fix: keep the interface visible while fonts load

Render fallback fonts immediately and preload regular Maple in the background. Cache public fonts after use without eagerly downloading every font during PWA installation.

scripts/prepare-maple-font.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 """Rebuild local fonts from the specified v7.9 ZIP: python3 scripts/prepare-maple-font.py /path/to/MapleMonoNormalNL-NF-CN.zip.
+Use --css-only to regenerate declarations from checked-in chunks.
 Only font regeneration requires fonttools[woff]; application builds use the checked-in WOFF2 files.
 Source: https://github.com/subframe7536/maple-font/releases/tag/v7.9
 """
@@ -8,31 +9,37 @@ from pathlib import Path
 import sys
 import zipfile
 
-from fontTools import subset
-from fontTools.ttLib import TTFont
-
 root = Path(__file__).resolve().parents[1] / 'web/src/common/appearance'
 output = root / 'fonts/maple'
 output.mkdir(exist_ok=True)
 family = 'Maple Mono Normal NL NF CN'
+if sys.argv[1:] != ['--css-only']:
+    from fontTools import subset
+    from fontTools.ttLib import TTFont
+    with zipfile.ZipFile(sys.argv[1]) as archive:
+        (output / 'LICENSE.txt').write_bytes(archive.read('LICENSE.txt'))
+        for variant, weight, style in [('Regular', 400, 'normal'), ('Bold', 700, 'normal'), ('Italic', 400, 'italic'), ('BoldItalic', 700, 'italic')]:
+            data = archive.read('MapleMonoNormalNL-NF-CN-' + variant + '.ttf')
+            source = TTFont(io.BytesIO(data))
+            points = sorted(source.getBestCmap())
+            # Split by Unicode range so Chinese and Nerd Font glyphs need not download alongside Latin text.
+            for block in sorted({cp // 4096 for cp in points}):
+                unicodes = [cp for cp in points if cp // 4096 == block]
+                font = TTFont(io.BytesIO(data), recalcTimestamp=False)
+                options = subset.Options()
+                options.flavor = 'woff2'
+                subsetter = subset.Subsetter(options=options)
+                subsetter.populate(unicodes=unicodes)
+                subsetter.subset(font)
+                font.flavor = 'woff2'
+                name = f'{variant.lower()}-{block:02x}.woff2'
+                font.save(output / name)
 css = ['/* Maple Mono v7.9; generated by scripts/prepare-maple-font.py. See fonts/maple/LICENSE.txt for licensing. */']
-with zipfile.ZipFile(sys.argv[1]) as archive:
-    (output / 'LICENSE.txt').write_bytes(archive.read('LICENSE.txt'))
-    for variant, weight, style in [('Regular', 400, 'normal'), ('Bold', 700, 'normal'), ('Italic', 400, 'italic'), ('BoldItalic', 700, 'italic')]:
-        data = archive.read('MapleMonoNormalNL-NF-CN-' + variant + '.ttf')
-        source = TTFont(io.BytesIO(data))
-        points = sorted(source.getBestCmap())
-        # Split by Unicode range so Chinese and Nerd Font glyphs need not download alongside Latin text.
-        for block in sorted({cp // 4096 for cp in points}):
-            unicodes = [cp for cp in points if cp // 4096 == block]
-            font = TTFont(io.BytesIO(data), recalcTimestamp=False)
-            options = subset.Options()
-            options.flavor = 'woff2'
-            subsetter = subset.Subsetter(options=options)
-            subsetter.populate(unicodes=unicodes)
-            subsetter.subset(font)
-            font.flavor = 'woff2'
-            name = f'{variant.lower()}-{block:02x}.woff2'
-            font.save(output / name)
-            css.append(f"@font-face {{ font-family: '{family}'; font-style: {style}; font-weight: {weight}; font-display: block; src: url('./fonts/maple/{name}') format('woff2'); unicode-range: U+{block * 4096:X}-{(block + 1) * 4096 - 1:X}; }}")
+for variant, weight, style in [('regular', 400, 'normal'), ('bold', 700, 'normal'), ('italic', 400, 'italic'), ('bolditalic', 700, 'italic')]:
+    files = sorted(output.glob(f'{variant}-*.woff2'))
+    if not files:
+        raise ValueError(f'Missing checked-in font chunks: {variant}')
+    for file in files:
+        block = int(file.stem.split('-')[1], 16)
+        css.append(f"@font-face {{ font-family: '{family}'; font-style: {style}; font-weight: {weight}; font-display: swap; src: url('./fonts/maple/{file.name}') format('woff2'); unicode-range: U+{block * 4096:X}-{(block + 1) * 4096 - 1:X}; }}")
 (root / 'maple-font.css').write_text('\n'.join(css) + '\n')