feat(web): C2 Parts 2+3 — POST /backup/tier2/restore + "Fájlok visszaállítása" button

- Endpoint next to /backup/restore; handler mirrors backupRestoreHandler
  (ParseForm → validStackName → backupMgr guard → WARN with RemoteAddr →
  RestoreTier2Files → flash). Flash strings: "<stack>: N fájl visszaállítva a
  másodlagos másolatból." / "Nincs hiányzó fájl — minden fájl megvan a helyén."
  / "Fájl-visszaállítás sikertelen: <err>" (refusals carry the Hungarian
  reasons from the engine).
- backups.html: the button on the healthy Tier-2 layer row only (the
  Tier2Configured branch already excludes disconnected/inactive; additionally
  gated on Tier2LastRun), inline POST form with CSRF + confirm dialog naming
  the additive-only semantics and the last-copy timestamp. Template gates
  (id + emoji) green.
- Handler guard test (C6): traversal/empty → exact Hungarian flash, no work
  started (nil backupMgr would panic if reached).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PSK5g6qYLknKj8u3QAFEr6

controller/internal/web/handlers.go

@@ -896,6 +896,44 @@ func (s *Server) backupRestoreHandler(w http.ResponseWriter, r *http.Request) {
 	http.Redirect(w, r, "/backups?flash="+msg, http.StatusFound)
 }
 
+// backupTier2RestoreHandler (C2, closes F2) restores an app's MISSING user files in place from its
+// recorded Tier-2 copy — additive-only: existing live files are never overwritten and nothing is
+// ever deleted (see backup.RestoreTier2Files). Same handler shape as backupRestoreHandler.
+func (s *Server) backupTier2RestoreHandler(w http.ResponseWriter, r *http.Request) {
+	_ = r.ParseForm()
+	stackName := r.FormValue("stack_name")
+
+	if stackName == "" {
+		http.Redirect(w, r, "/backups?flash_error=Hi%C3%A1nyz%C3%B3+param%C3%A9terek", http.StatusFound)
+		return
+	}
+	// Same F2-defense as the unit restore: a stack name is a single segment, never a path.
+	if !validStackName(stackName) {
+		s.logger.Printf("[WARN] [web] Tier-2 file restore rejected: invalid stack_name %q from %s", stackName, r.RemoteAddr)
+		http.Redirect(w, r, "/backups?flash_error=%C3%89rv%C3%A9nytelen+alkalmaz%C3%A1sn%C3%A9v", http.StatusFound)
+		return
+	}
+	if s.backupMgr == nil {
+		http.Redirect(w, r, "/backups?flash_error=Ment%C3%A9s+nincs+be%C3%A1ll%C3%ADtva", http.StatusFound)
+		return
+	}
+
+	s.logger.Printf("[WARN] [web] Tier-2 file restore requested: stack=%s from %s", stackName, r.RemoteAddr)
+
+	n, err := s.backupMgr.RestoreTier2Files(stackName)
+	if err != nil {
+		s.logger.Printf("[ERROR] [web] Tier-2 file restore failed: %v", err)
+		http.Redirect(w, r, "/backups?flash_error="+url.QueryEscape("Fájl-visszaállítás sikertelen: "+err.Error()), http.StatusFound)
+		return
+	}
+
+	msg := "Nincs hiányzó fájl — minden fájl megvan a helyén."
+	if n > 0 {
+		msg = fmt.Sprintf("%s: %d fájl visszaállítva a másodlagos másolatból.", stackName, n)
+	}
+	http.Redirect(w, r, "/backups?flash="+url.QueryEscape(msg), http.StatusFound)
+}
+
 // settingsBaseData is the shared identity block used by every settings-family subpage
 // (D1 split: /settings, /settings/notifications, /settings/security, /storage).
 func (s *Server) settingsBaseData(page, title string) map[string]interface{} {

