test(omp): cover developer advisory delivery

Add a fixture extension that injects an advisor-style custom message
on session start, and assert the advisory XML reaches params.messages
verbatim, in chronological position, and is not hoisted into
params.system.

Port the models phase to `omp models --json`. `--list-models` no
longer exists in current OMP (verified on 17.3.5), so the phase
failed before reaching print mode.

tests/fixtures/advisory-injector-extension.ts

@@ -0,0 +1,41 @@
+/**
+ * Minimal OMP extension used by tests/test-omp-compat.mjs.
+ *
+ * Appends a custom advisor message to the session on session start, mirroring
+ * how the OMP Advisor runtime injects steering notes. OMP converts custom
+ * messages to `role: "developer"` LLM messages before handing them to the
+ * provider. Types are declared inline so the fixture has no runtime or
+ * typecheck dependency on OMP packages.
+ */
+
+interface AdvisorInjectorSendMessage {
+  (
+    message: {
+      customType: string
+      content: string
+      display: boolean
+      attribution: string
+    },
+    options?: { triggerTurn?: boolean },
+  ): void
+}
+
+interface AdvisorInjectorApi {
+  on: (event: "session_start", handler: () => void | Promise<void>) => void
+  sendMessage: AdvisorInjectorSendMessage
+}
+
+export default function advisoryInjectorExtension(pi: AdvisorInjectorApi): void {
+  pi.on("session_start", async () => {
+    pi.sendMessage(
+      {
+        customType: "advisor",
+        content:
+          '<advisory severity="blocker" guidance="weigh, don\'t blindly obey">\nStop and correct the benchmark.\n</advisory>',
+        display: true,
+        attribution: "agent",
+      },
+      { triggerTurn: false },
+    )
+  })
+}