Add the app side of Android App Links (M9 follow-up, docs/android/APP_LINKS.md),
layered on the M9 Part 2 native SSO callback:
- Build-time `appLinkHost` Gradle property -> BuildConfig.APP_LINK_HOST +
manifestPlaceholders["appLinkHost"]. autoVerify needs a literal host, so the
generic multi-tenant build leaves it empty (placeholder falls back to the
reserved runic-gateway.invalid sentinel, making the filter inert); a
white-label build bakes one host with -PappLinkHost=play.myshard.com.
- Manifest: an autoVerify https `/mobile/callback` intent-filter beside the
unchanged custom-scheme one (the permanent fallback).
- SsoAuthManager: request the https App Link redirect_uri iff the baked host
matches the paired shard host; matchesAppLinkCallback() enforces a paired-host
trust check (host must equal the currently-paired base URL host) as
defense-in-depth. Both matchers feed the same complete()/exchange path.
- MainActivity routes custom-scheme and App Link callbacks identically.
+5 JVM tests (SsoAuthManagerTest -> 14). Built green (JDK 21,
-Pksp.incremental=false); white-label host substitution verified in the merged
manifest.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NgyHnrNa8WwG3doxvxjuCr
