feat(editor): editor pane font size follows terminal font size setting

docs/plans/2026-07-08-editor-font-follows-setting-spec.md

@@ -0,0 +1,230 @@
+# Spec: Editor pane font size follows the terminal Font size setting
+
+- **Date**: 2026-07-08
+- **Branch**: `feat/editor-font-setting` (worktree `.worktrees/editor-font`, based on `origin/main` @ `b5daeea4`)
+- **Status**: Ready for implementation (Red-Green-Refactor TDD)
+- **Scope guard**: consume `settings.terminal.fontSize` in the editor pane only. Do NOT add a
+  separate editor font setting. Do NOT touch font family, line height, minimap, or any other
+  Monaco option. No server, schema, or settings-UI changes.
+
+## 1. Problem
+
+The Monaco-based editor pane hard-codes its font size:
+
+- `src/components/panes/EditorPane.tsx:1033` — `fontSize: 14,` inside the inline `options`
+  literal passed to `<Editor>` (`src/components/panes/EditorPane.tsx:1024-1041`).
+
+Every other text surface follows the local terminal Font size setting
+(`settings.terminal.fontSize`, clamped 12–64, default 16):
+
+- xterm initial: `src/components/TerminalView.tsx:1727` (`fontSize: settings.terminal.fontSize`)
+- xterm live: `src/components/TerminalView.tsx:2638` (`term.options.fontSize = settings.terminal.fontSize`)
+- fresh-agent transcript: `src/components/fresh-agent/FreshAgentView.tsx:512-514` (selector) feeding
+  an inline CSS var
+- UI chrome: `src/hooks/useTheme.ts:8-12` — `--ui-scale = (terminalFontSize / 16) * uiScale`
+
+Monaco sizes in raw px and does not inherit the rem-based `--ui-scale`, so the editor is the one
+pane that ignores the setting entirely (this is the gap left by PR #511 / #509).
+
+## 2. Verified facts (worktree @ b5daeea4)
+
+| Fact | Evidence |
+|---|---|
+| Hard-coded editor font | `src/components/panes/EditorPane.tsx:1033` |
+| Options passed as **inline literal**, new identity every render | `src/components/panes/EditorPane.tsx:1031-1040` |
+| Editor instance held in ref via `onMount` | `editorRef` at `src/components/panes/EditorPane.tsx:175`; `handleEditorMount` at `:294-297`; `onMount={handleEditorMount}` at `:1029` |
+| EditorPane already subscribes to settings | `useMonacoTheme` at `src/components/panes/EditorPane.tsx:21-26` uses `useAppSelector((s) => s.settings.settings.theme)` |
+| `@monaco-editor/react` `^4.6.0` applies `options` changes live | `package.json`; installed dist (`node_modules/@monaco-editor/react/dist/index.mjs`) contains a post-ready update effect equivalent to `useUpdate(() => editor.updateOptions(options), [options], isEditorReady)`, and the mount path spreads options into `editor.create(..., { model, automaticLayout: true, ...options })` |
+| Precedent selector shape (exact) | `src/components/fresh-agent/FreshAgentView.tsx:512-514`: `useAppSelector((state) => state.settings.settings.terminal?.fontSize) ?? 16` — plain primitive selector, **no** memoization/`shallowEqual` (correct for a primitive) |
+| Clamp/normalize is shared and local-only | `shared/settings.ts:44-45` (`TERMINAL_FONT_SIZE_MIN = 12`, `TERMINAL_FONT_SIZE_MAX = 64`, module-private), `:504-511` (`normalizeRoundedClampedNumber`), `:854` (default `fontSize: 16`); local-only persistence at `src/store/browserPreferencesPersistence.ts:94` |
+| Store action the slider dispatches | `src/components/settings/AppearanceSettings.tsx:360-369` → `applyLocalSetting({ terminal: { fontSize: v } })` → `updateSettingsLocal` (`src/store/settingsSlice.ts:117-122`), which re-normalizes through the shared clamp path — dispatching an out-of-range value lands clamped in `state.settings.settings.terminal.fontSize` |
+| Default slice state already resolves to 16 | `src/store/settingsSlice.ts:85-90` (`initialState.settings = resolveSettings(defaults, ...)`) |
