fix(api): wake 与回档/备份/改文件按服务器互斥

cmd/felis/operator.go

@@ -107,6 +107,9 @@ func cmdOperator(args []string, _, stderr io.Writer) int {
 		// injects into user servers. The Deployment passes it as FELIS_IMAGE (see
 		// platform.OperatorDeployment); absent, that injection is simply skipped.
 		FelisImage: os.Getenv("FELIS_IMAGE"),
+		// Uncached: the maintenance-lock check lists Jobs only when a server is
+		// about to start, which does not justify a namespace-wide Job informer.
+		Jobs: mgr.GetAPIReader(),
 	}
 	if err := r.SetupWithManager(mgr); err != nil {
 		fmt.Fprintf(stderr, "felis operator: setup controller: %v\n", err)

docs/openapi.yaml

@@ -741,6 +741,11 @@ paths:
           $ref: '#/components/responses/Forbidden'
         '404':
           $ref: '#/components/responses/NotFound'
+        '409':
+          description: A restore, backup or file write holds the server's world volume (maintenance_in_progress); nothing was started.
+          content:
+            application/json:
+              schema: { $ref: '#/components/schemas/Error' }
         '429':
           description: Wake cooldown is still active for this server.
           content:
@@ -1193,7 +1198,7 @@ paths:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }
         '409':
-          description: Server is not stopped (its world PVC is still mounted).
+          description: Server is not stopped (not_stopped), or a restore, backup or file write already holds its world volume (maintenance_in_progress).
           content:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }
@@ -1228,6 +1233,11 @@ paths:
           $ref: '#/components/responses/Forbidden'
         '404':
           $ref: '#/components/responses/NotFound'
+        '409':
+          description: A restore, backup or file write holds the server's world volume (maintenance_in_progress); nothing was started.
+          content:
+            application/json:
+              schema: { $ref: '#/components/schemas/Error' }
         '429':
           description: Wake cooldown is still active.
           content:
@@ -2828,7 +2838,7 @@ paths:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }
         '409':
-          description: Submission has already been reviewed.
+          description: Server is not stopped (not_stopped), or a restore, backup or file write already holds its world volume (maintenance_in_progress).
           content:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }
@@ -2873,7 +2883,7 @@ paths:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }
         '409':
-          description: Server is not stopped (its world PVC is still mounted).
+          description: Server is not stopped (not_stopped), or a restore, backup or file write already holds its world volume (maintenance_in_progress).
           content:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }
@@ -3122,7 +3132,7 @@ paths:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }
         '409':
-          description: Server is not stopped (its world PVC is still mounted).
+          description: Server is not stopped (not_stopped), or a restore, backup or file write already holds its world volume (maintenance_in_progress).
           content:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }

docs/troubleshooting.md

@@ -185,6 +185,7 @@ per-server cooldown → global running cap**. Map the API result:
 | HTTP | Code | Cause | Fix |
 |---|---|---|---|
 | `403` | `forbidden` | `autostartPolicy=allowlist` and UUID not allowlisted, or `ownerOnly` and caller is not owner | Add the UUID / claim the server / set `autostartPolicy=public` |
+| `409` | `maintenance_in_progress` | A restore, backup or file write holds the server's world volume (§3b) | Wait for the Job to finish |
 | `429` | (cooldown) | Wake retried within the 30s per-server `WakeCooldown` | Wait out the cooldown |
 | `503` | `at_capacity` | Global `MaxRunningServers` cap reached | Stop another server or raise the cap |
 
@@ -194,11 +195,54 @@ gate; the proxy polls `GET /api/v1/internal/servers/{name}/status` every ~2s and
 teleports when `ready=true`.
 
 The Velocity-side consumption of these codes (`403` → "You're not allowed to
-start «server»"; `429` → re-queue; other → "Couldn't start … Try again
+start «server»"; `409 maintenance_in_progress` → "«server» is under
+maintenance", not queued; `429` → re-queue; other → "Couldn't start … Try again
 shortly.") lives in the Java plugin and is **[CODE-ONLY]** — the codes it reacts
 to are produced by the Go-tested `authorizeWakeByUUID` / cooldown limiter, so
 grade the two halves separately.
 
+### 3b. Wake, restore, backup or file save refused with `maintenance_in_progress`
+
+A server's world volume is ReadWriteOnce, and on a single node RWO lets a game
+pod and a restore Job mount it side by side. So felis-api serialises them per
+server: a restore, a backup, or a file write takes the world, and until its Job
+finishes every wake (panel or join) and every other world operation on that
+server gets `409 maintenance_in_progress`. File reads and listings never hold
+it. The operator applies the same rule when `desiredState` is flipped to
+`Running` by anything other than felis-api: the StatefulSet is not scaled up,
+and the `Ready` condition reads `MaintenanceInProgress` until the Job ends.
+
+What holds the world, in order:
+
+1. An unfinished Job labelled `felis.lolicon.best/server=<name>` with
+   `app.kubernetes.io/managed-by` `felis-restore`, `felis-backup`, or
+   `felis-files` plus `felis.lolicon.best/files-mode=write`:
+
+   ```sh
+   kubectl -n minecraft get jobs -l felis.lolicon.best/server=<name>
+   ```
+
+   A Job that is genuinely wedged is ended by its own `activeDeadlineSeconds`;
+   deleting it by hand releases the world at once (`kubectl -n minecraft delete
+   job <job>`), at the cost of whatever it was writing.
+
+2. The admission lock `felis.lolicon.best/maintenance=<kind>@<RFC3339>` on the
+   MinecraftServer. felis-api sets it for the milliseconds between admitting an
+   operation and creating its Job; it holds for at most two minutes if felis-api
+   died in between, and the next wake clears a stale one. To drop it by hand:
+
+   ```sh
+   kubectl -n minecraft annotate minecraftserver <name> felis.lolicon.best/maintenance-
+   ```
+
+A restore, backup or file write refused with `409 not_stopped` although the
+panel shows `Stopped` means the game pod is still terminating (its preStop save
+can take a while); retry once `kubectl -n minecraft get pods -l
+felis.lolicon.best/server=<name>` shows nothing.
+
+[GO-TESTED: `internal/maintenance`, `k8scluster_maintenance_test.go`,
+`handlers_maintenance_test.go`, operator `maintenance_test.go`.]
+
 ---
 
 ## 4. Routing is disabled even though servers are up (online-mode coupling)
@@ -947,7 +991,8 @@ installer built — only hand-built tags need a manual re-mirror.
 | RCON secret/auth/port errors | §1b, §1c |
 | Phase `Failed` | §2 |
 | Players land in lobby / wrong place | §3, §4 |
-| Wake refused / rate-limited (403/429/503) | §3a |
+| Wake refused / rate-limited (403/409/429/503) | §3a |
+| `maintenance_in_progress`; server won't start after a restore | §3b |
 | Routing disabled, offline-mode | §4 |
 | Panel 401/403; fails-closed; audience error | §5 |
 | Local password login rejected | §5c |

internal/api/api_test.go

@@ -1454,12 +1454,19 @@ type fakeCluster struct {
 	noWorld   map[string]bool              // server names modeled WITHOUT a world volume (never started / reaped)
 	createErr error
 	pingErr   error
+	// maintErr / wakeErr: what AcquireMaintenance / SetDesiredState(Running)
+	// return for a server (the world-volume lock, internal/maintenance).
+	maintErr map[string]error
+	wakeErr  map[string]error
+	acquired []string // "name:kind" per admitted AcquireMaintenance
+	released []string // names per ReleaseMaintenance
 }
 
 func newFakeCluster() *fakeCluster {
 	return &fakeCluster{byName: map[string]*ServerInfo{}, bySub: map[string]*ServerInfo{},
 		desired: map[string]v1alpha1.DesiredState{}, created: map[string]CreateServerInput{},
-		patched: map[string]ServerSpecPatch{}, noWorld: map[string]bool{}}
+		patched: map[string]ServerSpecPatch{}, noWorld: map[string]bool{},
+		maintErr: map[string]error{}, wakeErr: map[string]error{}}
 }
 func (c *fakeCluster) GetServer(_ context.Context, n string) (*ServerInfo, error) {
 	if s, ok := c.byName[n]; ok {
@@ -1483,9 +1490,23 @@ func (c *fakeCluster) WorldVolumeExists(_ context.Context, n string) (bool, erro
 }
 
 func (c *fakeCluster) SetDesiredState(_ context.Context, n string, s v1alpha1.DesiredState) error {
+	if err := c.wakeErr[n]; err != nil && s == v1alpha1.DesiredRunning {
+		return err
+	}
 	c.desired[n] = s
 	return nil
 }
+func (c *fakeCluster) AcquireMaintenance(_ context.Context, n, kind string) error {
+	if err := c.maintErr[n]; err != nil {
+		return err
+	}
+	c.acquired = append(c.acquired, n+":"+kind)
+	return nil
+}
+func (c *fakeCluster) ReleaseMaintenance(_ context.Context, n string) error {
+	c.released = append(c.released, n)
+	return nil
+}
 func (c *fakeCluster) CreateServer(_ context.Context, in CreateServerInput) error {
 	if c.createErr != nil {
 		return c.createErr

internal/api/cluster.go

@@ -94,8 +94,18 @@ type Cluster interface {
 	// velocity registration pull (spec §7 GET /servers).
 	ListServers(ctx context.Context) ([]ServerInfo, error)
 	// SetDesiredState flips spec.desiredState — the only write the API performs
-	// against the CRD (spec §9.1). It is idempotent.
+	// against the CRD (spec §9.1). It is idempotent. Flipping to Running returns a
+	// *MaintenanceBusyError (errors.Is ErrMaintenanceInProgress) while a restore,
+	// backup or file write holds the world volume.
 	SetDesiredState(ctx context.Context, name string, state v1alpha1.DesiredState) error
+	// AcquireMaintenance admits one world-volume operation (internal/maintenance
+	// kind): ErrNotStopped unless the server is fully stopped, a
+	// *MaintenanceBusyError while another operation holds the volume. The check
+	// and the lock are one atomic write against a concurrent wake.
+	AcquireMaintenance(ctx context.Context, name, kind string) error
+	// ReleaseMaintenance drops the admission lock once the operation's Job exists
+	// (or could not be created). It is idempotent.
+	ReleaseMaintenance(ctx context.Context, name string) error
 	// CreateServer creates a MinecraftServer CRD from the validated form (spec
 	// §15). It returns ErrConflict if a server of that name already exists.
 	CreateServer(ctx context.Context, in CreateServerInput) error

internal/api/errors.go

@@ -82,8 +82,26 @@ var (
 	// sentinels so the handler answers 429 (a transient "too busy, retry" — the cap self-clears
 	// as challenges expire), never a 400 that invites an immediate retry.
 	ErrTooManyDiscoverableChallenges = errors.New("too many discoverable login challenges in flight")
+	// ErrNotStopped means a world-volume operation was refused because the server is
+	// not fully stopped: desiredState is not Stopped, or its pod is still shutting
+	// down (phase Stopping) and holds the volume while it saves.
+	ErrNotStopped = errors.New("server is not stopped")
+	// ErrMaintenanceInProgress means another operation holds the server's world
+	// volume (internal/maintenance). Cluster methods return it wrapped in a
+	// *MaintenanceBusyError that names the holder.
+	ErrMaintenanceInProgress = errors.New("world maintenance in progress")
 )
 
