test: pin the opencode v2 plugin module shape

CONTRIBUTING.md requires tests for behavior changes; the v2 port
(0.2.0) changed the module surface to a default export. Assert the
default export carries an id and the server plugin function, and that
the plugin exposes the meta auth hook, so a regression back to the v1
named-export shape fails in CI instead of as a startup WARN in
opencode.

Author: TheStreamCode

tests/plugin.test.ts

@@ -0,0 +1,29 @@
+// The opencode v2 plugin contract: opencode loads plugins ONLY from the
+// module's default export, which must carry an `id` and the `server` plugin
+// function (opencode 1.18.29+ accepts the same shape). A regression back to
+// the v1 named-export shape fails at every opencode startup with
+// PluginModule.LoadError — only visible as a WARN in the log — so pin the
+// exported shape here.
+import { test } from "node:test"
+import assert from "node:assert/strict"
+
+import plugin from "../dist/index.js"
+
+test("default export satisfies the opencode v2 PluginModule shape", () => {
+  assert.equal(typeof plugin, "object")
+  assert.ok(plugin && !Array.isArray(plugin))
+  assert.equal(typeof plugin.id, "string")
+  assert.ok(plugin.id.length > 0)
+  assert.equal(typeof plugin.server, "function")
+})
+
+test("server plugin returns the auth hook for provider meta", async () => {
+  const hooks = await plugin.server()
+  assert.ok(hooks.auth)
+  assert.equal(hooks.auth.provider, "meta")
+  assert.equal(typeof hooks.auth.loader, "function")
+  assert.ok(Array.isArray(hooks.auth.methods))
+  assert.equal(hooks.auth.methods.length, 1)
+  assert.equal(hooks.auth.methods[0].type, "oauth")
+  assert.equal(typeof hooks.auth.methods[0].authorize, "function")
+})