+| No test pins the editor's 14 | `grep 'fontSize:\s*14'` hits: `EditorPane.tsx:1033` (the source), plus terminal-settings *fixtures* in `test/unit/client/components/panes/PaneContainer.test.tsx:1687,2109`, `test/unit/client/components/panes/PanePicker.test.tsx:86`, `test/e2e/directory-picker-flow.test.tsx:144,237` — all preloaded `settings.terminal` state, none assert Monaco options. No change needed to any of them. |
+| Existing Monaco mocks ignore `options` | e.g. `test/unit/client/components/panes/EditorPane.test.tsx:23-36` and `EditorPane.connectivity.test.tsx:23-28` render a `<textarea data-testid="monaco-mock">` exposing only `value`/`onChange`/`theme`. Each test file declares its own mock, so a new options-aware mock in a new file collides with nothing. |
+| Docs mock irrelevant | `docs/index.html` contains no Monaco/editor-pane rendering (only the pane-picker "Editor" label at `:708` and the *external* editor settings section at `:1043-1048`). Per `AGENTS.md:26` only major UI changes need the mock updated — this is not one. No change. |
+
+## 3. Design
+
+### 3.1 Mapping: direct (`editor fontSize = settings.terminal.fontSize`)
+
+Chosen: **direct 1:1**, no scaling factor.
+
+- Consistency: xterm uses the value directly (`TerminalView.tsx:1727`), and `--ui-scale`
+  already equates UI text with terminal text at 100% scale (`useTheme.ts:10-12`). A scaled
+  mapping (e.g. `× 14/16`) would preserve the old default but create a permanent, inexplicable
+  offset between the editor and every other pane, plus a magic constant to maintain.
+- Monaco derives `lineHeight` from `fontSize` when `lineHeight` is unset (it is unset in
+  `EditorPane.tsx:1031-1040`), so no companion option needs touching. The minimap is disabled
+  (`minimap: { enabled: false }` at `:1032`), so there is no minimap-font interaction.
+- Consequence: the default editor font grows from 14 → 16px. Accepted — it *aligns* the editor
+  with the terminal default rather than changing it arbitrarily.
+
+### 3.2 Wiring: selector into the existing options literal — no effect, no ref plumbing
+
+`@monaco-editor/react` v4 already does the live-update work: its internal effect calls
+`editor.updateOptions(options)` whenever the `options` prop identity changes (verified in the
+installed dist, §2). EditorPane passes an inline literal, so every re-render produces a new
+identity. Therefore the entire implementation is:
+
+1. Subscribe: `useAppSelector` on the fontSize primitive → any settings change re-renders
+   EditorPane.
+2. Feed the value into the existing literal → the wrapper calls `updateOptions` (live, no
+   remount) and spreads it into `editor.create` for editors mounted later.
+
+A `useEffect` + `editorRef.current?.updateOptions(...)` would duplicate what the wrapper
+already does — rejected (abstraction with no justification). No memoized selector: it returns
+a primitive, matching FreshAgentView (`:512-514`) and useTheme (`:8`).
+
+### 3.3 Exact changes — `src/components/panes/EditorPane.tsx` (only file changed in `src/`)
+
+**(a)** Inside the `EditorPane` component body, next to the other selectors/refs (e.g. adjacent
+to `const dispatch = ...` / near `:175`), add:
+
+```tsx
+const editorFontSize = useAppSelector((s) => s.settings.settings.terminal?.fontSize) ?? 16
+```
+
+(`useAppSelector` is already imported at `:4`.)
+
+**(b)** At `:1033`, replace:
+
+```tsx
+              fontSize: 14,
+```
+
+with:
+
+```tsx
+              fontSize: editorFontSize,
+```
+
+All other options at `:1031-1040` stay byte-identical. Nothing else changes: `handleEditorMount`
+(`:294-297`), `editorRef` (`:175`), preview mode, and word wrap are untouched. When a pane is in
+preview mode `<Editor>` is not mounted; toggling back to source mounts it with the then-current
+value via the `editor.create` spread — no special handling needed.
+
+## 4. TDD plan (Red → Green → Refactor)
+
+### 4.1 RED — new test file
+
+**Create** `test/unit/client/components/panes/EditorPane.fontSize.test.tsx`.
