feat(appearance): apply UI zoom level to terminal and Monaco editors

Extend the existing appearance zoom setting so it also scales xterm.js
terminals and Monaco editors (diff viewer, three-pane merge editor, file
workspace editor), which previously rendered at a hard-coded 13px
regardless of zoom.

- Terminals read zoom at init and update term.options.fontSize live on
  zoom change, refitting after a double rAF so xterm's renderer has
  recomputed cell metrics. Font size is rounded to an integer to avoid
  subpixel blur in the canvas renderer.
- Monaco editors derive fontSize from zoomLevel; three-pane merge
  editor memoizes its options object to avoid redundant updateOptions
  calls on unrelated re-renders.

src/components/diff/diff-viewer.tsx

@@ -6,8 +6,11 @@ import { ChevronLeft, ChevronRight } from "lucide-react"
 import type { DiffOnMount } from "@monaco-editor/react"
 import type { editor as MonacoEditorNs } from "monaco-editor"
 import { defineMonacoThemes, useMonacoThemeSync } from "@/lib/monaco-themes"
+import { useZoomLevel } from "@/hooks/use-appearance"
 import { cn } from "@/lib/utils"
 
+const EDITOR_BASE_FONT_SIZE = 13
+
 import "@/lib/monaco-local"
 
 const MonacoDiffEditor = dynamic(
@@ -36,6 +39,7 @@ export function DiffViewer({
   className,
 }: DiffViewerProps) {
   const editorTheme = useMonacoThemeSync()
+  const { zoomLevel } = useZoomLevel()
   const diffEditorRef = useRef<MonacoEditorNs.IStandaloneDiffEditor | null>(
     null
   )
@@ -187,7 +191,7 @@ export function DiffViewer({
             renderSideBySide: true,
             renderSideBySideInlineBreakpoint: 0,
             automaticLayout: true,
-            fontSize: 13,
+            fontSize: (EDITOR_BASE_FONT_SIZE * zoomLevel) / 100,
             minimap: { enabled: false },
             scrollBeyondLastLine: false,
             renderOverviewRuler: false,

src/components/files/file-workspace-panel.tsx

@@ -24,7 +24,10 @@ import { Streamdown } from "streamdown"
 import { readFileBase64 } from "@/lib/api"
 import { normalizeMathDelimiters } from "@/components/ai-elements/message"
 import { defineMonacoThemes, useMonacoThemeSync } from "@/lib/monaco-themes"
+import { useZoomLevel } from "@/hooks/use-appearance"
 import { ScrollArea } from "@/components/ui/scroll-area"
+
+const EDITOR_BASE_FONT_SIZE = 13
 import "@/lib/monaco-local"
 
 const math = createMathPlugin({ singleDollarTextMath: true })
@@ -770,6 +773,7 @@ export function FileWorkspacePanel() {
   const cursorListenerRef = useRef<{ dispose: () => void } | null>(null)
   const gitChangeDecorationsRef = useRef<string[]>([])
   const editorTheme = useMonacoThemeSync()
+  const { zoomLevel } = useZoomLevel()
   const [editorMountVersion, setEditorMountVersion] = useState(0)
   const [cursorLine, setCursorLine] = useState(1)
   const [collapsedFiles, setCollapsedFiles] = useState<Record<string, boolean>>(
@@ -1610,7 +1614,7 @@ export function FileWorkspacePanel() {
                 readOnly: !canEdit,
                 minimap: { enabled: false },
                 automaticLayout: true,
-                fontSize: 13,
+                fontSize: (EDITOR_BASE_FONT_SIZE * zoomLevel) / 100,
                 lineNumbersMinChars,
                 lineDecorationsWidth: 10,
                 wordWrap: "off",

src/components/merge/three-pane-merge-editor.tsx

@@ -7,7 +7,10 @@ import type { editor as MonacoEditorNs, IRange } from "monaco-editor"
 import { ArrowLeft, ArrowRight, CheckCheck } from "lucide-react"
 import { useTranslations } from "next-intl"
 import { defineMonacoThemes, useMonacoThemeSync } from "@/lib/monaco-themes"
+import { useZoomLevel } from "@/hooks/use-appearance"
 import { cn } from "@/lib/utils"
+
+const EDITOR_BASE_FONT_SIZE = 13
 import { Button } from "@/components/ui/button"
 import {
   ResizableHandle,
@@ -55,6 +58,7 @@ export function ThreePaneMergeEditor({
 }: ThreePaneMergeEditorProps) {
   const t = useTranslations("MergePage")
   const editorTheme = useMonacoThemeSync()
+  const { zoomLevel } = useZoomLevel()
   const { registerEditor } = useSyncScroll()
 
