diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9f67b8c..a8e5453 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,21 @@
 ## Changelog
 
+### v0.126.4 — edge-safe error statuses + the native-alert ban (2026-07-13)
+
+Two defects surfaced by the agent-0.87.0 wizard leg's decommission attempt (the M1 refusal —
+correct policy — reached the operator as a JSON SyntaxError popup):
+
+- **502/504 never leave the origin:** Cloudflare replaces origin 502/504 bodies with its own
+  HTML error page, so every `writeDiskJSON(StatusBadGateway…)` refusal/error rendered as
+  "<!DOCTYPE … is not valid JSON" in the browser. `writeDiskJSON` now maps 502/504 → 500 at the
+  single choke point (JSON body crosses the edge intact); the M1 last-usable-drive refusal
+  became the typed `errLastUsableDrive` sentinel → **409** (policy verdict, not gateway
+  failure). Unit tests + red-proofs for both.
+- **Native `alert()` banned** (the F-11 OS-modal class, now complete): the decommission error
+  path's `alert()` froze browser automation exactly as F-11 predicted. All 29 native `alert(`
+  calls across 5 templates swept to the existing `showAlert` modal (layout.html);
+  `native_confirm_gate.py` extended to ban `alert(` alongside confirm/prompt.
+
 ### v0.126.3 — storage wizard on a CLAIMED box: the init/attach POST no longer dies on CSRF (2026-07-13)
 
 First live hit during the agent-0.87.0 drill wizard leg: /api/storage/init → "CSRF token missing
diff --git a/controller/internal/web/agent_disk_handlers.go b/controller/internal/web/agent_disk_handlers.go
index 0fe488f..80257ed 100644
--- a/controller/internal/web/agent_disk_handlers.go
+++ b/controller/internal/web/agent_disk_handlers.go
@@ -84,6 +84,14 @@ func (s *Server) ProbeAgentChannel(ctx context.Context) (constructionErr bool, e
 
 // writeDiskJSON writes the standard {ok,data,error} envelope used by the disk API.
 func writeDiskJSON(w http.ResponseWriter, status int, ok bool, errMsg string, data interface{}) {
+	// Cloudflare replaces origin 502/504 bodies with its OWN HTML error page (no passthru on
+	// this plan) — the page JS then fails to parse JSON and the customer sees a SyntaxError
+	// alert instead of the Hungarian message (live-hit 2026-07-13: the M1 decommission refusal
+	// surfaced as "<!DOCTYPE ... is not valid JSON"). App-level JSON errors must never leave
+	// the origin as 502/504; 500 carries the body through the edge intact.
+	if status == http.StatusBadGateway || status == http.StatusGatewayTimeout {
+		status = http.StatusInternalServerError
+	}
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(status)
 	resp := map[string]interface{}{"ok": ok}
diff --git a/controller/internal/web/edge_safe_status_test.go b/controller/internal/web/edge_safe_status_test.go
new file mode 100644
index 0000000..bda7848
--- /dev/null
+++ b/controller/internal/web/edge_safe_status_test.go
@@ -0,0 +1,68 @@
+package web
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"gitea.dooplex.hu/admin/felhom-controller/internal/settings"
+)
+
+// v0.126.4 — two defects surfaced by the 0.87.0 wizard leg's decommission attempt:
+//  1. writeDiskJSON emitted app-level errors as 502 — Cloudflare replaces origin 502/504
+//     bodies with its own HTML error page, so the browser saw "<!DOCTYPE ..." instead of the
+//     Hungarian refusal and threw a JSON SyntaxError alert.
+//  2. The M1 last-usable-drive refusal (a POLICY verdict) was indistinguishable from a real
+//     agent-gateway failure.
+// COMPANION red-proofs: (1) remove the 502→500 map in writeDiskJSON → the status assertions
+// fail; (2) return a non-sentinel fmt.Errorf from the mustBlock branch → the errors.Is
+// assertion fails.