+
+Follow the structure of `EditorPane.connectivity.test.tsx` (real reducers, no preloaded state)
+but with an **options-aware** Monaco mock:
+
+```tsx
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
+import { render, screen, act, cleanup } from '@testing-library/react'
+import { Provider } from 'react-redux'
+import { configureStore } from '@reduxjs/toolkit'
+import panesReducer from '@/store/panesSlice'
+import settingsReducer, { updateSettingsLocal } from '@/store/settingsSlice'
+import connectionReducer, { setStatus } from '@/store/connectionSlice'
+
+vi.mock('@monaco-editor/react', () => {
+  const MonacoMock = ({ value, onChange, options }: any) => (
+    <textarea
+      data-testid="monaco-mock"
+      data-font-size={String(options?.fontSize)}
+      data-minimap-enabled={String(options?.minimap?.enabled)}
+      data-tab-size={String(options?.tabSize)}
+      value={value}
+      onChange={(e: any) => onChange?.(e.target.value)}
+    />
+  )
+  return { default: MonacoMock, Editor: MonacoMock }
+})
+
+import EditorPane from '@/components/panes/EditorPane'
+```
+
+Store helper: `configureStore({ reducer: { panes, settings, connection } })` with **no**
+`preloadedState` (slice default resolves `terminal.fontSize` to 16, §2), then
+`store.dispatch(setStatus('ready'))`. Stub `fetch` as in `EditorPane.test.tsx:116-118` (a
+routed no-op resolver) so mount-time API calls don't reject. Render EditorPane with the standard
+props (`paneId="pane-1" tabId="tab-1" filePath="/test.ts" language="typescript"
+readOnly={false} content="const x = 1" viewMode="source"`).
+
+Tests, in order — **all four must fail against current code** (mock reports
+`data-font-size="14"`):
+
+1. **default follows setting (16, not 14)**
+   Render with the default store. Assert
+   `screen.getByTestId('monaco-mock').getAttribute('data-font-size')` is `'16'`.
+2. **non-default value at mount (editor opened after the setting changed)**
+   `store.dispatch(updateSettingsLocal({ terminal: { fontSize: 20 } }))` *before* `render`.
+   Assert `data-font-size === '20'`. (Dispatching through the real reducer exercises the shared
+   normalize path instead of hand-rolling preloaded state.)
+3. **live update without remount (slider drag)**
+   Render with default; capture the mock node. Then
+   `act(() => { store.dispatch(updateSettingsLocal({ terminal: { fontSize: 24 } })) })`.
+   Assert the *same* node (identity-compare with the captured element to prove no remount) now
+   has `data-font-size === '24'`.
+4. **clamped value flows through (selector must not bypass normalization)**
+   `act(() => { store.dispatch(updateSettingsLocal({ terminal: { fontSize: 999 } })) })` after
+   render. Assert `store.getState().settings.settings.terminal.fontSize === 64` and
+   `data-font-size === '64'`. (Min-side, 1 → 12, is already covered by
+   `test/unit/shared/settings.test.ts`; one boundary here is enough to pin the wiring.)
+
+Regression guard inside test 1: also assert `data-minimap-enabled === 'false'` and
+`data-tab-size === '2'` so the builder cannot satisfy the suite by replacing the options object
+wholesale.
+
+**Multi-editor edge (covered by construction, not a test):** each EditorPane instance runs its
+own `useAppSelector`, so N open editors each re-render on one dispatch. Test 3 proves the
+mechanism for one instance; a two-instance test would only re-test React-Redux. Omitted
+deliberately.
+
+Run (client vitest config):
+
+```
+npx vitest run --config config/vitest/vitest.config.ts test/unit/client/components/panes/EditorPane.fontSize.test.tsx
+```
+
+Confirm: 4 failures, each reporting actual `'14'`.
+
+### 4.2 GREEN — implementation
+
+Apply §3.3 (a) and (b) to `src/components/panes/EditorPane.tsx`. Re-run the file above → 4 pass.
+
+### 4.3 REFACTOR / full verification
+
+- No extraction: a one-line primitive selector does not justify a shared hook or constant.
