Wizard: idempotenter WAN-Apply fuer DHCP-Client/PPPoE (Bug 21)

Wizard erneut auf einem Interface durchlaufen, das schon einen
DHCP-Client hat (hier: aus einer zurueckgespielten Sicherung), scheiterte
live mit "failure: dhcp-client on that interface already exists" -
WanConfig.buildCommands() erzeugt fuer DHCP-Client/PPPoE immer .add, ohne
vorher zu pruefen, ob auf dem Interface schon einer existiert.

Fix: SetupViewModel.applyIdempotently faengt einen .add-Fehlschlag auf
/ip dhcp-client bzw. /interface pppoe-client ab und wiederholt ihn als
.set (nach "interface" gematcht) - bewusst nur fuer diese zwei Menues
mit "maximal ein Eintrag pro Interface"-Semantik, nicht generell fuer
jedes .add (z.B. /ip address erlaubt legitim mehrere Adressen pro
Interface).

Gefunden beim Versuch, M8 (Netzwerk-Isolation) live durchzutesten -
dieser Test selbst ist noch nicht abgeschlossen, naechste Session dort
weitermachen (siehe HANDOFF.md Naechste Schritte Punkt 1).

HANDOFF.md/CHATLOG.md aktualisiert: Bug 21, Sessionende-Stand.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CTgRxJTzaQwaRkngbaE1GJ

RouterOSAssistant/Features/Wizard/Steps/Setup/SetupViewModel.swift

@@ -213,7 +213,7 @@ final class SetupViewModel: ObservableObject {
 
                 for command in plannedCommands {
                     applyLog.append(command.summary)
-                    try await connectionService.apply(command)
+                    try await applyIdempotently(command)
                 }
 
                 didApplySuccessfully = true
@@ -223,4 +223,36 @@ final class SetupViewModel: ObservableObject {
             isApplying = false
         }
     }
+
+    /// RouterOS allows at most one item per interface on some menus (a DHCP client, a PPPoE
+    /// client) — re-running the wizard's WAN step on an interface that already has one makes the
+    /// wizard's own `.add` fail live-confirmed: "failure: dhcp-client on that interface already
+    /// exists". Rather than hard-fail the whole apply here, retry once as a `.set` matched by
+    /// "interface" instead — reconfigures the existing entry in place, which is what re-running
+    /// the wizard on the same interface should mean anyway. Scoped to exactly these two
+    /// known-unique-per-interface menus, not applied generally to every `.add` — other menus
+    /// (e.g. "/ip address") legitimately allow multiple items per interface, where silently
+    /// converting a would-be-duplicate `.add` into a `.set` would be wrong, not helpful.
+    private static let interfaceUniqueMenuPaths: Set<String> = ["/ip dhcp-client", "/interface pppoe-client"]
+
+    private func applyIdempotently(_ command: RouterOSCommand) async throws {
+        do {
+            try await connectionService.apply(command)
+        } catch {
+            guard case .add = command.operation,
+                  Self.interfaceUniqueMenuPaths.contains(command.menuPath),
+                  let interfaceName = command.arguments["interface"] else {
+                throw error
+            }
+            let retryCommand = RouterOSCommand.set(
+                menuPath: command.menuPath,
+                restPath: command.restPath,
+                matchField: "interface",
+                matchValue: interfaceName,
+                arguments: command.arguments,
+                summary: command.summary
+            )
+            try await connectionService.apply(retryCommand)
+        }
+    }
 }