+
+func TestWriteDiskJSON_EdgeSafeStatus(t *testing.T) {
+	cases := []struct {
+		in   int
+		want int
+	}{
+		{http.StatusBadGateway, http.StatusInternalServerError},     // CF would swallow 502
+		{http.StatusGatewayTimeout, http.StatusInternalServerError}, // CF would swallow 504
+		{http.StatusConflict, http.StatusConflict},                  // policy refusals pass as-is
+		{http.StatusBadRequest, http.StatusBadRequest},
+		{http.StatusOK, http.StatusOK},
+	}
+	for _, c := range cases {
+		rr := httptest.NewRecorder()
+		writeDiskJSON(rr, c.in, false, "hiba szöveg", nil)
+		if rr.Code != c.want {
+			t.Errorf("writeDiskJSON(%d): got status %d, want %d (502/504 must never leave the origin — CF replaces their body)", c.in, rr.Code, c.want)
+		}
+		if !strings.Contains(rr.Body.String(), `"hiba szöveg"`) {
+			t.Errorf("writeDiskJSON(%d): JSON body lost", c.in)
+		}
+	}
+}
+
+// The M1 refusal is the TYPED sentinel (so the handler can map it to 409, which crosses the
+// CF edge with its body intact), and it must refuse BEFORE any side-effect: no soft-mark, no
+// agent call.
+func TestFinalizeDecommission_LastDriveRefusalIsTypedAndSideEffectFree(t *testing.T) {
+	s := testServer(t)
+	_ = s.settings.AddStoragePath(settings.StoragePath{Path: "/mnt/only", Schedulable: true, IsDefault: true})
+	agent := &mockAgent{}
+
+	err := s.finalizeDecommissionWith(context.Background(), agent, "/mnt/only", "")
+	if err == nil {
+		t.Fatal("decommissioning the last usable drive must be refused (M1)")
+	}
+	if !errors.Is(err, errLastUsableDrive) {
+		t.Fatalf("refusal must be the typed errLastUsableDrive sentinel (409 mapping), got: %v", err)
+	}
+	if s.settings.IsDecommissioned("/mnt/only") {
+		t.Error("refusal must precede the soft-mark side-effect")
+	}
+	if len(agent.decommissionCalls) != 0 {
+		t.Errorf("agent must not be called on refusal, got %v", agent.decommissionCalls)
+	}
+}
diff --git a/controller/internal/web/storage_handlers.go b/controller/internal/web/storage_handlers.go
index 1811af6..274537f 100644
--- a/controller/internal/web/storage_handlers.go
+++ b/controller/internal/web/storage_handlers.go
@@ -419,7 +419,13 @@ func (s *Server) handleStorageDecommission(w http.ResponseWriter, r *http.Reques
 			}
 		}
 		if err := s.finalizeDecommission(r.Context(), req.Where, ""); err != nil {
-			writeDiskJSON(w, http.StatusBadGateway, false, err.Error(), nil)
+			// The M1 policy refusal is a 409 (CONFLICT with current state), not a gateway
+			// failure — and 409 passes the CF edge with its JSON body intact.
+			status := http.StatusBadGateway
+			if errors.Is(err, errLastUsableDrive) {
+				status = http.StatusConflict
+			}
+			writeDiskJSON(w, status, false, err.Error(), nil)
 			return
 		}
 		writeDiskJSON(w, http.StatusOK, true, "", map[string]any{"decommissioned": true, "where": req.Where, "stopped_apps": stopped})
@@ -429,6 +435,11 @@ func (s *Server) handleStorageDecommission(w http.ResponseWriter, r *http.Reques
 	}
 }
 
+// errLastUsableDrive is the M1 refusal (never leave zero default) — a POLICY verdict, not a
+// gateway failure. The decommission handler maps it to 409 so the JSON refusal reaches the
+// browser intact (a 502 would be swallowed by the Cloudflare edge error page).