+  (If a reviewer wants the `?? 16` fallback centralized later, that refactor belongs with the
+  three existing duplicates at `FreshAgentView.tsx:514` and `useTheme.ts:8` — out of scope.)
+- Confirm no stragglers: `grep -rn 'fontSize: 14' src/` → zero hits.
+- Existing suites that render EditorPane with Monaco mocked must pass **unchanged** (their mocks
+  ignore `options`; their fixtures already contain `terminal.fontSize`, and the `?.`/`?? 16`
+  fallback covers any store without it):
+  - `test/unit/client/components/panes/EditorPane.test.tsx`
+  - `test/unit/client/components/panes/EditorPane.connectivity.test.tsx`
+  - `test/unit/client/components/panes/EditorPane.autosave.test.tsx`
+  - `test/unit/client/components/panes/EditorPane.openInEditor.test.tsx`
+  - `test/unit/client/components/panes/PaneContainer.test.tsx`, `PaneContainer.createContent.test.tsx`
+  - `test/integration/client/editor-pane.test.tsx`
+  - `test/e2e/terminal-file-link-same-tab.test.tsx`, `test/e2e/terminal-font-settings.test.tsx`
+- Gates: `npm run typecheck:client` and the standard suite (`npm run test:balanced`, or minimally
+  `npm run test:client:standard`).
+
+## 5. Files touched (complete list)
+
+| File | Change |
+|---|---|
+| `src/components/panes/EditorPane.tsx` | Add 1 selector line; replace literal at `:1033` |
+| `test/unit/client/components/panes/EditorPane.fontSize.test.tsx` | New file, 4 tests (§4.1) |
+| `docs/plans/2026-07-08-editor-font-follows-setting-spec.md` | This spec |
+
+Explicitly **not** touched: `shared/settings.ts`, `src/store/*`, `AppearanceSettings.tsx`,
+`docs/index.html`, any e2e-browser spec, font family / line height / minimap options.
+
+## 6. Success criteria
+
+1. Editor pane text renders at `settings.terminal.fontSize` px on mount (default 16).
+2. Dragging the Font size slider updates open editor panes live — no remount, no reload — via
+   the `options` prop → `editor.updateOptions` path.
+3. Editors opened after a change pick up the current value; multiple simultaneous editors all
+   track it.
+4. Out-of-range values can never reach Monaco (store state is clamped 12–64 before the selector
+   reads it; test 4 pins this).
+5. `grep -rn 'fontSize: 14' src/` returns nothing; no new setting, prop, hook, or effect exists.
+6. New test file: 4/4 green; all pre-existing suites green; client typecheck green.

src/components/panes/EditorPane.tsx

@@ -171,6 +171,7 @@ export default function EditorPane({
     (err: unknown) => isTransientRequestFailure(err) || connectionStatusRef.current !== 'ready',
     []
   )
+  const editorFontSize = useAppSelector((s) => s.settings.settings.terminal?.fontSize) ?? 16
   const mountedRef = useRef(true)
   const editorRef = useRef<Monaco.editor.IStandaloneCodeEditor | null>(null)
   const fileInputRef = useRef<HTMLInputElement>(null)
@@ -1030,7 +1031,7 @@ export default function EditorPane({
             onChange={handleEditorChange}
             options={{
               minimap: { enabled: false },
-              fontSize: 14,
+              fontSize: editorFontSize,
               lineNumbers: 'on',
               scrollBeyondLastLine: false,
               automaticLayout: true,

test/unit/client/components/panes/EditorPane.fontSize.test.tsx

@@ -0,0 +1,131 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
+import { render, screen, act, cleanup } from '@testing-library/react'
+import { Provider } from 'react-redux'
+import { configureStore } from '@reduxjs/toolkit'
+import panesReducer from '@/store/panesSlice'
+import settingsReducer, { updateSettingsLocal } from '@/store/settingsSlice'
+import connectionReducer, { setStatus } from '@/store/connectionSlice'
+
+// Options-aware Monaco mock: exposes the options the pane passes so the tests
+// can pin fontSize wiring (plus a couple of neighbors as a regression guard).
