+
+	const pollInterval = 20 * time.Millisecond
+	const gracePeriod = 300 * time.Millisecond
+
+	start := time.Now()
+	err = killProcessWithTiming(pid, pollInterval, gracePeriod)
+	elapsed := time.Since(start)
+
+	require.NoError(t, err)
+	assert.GreaterOrEqual(t, elapsed, gracePeriod,
+		"must wait out the full grace period before escalating")
+	assert.Less(t, elapsed, gracePeriod+2*time.Second,
+		"escalation must be bounded near the grace period, not hang indefinitely")
+
+	select {
+	case <-done:
+	case <-time.After(2 * time.Second):
+		t.Fatal("process did not exit after KillProcess escalated to SIGKILL")
+	}
+	assert.False(t, ProcessAlive(pid), "process must be gone after SIGKILL escalation")
+}
diff --git a/spinifex/vm/errors.go b/spinifex/vm/errors.go
index f16ab8cca..0cb178b4c 100644
--- a/spinifex/vm/errors.go
+++ b/spinifex/vm/errors.go
@@ -46,3 +46,10 @@ var ErrENIPipelineTimeout = errors.New("ENI hot-plug pipeline timed out")
 // instance has no live QMPClient (daemon restart mid-launch, terminated
 // VM, etc).
 var ErrQMPUnavailable = errors.New("QMP unavailable for instance")
+
+// ErrStoppedInstanceClaimed is returned by StateStore.ClaimStoppedInstance
+// when a concurrent caller already claimed (or the record was otherwise
+// removed from) the stopped-instance store for the given id. The caller
+// lost the race and must not proceed to allocate resources or launch qemu
+// for that instance.
+var ErrStoppedInstanceClaimed = errors.New("stopped instance already claimed")
diff --git a/spinifex/vm/lifecycle.go b/spinifex/vm/lifecycle.go
index 78af61bf1..b0f31b2a7 100644
--- a/spinifex/vm/lifecycle.go
+++ b/spinifex/vm/lifecycle.go
@@ -197,8 +197,8 @@ func (m *Manager) launch(ctx context.Context, instance *VM) (err error) {
 		}
 	}
 
-	// Mark boot volumes as "in-use" now that instance is confirmed running.
-	m.markBootVolumesInUse(instance)
+	// Mark attached volumes as "in-use" now that instance is confirmed running.
+	m.markAttachedVolumesInUse(instance)
 
 	if m.deps.Hooks.OnInstanceUp != nil {
 		// Launch path: per-instance subscribe failures are logged and the
@@ -214,21 +214,24 @@ func (m *Manager) launch(ctx context.Context, instance *VM) (err error) {
 	return nil
 }
 
-// markBootVolumesInUse re-asserts "in-use" status for an instance's boot
-// volumes once it is confirmed running. Used by the launch path and the
-// daemon-restart reconnect path so both keep volume state consistent with a
-// running instance. Errors are logged, not fatal.
-func (m *Manager) markBootVolumesInUse(instance *VM) {
+// markAttachedVolumesInUse re-asserts "in-use" status for every volume an
+// instance currently has attached (boot and non-boot) once it is confirmed
+// running. Used by the launch path and the daemon-restart reconnect path so
+// both keep volume state consistent with a running instance — otherwise a
+// non-boot volume (e.g. an EKS stateful-pod data volume) can read "available"
+// while the instance still has it attached. Errors are logged, not fatal.
+func (m *Manager) markAttachedVolumesInUse(instance *VM) {
 	if m.deps.VolumeStateUpdater == nil {
 		return
 	}
 	instance.EBSRequests.Mu.Lock()
 	defer instance.EBSRequests.Mu.Unlock()
 	for _, ebsReq := range instance.EBSRequests.Requests {
-		if !ebsReq.Boot {
+		// EFI pflash is not a KV-tracked EBS volume; skip it like the unmount gate.
+		if ebsReq.EFI {
 			continue
 		}
-		if err := m.deps.VolumeStateUpdater.UpdateVolumeState(ebsReq.Name, "in-use", instance.ID, ""); err != nil {
+		if err := m.deps.VolumeStateUpdater.UpdateVolumeState(ebsReq.Name, "in-use", instance.ID, ebsReq.DeviceName); err != nil {
 			slog.Error("Failed to update volume state to in-use", "volumeId", ebsReq.Name, "err", err)
 		}
 	}
diff --git a/spinifex/vm/manager.go b/spinifex/vm/manager.go
index 5a2cb26db..bf72c3603 100644
--- a/spinifex/vm/manager.go
+++ b/spinifex/vm/manager.go
@@ -55,10 +55,19 @@ type Deps struct {
 	BindHost string
 
 	// DetachDelay is the pause between QMP device_del and blockdev-del
-	// during DetachVolume, and the polling interval for blockdev-del retry.
-	// Zero is acceptable in tests; production uses 1s.
+	// during DetachVolume when DeviceDeletedTimeout is unset, and the
+	// polling interval for blockdev-del retry. Zero is acceptable in tests;
+	// production uses 1s.
 	DetachDelay time.Duration
 
