feat(markdown): show the GitHub mark for github.com links

[juliusmarminge]

Every external link in assistant markdown gets the same generic ◉ ring, so a paragraph full of PR references reads as noise. GitHub links are by far the most common kind an agent emits, and the ring gives no hint which of them are GitHub.

Links whose host is github.com or gist.github.com (subdomains included) now show the GitHub mark instead. The mark follows the link color, so it stays correct across themes and in both light and dark mode. Other hosts keep the ring.

• web / desktop: ChatMarkdown swaps the ring for the existing GitHubIcon, currentColor.
• mobile, iOS native: a t3-link: attachment carries a tint flag through the shadow node, and the Obj-C side tints the PNG with the run's foreground color. The attachment string keeps NSForegroundColorAttributeName, so the async icon-load re-apply tints with the link color instead of falling back to labelColor.
• mobile, Android / JS fallback: an <Image tintColor> inline with the link text.
• Detection lives in markdownLinks.ts and is unit-tested (www.github.com, gist.github.com, github.com.evil.com rejected, non-http schemes ignored).

Before / after

Same seeded thread, iPhone 17 Pro sim, iOS 26.5. Left is main, right is this branch.

Light

Dark

Verification

• apps/mobile/src/lib/markdownLinks.test.ts (49 tests), mobile tsc, web tsgo, lint, format.
• iOS: Debug build on the simulator, both appearances; the dark capture is from the rebuilt binary with the re-tint fix.
• Not exercised on-device: Android emulator and the web swap. Both are plain JS and typecheck.

Model: Claude Fable 5. Harness: Claude Code in T3 Code.

Note

Render GitHub mark for github.com links in markdown

• Adds a host resolver matching github.com and subdomains to return a bundled GitHub icon for markdown links on mobile and web
• iOS passes the icon through a native attachment pipeline that tints the loaded image with the surrounding text color; Android renders it directly as a tinted image
• Web renders a theme-following GitHub SVG component instead of requesting a favicon for GitHub links
• Other external hosts retain the existing favicon request and globe fallback
• Behavioral Change: web MarkdownLinkFavicon skips favicon fetching for GitHub hosts; iOS T3MarkdownTextAttachmentRange gains a tint flag consumed by T3MarkdownTextApplyAttachments

^{Macroscope summarized a37d1c1.}

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[macroscopeapp]

Approvability

Verdict: Approved at a37d1c1

Macroscope's review found this PR approvable — This is a localized Markdown UI enhancement: GitHub links use a bundled, theme-tinted mark and no longer fetch a favicon, while other links retain their existing behavior. The native attachment changes and tests stay within the existing Markdown rendering path, with no schema, deployment, security, or static-analysis impact.

Notes:

• No code objects were reviewed. Approvability was decided on eligibility alone.

^{You can add or adjust custom eligibility rules. Learn more.}

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.5 KiB	13.6 KiB	+41 B (+0.3%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.0 KiB	7.0 KiB	−2 B (−0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.6 KiB	+43 B (+0.6%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	57.1 KiB	+88 B (+0.2%)	66.4 KiB	✅
Codex	Live turn messages	8	10	+2 (+25.0%)	21	✅
Claude	Total thread wire	13.6 KiB	13.5 KiB	−70 B (−0.5%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.0 KiB	7.0 KiB	−9 B (−0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.6 KiB	6.5 KiB	−61 B (−0.9%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.9 KiB	57.8 KiB	−88 B (−0.1%)	66.4 KiB	✅
Claude	Live turn messages	10	8	−2 (−20.0%)	21	✅

Baseline: a495385 · PR result: a37d1c1 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 113.8 KiB
• Claude decoded thread snapshot: 114.5 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

Dismissing prior approval to re-evaluate a37d1c1