Implement fit-mode rendering contract with container sizing and pane re-fit

src/app/infrastructure/settings-store.test.ts

@@ -1,5 +1,5 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
-import { loadUiTheme, saveUiTheme } from './settings-store';
+import { loadPreviewFitMode, loadUiTheme, savePreviewFitMode, saveUiTheme } from './settings-store';
 
 const KEY = 'astrolabe:settings';
 
@@ -84,3 +84,29 @@ describe('settings-store · ui.theme', () => {
     });
   });
 });
+
+describe('settings-store · preview.fitMode', () => {
+  beforeEach(() => vi.stubGlobal('localStorage', makeStorageStub()));
+  afterEach(() => vi.unstubAllGlobals());
+
+  it('defaults to Original (default) when nothing is stored', () => {
+    expect(loadPreviewFitMode()).toBe('default');
+  });
+
+  it('returns a stored valid fit mode', () => {
+    localStorage.setItem(KEY, JSON.stringify({ preview: { fitMode: 'full' } }));
+    expect(loadPreviewFitMode()).toBe('full');
+  });
+
+  it('falls back to default for an unrecognized value', () => {
+    localStorage.setItem(KEY, JSON.stringify({ preview: { fitMode: 'cover' } }));
+    expect(loadPreviewFitMode()).toBe('default');
+  });
+
+  it('round-trips through load and preserves the theme slice', () => {
+    saveUiTheme('dark');
+    savePreviewFitMode('height');
+    expect(loadPreviewFitMode()).toBe('height');
+    expect(loadUiTheme()).toBe('dark'); // the other slice survives the merge
+  });
+});

src/app/infrastructure/settings-store.ts

@@ -13,6 +13,7 @@
  * `localStorage`; everything else goes through these typed functions.
  */
 
+import type { FitMode } from '@core/rendering';
 import type { UiTheme } from '@core/theme';
 
 const KEY = 'astrolabe:settings';
@@ -20,9 +21,13 @@ const KEY = 'astrolabe:settings';
 /** Spec §07 Appearance default. */
 const DEFAULT_THEME: UiTheme = 'light';
 
+/** Spec §04 — the Fit control defaults to Original. */
+const DEFAULT_FIT_MODE: FitMode = 'default';
+
 /** Loose view of the stored record — M5 will give this its full typed shape. */
 interface StoredSettings {
   ui?: { theme?: unknown; [k: string]: unknown };
+  preview?: { fitMode?: unknown; [k: string]: unknown };
   [k: string]: unknown;
 }
 
@@ -61,6 +66,10 @@ function isUiTheme(v: unknown): v is UiTheme {
   return v === 'light' || v === 'dark';
 }
 
+function isFitMode(v: unknown): v is FitMode {
+  return v === 'default' || v === 'width' || v === 'height' || v === 'full';
+}
+
 /** The persisted UI theme, or the default — unknown/legacy values fall back. */
 export function loadUiTheme(): UiTheme {
   const stored = readRaw().ui?.theme;
@@ -74,3 +83,15 @@ export function saveUiTheme(theme: UiTheme): void {
   const current = readRaw();
   writeRaw({ ...current, ui: { ...current.ui, theme } });
 }
+
+/** The persisted preview fit mode, or the default — unknown values fall back. */
+export function loadPreviewFitMode(): FitMode {
+  const stored = readRaw().preview?.fitMode;
+  return isFitMode(stored) ? stored : DEFAULT_FIT_MODE;
+}
+
+/** Persist the preview fit mode, preserving every other key already in the record. */
+export function savePreviewFitMode(fitMode: FitMode): void {
+  const current = readRaw();
+  writeRaw({ ...current, preview: { ...current.preview, fitMode } });
+}