+// MaintenanceBusyError names what holds a server's world volume. errors.Is
+// matches it against ErrMaintenanceInProgress.
+type MaintenanceBusyError struct{ Kind string }
+
+func (e *MaintenanceBusyError) Error() string {
+	return "world maintenance in progress: " + e.Kind
+}
+
+func (e *MaintenanceBusyError) Is(target error) bool { return target == ErrMaintenanceInProgress }
+
 // apiError is a handler-level error carrying an HTTP status and a stable,
 // machine-readable code. The error envelope matches the platform convention:
 //

internal/api/handlers_backups.go

@@ -6,6 +6,7 @@ import (
 	"strings"
 
 	"felis.lolicon.best/internal/apis/felis/v1alpha1"
+	"felis.lolicon.best/internal/maintenance"
 	"felis.lolicon.best/internal/naming"
 )
 
@@ -69,7 +70,10 @@ func (a *API) handleListBackups(w http.ResponseWriter, r *http.Request) {
 //	   re-claims a released server could otherwise resurrect user A's world (the
 //	   backup still carries former_owner=A), a data leak. Admin skips this check.
 //	⑦ stopped gate: the world PVC must be free, so restore is refused unless the
-//	   server is fully stopped.
+//	   server is fully stopped. The world-volume lock (internal/maintenance) then
+//	   makes that atomic against a wake and refuses a second restore, backup or
+//	   file write on the same world with 409 maintenance_in_progress until the
+//	   restore Job finishes.
 //	⑧ hand off to the Restorer. Restore is asynchronous (a restore Job, like an
 //	   image build Job), so success means "enqueued" and the handler answers 202.
 //
@@ -152,7 +156,9 @@ func (a *API) handleRestoreBackup(w http.ResponseWriter, r *http.Request) {
 	// Refuse unless the server is fully stopped — Ready means it is up, and any
 	// desiredState other than Stopped means it is up or coming up and still owns the
 	// RWO volume (spec §141 readiness is an RCON probe; DesiredStopped is the
-	// intent). This yields a specific 409 instead of a restore Job that cannot mount.
+	// intent). This is the early, readable refusal from a snapshot; acquireWorld
+	// below is the atomic one (RWO is per node, so on a single node a restore Job
+	// WOULD mount beside a running server).
 	info, err := a.Cluster.GetServer(r.Context(), name)
 	if err != nil {
 		a.writeLookupError(w, r, err)
@@ -186,6 +192,16 @@ func (a *API) handleRestoreBackup(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// World-volume lock (internal/maintenance). The stopped gate above reads a
+	// snapshot; this is the atomic check, and it keeps a wake — the owner's, or a
+	// player's join through velocity — from booting the server on a half-extracted
+	// world until the restore Job has finished.
+	release, ok := a.acquireWorld(w, r, name, maintenance.KindRestore, "stop the server before restoring a backup")
+	if !ok {
+		return
+	}
+	defer release()
+
 	if err := a.Restorer.Restore(r.Context(), name, backup.BackupRef); err != nil {
 		// ErrNotFound (server vanished from the execution backend) → 404; else 500.
 		a.writeLookupError(w, r, err)
@@ -212,9 +228,10 @@ func (a *API) handleRestoreBackup(w http.ResponseWriter, r *http.Request) {
 //	② ServerByName — an unknown server is 404
 //	③ owner-or-admin, else 403 (an unowned server passes only for admin, so a
 //	   released world can still be snapshotted by an operator before disposal)
-//	④ stopped gate: the world PVC is RWO and held by a running server, so a backup
-//	   Job cannot double-mount it — refuse unless the server is fully stopped. This
-//	   also guarantees a quiescent, non-torn archive.
+//	④ stopped gate: refuse unless the server is fully stopped, so the archive is
+//	   quiescent and non-torn. The world-volume lock (internal/maintenance) keeps it
+//	   that way until the backup Job finishes: a wake meanwhile, or a second
+//	   restore/backup/file write, gets 409 maintenance_in_progress.
 //	⑤ hand off to the Backuper. Backup is asynchronous (a backup Job), so success
 //	   means "enqueued" and the handler answers 202.
 //
@@ -294,9 +311,10 @@ func (a *API) handleInternalBackup(w http.ResponseWriter, r *http.Request) {
 // (Principal vs trusted service token) and the audit actor/source — keeping the
 // security-critical stopped-gate single-sourced so the two faces cannot diverge.
 func (a *API) enqueueBackup(w http.ResponseWriter, r *http.Request, name string, rec *ServerRecord, actor, source string) {
-	// Stopped gate: the world PVC is RWO and held by a running server, so a backup
-	// Job cannot double-mount it (mirrors the restore gate). Ready means it is up;
-	// any desiredState other than Stopped means it owns the RWO volume.
+	// Stopped gate (mirrors the restore gate): Ready means it is up; any
+	// desiredState other than Stopped means it is up or coming up. RWO is per node,
+	// so on a single node the Job WOULD mount beside a live server and archive a
+	// torn world; acquireWorld below makes this check atomic.
 	info, err := a.Cluster.GetServer(r.Context(), name)
 	if err != nil {
 		a.writeLookupError(w, r, err)
@@ -329,6 +347,14 @@ func (a *API) enqueueBackup(w http.ResponseWriter, r *http.Request, name string,
 		return
 	}
 
+	// World-volume lock (internal/maintenance): a server woken mid-backup would
+	// leave a torn archive that a later restore makes permanent.
+	release, ok := a.acquireWorld(w, r, name, maintenance.KindBackup, "stop the server before backing up its world")
+	if !ok {
+		return
+	}
+	defer release()
+
 	if err := a.Backuper.Backup(r.Context(), name, rec.OwnerID); err != nil {
 		a.writeLookupError(w, r, err)
 		return

internal/api/handlers_files.go

@@ -7,6 +7,7 @@ import (
 
 	"felis.lolicon.best/internal/apis/felis/v1alpha1"
 	"felis.lolicon.best/internal/fileedit"
+	"felis.lolicon.best/internal/maintenance"
 	"felis.lolicon.best/internal/naming"
 )
 
@@ -149,6 +150,15 @@ func (a *API) handleWriteFile(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// A write holds the world volume for its Job's lifetime (internal/maintenance);
+	// reads and listings do not, since a read-only mount cannot hurt a server
+	// starting beside it.
+	release, ok := a.acquireWorld(w, r, name, maintenance.KindFileWrite, "stop the server before editing its files")
+	if !ok {
+		return
+	}
+	defer release()
+
 	if err := a.Files.Write(r.Context(), name, path, *body.Content); err != nil {
 		writeFileEditError(w, r, err)
 		return

internal/api/handlers_files_test.go

@@ -63,9 +63,9 @@ func mkFiles() (*API, *fakeRepo, *fakeCluster, *fakeFileEditor) {
 }
 
 // TestFileEditorStoppedGate is the gate this whole subsystem hinges on. The world
-// PVC is ReadWriteOnce, so a running server holds it and a file Job physically
-// cannot mount it — an ungated request would not fail cleanly, it would hang
-// waiting for a Pod that can never be scheduled. Every one of the three routes
+// PVC is ReadWriteOnce, but RWO is per node: on a single node a file Job mounts it
+// right beside a running server, and a write lands under a live world that the
+// server's next save overwrites or tears. Every one of the three routes
 // must therefore refuse a non-stopped server with 409 not_stopped BEFORE reaching
 // the executor, which is why each asserts calls == 0 as well as the status.
 func TestFileEditorStoppedGate(t *testing.T) {

internal/api/handlers_internal.go

@@ -153,8 +153,10 @@ func (a *API) handleInternalWake(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// A 409 maintenance_in_progress tells velocity nothing is coming up until the
+	// restore/backup/file write finishes, so it does not enqueue the player.
 	if err := a.Cluster.SetDesiredState(r.Context(), name, v1alpha1.DesiredRunning); err != nil {
-		writeError(w, r, err)
+		a.writeLookupError(w, r, err)
 		return
 	}
 	// Consume the shared per-server cooldown only after the wake flips, so a join
@@ -365,6 +367,8 @@ func (a *API) writeLookupError(w http.ResponseWriter, r *http.Request, err error
 		writeError(w, r, newError(http.StatusNotFound, "not_found", "not found"))
 	case errors.Is(err, ErrConflict):
 		writeError(w, r, newError(http.StatusConflict, "conflict", "conflict"))
+	case errors.Is(err, ErrMaintenanceInProgress), errors.Is(err, ErrNotStopped):
+		writeError(w, r, maintenanceError(err, "stop the server completely first"))
 	default:
 		writeError(w, r, err)
 	}

