Telegram.ttf is now built by Tools/IconFont from SVG sources and a manifest, instead of by icomoon.io from Telegram.json. The website is no longer in the loop and the repository holds every outline the font is made of.

663 manifest entries, 638 glyphs, 166 KB - down from 667 glyphs and 184 KB, because 29 codepoints that carried the same drawing now share one glyph.

An alias means one drawing serves several codepoints, so adopting a glyph moves all of them - and the one you are adopting may be the unreferenced half of the pair. compose_20_regular at U+E994 is used nowhere, but Icons.Compose at U+E932 aliases it and moved with it.

Two thirds of the font now follows upstream, so it stops going stale on its own.

Microsoft's icons come from npm rather than the GitHub repository on purpose. The repository has over a hundred thousand entries so the git tree API truncates, and an icon's folder name cannot be derived from its own name. The npm package is one request, is versioned, and lays every icon out flat.

iconfont verify compares two fonts by what each codepoint paints - rasterised coverage, not outline points, because contour order and winding direction are free choices that nonzero filling cannot see. iconfont changes --reference <ttf> renders the same comparison as a page, each changed glyph drawn before and after.

Against the IcoMoon font: 530 of 666 codepoints render identically. The 136 that differ are almost all deliberate - icons re-pointed at the live source, taking upstream's current drawing in place of a copy frozen years ago:

Nothing below 0.2% is counted at all; that is smaller than the cubic-to-quadratic conversion moves an edge, and every glyph went through it.

• Metrics. 1024 units per em, ascender 960, descender 64. Every glyph in the app is positioned against them.
• Codepoints are append-only. Besides Icons.cs, the app names codepoints directly in ~760  literals across 211 XAML files, and App.xaml points both TelegramThemeFontFamily and SymbolThemeFontFamily at this font. A reshuffled codepoint changes icons all over the app; a missing one renders as nothing rather than falling back to a system icon font.
• The left side bearing is the real xMin. IcoMoon wrote 0 for all 663 glyphs. fontTools translates every outline so xMin equals the lsb it is given, so passing that through shoves the whole font against the left edge of the em.

• SharedLinkCell.xaml.cs:250 draws "" for the Instant View bolt, but that glyph is at U+E60E - the two places that render it correctly (TLNavigationService.cs:164, WebPageContent.xaml.cs:670) use E60E. IcoMoon had named the glyph uniE611 while assigning it E60E, and someone read the name. It has always rendered blank. One-character fix, not made here.
• Seven more codepoints are referenced with no glyph behind them, all leftovers from before SymbolThemeFontFamily was overridden: U+E052, U+E1CD (Icons.Loading), U+E73C, U+E8B1 (shuffle), U+EE35, U+F13D and U+F13E (the poll ticks). iconfont missing --reference <segoe.ttf> --suggest shows what each used to draw and offers replacements from the MIT package.
• 46 glyphs are referenced nowhere in the app; 27 of those are local artwork.
• 101 local glyphs carry a Fluent name whose upstream drawing has since changed, 34 of them visibly. iconfont drift puts each next to today's upstream version.

• 8 glyphs were never identified and none is referenced by the app: uniE600, uniE602, uniE60B, uniE60C, uniE90A, uE6000 (outside the private use area), plus uniE601 and uniE603, which are the seen and empty message-state badges and keep their IcoMoon names on purpose - identified.txt marks those legacy rather than tbd. Four of the rest are the same 36x20 message-state family and probably belong with them.
• 46 glyphs are referenced nowhere in the app; 27 of those are local artwork rather than a live source, so they are the ones that cost anything to keep.
• 30 local glyphs still carry a Fluent name whose upstream drawing has changed. iconfont drift puts each next to today's version; iconfont adopt --only <name> takes one.
• Generating Icons.cs from the manifest, so a codepoint cannot drift between the font and the constants.

Everything is py -m iconfont <command> from Tools/IconFont, and adopt, identify, import, rename, tidy and update are dry runs until given --apply. README.md there is the reference; identified.txt records the by-hand identification of the glyphs IcoMoon left nameless, and re-running rename over it is a no-op.