+	// DeviceDeletedTimeout bounds how long DetachVolume waits for QEMU's
+	// DEVICE_DELETED event after device_del before falling back to the
+	// blockdev-del retry loop. This is the real signal that the guest has
+	// released the block node; when set (>0) it replaces the DetachDelay
+	// sleep for the common path. Zero disables the wait (old sleep+retry
+	// behavior); production uses 15s.
+	DeviceDeletedTimeout time.Duration
+
 	// ConsumeCleanShutdownMarker reports whether the previous run wrote a clean
 	// shutdown marker, consuming it. Nil is treated as "no marker" (cautious recovery).
 	ConsumeCleanShutdownMarker func() bool
diff --git a/spinifex/vm/manager_deps_test.go b/spinifex/vm/manager_deps_test.go
index 0e5685f16..37b515b63 100644
--- a/spinifex/vm/manager_deps_test.go
+++ b/spinifex/vm/manager_deps_test.go
@@ -1,6 +1,7 @@
 package vm
 
 import (
+	"errors"
 	"maps"
 	"sync"
 
@@ -81,6 +82,20 @@ func (f *fakeStateStore) ListStoppedInstances() ([]*VM, error) {
 	return out, nil
 }
 
+// ClaimStoppedInstance mimics the real atomic-delete claim for tests: under
+// the store lock, remove and return the entry, or ErrStoppedInstanceClaimed
+// if it is already gone (claimed by a concurrent caller, or never existed).
+func (f *fakeStateStore) ClaimStoppedInstance(id string) (*VM, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	v, ok := f.stopped[id]
+	if !ok {
+		return nil, ErrStoppedInstanceClaimed
+	}
+	delete(f.stopped, id)
+	return v, nil
+}
+
 func (f *fakeStateStore) WriteTerminatedInstance(id string, v *VM) error {
 	f.mu.Lock()
 	defer f.mu.Unlock()
@@ -105,6 +120,20 @@ func (f *fakeStateStore) DeleteTerminatedInstance(id string) error {
 	return nil
 }
 
+// UpdateTerminatedInstance mimics the real CAS semantics for tests: mutate
+// runs under the store lock against the stored value, matching the
+// read-modify-write contract without needing a real KV revision.
+func (f *fakeStateStore) UpdateTerminatedInstance(id string, mutate func(*VM)) (*VM, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	v, ok := f.terminated[id]
+	if !ok {
+		return nil, errors.New("terminated instance not found")
+	}
+	mutate(v)
+	return v, nil
+}
+
 var _ StateStore = (*fakeStateStore)(nil)
 
 // fakeVolumeMounter records every call so lifecycle tests can assert ordering.
diff --git a/spinifex/vm/restore.go b/spinifex/vm/restore.go
index c36de2954..7f1d49ad9 100644
--- a/spinifex/vm/restore.go
+++ b/spinifex/vm/restore.go
@@ -320,9 +320,10 @@ func (m *Manager) reconnectInstance(instance *VM) error {
 
 	instance.Status = StateRunning
 
-	// Re-assert boot-volume in-use state; a daemon restart otherwise leaves the
-	// root volume "available" while the instance runs (split-brain, siv-464).
-	m.markBootVolumesInUse(instance)
+	// Re-assert in-use state for every attached volume; a daemon restart
+	// otherwise leaves boot and non-boot volumes "available" while the
+	// instance runs (split-brain).
+	m.markAttachedVolumesInUse(instance)
 
 	if err := m.writeRunningState(); err != nil {
 		return fmt.Errorf("failed to persist reconnected instance state: %w", err)
diff --git a/spinifex/vm/restore_test.go b/spinifex/vm/restore_test.go
index 09a051cbc..897f99ee6 100644
--- a/spinifex/vm/restore_test.go
+++ b/spinifex/vm/restore_test.go
@@ -885,7 +885,7 @@ func TestReconnectInstance(t *testing.T) {
 		assert.NotNil(t, saved["i-no-hook"], "the reconnected instance must appear in the persisted snapshot")
 	})
 
-	t.Run("reconnect re-asserts boot-volume in-use, skips non-boot", func(t *testing.T) {
+	t.Run("reconnect re-asserts in-use for boot and non-boot volumes", func(t *testing.T) {
 		stateUpdater := &fakeVolumeStateUpdater{}
 		m := NewManager()
 		m.SetDeps(Deps{
@@ -901,17 +901,19 @@ func TestReconnectInstance(t *testing.T) {
 		instance := &VM{ID: "i-reconnect-vol", Status: StatePending}
 		instance.EBSRequests.Requests = []types.EBSRequest{
 			{Name: "vol-root", Boot: true},
-			{Name: "vol-data", Boot: false},
+			{Name: "vol-data", Boot: false, DeviceName: "/dev/sdf"},
 		}
 		m.Insert(instance)
 
 		require.NoError(t, m.reconnectInstance(instance))
 
 		calls := stateUpdater.snapshot()
-		require.Len(t, calls, 1,
-			"reconnect must re-assert exactly the boot volume — a daemon restart otherwise leaves the root volume 'available' while the VM runs (siv-464)")
+		require.Len(t, calls, 2,
+			"reconnect must re-assert every attached volume — a daemon restart otherwise leaves attached volumes 'available' while the VM runs, wedging stateful workloads that check volume availability")
 		assert.Equal(t, volumeStateUpdate{VolumeID: "vol-root", State: "in-use", InstanceID: "i-reconnect-vol"}, calls[0],
-			"the boot volume must be marked in-use under the running instance; non-boot volumes are owned by their own attach flow")
+			"the boot volume must be marked in-use under the running instance with no API device (boot volumes carry none)")
+		assert.Equal(t, volumeStateUpdate{VolumeID: "vol-data", State: "in-use", InstanceID: "i-reconnect-vol", AttachmentDevice: "/dev/sdf"}, calls[1],
+			"non-boot volumes must also be marked in-use, carrying the persisted API-form device name (not a guest/nbd path)")
 	})
 
