Web favicon follows the color scheme
网页图标随配色方案切换
`apps/web/public/favicon.svg` paints the DeepSeek mark solid black (`fill="#000"`), and `index.html` declares only that single SVG icon. Under an OS or browser dark color scheme the tab strip is dark too, so the black mark is effectively invisible. Safari versions before 26 do not render SVG favicons, so their users get no tab icon in any scheme.
English
Problem
apps/web/public/favicon.svg paints the DeepSeek mark solid black (fill="#000"), and index.html declares only that single SVG icon. Under an OS or browser dark color scheme the tab strip is dark too, so the black mark is effectively invisible. Safari versions before 26 do not render SVG favicons, so their users get no tab icon in any scheme.
Decision
The favicon stays one file and adapts through the browser's own color-scheme signal: favicon.svg embeds @media (prefers-color-scheme: dark) { path { fill: #fff } }, switching the mark to white under a dark scheme while the light scheme keeps black. index.html and manifest.webmanifest also declare a 32×32 PNG fallback (favicon-32x32.png, DeepSeek brand blue #4D6BFE) that Safari versions before 26 render and that stays visible on both light and dark tab strips, extending the web-install-manifest decision.
The theme signal is the OS/browser scheme, not the GUI's in-app dsh.theme toggle: the favicon lives in browser chrome, whose background follows the browser scheme, so prefers-color-scheme is the correct semantic and needs no JavaScript. Known browser quirks — Chromium may not repaint the tab icon until reload after a scheme switch, and Safari versions before 26 ignore the SVG variant — are accepted and the PNG fallback covers the older-Safari case.
Alternatives considered
- A second
<link rel="icon" media="(prefers-color-scheme: dark)">pointing at a separate dark SVG. Rejected: the same scheme semantics with two files to keep in sync, and no benefit over the in-file media query. - A theme-presenter that swaps the icon href on
theme/change. Rejected: it would follow the in-app toggle rather than the browser scheme that actually colors the tab strip, and it adds client code and a presenter for a chrome asset. - No PNG fallback. Rejected: Safari versions before 26 never render SVG favicons, so the fallback is the only way those versions get a tab icon at all.
Consequences
Light scheme still shows the black mark, dark scheme shows white, and Safari versions before 26 show the blue PNG in both. apps/web/tests/pwa-manifest.e2e.ts pins the PNG link and its order before the SVG, both manifest icons, the shipped PNG's format and dimensions, and the dark media query inside the shipped SVG. The Chromium repaint quirk remains a browser behavior the app cannot fix.
中文
问题
apps/web/public/favicon.svg 把 DeepSeek 图标绘制为纯黑色（fill="#000"），而 index.html 只声明了这一个 SVG 图标。当操作系统或浏览器处于暗色配色方案时，标签栏同样是深色，黑色图标实际上不可见。Safari 26 之前的版本不渲染 SVG favicon，因此这些版本的 Safari 用户无论何种配色方案都看不到标签页图标。
决策
favicon 保持单一文件，并通过浏览器自身的配色方案信号自适应：favicon.svg 内嵌 @media (prefers-color-scheme: dark) { path { fill: #fff } }，在暗色方案下把图标切换为白色，浅色方案保持黑色。index.html 与 manifest.webmanifest 同时声明 32×32 PNG 兜底（favicon-32x32.png，DeepSeek 品牌蓝 #4D6BFE），Safari 26 之前的版本会渲染该 PNG，且它在浅色与深色标签栏上都清晰可见；这是对 Web 安装 manifest 决策 的扩展。
主题信号取操作系统/浏览器方案，而不是 GUI 应用内 dsh.theme 开关：favicon 位于浏览器 chrome 中，其背景跟随浏览器方案，因此 prefers-color-scheme 是正确语义，无需任何 JavaScript。已知的浏览器怪癖——Chromium 在切换方案后可能要到刷新页面才重绘标签图标，Safari 26 之前的版本忽略 SVG 变体——均被接受，旧版 Safari 场景由 PNG 兜底覆盖。
曾考虑的替代方案
- 新增指向独立暗色 SVG 的第二个
<link rel="icon" media="(prefers-color-scheme: dark)">。 不予采纳：语义相同却要多维护一个文件，相比文件内媒体查询没有任何收益。 - 由主题 presenter 在
theme/change时替换图标 href。 不予采纳：它会跟随应用内开关，而不是真正决定标签栏颜色的浏览器方案，并且为一个 chrome 资源引入客户端代码和 presenter。 - 不提供 PNG 兜底。 不予采纳：Safari 26 之前的版本从不渲染 SVG favicon，兜底是这些版本获得标签图标的唯一途径。
后果
浅色方案仍显示黑色图标，暗色方案显示白色，Safari 26 之前的版本两种方案都显示蓝色 PNG。apps/web/tests/pwa-manifest.e2e.ts 固定断言 PNG 链接及其位于 SVG 之前的顺序、manifest 中的两个图标、交付 PNG 的格式与尺寸，以及交付 SVG 内部的暗色媒体查询。Chromium 的重绘怪癖仍是浏览器行为，应用无法修复。