Release the gate change as 0.3.0, and start a changelog

release-tooling/contract-version.test.ts

@@ -12,7 +12,7 @@ test("readHostApiVersion pulls the constant out of the real source, and returns
 test("bumping HOST_API_VERSION is a deliberate act, so pin the shipped value", () => {
   // Not a substitute for the release gate — this test cannot see a tag. It is the tripwire that
   // makes an accidental edit fail here rather than at release time.
-  assert.equal(readHostApiVersion(readFileSync("src/plugin-host/plugin.ts", "utf8")), "0.4.0");
+  assert.equal(readHostApiVersion(readFileSync("src/plugin-host/plugin.ts", "utf8")), "0.3.0");
 });
 
 test("every author-facing apiVersion sample matches the shipped contract", () => {

release-tooling/dockerhub-overview.md.tmpl

@@ -182,7 +182,7 @@ into the app. Create `plugins/hello/plugin.ts`:
 import { definePlugin } from "@plainpages/plugin-api";
 
 export default definePlugin({
-  apiVersion: "0.4.0",
+  apiVersion: "0.3.0",
   nav: [{ href: "/hello", id: "hello", label: "Hello", public: true }],
   routes: [
     { method: "GET", path: "/", public: true, handler: () => ({ html: "<h1>Hello from my plugin</h1>" }) },