Let a refused host count as unreachable and the switcher own every login

Residual round after the macOS fix verification, five closures:

A connection refusal or a failed DNS lookup arrived as APIError.unknown,
which no classifier reads — so an account pointed at a downed instance
never went unreachable, never fell back to local data, never armed a
retry. New APIError.connectionFailed carries the system's own sentence
and lands as unreachable/offline in AccountsManager, InstancesManager
and the credential probe; a refused host now classifies in seconds
instead of never.

Subscriptions' periodic retry armed only for networkError, while the
local fallback's yatteeServerRequired — shown exactly when the account's
server could not be reached — waited on a status expiry nothing was
watching. FeedLoadState.warrantsPeriodicRetry gates on the context's
unavailability, so that screen heals on its own too, and an account that
genuinely has no Yattee Server still never loops.

The switcher dropped every context of a switched-off source, leaving the
toolbar badge pointing at a menu its own selection had vanished from.
listedContexts keeps the rows with their status in the title ("— Source
switched off"), isSwitchable refuses the pick, and the current context
keeps its checkmark.

The sidebar footer's switcher row overflowed the 140 pt column minimum:
the width floor now sits on the menu itself and ViewThatFits drops the
caption — the part the icon already says — before the account name loses
characters.

The channel menu exposed a raw SF Symbol name as its accessibility
title; the label is now a real Label rendered iconOnly, so the AX bridge
hears "Subscription Options".

Yattee/Views/Components/DataContextSwitcherMenu.swift

@@ -22,7 +22,7 @@ struct DataContextSwitcherRows: View {
     private var validator: DataContextValidator? { appEnvironment?.dataContextValidator }
 
     var body: some View {
-        ForEach(validator?.availableContexts ?? [.local], id: \.self) { context in
+        ForEach(validator?.listedContexts ?? [.local], id: \.self) { context in
             row(for: context)
         }
     }
@@ -31,7 +31,10 @@ struct DataContextSwitcherRows: View {
     private func row(for context: DataContext) -> some View {
         // A menu row is a single label — a `VStack` inside one renders as
         // nothing on macOS — so the status travels in the title rather than as
-        // a second line.
+        // a second line. A context that cannot be switched to says so there
+        // too: `title(for:in:)` appends the *display* status, which is what
+        // turns a login on a switched-off source into "… — Source switched
+        // off" rather than a row that looks ordinary and does nothing.
         let title = DataContextSwitcherLabels.title(for: context, in: appEnvironment)
 
         #if os(macOS)
@@ -48,6 +51,7 @@ struct DataContextSwitcherRows: View {
         )) {
             Text(title)
         }
+        .disabled(isRefused(context))
         #else
         Button {
             switchTo(context)
@@ -58,6 +62,7 @@ struct DataContextSwitcherRows: View {
                 Text(title)
             }
         }
+        .disabled(isRefused(context))
         #if os(tvOS)
         .buttonStyle(TVSettingsButtonStyle())
         #endif
@@ -65,6 +70,10 @@ struct DataContextSwitcherRows: View {
     }
 
     private func switchTo(_ context: DataContext) {
+        // The row is disabled as well; this is what makes the refusal true on
+        // any presentation where a disabled control can still be activated.
+        guard !isRefused(context) else { return }
+
         appEnvironment?.switchDataContext(to: context)
         onSwitch?()
     }
@@ -72,6 +81,18 @@ struct DataContextSwitcherRows: View {
     private func isCurrent(_ context: DataContext) -> Bool {
         appEnvironment?.accountsManager.currentContext == context
     }
+
+    /// Listed, but not something the user may pick.
+    ///
+    /// The current context is never refused, whatever its source is doing: it
+    /// is already the selection, picking it changes nothing, and a disabled
+    /// macOS menu item is not the place to hang the app's only checkmark. It
+    /// carries its status in the title instead, which is the part that has to
+    /// survive.
+    private func isRefused(_ context: DataContext) -> Bool {
+        guard let validator, !isCurrent(context) else { return false }
+        return !validator.isSwitchable(context)
+    }
 }
 