+vi.mock('@monaco-editor/react', () => {
+  const MonacoMock = ({ value, onChange, options }: any) => (
+    <textarea
+      data-testid="monaco-mock"
+      data-font-size={String(options?.fontSize)}
+      data-minimap-enabled={String(options?.minimap?.enabled)}
+      data-tab-size={String(options?.tabSize)}
+      value={value}
+      onChange={(e: any) => onChange?.(e.target.value)}
+    />
+  )
+  return { default: MonacoMock, Editor: MonacoMock }
+})
+
+import EditorPane from '@/components/panes/EditorPane'
+
+const mockFetch = vi.fn()
+
+const createMockResponse = (body: object) => ({
+  ok: true,
+  statusText: 'OK',
+  text: () => Promise.resolve(JSON.stringify(body)),
+  json: () => Promise.resolve(body),
+})
+
+// Routed no-op resolver so mount-time API calls don't reject.
+const routedFetch = async (input: any) => {
+  const url = String(input)
+  if (url.startsWith('/api/terminals')) return createMockResponse([])
+  if (url.startsWith('/api/files/complete')) return createMockResponse({ suggestions: [] })
+  if (url.startsWith('/api/files/read')) return createMockResponse({ content: '' })
+  return createMockResponse({})
+}
+
+// No preloadedState: the settings slice default resolves terminal.fontSize to 16.
+const createStore = () => {
+  const store = configureStore({
+    reducer: {
+      panes: panesReducer,
+      settings: settingsReducer,
+      connection: connectionReducer,
+    },
+  })
+  store.dispatch(setStatus('ready'))
+  return store
+}
+
+const renderEditor = (store: ReturnType<typeof createStore>) =>
+  render(
+    <Provider store={store}>
+      <EditorPane
+        paneId="pane-1"
+        tabId="tab-1"
+        filePath="/test.ts"
+        language="typescript"
+        readOnly={false}
+        content="const x = 1"
+        viewMode="source"
+      />
+    </Provider>
+  )
+
+describe('EditorPane font size follows settings.terminal.fontSize', () => {
+  beforeEach(() => {
+    vi.stubGlobal('fetch', mockFetch)
+    mockFetch.mockReset()
+    mockFetch.mockImplementation(routedFetch as any)
+  })
+
+  afterEach(() => {
+    cleanup()
+    vi.unstubAllGlobals()
+  })
+
+  it('defaults to the terminal font size setting (16, not the old hard-coded 14)', () => {
+    const store = createStore()
+    renderEditor(store)
+
+    const mock = screen.getByTestId('monaco-mock')
+    expect(mock.getAttribute('data-font-size')).toBe('16')
+    // Regression guard: the rest of the options literal must be untouched.
+    expect(mock.getAttribute('data-minimap-enabled')).toBe('false')
+    expect(mock.getAttribute('data-tab-size')).toBe('2')
+  })
+
+  it('uses the current setting when the editor mounts after the setting changed', () => {
+    const store = createStore()
+    store.dispatch(updateSettingsLocal({ terminal: { fontSize: 20 } }))
+    renderEditor(store)
+
+    expect(screen.getByTestId('monaco-mock').getAttribute('data-font-size')).toBe('20')
+  })
+
+  it('updates live without remounting when the setting changes (slider drag)', () => {
+    const store = createStore()
+    renderEditor(store)
+
+    const mock = screen.getByTestId('monaco-mock')
+    expect(mock.getAttribute('data-font-size')).toBe('16')
+
+    act(() => {
+      store.dispatch(updateSettingsLocal({ terminal: { fontSize: 24 } }))
+    })
+
+    // Same node identity: the editor was updated, not remounted.
+    expect(screen.getByTestId('monaco-mock')).toBe(mock)
+    expect(mock.getAttribute('data-font-size')).toBe('24')
+  })
+
+  it('receives the clamped value for out-of-range settings (999 -> 64)', () => {
+    const store = createStore()
+    renderEditor(store)
+
+    act(() => {
+      store.dispatch(updateSettingsLocal({ terminal: { fontSize: 999 } }))
+    })
+
+    expect(store.getState().settings.settings.terminal.fontSize).toBe(64)
+    expect(screen.getByTestId('monaco-mock').getAttribute('data-font-size')).toBe('64')
+  })
+})