+var errLastUsableDrive = errors.New("ez az egyetlen használható tárhely — a leszerelés megtagadva (előbb adj hozzá vagy állíts be másik alapértelmezett meghajtót)")
+
 // finalizeDecommission resolves the agent client then soft-marks + decommissions (see *With).
 func (s *Server) finalizeDecommission(ctx context.Context, where, migratedTo string) error {
 	agent, err := s.agentClient()
@@ -448,7 +459,7 @@ func (s *Server) finalizeDecommissionWith(ctx context.Context, agent diskAgent,
 	// flips IsDefault/Schedulable on `where`).
 	promote, mustBlock := defaultPromotionTarget(s.settings.GetStoragePaths(), where, migratedTo)
 	if mustBlock {
-		return fmt.Errorf("ez az egyetlen használható tárhely — a leszerelés megtagadva (előbb adj hozzá vagy állíts be másik alapértelmezett meghajtót)")
+		return errLastUsableDrive
 	}
 	if err := s.settings.SetDecommissioned(where, migratedTo); err != nil {
 		return fmt.Errorf("nyilvántartás frissítése sikertelen: %w", err)
diff --git a/controller/internal/web/templates/app_info.html b/controller/internal/web/templates/app_info.html
index fc2a463..0e21803 100644
--- a/controller/internal/web/templates/app_info.html
+++ b/controller/internal/web/templates/app_info.html
@@ -101,11 +101,11 @@ function appMigWatch(){
 function appMigrate(btn,app,label){
     var sel=document.getElementById('app-migrate-target');
     var target=sel?sel.value:'';
-    if(!target){ alert('Válassz céltárhelyet.'); return; }
+    if(!target){ showAlert('Válassz céltárhelyet.'); return; }
     felhomConfirm(btn,'Áthelyezed a(z) '+label+' adatait ide: '+target+'? Az alkalmazás rövid időre leáll. A régi adatok csak sikeres áthelyezés után törlődnek.',function(){
         fetch('/api/storage/migrate-app',{method:'POST',headers:Object.assign({'Content-Type':'application/json'},csrfHeaders()),body:JSON.stringify({app:app,target:target})})
-            .then(function(r){return r.json();}).then(function(d){ if(d.ok){ appMigWatch(); } else { alert('Hiba: '+(d.error||'ismeretlen')); } })
-            .catch(function(e){ alert('Hiba: '+e); });
+            .then(function(r){return r.json();}).then(function(d){ if(d.ok){ appMigWatch(); } else { showAlert('Hiba: '+(d.error||'ismeretlen')); } })
+            .catch(function(e){ showAlert('Hiba: '+e); });
     });
 }
 (function(){ fetch('/api/storage/migrate/status').then(function(r){return r.json();}).then(function(d){ if(d.data&&d.data.job){ appMigWatch(); } }).catch(function(){}); })();
diff --git a/controller/internal/web/templates/debug.html b/controller/internal/web/templates/debug.html
index 1a644f4..e767a7d 100644
--- a/controller/internal/web/templates/debug.html
+++ b/controller/internal/web/templates/debug.html
@@ -475,9 +475,9 @@ function simulateDisconnect(btn, path) {
             headers: Object.assign({'Content-Type':'application/json'}, csrfHeaders()),
             body: JSON.stringify({path: path})
         }).then(function(r){return r.json()}).then(function(data) {
-            if (!data.ok) alert('Hiba: ' + (data.error || 'ismeretlen'));
+            if (!data.ok) showAlert('Hiba: ' + (data.error || 'ismeretlen'));
             loadWatchdogStatus();
