When the PlayEveryWare EOS Unity plugin is present, the SDK now:
- Calls Identify() with the logged-in EpicAccountId automatically at Init
- Sets distribution_platform = "epic" in game_launch properties when
  the game was launched from the Epic Games Store

Detection uses C# reflection so there is no hard compile-time dependency;
games without EOS are completely unaffected. Both EOS Unity plugin install
methods are supported:
  - UPM package (com.playeveryware.eos / com.Epic.OnlineServices assembly)
  - Legacy DLL install (EOSSDK / PlayEveryWare.EpicOnlineServices assembly)

EGS detection is based on launcher-injected CLI args (-EpicPortal,
-epicapp=, -epicenv=), not EOS initialisation, so Steam-only games that
use EOS for cross-play are not misattributed.

link.xml: type-level preserve="all" entries for AuthInterface and
EpicAccountId prevent IL2CPP High stripping from removing the method
metadata that reflection depends on. Assembly-level preserve="all" only
protects type declarations, not method bodies or their metadata.
examples/audience/Assets/link.xml mirrors the same rules because Unity's
linker skips package link.xml when the package is a file: path (dev mode).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>