internal/api/handlers_maintenance_test.go

@@ -0,0 +1,176 @@
+package api
+
+import (
+	"errors"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"slices"
+	"testing"
+
+	"felis.lolicon.best/internal/apis/felis/v1alpha1"
+	"felis.lolicon.best/internal/maintenance"
+)
+
+// The world-volume lock (internal/maintenance) from the handlers' side: a wake
+// refused because a restore/backup/file write holds the world, and those three
+// operations refused while another one does. The lock itself (atomicity, stale
+// locks, Job-backed holds) is K8sCluster's and is tested in k8scluster_test.
+
+func TestWakeRefusedDuringMaintenance(t *testing.T) {
+	busy := &MaintenanceBusyError{Kind: maintenance.KindRestore}
+
+	t.Run("external wake -> 409 maintenance_in_progress, cooldown kept", func(t *testing.T) {
+		repo := newFakeRepo()
+		cl := newFakeCluster()
+		cl.byName["survival"] = &ServerInfo{Name: "survival", AutostartPolicy: "public"}
+		cl.wakeErr["survival"] = busy
+		api := newTestAPI(repo, cl)
+		api.External = staticExternal{p: &Principal{UserID: "u1", Role: "user"}}
+
+		w := do(api.ExternalHandler(), "POST", "/api/v1/servers/survival/wake", "", nil)
+		if w.Code != http.StatusConflict || decodeErr(t, w) != "maintenance_in_progress" {
+			t.Fatalf("code = %d body %s, want 409 maintenance_in_progress", w.Code, w.Body.String())
+		}
+		if _, set := cl.desired["survival"]; set {
+			t.Fatal("a refused wake must not flip desiredState")
+		}
+
+		// The refusal did not burn the cooldown: once the restore is done the very
+		// next wake goes through.
+		delete(cl.wakeErr, "survival")
+		if w := do(api.ExternalHandler(), "POST", "/api/v1/servers/survival/wake", "", nil); w.Code != http.StatusAccepted {
+			t.Fatalf("wake after maintenance: code = %d body %s", w.Code, w.Body.String())
+		}
+	})
+
+	t.Run("internal wake (velocity) -> 409 maintenance_in_progress, cooldown kept", func(t *testing.T) {
+		api, cl := newInternalWakeAPI("public")
+		cl.wakeErr["survival"] = busy
+		body := `{"mc_uuid":"` + wakeUUID + `"}`
+
+		w := internalWake(api, body)
+		if w.Code != http.StatusConflict || decodeErr(t, w) != "maintenance_in_progress" {
+			t.Fatalf("code = %d body %s, want 409 maintenance_in_progress", w.Code, w.Body.String())
+		}
+		delete(cl.wakeErr, "survival")
+		if w := internalWake(api, body); w.Code != http.StatusAccepted {
+			t.Fatalf("wake after maintenance: code = %d body %s", w.Code, w.Body.String())
+		}
+	})
+}
+
+// maintenanceOp is one world-volume operation as the external face serves it.
+type maintenanceOp struct {
+	name   string
+	kind   string
+	method string
+	path   string
+	body   string
+	calls  func() int
+}
+
+func maintenanceOps() (*API, *fakeCluster, []maintenanceOp) {
+	repo := newFakeRepo()
+	repo.byName["survival"] = &ServerRecord{Name: "survival", OwnerID: "owner1"}
+	repo.backups = []fakeBackup{{view: BackupView{ID: "bk1", ServerName: "survival",
+		FormerOwner: "owner1", Status: "present"}, ref: "world-archive-ref"}}
+	cl := newFakeCluster()
+	cl.byName["survival"] = &ServerInfo{Name: "survival", Phase: "Stopped",
+		DesiredState: string(v1alpha1.DesiredStopped)}
+	restorer, backuper, files := &fakeRestorer{}, &fakeBackuper{}, &fakeFileEditor{}
+	api := newTestAPI(repo, cl)
+	api.Restorer, api.Backuper, api.Files = restorer, backuper, files
+	api.External = staticExternal{p: &Principal{UserID: "owner1", Email: "[email protected]", Role: "user"}}
+	return api, cl, []maintenanceOp{
+		{"restore", maintenance.KindRestore, "POST", "/api/v1/servers/survival/restore-backup", "",
+			func() int { return restorer.calls }},
+		{"backup", maintenance.KindBackup, "POST", "/api/v1/servers/survival/backup", "",
+			func() int { return backuper.calls }},
+		{"file write", maintenance.KindFileWrite, "PUT", "/api/v1/servers/survival/file?path=server.properties",
+			`{"content":"aGk="}`, func() int { return files.calls }},
+	}
+}
+
+func (op maintenanceOp) do(api *API) *httptest.ResponseRecorder {
+	var hdr map[string]string
+	if op.body != "" {
+		hdr = jsonHeader
+	}
+	return do(api.ExternalHandler(), op.method, op.path, op.body, hdr)
+}
+
+func TestMaintenanceOpsTakeAndReleaseTheLock(t *testing.T) {
+	_, _, ops := maintenanceOps()
+	for i := range ops {
+		t.Run(ops[i].name, func(t *testing.T) {
+			api, cl, ops := maintenanceOps()
+			op := ops[i]
+			if w := op.do(api); w.Code/100 != 2 {
+				t.Fatalf("code = %d body %s", w.Code, w.Body.String())
+			}
+			if op.calls() != 1 {
+				t.Fatalf("executor calls = %d, want 1", op.calls())
+			}
+			if want := []string{"survival:" + op.kind}; !slices.Equal(cl.acquired, want) {
+				t.Fatalf("acquired = %v, want %v", cl.acquired, want)
+			}
+			if want := []string{"survival"}; !slices.Equal(cl.released, want) {
+				t.Fatalf("released = %v, want %v (the Job is the lock from here on)", cl.released, want)
+			}
+		})
+	}
+}
+
+func TestMaintenanceOpsRefusedWhileHeld(t *testing.T) {
+	refusals := []struct {
+		name string
+		err  error
+		code string
+	}{
+		{"another holder", &MaintenanceBusyError{Kind: maintenance.KindBackup}, "maintenance_in_progress"},
+		// The snapshot said Stopped but the atomic re-check found it waking: the
+		// wake won the race.
+		{"server not stopped", fmt.Errorf("wrapped: %w", ErrNotStopped), "not_stopped"},
+	}
+	_, _, ops := maintenanceOps()
+	for i := range ops {
+		for _, rf := range refusals {
+			t.Run(ops[i].name+" / "+rf.name, func(t *testing.T) {
+				api, cl, ops := maintenanceOps()
+				op := ops[i]
+				cl.maintErr["survival"] = rf.err
+				w := op.do(api)
+				if w.Code != http.StatusConflict || decodeErr(t, w) != rf.code {
+					t.Fatalf("code = %d body %s, want 409 %s", w.Code, w.Body.String(), rf.code)
+				}
+				if op.calls() != 0 {
+					t.Fatal("a refused operation must not reach its executor")
+				}
+				if len(cl.released) != 0 {
+					t.Fatalf("released %v a lock that was never taken", cl.released)
+				}
+			})
+		}
+	}
+}
+
+func TestMaintenanceErrorMapping(t *testing.T) {
+	for _, tc := range []struct {
+		err  error
+		code string
+	}{
+		{&MaintenanceBusyError{Kind: maintenance.KindFileWrite}, "maintenance_in_progress"},
+		{fmt.Errorf("x: %w", ErrMaintenanceInProgress), "maintenance_in_progress"},
+		{ErrNotStopped, "not_stopped"},
+	} {
+		var ae *apiError
+		if !errors.As(maintenanceError(tc.err, "stop it"), &ae) || ae.code != tc.code || ae.status != http.StatusConflict {
+			t.Errorf("%v -> %+v, want 409 %s", tc.err, ae, tc.code)
+		}
+	}
+	other := errors.New("boom")
+	if got := maintenanceError(other, "stop it"); got != other {
+		t.Errorf("unrelated error rewritten to %v", got)
+	}
+}

internal/api/handlers_user.go

@@ -56,8 +56,10 @@ func (a *API) handleWake(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Refused with 409 maintenance_in_progress while a restore, backup or file
+	// write holds the world volume: starting on a half-written world corrupts it.
 	if err := a.Cluster.SetDesiredState(r.Context(), name, v1alpha1.DesiredRunning); err != nil {
-		writeError(w, r, err)
+		a.writeLookupError(w, r, err)
 		return
 	}
 	// The wake actually flipped, so consume the per-server cooldown only now: a 503

internal/api/k8scluster.go

@@ -2,13 +2,18 @@ package api
 
 import (
 	"context"
+	"errors"
+	"time"
 
 	"felis.lolicon.best/internal/apis/felis/v1alpha1"
+	"felis.lolicon.best/internal/maintenance"
 	"felis.lolicon.best/internal/naming"
+	batchv1 "k8s.io/api/batch/v1"
 	corev1 "k8s.io/api/core/v1"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/client-go/util/retry"
 	"sigs.k8s.io/controller-runtime/pkg/client"
 )
 
@@ -20,6 +25,8 @@ import (
 type K8sCluster struct {
 	c         client.Client
 	namespace string
+	// now is injectable for the maintenance-lock tests; nil means time.Now.
+	now func() time.Time
 }
 
 // NewK8sCluster builds a Cluster over c, scoped to namespace.
@@ -142,13 +149,15 @@ func (k *K8sCluster) CreateServer(ctx context.Context, in CreateServerInput) err
 }
 
 // SetDesiredState patches spec.desiredState with a merge patch so concurrent
-// status writes by the operator are never clobbered (spec §9.1).
+// status writes by the operator are never clobbered (spec §9.1). A stop always
+// goes through. A start goes through start, which refuses while a maintenance
+// operation holds the world volume.
 func (k *K8sCluster) SetDesiredState(ctx context.Context, name string, state v1alpha1.DesiredState) error {
+	if state == v1alpha1.DesiredRunning {
+		return k.start(ctx, name)
+	}
 	var ms v1alpha1.MinecraftServer
-	if err := k.c.Get(ctx, types.NamespacedName{Namespace: k.namespace, Name: name}, &ms); err != nil {
-		if apierrors.IsNotFound(err) {
-			return ErrNotFound
-		}
+	if err := k.getServer(ctx, name, &ms); err != nil {
 		return err
 	}
 	patch := client.MergeFrom(ms.DeepCopy())
@@ -156,6 +165,140 @@ func (k *K8sCluster) SetDesiredState(ctx context.Context, name string, state v1a
 	return k.c.Patch(ctx, &ms, patch)
 }
 
