Merge nucleic/warm-coral-viper-sn0m into dev

NucleicRemote/NucleicRemote/Views/SessionDetailView.swift

@@ -352,10 +352,13 @@ struct SessionDetailView: View {
     @ViewBuilder
     private func modelEffortMenu(_ summary: WireSessionSummary) -> some View {
         if !store.routesIntelligence {
-            // A session's backend is fixed at creation, so only same-backend models are offered.
+            // Context Switch can replace the backend between turns. The summary is the live source
+            // of truth, and the explicit identity rebuilds a native Menu that happened to be open
+            // across the update instead of retaining its old provider's snapshot.
             ModelMenu(model: modelBinding, catalog: store.modelCatalog, backend: summary.backend)
+                .id(summary.backend)
             EffortMenu(effort: effortBinding, catalog: store.modelCatalog,
-                       // No explicit model yet → use the session backend's default, so the menu
+                       // No explicit model yet → use the current backend's default, so the menu
                        // shows that backend's effort range rather than collapsing to one level.
                        modelSKU: summary.model ?? store.modelCatalog.models(for: summary.backend).first?.sku,
                        controlled: controlled,
@@ -368,7 +371,7 @@ struct SessionDetailView: View {
     // MARK: - The in-session Intelligence rail
 
     /// The stop this chat's rail sits at. The host owns it — moving the rail sends the stop and
-    /// the host re-routes within the chat's fixed backend lane, then broadcasts the resulting
+    /// the host re-routes within the chat's current backend lane, then broadcasts the resulting
     /// model/effort — so the committed value is *derived* from the summary rather than held here.
     /// `pendingIntelligence` covers only the round trip, and `intelligencePreview` the drag.
     private var sessionIntelligence: Int {
@@ -433,6 +436,7 @@ struct SessionDetailView: View {
             .onChange(of: summary.routedLevel) { _, _ in pendingIntelligence = nil }
             .onChange(of: summary.model) { _, _ in pendingIntelligence = nil }
             .onChange(of: summary.effort) { _, _ in pendingIntelligence = nil }
+            .onChange(of: summary.backend) { _, _ in pendingIntelligence = nil }
             // A refused move — every candidate for that stop is inside a reached quota window —
             // changes nothing at all; the host answers with an error instead. Without this the
             // rail would stay parked on a stop the chat never reached, so it springs back here

NucleicRemote/NucleicRemote/Views/Theme.swift

@@ -477,8 +477,10 @@ extension WireModelCatalog {
 
 /// A compact model selector driven by the wire catalog (SYNC §5.2). `backend == nil` — the
 /// home composer, where the model also selects the backend — shows every provider group with
-/// dividers; a fixed `backend` (in-session, where the backend is immutable) shows only that
+/// dividers; an in-session `backend` shows only the models for the session summary's *current*
-/// provider's models. Selecting sets the SKU; the binding's `nil` means "host default".
+/// provider. Context Switch may change that field between turns, so callers pass the live summary
+/// rather than retaining the creation-time lane. Selecting sets the SKU; the binding's `nil` means
+/// "host default".
 struct ModelMenu: View {
     @Binding var model: String?
     let catalog: WireModelCatalog