   const leftEditorRef = useRef<MonacoEditorNs.IStandaloneCodeEditor | null>(
@@ -497,23 +501,30 @@ export function ThreePaneMergeEditor({
   // ---------------------------------------------------------------------------
   // Editor options
   // ---------------------------------------------------------------------------
-  const editorOptions: MonacoEditorNs.IStandaloneEditorConstructionOptions = {
-    fontSize: 13,
-    minimap: { enabled: false },
-    scrollBeyondLastLine: false,
-    automaticLayout: true,
-    lineNumbers: "on",
-    glyphMargin: true,
-    folding: false,
-    wordWrap: "off",
-    overviewRulerLanes: 0,
-  }
+  const editorOptions =
+    useMemo<MonacoEditorNs.IStandaloneEditorConstructionOptions>(
+      () => ({
+        fontSize: (EDITOR_BASE_FONT_SIZE * zoomLevel) / 100,
+        minimap: { enabled: false },
+        scrollBeyondLastLine: false,
+        automaticLayout: true,
+        lineNumbers: "on",
+        glyphMargin: true,
+        folding: false,
+        wordWrap: "off",
+        overviewRulerLanes: 0,
+      }),
+      [zoomLevel]
+    )
 
-  const readonlyOptions = {
-    ...editorOptions,
-    readOnly: true,
-    domReadOnly: true,
-  }
+  const readonlyOptions = useMemo(
+    () => ({
+      ...editorOptions,
+      readOnly: true,
+      domReadOnly: true,
+    }),
+    [editorOptions]
+  )
 
   const loadingEl = (
     <div className="flex h-full items-center justify-center text-xs text-muted-foreground">

src/components/terminal/terminal-view.tsx

@@ -8,8 +8,15 @@ import {
   terminalResize,
   terminalKill,
 } from "@/lib/api"
+import { useZoomLevel } from "@/hooks/use-appearance"
 import type { TerminalEvent } from "@/lib/types"
-import type { ITheme } from "@xterm/xterm"
+import type { ITheme, Terminal as XTermTerminal } from "@xterm/xterm"
+
+const TERMINAL_BASE_FONT_SIZE = 13
+
+function computeTerminalFontSize(zoomLevel: number): number {
+  return Math.round((TERMINAL_BASE_FONT_SIZE * zoomLevel) / 100)
+}
 
 const DARK_THEME: ITheme = {
   background: "#1a1a1a",
@@ -108,11 +115,13 @@ export function TerminalView({
 }: TerminalViewProps) {
   const containerRef = useRef<HTMLDivElement>(null)
   const fitAddonRef = useRef<{ fit: () => void } | null>(null)
-  const termRef = useRef<{ focus: () => void } | null>(null)
+  const termRef = useRef<XTermTerminal | null>(null)
   const lastResizeRef = useRef<{ cols: number; rows: number } | null>(null)
   const isActiveRef = useRef(isActive)
   const isVisibleRef = useRef(isVisible)
   const onProcessExitedRef = useRef(onProcessExited)
+  const { zoomLevel } = useZoomLevel()
+  const zoomLevelRef = useRef(zoomLevel)
   const [loading, setLoading] = useState(true)
 
   useEffect(() => {
@@ -140,7 +149,7 @@ export function TerminalView({
 
       const term = new Terminal({
         cursorBlink: true,
-        fontSize: 13,
+        fontSize: computeTerminalFontSize(zoomLevelRef.current),
         fontFamily: "Menlo, Monaco, 'Courier New', monospace",
         theme: getTerminalTheme(containerRef.current),
         allowProposedApi: true,
@@ -292,6 +301,25 @@ export function TerminalView({
     }
   }, [isActive, isVisible])
 
+  // React to zoom level changes. Updates the ref synchronously so async init()
+  // always reads the latest zoom, and pushes the new font size to already-mounted
+  // terminals. Double rAF ensures xterm's renderer has recomputed cell metrics
+  // before we refit.
+  useEffect(() => {
+    zoomLevelRef.current = zoomLevel
+    const term = termRef.current
+    if (!term) return
+    term.options.fontSize = computeTerminalFontSize(zoomLevel)
+    requestAnimationFrame(() => {
+      requestAnimationFrame(() => {
+        const el = containerRef.current
+        if (el && el.clientWidth > 0 && el.clientHeight > 0) {
+          fitAddonRef.current?.fit()
+        }
+      })
+    })
+  }, [zoomLevel])
+
   return (
     <div
       className="absolute inset-0 h-full w-full p-2"