+// start flips desiredState to Running unless a restore, backup or file write
+// holds the world volume (internal/maintenance), in which case it returns a
+// *MaintenanceBusyError. The patch carries the resourceVersion it checked
+// against, the same as AcquireMaintenance's: whichever of a racing wake and
+// admission writes second gets a conflict, re-reads, and sees the other.
+func (k *K8sCluster) start(ctx context.Context, name string) error {
+	return retry.RetryOnConflict(retry.DefaultRetry, func() error {
+		var ms v1alpha1.MinecraftServer
+		if err := k.getServer(ctx, name, &ms); err != nil {
+			return err
+		}
+		kind, held, err := k.maintenanceHolder(ctx, &ms)
+		if err != nil {
+			return err
+		}
+		if held {
+			return &MaintenanceBusyError{Kind: kind}
+		}
+		patch := client.MergeFromWithOptions(ms.DeepCopy(), client.MergeFromWithOptimisticLock{})
+		ms.Spec.DesiredState = v1alpha1.DesiredRunning
+		// A lock still on the object here no longer holds anything (Holder said
+		// so): drop it in the same write.
+		delete(ms.Annotations, maintenance.Annotation)
+		return k.c.Patch(ctx, &ms, patch)
+	})
+}
+
+// AcquireMaintenance admits one world-volume operation of the given kind: the
+// server must be fully stopped (desiredState Stopped, phase Stopped, and no game
+// pod left, so a pod still saving on its way down is waited out) and nothing else
+// may hold the volume. Admission writes the maintenance lock under the resourceVersion it
+// checked; the caller creates its Job and then calls ReleaseMaintenance, after
+// which the Job itself is the lock.
+func (k *K8sCluster) AcquireMaintenance(ctx context.Context, name, kind string) error {
+	return retry.RetryOnConflict(retry.DefaultRetry, func() error {
+		var ms v1alpha1.MinecraftServer
+		if err := k.getServer(ctx, name, &ms); err != nil {
+			return err
+		}
+		desired := ms.Spec.DesiredState
+		if desired == "" {
+			desired = v1alpha1.DesiredStopped
+		}
+		if desired != v1alpha1.DesiredStopped || ms.Status.Ready || ms.Status.Phase != v1alpha1.PhaseStopped {
+			return ErrNotStopped
+		}
+		if up, err := k.gamePodExists(ctx, name); err != nil {
+			return err
+		} else if up {
+			return ErrNotStopped
+		}
+		holder, held, err := k.maintenanceHolder(ctx, &ms)
+		if err != nil {
+			return err
+		}
+		if held {
+			return &MaintenanceBusyError{Kind: holder}
+		}
+		patch := client.MergeFromWithOptions(ms.DeepCopy(), client.MergeFromWithOptimisticLock{})
+		if ms.Annotations == nil {
+			ms.Annotations = map[string]string{}
+		}
+		ms.Annotations[maintenance.Annotation] = maintenance.LockValue(kind, k.clock())
+		return k.c.Patch(ctx, &ms, patch)
+	})
+}
+
+// ReleaseMaintenance drops the admission lock. It is called once the Job exists
+// (or failed to be created); a lock that is never released stops holding after
+// maintenance.Grace on its own.
+func (k *K8sCluster) ReleaseMaintenance(ctx context.Context, name string) error {
+	var ms v1alpha1.MinecraftServer
+	if err := k.getServer(ctx, name, &ms); err != nil {
+		if errors.Is(err, ErrNotFound) {
+			return nil
+		}
+		return err
+	}
+	if _, ok := ms.Annotations[maintenance.Annotation]; !ok {
+		return nil
+	}
+	patch := client.MergeFrom(ms.DeepCopy())
+	delete(ms.Annotations, maintenance.Annotation)
+	return k.c.Patch(ctx, &ms, patch)
+}
+
+// maintenanceHolder reads what holds ms's world volume right now. The Jobs are
+// listed through the same direct client as the object, so a Job created before
+// the lock was released is always visible here.
+func (k *K8sCluster) maintenanceHolder(ctx context.Context, ms *v1alpha1.MinecraftServer) (string, bool, error) {
+	var jobs batchv1.JobList
+	if err := k.c.List(ctx, &jobs, client.InNamespace(k.namespace),
+		client.MatchingLabels{maintenance.LabelServer: ms.Name}); err != nil {
+		return "", false, err
+	}
+	kind, held := maintenance.Holder(ms.Name, ms.Annotations, jobs.Items, k.clock())
+	return kind, held, nil
+}
+
+// gamePodComponent is the operator's component label value on a game server's
+// pod (internal/operator.ComponentValue; k8scluster_test pins the two).
+const gamePodComponent = "server"
+
+// gamePodExists reports whether the server's game pod still exists, terminating
+// or not. Phase Stopped is the operator's reading of the StatefulSet's replica
+// counts; the pod object itself is the ground truth for "is anything of the
+// server still running its preStop save against the volume".
+func (k *K8sCluster) gamePodExists(ctx context.Context, name string) (bool, error) {
+	var pods corev1.PodList
+	if err := k.c.List(ctx, &pods, client.InNamespace(k.namespace), client.MatchingLabels{
+		v1alpha1.LabelServer: name, v1alpha1.LabelComponent: gamePodComponent,
+	}); err != nil {
+		return false, err
+	}
+	return len(pods.Items) > 0, nil
+}
+
+func (k *K8sCluster) getServer(ctx context.Context, name string, ms *v1alpha1.MinecraftServer) error {
+	if err := k.c.Get(ctx, types.NamespacedName{Namespace: k.namespace, Name: name}, ms); err != nil {
+		if apierrors.IsNotFound(err) {
+			return ErrNotFound
+		}
+		return err
+	}
+	return nil
+}
+
+func (k *K8sCluster) clock() time.Time {
+	if k.now != nil {
+		return k.now()
+	}
+	return time.Now()
+}
+
 // PatchServerSpec applies the admin-tier spec mutation (spec §7) with the same
 // merge-patch discipline as SetDesiredState: read, copy, mutate only the fields
 // the admin set, patch — so an operator status write racing in parallel survives.

