The cross-version matrix (#782) used a 55-char 'otua_matrix_' key, which stayed under
SDK 2's 64-byte RsaEncryptedSecret threshold and hid #880. It now uses the
ApiKeySecret.Generate shape (65 chars, random per run, never recorded). Every Shared
leg adds production-length-API-key-wrong-secret-reaches-key-check, which must get
BadIdentityTokenRejected rather than a format failure. SDK 2 clients also add
sdk2-default-RsaEncryptedSecret-control, the negative control: the SDK's default
handler must be refused with BadIdentityTokenInvalid by a 1.x server and admitted
by an SDK 2 server. The runner passes the server SDK version from ready.json.
Claude-Session: https://claude.ai/code/session_01GT67ACmpMR7b9LGRPLijMi
Probe 'prepare' provisions the consumer identity via OpcUaApplicationIdentity.EnsureApplicationCertificateAsync
and exports the public DER; runner installs it in the server trusted store before start. Adds Sign
(OPCUA_MATRIX_SERVER_SECURITY=sign), untrusted-client / untrusted-server fail-closed controls per secure
mode, and OPCUA_MATRIX_ACL=off. Autoaccept stays false everywhere.
Joseph Doherty