feat(plugin): add namespaced hook API (#33416)

packages/core/test/config/fixtures/plugin/directory-plugin.ts

@@ -0,0 +1,13 @@
+import { define } from "@opencode-ai/plugin/v2/promise"
+
+export default define({
+  id: "directory-plugin",
+  setup: async (ctx) => {
+    await ctx.agent.transform((agents) => {
+      agents.update("directory", (agent) => {
+        agent.description = "Loaded from plugin directory"
+        agent.mode = "subagent"
+      })
+    })
+  },
+})