feat(mobile,web): copied thread links open the mobile app#29815

Stacked on #26290. On a phone, a copied thread link (https://app.t3.codes/threads/<env>/<thread>) opened the browser, which then offered the app. With T3 Code installed, the link now opens the thread in the app directly. Both PRs already change native code, so they can ship in one release.

How it works

• app.t3.codes claims its thread links. apps/web/public/.well-known/ gets apple-app-site-association.json and assetlinks.json, both scoped to /threads/* and listing the production, preview, and dev apps. Apple fetches the file without an extension, so vercel.ts rewrites /.well-known/apple-app-site-association to the .json file, which Vercel serves as application/json. A rewrite is not a redirect, which Apple refuses. On app.t3.codes, requests go through to the latest channel's deployment, which serves both files.
• The apps claim app.t3.codes. iOS adds applinks:app.t3.codes next to the existing Clerk domains. Android adds a verified (autoVerify) intent filter for https://app.t3.codes/threads/.
• The app routes the link. https://app.t3.codes is a linking prefix, so /threads/<env>/<thread> reaches the existing threads/:environmentId/:threadId route that t3code://threads/… already uses, including ?prompt= handling. Other app.t3.codes paths are not claimed and stay in the browser.
• Identifiers. The Apple team ID (ARK85ZXQ4Z) and bundle IDs come from app.config.ts. The Android SHA-256 signing fingerprints are copied from https://clerk.t3.codes/.well-known/assetlinks.json, which already verifies these apps for passkeys. app.config.test.ts checks that every variant's identifiers appear in both files and that its native config claims the hosted app's host.
• Desktop. No change. There is no cross-browser way for a desktop app installed outside a store to claim https links, so the chooser and Remember my choice stay the way there.

Shipping order

• The files must be live on app.t3.codes before the new mobile builds reach users. Android verifies autoVerify filters at install time, and iOS fetches through Apple's CDN, which caches. After the web deploy, check https://app-site-association.cdn-apple.com/a/v1/app.t3.codes and Google's Digital Asset Links API for each package.
• The native config changes, so this needs a store build, as #26290 already does.

Behaviour to know

• With the app installed, a phone skips the chooser. Someone not connected to the thread's machine lands in the app's existing "Thread on another machine" handling instead of the chooser. They can still open the link in the browser (long-press on iOS) to get the chooser.

Testing

• apps/mobile/app.config.test.ts: each variant's bundle ID and package appear in the two files, and its config claims applinks:app.t3.codes and the /threads/ intent filter. Dropping the dev app from the Apple file fails the development row.
• vp run check:changed: format, lint, knip, typecheck (34 packages), tests (22 files), and the React compiler check pass.
• Not run: a native build, a device install, or a deploy. Universal links and app links can only be verified against the deployed files with a signed build.

Claude Opus 5.5 in Claude Code, run from T3 Code.

🤖 Generated with Claude Code