 // MARK: - Labels
@@ -352,23 +373,13 @@ struct DataContextSwitcherSettingsRow: View {
         // trailing name was dropped at every width, leaving the row silent
         // about which account is selected. So the name is the menu's *own*
         // label, and the row carries only what names the control.
-        LabeledContent {
-            Menu {
-                DataContextSwitcherRows()
-            } label: {
-                Text(contextTitle)
-                    .lineLimit(1)
-            }
-            .menuStyle(.borderlessButton)
-            .help(contextTitle)
-            .accessibilityLabel(Text(String(localized: "accounts.switcher.title")))
-            .accessibilityValue(Text(contextTitle))
-        } label: {
-            Label {
-                Text(String(localized: "accounts.switcher.title"))
-            } icon: {
-                DataContextSwitcherIcon()
-            }
+        // `LabeledContent` overflows rather than compress its label, so at the
+        // sidebar's 140 pt minimum a captioned row (caption + spacing + the
+        // name's floor ≈ 158 pt) juts past both edges. The caption is the one
+        // part the icon already says, so it is the part that goes.
+        ViewThatFits(in: .horizontal) {
+            macOSRow(captioned: true)
+            macOSRow(captioned: false)
         }
         #else
         Menu {
@@ -379,11 +390,58 @@ struct DataContextSwitcherSettingsRow: View {
         #endif
     }
 
+    #if os(macOS)
+    @ViewBuilder private func macOSRow(captioned: Bool) -> some View {
+        LabeledContent {
+            Menu {
+                DataContextSwitcherRows()
+            } label: {
+                Text(contextTitle)
+                    .lineLimit(1)
+                    .truncationMode(.tail)
+            }
+            .menuStyle(.borderlessButton)
+            // The floor must sit on the menu itself: a borderless menu button
+            // lays out its label alone, so a frame inside it never reaches the
+            // row's layout, and the caption would keep its ideal width while
+            // the name shrank to an ellipsis. Out here the menu claims the
+            // width and the caption is what gives way.
+            .frame(minWidth: Self.minimumNameWidth, alignment: .trailing)
+            .layoutPriority(1)
+            .help(contextTitle)
+            .accessibilityLabel(Text(String(localized: "accounts.switcher.title")))
+            .accessibilityValue(Text(contextTitle))
+        } label: {
+            Label {
+                if captioned {
+                    Text(String(localized: "accounts.switcher.title"))
+                        .lineLimit(1)
+                        .truncationMode(.tail)
+                }
+            } icon: {
+                DataContextSwitcherIcon()
+            }
+        }
+    }
+    #endif
+
+    /// What the trailing name may never be squeezed below.
+    ///
+    /// A row this narrow — the macOS sidebar's footer at a dragged-in column
+    /// width — hands the leading label its ideal width first and leaves the
+    /// name whatever is left, and a `Text` will shrink all the way to a lone
+    /// ellipsis before it complains. A floor turns that around: the name keeps
+    /// enough characters to be recognised, and the word naming the control —
+    /// which the icon beside it already says — is what truncates instead.
+    private static let minimumNameWidth: CGFloat = 80
+
     #if !os(macOS)
     private var rowLabel: some View {
         HStack {
             Label {
                 Text(String(localized: "accounts.switcher.title"))
+                    .lineLimit(1)
+                    .truncationMode(.tail)
             } icon: {
                 DataContextSwitcherIcon()
             }
@@ -391,6 +449,8 @@ struct DataContextSwitcherSettingsRow: View {
             Text(contextTitle)
                 .foregroundStyle(.secondary)
                 .lineLimit(1)
+                .truncationMode(.tail)
+                .frame(minWidth: Self.minimumNameWidth, alignment: .trailing)
         }
     }
     #endif