 	t.Run("AttachQMP succeeds, OnInstanceUp errors: QMP closed and nil'd", func(t *testing.T) {
diff --git a/spinifex/vm/shutdown_test.go b/spinifex/vm/shutdown_test.go
index dc37c53b4..ded834aa4 100644
--- a/spinifex/vm/shutdown_test.go
+++ b/spinifex/vm/shutdown_test.go
@@ -1172,13 +1172,19 @@ func (s *signalingStore) SaveRunningState(string, map[string]*VM) error {
 func (s *signalingStore) LoadRunningState(string) (map[string]*VM, error) {
 	return map[string]*VM{}, nil
 }
-func (s *signalingStore) WriteStoppedInstance(string, *VM) error    { return nil }
-func (s *signalingStore) LoadStoppedInstance(string) (*VM, error)   { return nil, nil }
-func (s *signalingStore) DeleteStoppedInstance(string) error        { return nil }
-func (s *signalingStore) ListStoppedInstances() ([]*VM, error)      { return nil, nil }
+func (s *signalingStore) WriteStoppedInstance(string, *VM) error  { return nil }
+func (s *signalingStore) LoadStoppedInstance(string) (*VM, error) { return nil, nil }
+func (s *signalingStore) DeleteStoppedInstance(string) error      { return nil }
+func (s *signalingStore) ListStoppedInstances() ([]*VM, error)    { return nil, nil }
+func (s *signalingStore) ClaimStoppedInstance(string) (*VM, error) {
+	return nil, ErrStoppedInstanceClaimed
+}
 func (s *signalingStore) WriteTerminatedInstance(string, *VM) error { return nil }
 func (s *signalingStore) ListTerminatedInstances() ([]*VM, error)   { return nil, nil }
 func (s *signalingStore) DeleteTerminatedInstance(string) error     { return nil }
+func (s *signalingStore) UpdateTerminatedInstance(string, func(*VM)) (*VM, error) {
+	return nil, nil
+}
 
 var _ StateStore = (*signalingStore)(nil)
 
diff --git a/spinifex/vm/state_store.go b/spinifex/vm/state_store.go
index 34ba2060a..250da12ac 100644
--- a/spinifex/vm/state_store.go
+++ b/spinifex/vm/state_store.go
@@ -16,8 +16,20 @@ type StateStore interface {
 	LoadStoppedInstance(id string) (*VM, error)
 	DeleteStoppedInstance(id string) error
 	ListStoppedInstances() ([]*VM, error)
+	// ClaimStoppedInstance atomically removes id's record from the shared
+	// store and returns the VM it held, so that at most one caller across
+	// the cluster can ever win a race to (re)launch the same stopped
+	// instance. Returns ErrStoppedInstanceClaimed if a concurrent caller
+	// already claimed (or otherwise removed) the record.
+	ClaimStoppedInstance(id string) (*VM, error)
 
 	WriteTerminatedInstance(id string, v *VM) error
 	ListTerminatedInstances() ([]*VM, error)
 	DeleteTerminatedInstance(id string) error
+	// UpdateTerminatedInstance atomically applies mutate to the current
+	// record for id and writes it back using optimistic concurrency (CAS),
+	// so a concurrent writer to the same record (e.g. two teardown-reaper
+	// sweeps advancing different dependents) cannot clobber the other's
+	// progress. Returns an error if no record exists for id.
+	UpdateTerminatedInstance(id string, mutate func(*VM)) (*VM, error)
 }
diff --git a/spinifex/vm/teardown.go b/spinifex/vm/teardown.go
index 33ac32b37..be6f067b3 100644
--- a/spinifex/vm/teardown.go
+++ b/spinifex/vm/teardown.go
@@ -38,11 +38,16 @@ func (m *Manager) markTeardown(instance *VM, dep string, state TeardownState) {
 
 // markTeardownResult records done on nil error, failed otherwise.
 func (m *Manager) markTeardownResult(instance *VM, dep string, err error) {
+	m.markTeardown(instance, dep, resultState(err))
+}
+
+// resultState maps a cleaner call's error into its teardown mark: done on
+// nil, failed otherwise.
+func resultState(err error) TeardownState {
 	if err != nil {
-		m.markTeardown(instance, dep, TeardownFailed)
-		return
+		return TeardownFailed
 	}
-	m.markTeardown(instance, dep, TeardownDone)
+	return TeardownDone
 }
 
 // TeardownComplete reports whether every tracked dependent is done. A terminated
diff --git a/spinifex/vm/teardown_reaper.go b/spinifex/vm/teardown_reaper.go
index ffba217a9..94a255e1b 100644
--- a/spinifex/vm/teardown_reaper.go
+++ b/spinifex/vm/teardown_reaper.go
@@ -59,7 +59,13 @@ func (r *TerminatedTeardownReaper) Sweep(context.Context) (int, error) {
 			continue // already done on arrival: leave to the 1h bucket TTL
 		}
 