internal/api/k8scluster_maintenance_test.go

@@ -0,0 +1,237 @@
+package api
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"felis.lolicon.best/internal/apis/felis/v1alpha1"
+	"felis.lolicon.best/internal/maintenance"
+	"felis.lolicon.best/internal/operator"
+	"felis.lolicon.best/internal/restore"
+	batchv1 "k8s.io/api/batch/v1"
+	corev1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/types"
+	clientgoscheme "k8s.io/client-go/kubernetes/scheme"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/controller-runtime/pkg/client/fake"
+)
+
+// The world-volume lock against a fake API server. The fake client honours
+// resourceVersion on an optimistic-lock patch, so the atomic half is exercised
+// for real; what it cannot model is two felis-api replicas racing, which the
+// resourceVersion check is precisely the defence against.
+
+var lockNow = time.Date(2026, 9, 24, 12, 0, 0, 0, time.UTC)
+
+func stoppedServer() *v1alpha1.MinecraftServer {
+	return &v1alpha1.MinecraftServer{
+		ObjectMeta: metav1.ObjectMeta{Name: "survival", Namespace: "minecraft"},
+		Spec:       v1alpha1.MinecraftServerSpec{DesiredState: v1alpha1.DesiredStopped},
+		Status:     v1alpha1.MinecraftServerStatus{Phase: v1alpha1.PhaseStopped},
+	}
+}
+
+func lockCluster(t *testing.T, objs ...client.Object) (*K8sCluster, client.Client) {
+	t.Helper()
+	scheme := runtime.NewScheme()
+	if err := clientgoscheme.AddToScheme(scheme); err != nil {
+		t.Fatalf("scheme: %v", err)
+	}
+	if err := v1alpha1.AddToScheme(scheme); err != nil {
+		t.Fatalf("scheme: %v", err)
+	}
+	c := fake.NewClientBuilder().WithScheme(scheme).WithObjects(objs...).
+		WithStatusSubresource(&v1alpha1.MinecraftServer{}).Build()
+	k := NewK8sCluster(c, "minecraft")
+	k.now = func() time.Time { return lockNow }
+	return k, c
+}
+
+func runningRestore(t *testing.T) *batchv1.Job {
+	t.Helper()
+	j, err := restore.RestoreJob(restore.JobParams{
+		Server: "survival", WorldPVC: "world-survival-0", BackupPVC: "felis-backups",
+		BackupRef: "/backups/survival/a.tar.gz", ArchiveStore: "tarLocal",
+		Namespace: "minecraft", ServiceAccount: "felis-restore", Image: "felis:1",
+		BackupRoot: "/backups", WorldsRoot: "/world", Deadline: time.Minute,
+		CPULimit: "1", MemLimit: "1Gi", TTLAfterFinished: time.Minute,
+	})
+	if err != nil {
+		t.Fatalf("RestoreJob: %v", err)
+	}
+	return j
+}
+
+func annotations(t *testing.T, c client.Client) (map[string]string, v1alpha1.DesiredState) {
+	t.Helper()
+	var ms v1alpha1.MinecraftServer
+	if err := c.Get(context.Background(), types.NamespacedName{Namespace: "minecraft", Name: "survival"}, &ms); err != nil {
+		t.Fatalf("get: %v", err)
+	}
+	return ms.Annotations, ms.Spec.DesiredState
+}
+
+func TestAcquireMaintenance(t *testing.T) {
+	ctx := context.Background()
+
+	t.Run("stopped and free -> lock written", func(t *testing.T) {
+		k, c := lockCluster(t, stoppedServer())
+		if err := k.AcquireMaintenance(ctx, "survival", maintenance.KindRestore); err != nil {
+			t.Fatalf("AcquireMaintenance: %v", err)
+		}
+		ann, _ := annotations(t, c)
+		if got, want := ann[maintenance.Annotation], maintenance.LockValue(maintenance.KindRestore, lockNow); got != want {
+			t.Fatalf("lock = %q, want %q", got, want)
+		}
+		// A second admission while the first holds (its Job not yet created) is refused.
+		var busy *MaintenanceBusyError
+		if err := k.AcquireMaintenance(ctx, "survival", maintenance.KindBackup); !errors.As(err, &busy) || busy.Kind != maintenance.KindRestore {
+			t.Fatalf("second admission: %v, want busy(restore)", err)
+		}
+		if err := k.ReleaseMaintenance(ctx, "survival"); err != nil {
+			t.Fatalf("ReleaseMaintenance: %v", err)
+		}
+		if ann, _ := annotations(t, c); ann[maintenance.Annotation] != "" {
+			t.Fatalf("lock survived release: %q", ann[maintenance.Annotation])
+		}
+	})
+
+	notStopped := []struct {
+		name string
+		mut  func(*v1alpha1.MinecraftServer)
+	}{
+		{"desired Running", func(ms *v1alpha1.MinecraftServer) { ms.Spec.DesiredState = v1alpha1.DesiredRunning }},
+		{"still Stopping", func(ms *v1alpha1.MinecraftServer) { ms.Status.Phase = v1alpha1.PhaseStopping }},
+		{"Ready", func(ms *v1alpha1.MinecraftServer) { ms.Status.Ready = true }},
+		{"never reconciled", func(ms *v1alpha1.MinecraftServer) { ms.Status.Phase = "" }},
+	}
+	for _, tc := range notStopped {
+		t.Run(tc.name+" -> ErrNotStopped", func(t *testing.T) {
+			ms := stoppedServer()
+			tc.mut(ms)
+			k, c := lockCluster(t, ms)
+			if err := k.AcquireMaintenance(ctx, "survival", maintenance.KindRestore); !errors.Is(err, ErrNotStopped) {
+				t.Fatalf("err = %v, want ErrNotStopped", err)
+			}
+			if ann, _ := annotations(t, c); ann[maintenance.Annotation] != "" {
+				t.Fatal("a refused admission wrote the lock")
+			}
+		})
+	}
+
+	t.Run("game pod still terminating -> ErrNotStopped", func(t *testing.T) {
+		pod := &corev1.Pod{ObjectMeta: metav1.ObjectMeta{Name: "survival-0", Namespace: "minecraft",
+			Labels: map[string]string{v1alpha1.LabelServer: "survival", v1alpha1.LabelComponent: gamePodComponent}}}
+		k, _ := lockCluster(t, stoppedServer(), pod)
+		if err := k.AcquireMaintenance(ctx, "survival", maintenance.KindBackup); !errors.Is(err, ErrNotStopped) {
+			t.Fatalf("err = %v, want ErrNotStopped", err)
+		}
+	})
+
+	t.Run("a Job's own pod is not the game pod", func(t *testing.T) {
+		pod := &corev1.Pod{ObjectMeta: metav1.ObjectMeta{Name: "files-x", Namespace: "minecraft",
+			Labels: map[string]string{v1alpha1.LabelServer: "survival"}}}
+		k, _ := lockCluster(t, stoppedServer(), pod)
+		if err := k.AcquireMaintenance(ctx, "survival", maintenance.KindBackup); err != nil {
+			t.Fatalf("err = %v", err)
+		}
+	})
+
+	t.Run("running restore Job -> busy", func(t *testing.T) {
+		k, _ := lockCluster(t, stoppedServer(), runningRestore(t))
+		var busy *MaintenanceBusyError
+		if err := k.AcquireMaintenance(ctx, "survival", maintenance.KindFileWrite); !errors.As(err, &busy) || busy.Kind != maintenance.KindRestore {
+			t.Fatalf("err = %v, want busy(restore)", err)
+		}
+	})
+
+	t.Run("unknown server -> ErrNotFound", func(t *testing.T) {
+		k, _ := lockCluster(t)
+		if err := k.AcquireMaintenance(ctx, "survival", maintenance.KindRestore); !errors.Is(err, ErrNotFound) {
+			t.Fatalf("err = %v, want ErrNotFound", err)
+		}
+		if err := k.ReleaseMaintenance(ctx, "survival"); err != nil {
+			t.Fatalf("release on a deleted server: %v", err)
+		}
+	})
+}
+
+func TestStartRespectsMaintenance(t *testing.T) {
+	ctx := context.Background()
+
+	t.Run("fresh lock -> busy, desiredState untouched", func(t *testing.T) {
+		ms := stoppedServer()
+		ms.Annotations = map[string]string{maintenance.Annotation: maintenance.LockValue(maintenance.KindBackup, lockNow.Add(-10*time.Second))}
+		k, c := lockCluster(t, ms)
+		var busy *MaintenanceBusyError
+		if err := k.SetDesiredState(ctx, "survival", v1alpha1.DesiredRunning); !errors.As(err, &busy) || busy.Kind != maintenance.KindBackup {
+			t.Fatalf("err = %v, want busy(backup)", err)
+		}
+		if !errors.Is(&MaintenanceBusyError{}, ErrMaintenanceInProgress) {
+			t.Fatal("MaintenanceBusyError must match ErrMaintenanceInProgress")
+		}
+		if _, desired := annotations(t, c); desired != v1alpha1.DesiredStopped {
+			t.Fatalf("desiredState = %q, want Stopped", desired)
+		}
+	})
+
+	t.Run("running restore Job -> busy", func(t *testing.T) {
+		k, _ := lockCluster(t, stoppedServer(), runningRestore(t))
+		if err := k.SetDesiredState(ctx, "survival", v1alpha1.DesiredRunning); !errors.Is(err, ErrMaintenanceInProgress) {
+			t.Fatalf("err = %v, want maintenance in progress", err)
+		}
+	})
+
+	t.Run("finished restore Job -> starts", func(t *testing.T) {
+		j := runningRestore(t)
+		j.Status.Conditions = []batchv1.JobCondition{{Type: batchv1.JobComplete, Status: corev1.ConditionTrue}}
+		k, c := lockCluster(t, stoppedServer(), j)
+		if err := k.SetDesiredState(ctx, "survival", v1alpha1.DesiredRunning); err != nil {
+			t.Fatalf("err = %v", err)
+		}
+		if _, desired := annotations(t, c); desired != v1alpha1.DesiredRunning {
+			t.Fatalf("desiredState = %q, want Running", desired)
+		}
+	})
+
+	t.Run("stale lock -> starts and the lock is dropped", func(t *testing.T) {
+		ms := stoppedServer()
+		ms.Annotations = map[string]string{maintenance.Annotation: maintenance.LockValue(maintenance.KindRestore, lockNow.Add(-maintenance.Grace-time.Second))}
+		k, c := lockCluster(t, ms)
+		if err := k.SetDesiredState(ctx, "survival", v1alpha1.DesiredRunning); err != nil {
+			t.Fatalf("err = %v", err)
+		}
+		ann, desired := annotations(t, c)
+		if desired != v1alpha1.DesiredRunning {
+			t.Fatalf("desiredState = %q, want Running", desired)
+		}
+		if _, ok := ann[maintenance.Annotation]; ok {
+			t.Fatal("the stale lock was left behind")
+		}
+	})
+
+	t.Run("stop ignores the lock", func(t *testing.T) {
+		ms := stoppedServer()
+		ms.Spec.DesiredState = v1alpha1.DesiredRunning
+		ms.Annotations = map[string]string{maintenance.Annotation: maintenance.LockValue(maintenance.KindRestore, lockNow)}
+		k, c := lockCluster(t, ms)
+		if err := k.SetDesiredState(ctx, "survival", v1alpha1.DesiredStopped); err != nil {
+			t.Fatalf("err = %v", err)
+		}
+		if _, desired := annotations(t, c); desired != v1alpha1.DesiredStopped {
+			t.Fatalf("desiredState = %q, want Stopped", desired)
+		}
+	})
+}
+
+// gamePodComponent is a copy of the operator's pod label value; a drift would
+// let a restore start beside a terminating server.
+func TestGamePodComponentMatchesOperator(t *testing.T) {
+	if gamePodComponent != operator.ComponentValue {
+		t.Fatalf("gamePodComponent = %q, operator labels its pods %q", gamePodComponent, operator.ComponentValue)
+	}
+}

internal/api/maintenance.go

@@ -0,0 +1,64 @@
+package api
+
+import (
+	"context"
+	"errors"
+	"log"
+	"net/http"
+	"time"
+
+	"felis.lolicon.best/internal/maintenance"
+)
+
+// maintenanceError maps the world-volume lock's refusals onto their 409s:
+// maintenance_in_progress while a restore, backup or file write holds the volume,
+// not_stopped (with the caller's wording) while the server is not fully down.
+// Anything else passes through unchanged.
+func maintenanceError(err error, notStopped string) error {
+	var busy *MaintenanceBusyError
+	switch {
+	case errors.As(err, &busy):
+		return newError(http.StatusConflict, "maintenance_in_progress",
+			"%s is running on this server's world; retry once it finishes", maintenanceLabel(busy.Kind))
+	case errors.Is(err, ErrMaintenanceInProgress):
+		return newError(http.StatusConflict, "maintenance_in_progress",
+			"another operation is running on this server's world; retry once it finishes")
+	case errors.Is(err, ErrNotStopped):
+		return newError(http.StatusConflict, "not_stopped", "%s", notStopped)
+	}
+	return err
+}
+
+func maintenanceLabel(kind string) string {
+	switch kind {
+	case maintenance.KindRestore:
+		return "a restore"
+	case maintenance.KindBackup:
+		return "a backup"
+	case maintenance.KindFileWrite:
+		return "a file write"
+	}
+	return "another operation"
+}
+
+// acquireWorld admits one world-volume operation of the given kind
+// (internal/maintenance) and returns the release to run once its Job exists, or
+// false after writing the refusal. notStopped is the not_stopped wording the
+// calling face uses.
+//
+// The release runs on a context detached from the request: a client that hangs
+// up the moment its 202 is written must not leave the lock behind to refuse the
+// owner's next wake for maintenance.Grace.
+func (a *API) acquireWorld(w http.ResponseWriter, r *http.Request, name, kind, notStopped string) (func(), bool) {
+	if err := a.Cluster.AcquireMaintenance(r.Context(), name, kind); err != nil {
+		a.writeLookupError(w, r, maintenanceError(err, notStopped))
+		return nil, false
+	}
+	return func() {
+		ctx, cancel := context.WithTimeout(context.WithoutCancel(r.Context()), 10*time.Second)
+		defer cancel()
+		if err := a.Cluster.ReleaseMaintenance(ctx, name); err != nil {
+			log.Printf("api: release the maintenance lock on %s: %v (it lapses after %s)", name, err, maintenance.Grace)
+		}
+	}, true
+}

internal/fileedit/jobspec.go

@@ -16,12 +16,15 @@ import (
 // way. LabelOpID is the one addition: it is how felis-api finds THIS invocation's
 // Pod among any others, which matters here in a way it does not for restore —
 // file operations are interactive and repeated, so several may be in flight or
-// lingering inside their TTL at once.
+// lingering inside their TTL at once. LabelMode carries the operation so the
+// world-volume lock (internal/maintenance) can tell a write, which holds the
+// volume, from a read or listing, which does not.
 const (
 	LabelManagedBy = "app.kubernetes.io/managed-by"
 	LabelComponent = "app.kubernetes.io/component"
 	LabelServer    = "felis.lolicon.best/server"
 	LabelOpID      = "felis.lolicon.best/files-op"
+	LabelMode      = "felis.lolicon.best/files-mode"
 