-        }).catch(function(e) { alert('Hiba: ' + e.message); });
+        }).catch(function(e) { showAlert('Hiba: ' + e.message); });
     });
 }
 function simulateReconnect(path) {
@@ -486,9 +486,9 @@ function simulateReconnect(path) {
         headers: Object.assign({'Content-Type':'application/json'}, csrfHeaders()),
         body: JSON.stringify({path: path})
     }).then(function(r){return r.json()}).then(function(data) {
-        if (!data.ok) alert('Hiba: ' + (data.error || 'ismeretlen'));
+        if (!data.ok) showAlert('Hiba: ' + (data.error || 'ismeretlen'));
         loadWatchdogStatus();
-    }).catch(function(e) { alert('Hiba: ' + e.message); });
+    }).catch(function(e) { showAlert('Hiba: ' + e.message); });
 }
 
 // ── Section 5: Hub ──
diff --git a/controller/internal/web/templates/deploy.html b/controller/internal/web/templates/deploy.html
index 2e9d0c3..fc49f37 100644
--- a/controller/internal/web/templates/deploy.html
+++ b/controller/internal/web/templates/deploy.html
@@ -165,14 +165,14 @@
             var data = await resp.json();
             if (!data.ok) {
                 checkbox.checked = !enable;
-                alert(data.error || 'Hiba történt');
+                showAlert(data.error || 'Hiba történt');
             } else {
                 setTimeout(function(){ location.reload(); }, 500);
                 return;
             }
         } catch(err) {
             checkbox.checked = !enable;
-            alert('Hálózati hiba');
+            showAlert('Hálózati hiba');
         }
         checkbox.disabled = false;
     }
diff --git a/controller/internal/web/templates/storage.html b/controller/internal/web/templates/storage.html
index fe88285..2eb45b9 100644
--- a/controller/internal/web/templates/storage.html
+++ b/controller/internal/web/templates/storage.html
@@ -207,13 +207,13 @@
     function storageMigrateAll(source,label){
         var sel=document.getElementById('migrate-target-'+source);
         var target=sel?sel.value:'';
-        if(!target){ alert('Válassz céltárolót a legördülő menüből.'); return; }
+        if(!target){ showAlert('Válassz céltárolót a legördülő menüből.'); return; }
         openDialog({title:'Összes adat áthelyezése', confirmLabel:'Áthelyezés',
             message:'Áthelyezed a(z) '+label+' ÖSSZES adatát ide: '+target+'?\n\nAz alkalmazások az áthelyezés alatt rövid időre leállnak. A forrás adatai csak az ellenőrzés és a sikeres újraindítás után törlődnek.',
             onConfirm:function(){
         fetch('/api/storage/migrate',{method:'POST',headers:Object.assign({'Content-Type':'application/json'},csrfHeaders()),body:JSON.stringify({source:source,target:target})})
-            .then(function(r){return r.json();}).then(function(d){ if(d.ok){ migWatch(); } else { alert('Hiba: '+(d.error||'ismeretlen')); } })
-            .catch(function(e){ alert('Hiba: '+e); });
+            .then(function(r){return r.json();}).then(function(d){ if(d.ok){ migWatch(); } else { showAlert('Hiba: '+(d.error||'ismeretlen')); } })
+            .catch(function(e){ showAlert('Hiba: '+e); });
             }});
     }
     // Resume view: if a migration is STILL IN PROGRESS when the page loads, show the panel and watch.
