improved roots parity, architecture enforcement coverage, and stdio timeout shutdown handling

Author: rianna-parla

.gitignore

@@ -107,4 +107,7 @@ build-issues.md
 
 # Local CI artifacts
 .ci/
-.ci/*.tar
+.ci/*.tar
+
+# Local planning artifacts (gitignored by request)
+planning/

CMakeLists.txt

@@ -51,6 +51,7 @@ add_library(mcp_cpp STATIC
     src/mcp/Server.cpp
     src/mcp/auth/OAuthClient.cpp
     src/mcp/auth/OAuth2ClientCredentialsAuth.cpp
+    src/mcp/auth/OAuthDiscovery.cpp
     src/mcp/auth/WwwAuthenticate.cpp
     src/mcp/auth/ServerAuth.cpp
     src/mcp/JsonRpcMessageRouter.cpp