 	managedByValue = "felis-files"
 	componentValue = "world-files"
@@ -80,6 +83,7 @@ func filesLabels(p JobParams) map[string]string {
 		LabelComponent: componentValue,
 		LabelServer:    p.Server,
 		LabelOpID:      p.OpID,
+		LabelMode:      p.Op,
 	}
 }
 

internal/maintenance/maintenance.go

@@ -0,0 +1,141 @@
+// Package maintenance is the per-server mutual exclusion between a game server
+// and the Jobs that write or snapshot its world volume (restore, backup, file
+// write). The world PVC is ReadWriteOnce, and RWO is exclusive per NODE: on a
+// single-node cluster the game pod and a restore pod mount it side by side, so
+// the access mode alone guards nothing. A server woken mid-restore boots on a
+// half-extracted world and the restore then prunes what it wrote; a server woken
+// mid-backup produces a torn archive that a later restore makes permanent.
+//
+// Two signals mark a volume as held:
+//
+//   - an unfinished maintenance Job labelled for the server. Once the Job exists
+//     it IS the lock, for as long as it runs, however long that is.
+//   - the Annotation on the MinecraftServer, written by felis-api with an
+//     optimistic-lock patch before it creates the Job and removed right after.
+//     It bridges the gap between "admitted" and "the Job is visible", and it is
+//     what serialises admission against a wake: both write the same object under
+//     its resourceVersion, so one of two racing writers always loses with a
+//     conflict and re-checks.
+//
+// A lock older than Grace with no Job behind it is stale (felis-api died between
+// the two writes) and holds nothing.
+//
+// File reads and listings are not holders. They mount the volume read-only for a
+// second or two, and a server starting beside one cannot hurt either side, so
+// nobody waits for them.
+package maintenance
+
+import (
+	"strings"
+	"time"
+
+	batchv1 "k8s.io/api/batch/v1"
+	corev1 "k8s.io/api/core/v1"
+)
+
+const (
+	// Annotation is the admission lock on a MinecraftServer. Its value is
+	// "<kind>@<RFC3339 time>" (LockValue).
+	Annotation = "felis.lolicon.best/maintenance"
+	// Grace is how long a lock counts as held when no Job backs it. felis-api
+	// creates the Job within milliseconds of taking the lock and then drops it, so
+	// a lock this old means the process died in between.
+	Grace = 2 * time.Minute
+
+	// LabelServer / LabelManagedBy are the labels every maintenance executor puts
+	// on its Job (internal/restore, internal/backupjob, internal/fileedit keep
+	// their own copies; maintenance_test pins them against these).
+	LabelServer    = "felis.lolicon.best/server"
+	LabelManagedBy = "app.kubernetes.io/managed-by"
+	// LabelFilesMode is the file-editor operation (list, read, write) a files Job
+	// performs. Only write holds the volume.
+	LabelFilesMode = "felis.lolicon.best/files-mode"
+)
+
+// Kinds of holder.
+const (
+	KindRestore   = "restore"
+	KindBackup    = "backup"
+	KindFileWrite = "file-write"
+)
+
+// FilesModeWrite is the LabelFilesMode value of a file write.
+const FilesModeWrite = "write"
+
+// JobKind names the holder a Job represents, or reports false for a Job that
+// holds nothing (a file read, a build, anything else in the namespace). A files
+// Job without LabelFilesMode predates the label and is counted as a write: it can
+// only be an old Job still inside its TTL, and over-counting it for that window
+// is the safe side.
+func JobKind(j *batchv1.Job) (string, bool) {
+	switch j.Labels[LabelManagedBy] {
+	case "felis-restore":
+		return KindRestore, true
+	case "felis-backup":
+		return KindBackup, true
+	case "felis-files":
+		mode, ok := j.Labels[LabelFilesMode]
+		if !ok || mode == FilesModeWrite {
+			return KindFileWrite, true
+		}
+	}
+	return "", false
+}
+
+// JobFinished reports whether a Job has reached a terminal condition. The
+// success/failure-target conditions count as terminal: the Job controller sets
+// them the moment the outcome is decided, before it finishes tearing the pods
+// down, and waiting for Complete would keep a wake refused for no reason.
+func JobFinished(j *batchv1.Job) bool {
+	for _, c := range j.Status.Conditions {
+		if c.Status != corev1.ConditionTrue {
+			continue
+		}
+		switch c.Type {
+		case batchv1.JobComplete, batchv1.JobFailed, batchv1.JobSuccessCriteriaMet, batchv1.JobFailureTarget:
+			return true
+		}
+	}
+	return false
+}
+
+// LockValue renders the Annotation value for a holder admitted at `at`.
+func LockValue(kind string, at time.Time) string {
+	return kind + "@" + at.UTC().Format(time.RFC3339)
+}
+
+// parseLock splits a lock value. A value that does not parse is stale: a lock
+// nobody can date must not be able to hold a server down forever.
+func parseLock(v string) (string, time.Time, bool) {
+	kind, stamp, ok := strings.Cut(v, "@")
+	if !ok || kind == "" {
+		return "", time.Time{}, false
+	}
+	at, err := time.Parse(time.RFC3339, stamp)
+	if err != nil {
+		return "", time.Time{}, false
+	}
+	return kind, at, true
+}
+
+// Holder reports what, if anything, holds the server's world volume at `now`:
+// the first unfinished maintenance Job among jobs, else a lock in annotations
+// younger than Grace. jobs may contain unrelated Jobs; only the server's own
+// holders count.
+func Holder(server string, annotations map[string]string, jobs []batchv1.Job, now time.Time) (string, bool) {
+	for i := range jobs {
+		j := &jobs[i]
+		if j.Labels[LabelServer] != server || JobFinished(j) {
+			continue
+		}
+		if kind, ok := JobKind(j); ok {
+			return kind, true
+		}
+	}
+	if v, ok := annotations[Annotation]; ok {
+		if kind, at, ok := parseLock(v); ok && now.Sub(at) < Grace && at.Sub(now) < Grace {
+			return kind, true
+		}
+	}
+	return "", false
+}

internal/maintenance/maintenance_test.go

@@ -0,0 +1,150 @@
+package maintenance
+
+import (
+	"testing"
+	"time"
+
+	"felis.lolicon.best/internal/backupjob"
+	"felis.lolicon.best/internal/fileedit"
+	"felis.lolicon.best/internal/restore"
+	batchv1 "k8s.io/api/batch/v1"
+	corev1 "k8s.io/api/core/v1"
+)
+
+var now = time.Date(2026, 9, 24, 12, 0, 0, 0, time.UTC)
+
+func restoreJob(t *testing.T, server string) batchv1.Job {
+	t.Helper()
+	j, err := restore.RestoreJob(restore.JobParams{
+		Server: server, WorldPVC: "world-" + server + "-0", BackupPVC: "felis-backups",
+		BackupRef: "/backups/" + server + "/a.tar.gz", ArchiveStore: "tarLocal",
+		Namespace: "minecraft", ServiceAccount: "felis-restore", Image: "felis:1",
+		BackupRoot: "/backups", WorldsRoot: "/world", Deadline: time.Minute,
+		CPULimit: "1", MemLimit: "1Gi", TTLAfterFinished: time.Minute,
+	})
+	if err != nil {
+		t.Fatalf("RestoreJob: %v", err)
+	}
+	return *j
+}
+
+func backupJob(t *testing.T, server string) batchv1.Job {
+	t.Helper()
+	j, err := backupjob.BackupJob(backupjob.JobParams{
+		Server: server, FormerOwner: "u", WorldPVC: "world-" + server + "-0", BackupPVC: "felis-backups",
+		Namespace: "minecraft", ServiceAccount: "felis-restore", Image: "felis:1",
+		ConfigSecret: "felis-config", ConfigMount: "/etc/felis", BackupRoot: "/backups",
+		WorldsRoot: "/world", Deadline: time.Minute, CPULimit: "1", MemLimit: "1Gi",
+		TTLAfterFinished: time.Minute,
+	})
+	if err != nil {
+		t.Fatalf("BackupJob: %v", err)
+	}
+	return *j
+}
+
+func filesJob(t *testing.T, server, op string) batchv1.Job {
+	t.Helper()
+	p := fileedit.JobParams{
+		Server: server, OpID: "0011223344556677", Op: op, Path: "server.properties",
+		WorldPVC: "world-" + server + "-0", Namespace: "minecraft", ServiceAccount: "felis-restore",
+		Image: "felis:1", WorldsRoot: "/data", Deadline: time.Minute, CPULimit: "500m",
+		MemLimit: "256Mi", TTLAfterFinished: time.Minute,
+	}
+	if op == fileedit.OpWrite {
+		p.Content = []byte("motd=hi\n")
+	}
+	j, err := fileedit.FilesJob(p)
+	if err != nil {
+		t.Fatalf("FilesJob: %v", err)
+	}
+	return *j
+}
+
+func finished(j batchv1.Job, cond batchv1.JobConditionType) batchv1.Job {
+	j.Status.Conditions = append(j.Status.Conditions, batchv1.JobCondition{Type: cond, Status: corev1.ConditionTrue})
+	return j
+}
+
+// The executors keep their own label copies (they must not import each other or
+// this package's callers); this pins what they actually render against JobKind.
+func TestJobKindMatchesTheExecutors(t *testing.T) {
+	for _, tc := range []struct {
+		name string
+		job  batchv1.Job
+		kind string
+		ok   bool
+	}{
+		{"restore", restoreJob(t, "survival"), KindRestore, true},
+		{"backup", backupJob(t, "survival"), KindBackup, true},
+		{"file write", filesJob(t, "survival", fileedit.OpWrite), KindFileWrite, true},
+		{"file read", filesJob(t, "survival", fileedit.OpRead), "", false},
+		{"file list", filesJob(t, "survival", fileedit.OpList), "", false},
+	} {
+		kind, ok := JobKind(&tc.job)
+		if kind != tc.kind || ok != tc.ok {
+			t.Errorf("%s: JobKind = %q, %v; want %q, %v", tc.name, kind, ok, tc.kind, tc.ok)
+		}
+		if tc.job.Labels[LabelServer] != "survival" {
+			t.Errorf("%s: server label = %q", tc.name, tc.job.Labels[LabelServer])
+		}
+	}
+}
+
+func TestUnlabelledFilesJobCountsAsWrite(t *testing.T) {
+	j := filesJob(t, "survival", fileedit.OpRead)
+	delete(j.Labels, LabelFilesMode)
+	if kind, ok := JobKind(&j); !ok || kind != KindFileWrite {
+		t.Fatalf("a files Job from before the mode label = %q, %v; want file-write", kind, ok)
+	}
+}
+
+func TestHolderFromJobs(t *testing.T) {
+	restoreRunning := restoreJob(t, "survival")
+	if kind, ok := Holder("survival", nil, []batchv1.Job{restoreRunning}, now); !ok || kind != KindRestore {
+		t.Fatalf("running restore: Holder = %q, %v", kind, ok)
+	}
+	for _, cond := range []batchv1.JobConditionType{
+		batchv1.JobComplete, batchv1.JobFailed, batchv1.JobSuccessCriteriaMet, batchv1.JobFailureTarget,
+	} {
+		if kind, ok := Holder("survival", nil, []batchv1.Job{finished(restoreRunning, cond)}, now); ok {
+			t.Errorf("restore with %s still holds as %q", cond, kind)
+		}
+	}
+	other := backupJob(t, "creative")
+	if kind, ok := Holder("survival", nil, []batchv1.Job{other}, now); ok {
+		t.Fatalf("another server's backup holds survival as %q", kind)
+	}
+	read := filesJob(t, "survival", fileedit.OpRead)
+	if kind, ok := Holder("survival", nil, []batchv1.Job{read}, now); ok {
+		t.Fatalf("a running file read holds the volume as %q", kind)
+	}
+	write := filesJob(t, "survival", fileedit.OpWrite)
+	if kind, ok := Holder("survival", nil, []batchv1.Job{read, write}, now); !ok || kind != KindFileWrite {
+		t.Fatalf("running file write: Holder = %q, %v", kind, ok)
+	}
+}
+
+func TestHolderFromLock(t *testing.T) {
+	for _, tc := range []struct {
+		name  string
+		value string
+		held  bool
+	}{
+		{"fresh", LockValue(KindBackup, now.Add(-10*time.Second)), true},
+		{"just inside grace", LockValue(KindBackup, now.Add(-Grace+time.Second)), true},
+		{"stale", LockValue(KindBackup, now.Add(-Grace)), false},
+		{"far future", LockValue(KindBackup, now.Add(time.Hour)), false},
+		{"garbage", "yes", false},
+		{"no kind", "@" + now.Format(time.RFC3339), false},
+		{"bad time", "restore@yesterday", false},
+	} {
+		kind, held := Holder("survival", map[string]string{Annotation: tc.value}, nil, now)
+		if held != tc.held {
+			t.Errorf("%s (%q): held = %v, want %v", tc.name, tc.value, held, tc.held)
+		}
+		if held && kind != KindBackup {
+			t.Errorf("%s: kind = %q", tc.name, kind)
+		}
+	}
+}