@@ -408,9 +408,9 @@ window.__registeredPaths=[{{range .StoragePaths}}{{if .Path}}"{{.Path}}",{{end}}
   window.registerDrive=async function(where){
     try{
       var r=await fetch('/api/storage/register',{method:'POST',headers:Object.assign({'Content-Type':'application/json'},csrfHeaders()),body:JSON.stringify({where:where})});
-      var j=await r.json(); if(!j.ok){ alert('Regisztráció sikertelen: '+(j.error||'')); return; }
+      var j=await r.json(); if(!j.ok){ showAlert('Regisztráció sikertelen: '+(j.error||'')); return; }
       location.reload();
-    }catch(e){ alert('Hiba: '+e.message); }
+    }catch(e){ showAlert('Hiba: '+e.message); }
   };
   window.confirmEject=function(where){
     // The confirm name is the drive BASENAME (matches the server's path.Base(where) check); `where` may
@@ -530,12 +530,12 @@ function doStorageDisconnect(path) {
         body: JSON.stringify({where: path})
     }).then(function(r) { return r.json(); }).then(function(data) {
         if (data.ok) {
-            alert('A meghajtó biztonságosan eltávolítható.');
+            showAlert('A meghajtó biztonságosan eltávolítható.');
             location.reload();
         } else {
-            alert('Hiba: ' + (data.error || 'ismeretlen'));
+            showAlert('Hiba: ' + (data.error || 'ismeretlen'));
         }
-    }).catch(function(e) { alert('Hiba: ' + e); });
+    }).catch(function(e) { showAlert('Hiba: ' + e); });
 }
 function storageReconnect(path) {
     var actionsDiv = document.getElementById('storage-actions-' + path);
@@ -548,11 +548,11 @@ function storageReconnect(path) {
         if (data.ok) {
             location.reload();
         } else {
-            alert('Hiba: ' + (data.error || 'ismeretlen'));
+            showAlert('Hiba: ' + (data.error || 'ismeretlen'));
             if (actionsDiv) actionsDiv.innerHTML = '<button class="btn btn-xs btn-primary" onclick="storageReconnect(\'' + path + '\')">Csatlakoztatás</button>';
         }
     }).catch(function(e) {
-        alert('Hiba: ' + e);
+        showAlert('Hiba: ' + e);
         if (actionsDiv) actionsDiv.innerHTML = '<button class="btn btn-xs btn-primary" onclick="storageReconnect(\'' + path + '\')">Csatlakoztatás</button>';
     });
 }
@@ -564,12 +564,12 @@ function storageRestartApps(path) {
     }).then(function(r) { return r.json(); }).then(function(data) {
         if (data.ok) {
             var r2 = data.restarted || [];
-            if (r2.length) alert('Elindítva: ' + r2.join(', '));
+            if (r2.length) showAlert('Elindítva: ' + r2.join(', '));
             location.reload();
         } else {
-            alert('Hiba: ' + (data.error || 'ismeretlen'));
+            showAlert('Hiba: ' + (data.error || 'ismeretlen'));
         }
-    }).catch(function(e) { alert('Hiba: ' + e); });
+    }).catch(function(e) { showAlert('Hiba: ' + e); });
 }
 // H2: decommission a drive (non-destructive). If a migrate target is picked in the inline select →
 // migrate-then-decommission; otherwise decommission-anyway with type-to-confirm.
@@ -594,9 +594,9 @@ function doStorageDecommission(body) {
         headers: Object.assign({'Content-Type': 'application/json'}, csrfHeaders()),
         body: JSON.stringify(body)
     }).then(function(r) { return r.json(); }).then(function(data) {
-        if (data.ok) { alert('Leszerelés elindítva.'); location.reload(); }
-        else { alert('Hiba: ' + (data.error || 'ismeretlen')); }
-    }).catch(function(e) { alert('Hiba: ' + e); });
+        if (data.ok) { showAlert('Leszerelés elindítva.'); location.reload(); }
+        else { showAlert('Hiba: ' + (data.error || 'ismeretlen')); }
+    }).catch(function(e) { showAlert('Hiba: ' + e); });
 }
 // H3: one-click re-enroll a decommissioned/ejected drive — clears the marker, re-attaches under the
 // parent, restarts the gate-stopped apps (data is intact).