-		r.retryOutstanding(v)
+		results := r.retryOutstanding(v)
+		for dep, state := range results {
+			if v.Teardown == nil {
+				v.Teardown = make(map[string]string)
+			}
+			v.Teardown[dep] = string(state)
+		}
 
 		if v.TeardownComplete() && time.Since(v.TerminatedAt) >= terminatedVisibilityWindow {
 			if r.purge(v) {
@@ -68,40 +74,55 @@ func (r *TerminatedTeardownReaper) Sweep(context.Context) (int, error) {
 			continue
 		}
 		// Either still incomplete (retry next sweep), or complete but inside the
-		// describe-visibility window: persist progress and leave the record to
-		// the 1h bucket TTL so the instance stays describable as terminated.
-		if err := r.m.deps.StateStore.WriteTerminatedInstance(v.ID, v); err != nil {
-			slog.Warn("vm/gc: failed to persist advanced teardown marks",
-				"instanceId", v.ID, "err", err)
+		// describe-visibility window: merge this sweep's marks into whatever is
+		// currently in KV via CAS, so a concurrent writer advancing a different
+		// dependent for the same record isn't clobbered by our local snapshot.
+		if len(results) > 0 {
+			if _, err := r.m.deps.StateStore.UpdateTerminatedInstance(v.ID, func(fresh *VM) {
+				if fresh.Teardown == nil {
+					fresh.Teardown = make(map[string]string)
+				}
+				for dep, state := range results {
+					fresh.Teardown[dep] = string(state)
+				}
+			}); err != nil {
+				slog.Warn("vm/gc: failed to persist advanced teardown marks",
+					"instanceId", v.ID, "err", err)
+			}
 		}
 	}
 	return reaped, nil
 }
 
 // retryOutstanding re-drives every not-`done` dependent through the idempotent
-// cleaner and re-stamps the result. The cleaner calls are idempotent (absent →
-// success), so a successful re-drive confirms the Spinifex-side teardown; the
-// dataplane object (OVN LSP, NAT rule) is pruned by the cluster reconciler.
-func (r *TerminatedTeardownReaper) retryOutstanding(v *VM) {
+// cleaner and returns the dep→result map for whatever was retried. The cleaner
+// calls are idempotent (absent → success), so a successful re-drive confirms
+// the Spinifex-side teardown; the dataplane object (OVN LSP, NAT rule) is
+// pruned by the cluster reconciler. Pure w.r.t. KV/local state — callers merge
+// the results atomically via StateStore.UpdateTerminatedInstance so the cleaner
+// calls (which have real side effects) never run twice for a single CAS retry.
+func (r *TerminatedTeardownReaper) retryOutstanding(v *VM) map[string]TeardownState {
 	c := r.m.deps.InstanceCleaner
 	if c == nil {
-		return
+		return nil
 	}
 
+	results := make(map[string]TeardownState)
+
 	if outstanding(v, TeardownVolumes) {
-		r.m.markTeardownResult(v, TeardownVolumes, c.DeleteVolumes(v))
+		results[TeardownVolumes] = resultState(c.DeleteVolumes(v))
 	}
 	if outstanding(v, TeardownGPU) {
-		r.m.markTeardownResult(v, TeardownGPU, c.ReleaseGPU(v))
+		results[TeardownGPU] = resultState(c.ReleaseGPU(v))
 	}
 	if outstanding(v, TeardownPlacement) {
-		r.m.markTeardownResult(v, TeardownPlacement, c.RemoveFromPlacementGroup(v))
+		results[TeardownPlacement] = resultState(c.RemoveFromPlacementGroup(v))
 	}
 
 	// NAT: re-publishes vpc.delete-nat + frees the IPAM slot. The cluster
 	// reconciler heals the dataplane NAT rule.
 	if outstanding(v, TeardownNAT) {
-		r.m.markTeardownResult(v, TeardownNAT, c.ReleasePublicIP(v))
+		results[TeardownNAT] = resultState(c.ReleasePublicIP(v))
 	}
 
 	// ENI delete + OVN: deleting the ENI KV record turns its LSP into an orphan
@@ -109,9 +130,11 @@ func (r *TerminatedTeardownReaper) retryOutstanding(v *VM) {
 	// both eni and ovn.
 	if outstanding(v, TeardownENI) || outstanding(v, TeardownOVN) {
 		eniErr := c.DetachAndDeleteENI(v)
-		r.m.markTeardownResult(v, TeardownENI, eniErr)
-		r.m.markTeardownResult(v, TeardownOVN, eniErr)
+		results[TeardownENI] = resultState(eniErr)
+		results[TeardownOVN] = resultState(eniErr)
 	}
+
+	return results
 }
 
 func (r *TerminatedTeardownReaper) purge(v *VM) bool {
diff --git a/spinifex/vm/volumes.go b/spinifex/vm/volumes.go
index c3c3194aa..434d6b656 100644
--- a/spinifex/vm/volumes.go
+++ b/spinifex/vm/volumes.go
@@ -15,9 +15,10 @@ import (
 	"github.com/mulgadc/spinifex/spinifex/utils"
 )
 