internal/operator/maintenance_test.go

@@ -0,0 +1,108 @@
+package operator_test
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"felis.lolicon.best/internal/apis/felis/v1alpha1"
+	"felis.lolicon.best/internal/maintenance"
+	appsv1 "k8s.io/api/apps/v1"
+	batchv1 "k8s.io/api/batch/v1"
+	corev1 "k8s.io/api/core/v1"
+	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	"k8s.io/apimachinery/pkg/api/meta"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/types"
+)
+
+func maintenanceJob(managedBy string, finished bool) *batchv1.Job {
+	j := &batchv1.Job{ObjectMeta: metav1.ObjectMeta{Name: "restore-survival", Namespace: "minecraft",
+		Labels: map[string]string{maintenance.LabelServer: "survival", maintenance.LabelManagedBy: managedBy}}}
+	if finished {
+		j.Status.Conditions = []batchv1.JobCondition{{Type: batchv1.JobComplete, Status: corev1.ConditionTrue}}
+	}
+	return j
+}
+
+// A desiredState flipped to Running behind felis-api's back (kubectl, a script)
+// while a restore Job is unpacking into the world must not get a game pod.
+func TestReconcileRunning_HeldDuringMaintenance(t *testing.T) {
+	r, c := newReconciler(t, fakeProber{}, runningServer(), rconSecret(), maintenanceJob("felis-restore", false))
+	r.Jobs = c
+
+	res := reconcile(t, r, "survival")
+	if res.RequeueAfter <= 0 {
+		t.Fatal("a held server must requeue to notice the Job finishing")
+	}
+	var sts appsv1.StatefulSet
+	err := c.Get(context.Background(), types.NamespacedName{Namespace: "minecraft", Name: "survival"}, &sts)
+	if !apierrors.IsNotFound(err) {
+		t.Fatalf("StatefulSet created while the restore runs (err=%v)", err)
+	}
+	s := getServer(t, c, "survival")
+	cond := meta.FindStatusCondition(s.Status.Conditions, v1alpha1.ConditionReady)
+	if cond == nil || cond.Reason != "MaintenanceInProgress" {
+		t.Fatalf("Ready condition = %+v, want reason MaintenanceInProgress", cond)
+	}
+	if s.Status.StartRequestedAt != nil {
+		t.Fatal("the hold must not start the startup-timeout clock")
+	}
+
+	// The Job finishes: the next pass starts the server.
+	var j batchv1.Job
+	if err := c.Get(context.Background(), types.NamespacedName{Namespace: "minecraft", Name: "restore-survival"}, &j); err != nil {
+		t.Fatalf("get job: %v", err)
+	}
+	j.Status.Conditions = []batchv1.JobCondition{{Type: batchv1.JobComplete, Status: corev1.ConditionTrue}}
+	if err := c.Status().Update(context.Background(), &j); err != nil {
+		if err := c.Update(context.Background(), &j); err != nil {
+			t.Fatalf("finish job: %v", err)
+		}
+	}
+	reconcile(t, r, "survival")
+	if err := c.Get(context.Background(), types.NamespacedName{Namespace: "minecraft", Name: "survival"}, &sts); err != nil {
+		t.Fatalf("StatefulSet not created after the restore finished: %v", err)
+	}
+}
+
+func TestReconcileRunning_FreshLockHolds(t *testing.T) {
+	ms := runningServer()
+	ms.Annotations = map[string]string{maintenance.Annotation: maintenance.LockValue(maintenance.KindBackup, fixedNow().Add(-5*time.Second))}
+	r, c := newReconciler(t, fakeProber{}, ms, rconSecret())
+	r.Jobs = c
+	reconcile(t, r, "survival")
+	var sts appsv1.StatefulSet
+	if err := c.Get(context.Background(), types.NamespacedName{Namespace: "minecraft", Name: "survival"}, &sts); !apierrors.IsNotFound(err) {
+		t.Fatalf("StatefulSet created under a fresh maintenance lock (err=%v)", err)
+	}
+}
+
+func TestReconcileRunning_NotHeldByReadsOrFinishedJobs(t *testing.T) {
+	read := maintenanceJob("felis-files", false)
+	read.Name = "files-survival-read"
+	read.Labels[maintenance.LabelFilesMode] = "read"
+	r, c := newReconciler(t, fakeProber{}, runningServer(), rconSecret(), read, maintenanceJob("felis-backup", true))
+	r.Jobs = c
+	reconcile(t, r, "survival")
+	var sts appsv1.StatefulSet
+	if err := c.Get(context.Background(), types.NamespacedName{Namespace: "minecraft", Name: "survival"}, &sts); err != nil {
+		t.Fatalf("StatefulSet not created: %v", err)
+	}
+}
+
+// A server that is already up is never held: its pod is the one on the volume,
+// and holding would only stall its readiness bookkeeping.
+func TestReconcileRunning_RunningServerNotHeld(t *testing.T) {
+	r, c := newReconciler(t, fakeProber{}, runningServer(), rconSecret())
+	reconcile(t, r, "survival") // creates the StatefulSet at replicas 1
+	if err := c.Create(context.Background(), maintenanceJob("felis-restore", false)); err != nil {
+		t.Fatalf("create job: %v", err)
+	}
+	r.Jobs = c
+	reconcile(t, r, "survival")
+	cond := meta.FindStatusCondition(getServer(t, c, "survival").Status.Conditions, v1alpha1.ConditionReady)
+	if cond != nil && cond.Reason == "MaintenanceInProgress" {
+		t.Fatal("a scaled-up server was held")
+	}
+}

internal/operator/reconciler.go

@@ -13,8 +13,10 @@ import (
 	"time"
 
 	"felis.lolicon.best/internal/apis/felis/v1alpha1"
+	"felis.lolicon.best/internal/maintenance"
 	"felis.lolicon.best/internal/metrics"
 	appsv1 "k8s.io/api/apps/v1"
+	batchv1 "k8s.io/api/batch/v1"
 	corev1 "k8s.io/api/core/v1"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	"k8s.io/apimachinery/pkg/api/meta"
@@ -37,6 +39,7 @@ const (
 	requeueStopping            = 5 * time.Second
 	requeueSecret              = 10 * time.Second
 	requeueIdleProbe           = 30 * time.Second
+	requeueMaintenance         = 5 * time.Second
 	defaultTimeoutSeconds      = 300
 	defaultReadinessTimeoutSec = 300
 )
@@ -69,6 +72,10 @@ type Reconciler struct {
 	// Now is injectable for deterministic timestamps in tests; defaults to
 	// metav1.Now.
 	Now func() metav1.Time
+	// Jobs reads the minecraft namespace's Jobs for the world-volume lock
+	// (internal/maintenance). It is the manager's uncached API reader, so the
+	// operator needs jobs:list and no Job informer. Nil skips the check.
+	Jobs client.Reader
 }
 
 func (r *Reconciler) now() metav1.Time {
@@ -111,6 +118,20 @@ func (r *Reconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Resu
 }
 
 func (r *Reconciler) reconcileRunning(ctx context.Context, server *v1alpha1.MinecraftServer) (ctrl.Result, error) {
+	if kind, held, err := r.maintenanceHold(ctx, server); err != nil {
+		return ctrl.Result{}, err
+	} else if held {
+		// Leave phase and the start anchor alone: nothing is starting yet, and a
+		// long restore must not be charged to the startup timeout.
+		server.Status.ObservedGeneration = server.Generation
+		r.setCondition(server, v1alpha1.ConditionReady, metav1.ConditionFalse, "MaintenanceInProgress",
+			"waiting for the "+kind+" on this server's world to finish before starting")
+		if err := r.patchStatus(ctx, server); err != nil {
+			return ctrl.Result{}, err
+		}
+		return ctrl.Result{RequeueAfter: requeueMaintenance}, nil
+	}
+
 	endpointAddress, err := r.ensureServices(ctx, server)
 	if err != nil {
 		return ctrl.Result{}, err
@@ -283,6 +304,35 @@ func (r *Reconciler) reconcileStopped(ctx context.Context, server *v1alpha1.Mine
 	return ctrl.Result{}, r.patchStatus(ctx, server)
 }
 