controller/internal/web/server.go

@@ -299,6 +299,9 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		http.Redirect(w, r, "/storage/attach", http.StatusMovedPermanently)
 	case path == "/backup/restore" && r.Method == http.MethodPost:
 		s.backupRestoreHandler(w, r)
+	// C2: in-place, additive-only file restore from the Tier-2 copy (class-C user files)
+	case path == "/backup/tier2/restore" && r.Method == http.MethodPost:
+		s.backupTier2RestoreHandler(w, r)
 	// Off-box (NAS) restic-SFTP backup (Part B)
 	case path == "/backup/offbox/config" && r.Method == http.MethodPost:
 		s.offboxConfigHandler(w, r)

controller/internal/web/templates/backups.html

@@ -436,6 +436,12 @@
                         <span class="tier-contents">{{.BackupContents}}</span>
                         <span class="tier-browsable" title="A mentés böngészhető fájlrendszerben"><svg class="ico ico-sm"><use href="#i-file-text"/></svg></span>
                         <div class="layer-actions">
+                            {{if .Tier2LastRun}}
+                            <form method="POST" action="/backup/tier2/restore" style="display:inline" onsubmit="return confirm('Visszaállítja a hiányzó fájlokat a másodlagos másolatból? A meglévő fájlok NEM módosulnak és NEM törlődnek. Az alkalmazás a művelet idejére leáll. Legutóbbi másolat: {{.Tier2LastRun}}')">{{$.CSRFField}}
+                                <input type="hidden" name="stack_name" value="{{.StackName}}">
+                                <button type="submit" class="btn btn-xs btn-outline">Fájlok visszaállítása</button>
+                            </form>
+                            {{end}}
                             <a href="/stacks/{{.StackName}}/backup" class="btn btn-xs btn-outline">Beállítás</a>
                         </div>
                     {{else}}

controller/internal/web/tier2_restore_handler_test.go

@@ -0,0 +1,50 @@
+package web
+
+import (
+	"io"
+	"log"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"testing"
+)
+
+// postTier2Restore drives the handler with a form body, as the UI's inline form does.
+func postTier2Restore(t *testing.T, s *Server, stackName string) *httptest.ResponseRecorder {
+	t.Helper()
+	form := url.Values{"stack_name": {stackName}}
+	req := httptest.NewRequest(http.MethodPost, "/backup/tier2/restore", strings.NewReader(form.Encode()))
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	rec := httptest.NewRecorder()
+	s.backupTier2RestoreHandler(rec, req)
+	return rec
+}
+
+// TestTier2RestoreHandler_Guards proves Scenario C6 + the missing-param guard: traversal and empty
+// names are rejected with the exact Hungarian flash BEFORE any restore work (backupMgr is nil here —
+// reaching it would panic, so a pass also proves no work started).
+func TestTier2RestoreHandler_Guards(t *testing.T) {
+	s := &Server{logger: log.New(io.Discard, "", 0)} // backupMgr nil on purpose
+
+	for name, want := range map[string]string{
+		"../../etc": "%C3%89rv%C3%A9nytelen+alkalmaz%C3%A1sn%C3%A9v", // Érvénytelen alkalmazásnév
+		"a/b":       "%C3%89rv%C3%A9nytelen+alkalmaz%C3%A1sn%C3%A9v",
+		"":          "Hi%C3%A1nyz%C3%B3+param%C3%A9terek", // Hiányzó paraméterek
+	} {
+		rec := postTier2Restore(t, s, name)
+		if rec.Code != http.StatusFound {
+			t.Errorf("%q: status = %d, want 302", name, rec.Code)
+			continue
+		}
+		if loc := rec.Header().Get("Location"); !strings.Contains(loc, want) {
+			t.Errorf("%q: redirect = %q, want flash %q", name, loc, want)
+		}
+	}
+
+	// Valid name but no backup manager → the not-configured flash (still no panic, no work).
+	rec := postTier2Restore(t, s, "nextcloud")
+	if loc := rec.Header().Get("Location"); !strings.Contains(loc, "Ment%C3%A9s+nincs+be%C3%A1ll%C3%ADtva") {
+		t.Errorf("nil backupMgr: redirect = %q", loc)
+	}
+}