-// blockdevDelMaxAttempts caps the bounded retry on "node is in use" while
-// QEMU drains pending I/O after device_del. 20 × DetachDelay (default 1s)
-// gives a 20s budget.
+// blockdevDelMaxAttempts caps the bounded retry on "node is in use" as a
+// safety net after the DEVICE_DELETED wait (see DeviceDeletedTimeout): a miss
+// on the event (timeout, or a client not opted in) falls back to polling at
+// DetachDelay. 20 × DetachDelay (default 1s) gives a 20s budget.
 const blockdevDelMaxAttempts = 20
 
 // rollbackUnmount best-effort unmounts a volume while unwinding a failed
@@ -320,12 +321,14 @@ func (m *Manager) DetachVolume(ctx context.Context, id, volumeID, device string,
 	// device_del is idempotent on DeviceNotFound so a second AWS-CLI
 	// retry can drive blockdev-del to completion when a prior detach left
 	// the guest device gone but the block node intact.
+	deviceDelIssued := false
 	_, err := sendQMPCommand(ctx, instance.QMPClient, qmp.QMPCommand{
 		Execute:   "device_del",
 		Arguments: map[string]any{"id": deviceID},
 	}, instance.ID)
 	switch {
 	case err == nil:
+		deviceDelIssued = true
 	case isQMPDeviceNotFound(err):
 		slog.InfoContext(ctx, "DetachVolume: guest device already removed (resuming detach)",
 			"volumeId", volumeID, "err", err)
@@ -337,7 +340,18 @@ func (m *Manager) DetachVolume(ctx context.Context, id, volumeID, device string,
 		return "", fmt.Errorf("QMP device_del: %w", err)
 	}
 
-	if m.deps.DetachDelay > 0 {
+	// device_del only requests the unplug; QEMU frees the block node once the
+	// guest ACKs it (DEVICE_DELETED). Wait for that real completion signal
+	// instead of blindly sleeping, so blockdev-del isn't attempted while the
+	// node still has a user. A miss (timeout, event drained by a racing read,
+	// or a resumed/forced detach with no fresh unplug in flight) falls
+	// through to the bounded retry below unchanged.
+	if deviceDelIssued && m.deps.DeviceDeletedTimeout > 0 {
+		if waitErr := waitForDeviceDeletedEvent(ctx, instance.QMPClient, deviceID, m.deps.DeviceDeletedTimeout, instance.ID); waitErr != nil {
+			slog.DebugContext(ctx, "DetachVolume: DEVICE_DELETED not observed, falling back to blockdev-del retry",
+				"volumeId", volumeID, "err", waitErr)
+		}
+	} else if m.deps.DetachDelay > 0 {
 		time.Sleep(m.deps.DetachDelay)
 	}
 
@@ -408,6 +422,62 @@ func (m *Manager) DetachVolume(ctx context.Context, id, volumeID, device string,
 	return ebsReq.DeviceName, nil
 }
 
+// waitForDeviceDeletedEvent blocks until QEMU emits a DEVICE_DELETED event
+// matching deviceID or timeout elapses, returning nil only on a match. It
+// takes over the QMP connection directly (no in-flight command is expected
+// while it runs) rather than going through sendQMPCommand, since the signal
+// we need is an async event, not a command reply.
+//
+// A timeout is treated the same as any other decode failure: q.Decoder is a
+// single shared *json.Decoder, and once Decode returns an error — including a
+// read-deadline timeout — that Decoder instance is permanently unusable, so
+// q.Dead is set exactly as sendQMPCommand does. The next QMP command
+// transparently redials via reconnectQMP. This is non-fatal either way:
+// DetachVolume falls back to the bounded blockdev-del retry, so a missed
+// event never blocks the caller forever.
+func waitForDeviceDeletedEvent(ctx context.Context, q *qmp.QMPClient, deviceID string, timeout time.Duration, instanceID string) error {
+	if q == nil || q.Conn == nil || q.Decoder == nil {
+		return fmt.Errorf("QMP client is not initialized")
+	}
+
+	q.Mu.Lock()
+	defer q.Mu.Unlock()
+
+	if q.Dead {
+		return fmt.Errorf("QMP client is disconnected")
+	}
+
+	if err := q.Conn.SetReadDeadline(time.Now().Add(timeout)); err != nil {
+		return fmt.Errorf("set read deadline: %w", err)
+	}
+	defer func() { _ = q.Conn.SetReadDeadline(time.Time{}) }()
+
+	for {
+		var msg struct {
+			Event string `json:"event"`
+			Data  struct {
+				Device string `json:"device"`
+				Path   string `json:"path"`
+			} `json:"data"`
+		}
+		if err := q.Decoder.Decode(&msg); err != nil {
+			q.Dead = true
+			return fmt.Errorf("decode error waiting for DEVICE_DELETED: %w", err)
+		}
+		if msg.Event != "DEVICE_DELETED" {
+			// Nothing else should be in flight on this connection while we
+			// hold q.Mu, but tolerate and skip any stray message rather than
+			// treating it as our signal.
+			continue
+		}
+		if msg.Data.Device == deviceID || strings.Contains(msg.Data.Path, deviceID) {
+			return nil
+		}
+		slog.DebugContext(ctx, "waitForDeviceDeletedEvent: DEVICE_DELETED for a different device, still waiting",
+			"wantDevice", deviceID, "gotDevice", msg.Data.Device, "instanceId", instanceID)
+	}
+}
+
 // tryBlockdevDel issues blockdev-del with bounded retry on "is in use" errors.
 // QEMU surfaces this as GenericError while NBD teardown and in-flight I/O drain.
 func (m *Manager) tryBlockdevDel(ctx context.Context, instance *VM, nodeName string) error {
diff --git a/spinifex/vm/volumes_test.go b/spinifex/vm/volumes_test.go
index a46e05a06..ba9f9232f 100644
--- a/spinifex/vm/volumes_test.go
+++ b/spinifex/vm/volumes_test.go
@@ -7,9 +7,11 @@ import (
 	"fmt"
 	"log/slog"
 	"net"
+	"path/filepath"
 	"sync"
 	"sync/atomic"
 	"testing"
+	"time"
 
