[cmux] add global font magnification across terminals and chrome

Resources/Localizable.xcstrings

@@ -49469,6 +49469,74 @@
         }
       }
     },
+    "settings.app.globalFontMagnification" : {
+      "extractionState" : "manual",
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Global Font Magnification"
+          }
+        },
+        "ja" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "グローバルフォント倍率"
+          }
+        }
+      }
+    },
+    "settings.app.globalFontMagnification.subtitleOff" : {
+      "extractionState" : "manual",
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Scale every font in cmux by the same percentage. 100% = design size."
+          }
+        },
+        "ja" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "cmux のすべてのフォントを同じ割合でスケーリングします。100% = 設計サイズ。"
+          }
+        }
+      }
+    },
+    "settings.app.globalFontMagnification.subtitleOn" : {
+      "extractionState" : "manual",
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Terminals, tabs, and chrome all render at this magnification. Per-pane zoom (⌘= / ⌘-) still overrides for the focused pane."
+          }
+        },
+        "ja" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "ターミナル、タブ、UI をこの倍率で描画します。ペインごとのズーム (⌘= / ⌘-) はフォーカス中のペインに対して引き続き優先されます。"
+          }
+        }
+      }
+    },
+    "settings.app.globalFontMagnification.reset" : {
+      "extractionState" : "manual",
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Reset"
+          }
+        },
+        "ja" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "リセット"
+          }
+        }
+      }
+    },
     "settings.app.newWorkspacePlacement": {
       "extractionState": "manual",
       "localizations": {

Sources/AppDelegate.swift

@@ -638,6 +638,7 @@ final class AppDelegate: NSObject, NSApplicationDelegate, UNUserNotificationCent
     private var activeConfiguredShortcutChordPrefixForCurrentEvent: ShortcutStroke?
     private var configuredShortcutChordActions: [KeyboardShortcutSettings.Action] = []
     private var ghosttyConfigObserver: NSObjectProtocol?
+    private var globalFontSizeObserver: NSObjectProtocol?
     private var ghosttyGotoSplitLeftShortcut: StoredShortcut?
     private var ghosttyGotoSplitRightShortcut: StoredShortcut?
     private var ghosttyGotoSplitUpShortcut: StoredShortcut?
@@ -1010,6 +1011,7 @@ final class AppDelegate: NSObject, NSApplicationDelegate, UNUserNotificationCent
         installMainWindowKeyObserver()
         refreshGhosttyGotoSplitShortcuts()
         installGhosttyConfigObserver()
+        installGlobalFontSizeObserver()
         installWindowResponderSwizzles()
         installBrowserAddressBarFocusObservers()
         installShortcutMonitor()
@@ -9039,6 +9041,24 @@ final class AppDelegate: NSObject, NSApplicationDelegate, UNUserNotificationCent
         }
     }
 
+    private func installGlobalFontSizeObserver() {
+        guard globalFontSizeObserver == nil else { return }
+        globalFontSizeObserver = NotificationCenter.default.addObserver(
+            forName: GlobalFontMagnification.didChangeNotification,
+            object: nil,
+            queue: .main
+        ) { _ in
+            // Push the new magnification into the live Ghostty config so existing
+            // terminals reflow. Called for UI-driven and cmux.json-driven
+            // changes — the reload is idempotent so double-reloads are fine.
+            GhosttyConfig.invalidateLoadCache()
+            GhosttyApp.shared.reloadConfiguration(
+                source: "globalFontMagnificationDidChange",
+                reloadSettingsFromFile: false
+            )
+        }
+    }
+
     private func refreshGhosttyGotoSplitShortcuts() {
         guard let config = GhosttyApp.shared.config else {
             ghosttyGotoSplitLeftShortcut = nil