@@ -612,8 +612,8 @@ function doStorageReEnroll(path) {
         body: JSON.stringify({where: path})
     }).then(function(r) { return r.json(); }).then(function(data) {
         if (data.ok) { location.reload(); }
-        else { alert('Hiba: ' + (data.error || 'ismeretlen')); }
-    }).catch(function(e) { alert('Hiba: ' + e); });
+        else { showAlert('Hiba: ' + (data.error || 'ismeretlen')); }
+    }).catch(function(e) { showAlert('Hiba: ' + e); });
 }
 function cancelEditLabel(path, label) {
     var wrap = document.getElementById('label-wrap-' + path);
diff --git a/controller/internal/web/templates/storage_network.html b/controller/internal/web/templates/storage_network.html
index 907bf9f..2730c9a 100644
--- a/controller/internal/web/templates/storage_network.html
+++ b/controller/internal/web/templates/storage_network.html
@@ -218,8 +218,8 @@ function netStorageRemove(name,label){
         onConfirm:function(){
     fetch('/api/storage/netstorage/remove',{method:'POST',headers:Object.assign({'Content-Type':'application/json'},csrfHeaders()),body:JSON.stringify({name:name})})
         .then(function(r){return r.json();}).then(function(d){
-            if(d.ok){ location.reload(); } else { alert('Hiba: '+(d.error||'ismeretlen')); }
-        }).catch(function(e){ alert('Hiba: '+e); });
+            if(d.ok){ location.reload(); } else { showAlert('Hiba: '+(d.error||'ismeretlen')); }
+        }).catch(function(e){ showAlert('Hiba: '+e); });
         }});
 }
 if(document.getElementById('ns-add-form')){ nsToggleSmb(); nsUpdateHostID(); } // form absent on the capability banner
diff --git a/controller/scripts/native_confirm_gate.py b/controller/scripts/native_confirm_gate.py
index 3e2de5c..a18ce2e 100644
--- a/controller/scripts/native_confirm_gate.py
+++ b/controller/scripts/native_confirm_gate.py
@@ -1,10 +1,13 @@
 # -*- coding: utf-8 -*-
-"""Native-confirm gate (drill F-11) — native confirm()/prompt() dialogs are OS-modals that block
-browser automation (CDP freezes) and are banned from the UI; consequential actions use the inline
-felhomConfirm helper (layout.html) or the .confirm-overlay dialog.
+"""Native-confirm gate (drill F-11; alert added v0.126.4) — native confirm()/prompt()/alert()
+dialogs are OS-modals that block browser automation (CDP freezes) and are banned from the UI;
+consequential actions use the inline felhomConfirm helper (layout.html) or the .confirm-overlay
+dialog; error/info surfaces use showAlert (layout.html modal). alert() joined the ban after the
+0.87.0 wizard leg: a decommission error path alert() froze the automation exactly like F-11
+predicted (the operator had to click the OS-modal away).
 
 Run from controller/:  python scripts/native_confirm_gate.py
-Exit 1 if any native confirm(/prompt( call remains in the templates.
+Exit 1 if any native confirm(/prompt(/alert( call remains in the templates.
 """
 import io, os, re, sys
 
@@ -13,9 +16,10 @@ ROOTS = [
     os.path.join("internal", "setup", "templates"),
 ]
 
-# A bare confirm(/prompt( CALL with an argument: not preceded by an identifier character, so felhomConfirm( and
-# onRestoreConfirmChange( never match. window.confirm( still matches ('.' is not identifier).
-NATIVE = re.compile(r"(?<![A-Za-z0-9_$])(?:confirm|prompt)\(\s*[^)\s]")
+# A bare confirm(/prompt(/alert( CALL with an argument: not preceded by an identifier character,
+# so felhomConfirm(, showAlert( and onRestoreConfirmChange( never match. window.confirm( /
+# window.alert( still match ('.' is not an identifier character).
+NATIVE = re.compile(r"(?<![A-Za-z0-9_$])(?:confirm|prompt|alert)\(\s*[^)\s]")
 
 
 def main():
@@ -30,9 +34,9 @@ def main():
                     total += 1
                     print("%s:%d  %s" % (fn, lineno, line.strip()[:120].encode('ascii', 'backslashreplace').decode()))
     if total:
-        print("NATIVE CONFIRM GATE FAILED: %d native confirm()/prompt() call(s) remain" % total)
+        print("NATIVE CONFIRM GATE FAILED: %d native confirm()/prompt()/alert() call(s) remain" % total)
         sys.exit(1)
-    print("native-confirm gate OK — no native confirm()/prompt() in templates")
+    print("native-confirm gate OK — no native confirm()/prompt()/alert() in templates")
 
 
 if __name__ == "__main__":