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/service/ec2"
@@ -64,6 +66,119 @@ func newMockQMPClient(t *testing.T, responder func(qmp.QMPCommand) map[string]an
 	return client, cancel
 }
 
+// mockQMPServer lets a responder push asynchronous QMP events (e.g.
+// DEVICE_DELETED) onto the same stream as command replies. Writes are
+// serialized so a delayed event push never interleaves with a reply.
+type mockQMPServer struct {
+	mu  sync.Mutex
+	enc *json.Encoder
+}
+
+func (s *mockQMPServer) pushEvent(ev map[string]any) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	return s.enc.Encode(ev)
+}
+
+// newMockQMPClientWithEvents is newMockQMPClient plus a *mockQMPServer handle
+// so the responder can schedule out-of-band events (typically from a
+// goroutine) in addition to its synchronous command reply.
+//
+// This uses a real unix socket rather than net.Pipe: net.Pipe's deadline
+// implementation does not reliably support "timeout, then clear the deadline,
+// then read again" on the same conn (verified against Go's net.Pipe — a real
+// unix socket, matching production QMP transport, does not have this
+// limitation), and DEVICE_DELETED-wait tests need exactly that sequence.
+//
+// The listener keeps accepting connections for the life of the test (each
+// served on its own goroutine, greeting first) so a client-side reconnect —
+// e.g. reconnectQMP redialing after waitForDeviceDeletedEvent marks the
+// client Dead on timeout — is served exactly like the first connection.
+func newMockQMPClientWithEvents(t *testing.T, responder func(qmp.QMPCommand, *mockQMPServer) map[string]any) (*qmp.QMPClient, func()) {
+	t.Helper()
+
+	sockPath := filepath.Join(t.TempDir(), "qmp.sock")
+	ln, err := net.Listen("unix", sockPath)
+	require.NoError(t, err)
+
+	var wg sync.WaitGroup
+	serveConn := func(conn net.Conn) {
+		defer wg.Done()
+		defer conn.Close()
+
+		srv := &mockQMPServer{enc: json.NewEncoder(conn)}
+		if err := srv.pushEvent(map[string]any{
+			"QMP": map[string]any{
+				"version":      map[string]any{"qemu": map[string]any{"major": 8, "minor": 0}},
+				"capabilities": []string{},
+			},
+		}); err != nil {
+			return
+		}
+
+		dec := json.NewDecoder(conn)
+		for {
+			var cmd qmp.QMPCommand
+			if err := dec.Decode(&cmd); err != nil {
+				return
+			}
+			if cmd.Execute == "qmp_capabilities" {
+				if err := srv.pushEvent(map[string]any{"return": map[string]any{}}); err != nil {
+					return
+				}
+				continue
+			}
+			var reply map[string]any
+			if responder != nil {
+				reply = responder(cmd, srv)
+			}
+			if reply == nil {
+				reply = map[string]any{"return": map[string]any{}}
+			}
+			if err := srv.pushEvent(reply); err != nil {
+				return
+			}
+		}
+	}
+
+	acceptDone := make(chan struct{})
+	go func() {
+		defer close(acceptDone)
+		for {
+			conn, err := ln.Accept()
+			if err != nil {
+				return
+			}
+			wg.Add(1)
+			go serveConn(conn)
+		}
+	}()
+
+	clientConn, err := net.Dial("unix", sockPath)
+	require.NoError(t, err)
+
+	dec := json.NewDecoder(clientConn)
+	var greeting qmp.QMPGreeting
+	require.NoError(t, dec.Decode(&greeting), "mock QMP server greeting")
+
+	client := &qmp.QMPClient{
+		Conn:    clientConn,
+		Decoder: dec,
+		Encoder: json.NewEncoder(clientConn),
+		Path:    sockPath,
+	}
+
+	cancel := func() {
+		_ = ln.Close()
+		// client.Conn may have been swapped by reconnectQMP after a Dead
+		// redial, so close the current field value, not the initial dial.
+		_ = client.Conn.Close()
+		<-acceptDone
+		wg.Wait()
+	}
+	return client, cancel
+}
+
 // qmpRecorder records the order of QMP commands for assertion in rollback
 // tests. Safe for concurrent use because sendQMPCommand serializes via the
 // QMPClient mutex, but we lock anyway for clarity.
@@ -911,3 +1026,238 @@ func TestTryBlockdevDel(t *testing.T) {
 			"retry must cap at blockdevDelMaxAttempts attempts")
 	})
 }
+
+// newMockQMPServerConn wires a QMPClient over net.Pipe with no command-reply
+// loop at all — the test drives the server side directly via the returned
+// json.Encoder, which is what waitForDeviceDeletedEvent tests need: an event
+// pushed independently of any command/response exchange.
