Refuse a shadowing barrel copy, and record the packaging contract

src/plugin-host/discovery.test.ts

@@ -57,6 +57,7 @@ const badCases: Array<{ name: string; files: Record<string, string>; match: RegE
   { name: "a route gating on a bare word", files: { "bare/plugin.ts": `export default { apiVersion: "1.0.0", routes: [{ method: "GET", path: "/", permission: "admin", handler: () => ({ html: "x" }) }] };` }, match: /bare.*admin.*<resource>:<action>/s },
   { name: "a nav node gating on a bare word", files: { "barenav/plugin.ts": `export default { apiVersion: "1.0.0", nav: [{ id: "n", label: "N", permission: "admin" }] };` }, match: /barenav.*admin.*<resource>:<action>/s },
   { name: "a declared permission that is a bare word", files: { "baredecl/plugin.ts": `export default { apiVersion: "1.0.0", permissions: [{ name: "admin" }] };` }, match: /baredecl.*admin.*<resource>:<action>/s },
+  { name: "a plugin shipping its own copy of the barrel", files: { "shadow/node_modules/@plainpages/plugin-api/index.js": `export class GuardError extends Error {}`, "shadow/plugin.ts": full("shadow") }, match: /shadow.*@plainpages\/plugin-api/s },
   { name: "a plugin package.json that forgets type: module", files: { "cjs/package.json": `{ "name": "cjs" }`, "cjs/plugin.ts": full("cjs") }, match: /cjs.*"type": "module"/s },
   { name: "a plugin package.json that is not valid JSON", files: { "bent/package.json": `{`, "bent/plugin.ts": full("bent") }, match: /bent.*package\.json.*JSON/s },
   { name: "two plugins claim the public home", files: { "a/plugin.ts": `export default { apiVersion: "1.0.0", home: () => ({ html: "a" }) };`, "b/plugin.ts": `export default { apiVersion: "1.0.0", home: () => ({ html: "b" }) };` }, match: /home/ },