+// maintenanceHold reports whether a restore, backup or file write holds the
+// server's world volume (internal/maintenance) while its pod is about to be
+// created. felis-api already refuses a wake in that state; this is the same rule
+// for a desiredState flipped by anything else (kubectl, a script), since a game
+// pod scheduled beside a restore Job boots on a half-extracted world. A server
+// whose StatefulSet is already scaled up is never held: its pod exists, and
+// stopping it here would only lose the players on it.
+func (r *Reconciler) maintenanceHold(ctx context.Context, server *v1alpha1.MinecraftServer) (string, bool, error) {
+	if r.Jobs == nil {
+		return "", false, nil
+	}
+	var sts appsv1.StatefulSet
+	err := r.Get(ctx, types.NamespacedName{Namespace: server.Namespace, Name: server.Name}, &sts)
+	switch {
+	case apierrors.IsNotFound(err):
+	case err != nil:
+		return "", false, err
+	case sts.Spec.Replicas == nil || *sts.Spec.Replicas > 0 || sts.Status.Replicas > 0:
+		return "", false, nil
+	}
+	var jobs batchv1.JobList
+	if err := r.Jobs.List(ctx, &jobs, client.InNamespace(server.Namespace),
+		client.MatchingLabels{maintenance.LabelServer: server.Name}); err != nil {
+		return "", false, err
+	}
+	kind, held := maintenance.Holder(server.Name, server.Annotations, jobs.Items, r.now().Time)
+	return kind, held, nil
+}
+
 func (r *Reconciler) ensureServices(ctx context.Context, server *v1alpha1.MinecraftServer) (string, error) {
 	endpointAddress := ""
 	for _, svc := range []*corev1.Service{buildHeadlessService(server), buildClientService(server)} {

internal/platform/rbac.go

@@ -145,8 +145,11 @@ func APIBuildRole(p Params) *rbacv1.Role {
 // status (Status().Update — `update` only) and patches spec.desiredState to
 // Stopped for idle auto-stop (spec §8 — the one spec field it may write, using
 // the same merge patch as the reaper's Stop: without the grant the auto-stop
-// call fails closed with a 403), and reads RCON Secrets. It never touches pods,
-// PVCs, Events, or finalizers, so none appear here.
+// call fails closed with a 403), and reads RCON Secrets. Jobs are list-only,
+// through the manager's uncached API reader: before scaling a server up from zero
+// the operator checks that no restore/backup/file-write Job holds its world
+// (internal/maintenance). It never touches pods, PVCs, Events, or finalizers, so
+// none appear here.
 func OperatorRole(p Params) *rbacv1.Role {
 	p = p.withDefaults()
 	return role(p.MinecraftNamespace, "felis-operator", ComponentOperator, []rbacv1.PolicyRule{
@@ -161,6 +164,9 @@ func OperatorRole(p Params) *rbacv1.Role {
 		// did not already have. No update/delete — the password is written once and
 		// removed by garbage collection through its controller reference.
 		rule([]string{groupCore}, []string{"secrets"}, []string{"get", "list", "watch", "create"}),
+		// list only: an uncached List (no informer, so no watch) of the world-volume
+		// maintenance Jobs; the operator never creates or deletes a Job.
+		rule([]string{groupBatch}, []string{"jobs"}, []string{"list"}),
 	})
 }
 

internal/platform/rbac_test.go

@@ -188,6 +188,15 @@ func TestOperatorRole_ScopeExact(t *testing.T) {
 			t.Errorf("operator must NOT touch core/%s", res)
 		}
 	}
+	// The world-volume lock check lists Jobs uncached; it never writes one.
+	if !hasRule(op, groupBatch, "jobs", "list") {
+		t.Error("operator must have jobs:list (maintenance hold before scale-up)")
+	}
+	for _, v := range []string{"get", "watch", "create", "update", "patch", "delete"} {
+		if hasRule(op, groupBatch, "jobs", v) {
+			t.Errorf("operator must NOT have jobs:%s (list-only)", v)
+		}
+	}
 }
 
 // TestReaperRole_ScopeExact pins the reaper's two destructive powers and confirms

panel/src/i18n/resources/en-US/errors.json

@@ -14,6 +14,7 @@
   "console_unavailable": "Can't reach the server console right now — try again shortly.",
   "no_backup": "There's no restorable backup for this server yet.",
   "not_stopped": "Stop the server completely before restoring — a restore overwrites the live world volume.",
+  "maintenance_in_progress": "This server's world is busy with a restore, backup or file write — try again once it finishes, usually within a minute or two.",
   "no_world_volume": "This server has no world volume yet — start it once so it is created, then retry.",
   "restore_unavailable": "Restore isn't available right now — try again later.",
   "session_expired": "Your session expired — please sign in again.",

panel/src/i18n/resources/zh-CN/errors.json

@@ -14,6 +14,7 @@
   "console_unavailable": "暂时无法连接服务器控制台，请稍后重试。",
   "no_backup": "这台服务器暂时没有可回档的备份。",
   "not_stopped": "回档会覆盖世界的实时存储卷，请先把服务器完全停止再回档。",
+  "maintenance_in_progress": "这台服务器的世界正在回档、备份或写入文件——等它完成后再试，通常不超过一两分钟。",
   "no_world_volume": "这台服务器还没有世界卷——先启动一次让它创建，然后再试。",
   "restore_unavailable": "回档功能当前不可用，请稍后再试。",
   "session_expired": "会话已过期——请重新登录。",

panel/src/lib/api.ts

@@ -705,6 +705,11 @@ export function humanizeError(e: unknown): string {
       return t("no_backup");
     case "not_stopped":
       return t("not_stopped");
+    // World-volume lock: a restore, backup or file write is running on this
+    // server's world, so a wake or a second world operation is refused until the
+    // Job finishes (internal/maintenance).
+    case "maintenance_in_progress":
+      return t("maintenance_in_progress");
     case "no_world_volume":
       return t("no_world_volume");
     case "restore_unavailable":

plugins/shared/src/main/java/best/lolicon/felis/link/FelisApiClient.java

@@ -79,7 +79,8 @@ public final class FelisApiClient {
      * wake pulls the domain-autostart lever for {@code name} on behalf of the
      * joining player (spec §9.1, §14). The reply (202) carries the current phase
      * and ready flag so the caller can decide whether to wait. A 403 (policy gate),
-     * 429 (cooldown), or 503 {@code at_capacity} (running cap) arrives as a
+     * 409 {@code maintenance_in_progress} (a restore, backup or file write holds the
+     * world), 429 (cooldown), or 503 {@code at_capacity} (running cap) arrives as a
      * LinkException the caller branches on.
      */
     public ServerView wake(String name, UUID mcUuid) throws LinkException {

plugins/velocity/src/main/java/best/lolicon/felis/velocity/WaitingRouter.java

@@ -498,6 +498,20 @@ public final class WaitingRouter {
                             zh ? "你无权启动「" + serverName + "」。"
                                : "You're not allowed to start « " + serverName + " ».", NamedTextColor.RED));
                     return;
+                case 409:
+                    if ("maintenance_in_progress".equals(e.errorCode())) {
+                        // A restore, backup or file write owns the world right now and
+                        // the server will not start until it finishes (minutes at most),
+                        // so waiting here would only run into the queue timeout.
+                        player.sendMessage(Component.text(
+                                zh ? "「" + serverName + "」正在维护（回档、备份或改文件），请稍后再试。"
+                                   : "« " + serverName + " » is under maintenance (restore, backup or file edit)."
+                                     + " Please try again shortly.",
+                                NamedTextColor.YELLOW));
+                        return;
+                    }
+                    logWakeFailure(player, serverName, zh, e);
+                    return;
                 case 429:
                     break; // a wake is already in flight → join the existing wait
                 case 503:
@@ -513,13 +527,10 @@ public final class WaitingRouter {
                     }
                     // A 503 without the at_capacity code is a plain outage, not a
                     // capacity verdict — report it like any other failure.
-                    // fall through
+                    logWakeFailure(player, serverName, zh, e);
+                    return;
                 default:
-                    log.warn("Felis: wake {} failed (status={}): {}", serverName, e.statusCode(), e.getMessage());
-                    player.sendMessage(Component.text(
-                            zh ? "现在无法启动「" + serverName + "」。请稍后再试。"
-                               : "Couldn't start « " + serverName + " » right now. Try again shortly.",
-                            NamedTextColor.RED));
+                    logWakeFailure(player, serverName, zh, e);
                     return;
             }
         }
@@ -531,6 +542,14 @@ public final class WaitingRouter {
                 serverName, System.currentTimeMillis() + WAIT_TIMEOUT_MILLIS, fromMenu));
     }
 
+    private void logWakeFailure(Player player, String serverName, boolean zh, LinkException e) {
+        log.warn("Felis: wake {} failed (status={}): {}", serverName, e.statusCode(), e.getMessage());
+        player.sendMessage(Component.text(
+                zh ? "现在无法启动「" + serverName + "」。请稍后再试。"
+                   : "Couldn't start « " + serverName + " » right now. Try again shortly.",
+                NamedTextColor.RED));
+    }
+
     private void transfer(Player player, String serverName, RegisteredServer backend) {
         player.createConnectionRequest(backend).connect().whenComplete((result, err) -> {
             if (err != null || (result != null && !result.isSuccessful())) {