+func newMockQMPServerConn(t *testing.T) (*qmp.QMPClient, *json.Encoder, func()) {
+	t.Helper()
+
+	sockPath := filepath.Join(t.TempDir(), "qmp.sock")
+	ln, err := net.Listen("unix", sockPath)
+	require.NoError(t, err)
+
+	accepted := make(chan net.Conn, 1)
+	go func() {
+		conn, err := ln.Accept()
+		if err != nil {
+			close(accepted)
+			return
+		}
+		accepted <- conn
+	}()
+
+	clientConn, err := net.Dial("unix", sockPath)
+	require.NoError(t, err)
+
+	serverConn := <-accepted
+	_ = ln.Close()
+	require.NotNil(t, serverConn, "mock QMP server failed to accept")
+
+	client := &qmp.QMPClient{
+		Conn:    clientConn,
+		Decoder: json.NewDecoder(clientConn),
+		Encoder: json.NewEncoder(clientConn),
+		Path:    sockPath,
+	}
+	enc := json.NewEncoder(serverConn)
+
+	cancel := func() {
+		_ = clientConn.Close()
+		_ = serverConn.Close()
+	}
+	return client, enc, cancel
+}
+
+// TestWaitForDeviceDeletedEvent covers waitForDeviceDeletedEvent directly:
+// matching event, non-matching event followed by a match, and timeout. Uses
+// a short timeout so the timeout sub-test stays fast.
+func TestWaitForDeviceDeletedEvent(t *testing.T) {
+	t.Run("matching event returns nil", func(t *testing.T) {
+		qmpClient, enc, cancel := newMockQMPServerConn(t)
+		defer cancel()
+
+		errCh := make(chan error, 1)
+		go func() {
+			errCh <- waitForDeviceDeletedEvent(t.Context(), qmpClient, "vdisk-vol-1", 2*time.Second, "i-1")
+		}()
+
+		require.NoError(t, enc.Encode(map[string]any{
+			"event": "DEVICE_DELETED",
+			"data":  map[string]any{"device": "vdisk-vol-1", "path": "/machine/peripheral/vdisk-vol-1"},
+		}))
+		require.NoError(t, <-errCh)
+	})
+
+	t.Run("non-matching event is skipped, later match returns nil", func(t *testing.T) {
+		qmpClient, enc, cancel := newMockQMPServerConn(t)
+		defer cancel()
+
+		errCh := make(chan error, 1)
+		go func() {
+			errCh <- waitForDeviceDeletedEvent(t.Context(), qmpClient, "vdisk-vol-2", 2*time.Second, "i-1")
+		}()
+
+		require.NoError(t, enc.Encode(map[string]any{
+			"event": "DEVICE_DELETED",
+			"data":  map[string]any{"device": "vdisk-vol-1", "path": "/machine/peripheral/vdisk-vol-1"},
+		}))
+		require.NoError(t, enc.Encode(map[string]any{
+			"event": "DEVICE_DELETED",
+			"data":  map[string]any{"device": "vdisk-vol-2", "path": "/machine/peripheral/vdisk-vol-2"},
+		}))
+		require.NoError(t, <-errCh)
+	})
+
+	t.Run("no event before timeout returns error and marks the client dead", func(t *testing.T) {
+		qmpClient, _, cancel := newMockQMPServerConn(t)
+		defer cancel()
+
+		err := waitForDeviceDeletedEvent(t.Context(), qmpClient, "vdisk-vol-1", 50*time.Millisecond, "i-1")
+		require.Error(t, err)
+		// q.Decoder is a single shared *json.Decoder: once Decode returns any
+		// error (including a deadline timeout) that instance is permanently
+		// unusable, so Dead must be set — exactly like sendQMPCommand — so the
+		// next QMP command redials via reconnectQMP instead of reusing it.
+		assert.True(t, qmpClient.Dead,
+			"a decode timeout must mark the client dead so the next command reconnects")
+	})
+
+	t.Run("nil client returns error", func(t *testing.T) {
+		err := waitForDeviceDeletedEvent(t.Context(), nil, "vdisk-vol-1", time.Second, "i-1")
+		require.Error(t, err)
+	})
+}
+
+// TestDetachVolume_WaitsForDeviceDeletedBeforeBlockdevDel is the regression
+// guard for the "node in use" wedge: blockdev-del only ever succeeds once
+// DEVICE_DELETED has been observed, so if DetachVolume attempted it before
+// waiting for the event, this test would exhaust blockdevDelMaxAttempts and
+// fail exactly like the reported bug. Release of the event is gated on an
+// explicit signal (not a race against wall-clock timing) so the test is
+// deterministic; a minimum-elapsed-time assertion confirms DetachVolume
+// actually blocked on the event rather than skipping the wait.
+func TestDetachVolume_WaitsForDeviceDeletedBeforeBlockdevDel(t *testing.T) {
+	var blockdevAttempts atomic.Int32
+	releaseEvent := make(chan struct{})
+
+	qmpClient, cancel := newMockQMPClientWithEvents(t, func(cmd qmp.QMPCommand, srv *mockQMPServer) map[string]any {
+		switch cmd.Execute {
+		case "device_del":
+			go func() {
+				<-releaseEvent
+				_ = srv.pushEvent(map[string]any{
+					"event": "DEVICE_DELETED",
+					"data":  map[string]any{"device": "vdisk-vol-1", "path": "/machine/peripheral/vdisk-vol-1"},
+				})
+			}()
+			return nil
+		case "blockdev-del":
+			blockdevAttempts.Add(1)
+			return nil
+		}
+		return nil
+	})
+	defer cancel()
+
+	mounter := &fakeVolumeMounter{}
+	m := NewManagerWithDeps(Deps{VolumeMounter: mounter, DeviceDeletedTimeout: 5 * time.Second})
+	m.Insert(&VM{
+		ID:        "i-1",
+		Status:    StateRunning,
+		Instance:  &ec2.Instance{},
+		QMPClient: qmpClient,
+		EBSRequests: types.EBSRequests{
+			Requests: []types.EBSRequest{{Name: "vol-1", DeviceName: "/dev/sdf"}},
+		},
+	})
+
+	const releaseDelay = 100 * time.Millisecond
+	go func() {
+		time.Sleep(releaseDelay)
+		close(releaseEvent)
+	}()
+
+	start := time.Now()
+	device, err := m.DetachVolume(t.Context(), "i-1", "vol-1", "", false)
+	elapsed := time.Since(start)
+
+	require.NoError(t, err)
+	assert.Equal(t, "/dev/sdf", device)
+	assert.Equal(t, int32(1), blockdevAttempts.Load(),
+		"waiting for DEVICE_DELETED before the first blockdev-del attempt must avoid any 'node in use' retry")
+	assert.GreaterOrEqual(t, elapsed, releaseDelay/2,
+		"DetachVolume must actually block on the DEVICE_DELETED event rather than proceeding immediately")
+}
+
+// TestDetachVolume_DeviceDeletedTimeout_FallsBackToRetry covers the case
+// where DEVICE_DELETED is never observed within DeviceDeletedTimeout (e.g. a
+// lost event, or a QEMU version quirk): DetachVolume must still fall back to
+// the bounded blockdev-del retry and succeed once the node frees up, rather
+// than surfacing the wait timeout as a hard failure.
+func TestDetachVolume_DeviceDeletedTimeout_FallsBackToRetry(t *testing.T) {
+	var blockdevAttempts atomic.Int32
+
+	qmpClient, cancel := newMockQMPClientWithEvents(t, func(cmd qmp.QMPCommand, srv *mockQMPServer) map[string]any {
+		if cmd.Execute == "blockdev-del" {
+			n := blockdevAttempts.Add(1)
+			if n < 2 {
+				return map[string]any{"error": map[string]any{"class": "GenericError", "desc": "Node 'nbd-vol-1' is in use"}}
+			}
+		}
+		return nil
+	})
+	defer cancel()
+
+	mounter := &fakeVolumeMounter{}
+	m := NewManagerWithDeps(Deps{VolumeMounter: mounter, DeviceDeletedTimeout: 30 * time.Millisecond})
+	m.Insert(&VM{
+		ID:        "i-1",
+		Status:    StateRunning,
+		Instance:  &ec2.Instance{},
+		QMPClient: qmpClient,
+		EBSRequests: types.EBSRequests{
+			Requests: []types.EBSRequest{{Name: "vol-1", DeviceName: "/dev/sdf"}},
+		},
+	})
+
+	device, err := m.DetachVolume(t.Context(), "i-1", "vol-1", "", false)
+	require.NoError(t, err)
+	assert.Equal(t, "/dev/sdf", device)
+	assert.Equal(t, int32(2), blockdevAttempts.Load(),
+		"a missed DEVICE_DELETED event must still resolve via the bounded blockdev-del retry")
+}
+
+// TestDetachVolume_BlockdevDelAlreadyRemoved_IdempotentSuccess covers the
+// AWS-CLI-retry resume path end to end: a prior detach removed the block
+// node, so blockdev-del returns "Failed to find node" on the second call.
+// DetachVolume must treat that as success and complete the detach, not
+// surface it as a hard failure.
+func TestDetachVolume_BlockdevDelAlreadyRemoved_IdempotentSuccess(t *testing.T) {
+	qmpClient, cancel := newMockQMPClientWithEvents(t, func(cmd qmp.QMPCommand, srv *mockQMPServer) map[string]any {
+		if cmd.Execute == "blockdev-del" {
+			return map[string]any{"error": map[string]any{"class": "GenericError", "desc": "Failed to find node with node-name='nbd-vol-1'"}}
+		}
+		return nil
+	})
+	defer cancel()
+
+	mounter := &fakeVolumeMounter{}
+	m := NewManagerWithDeps(Deps{VolumeMounter: mounter, DeviceDeletedTimeout: 30 * time.Millisecond})
+	m.Insert(&VM{
+		ID:        "i-1",
+		Status:    StateRunning,
+		Instance:  &ec2.Instance{},
+		QMPClient: qmpClient,
+		EBSRequests: types.EBSRequests{
+			Requests: []types.EBSRequest{{Name: "vol-1", DeviceName: "/dev/sdf"}},
+		},
+	})
+
+	device, err := m.DetachVolume(t.Context(), "i-1", "vol-1", "", false)
+	require.NoError(t, err)
+	assert.Equal(t, "/dev/sdf", device)
+	assert.Equal(t, []string{"vol-1"}, mounter.unmountedOne,
+		"an already-removed block node must resume through to the unmount seal")
+}