feat: collapse plugin runtime to one tier behind a plugin SDK

src/backend/plugins/paths.ts

@@ -1,26 +1,30 @@
 import fs from "node:fs";
 import path from "node:path";
 import { fileURLToPath } from "node:url";
+import {
+  DEFAULT_BACKEND_ENTRY,
+  type PluginManifest,
+} from "@termix/plugin-sdk/manifest";
 
 /**
- * Where unpacked plugins live. Resolved per call rather than captured at module
- * scope: tests set DATA_DIR in beforeEach, and a module-scope constant would
- * freeze whatever the first import saw.
+ * Where user-installed plugins live. Resolved per call rather than captured at
+ * module scope: tests set DATA_DIR in beforeEach, and a module-scope constant
+ * would freeze whatever the first import saw.
  */
 export function getPluginsDir(): string {
   return path.join(process.env.DATA_DIR || "./db/data", "plugins");
 }
 
 /**
- * Where first-party plugins that ship with Termix live.
+ * Where the plugins that ship with Termix live.
  *
  * Separate from getPluginsDir() because that one is user data: a bundled
  * plugin is part of the install and must not be deletable or shadowable by
  * whatever happens to be in the data directory.
  *
- * Resolved from this module's location rather than cwd, same reasoning as the
- * worker bootstrap: the build emits to dist/backend/backend/plugins/, and the
- * bundled plugins sit beside dist/backend.
+ * Resolved from this module's location rather than cwd, because the build
+ * emits to dist/backend/backend/plugins/ and the bundled plugins sit beside
+ * dist/backend.
  */
 export function getBundledPluginsDir(): string {
   const override = process.env.TERMIX_BUNDLED_PLUGINS_DIR;
@@ -30,9 +34,10 @@ export function getBundledPluginsDir(): string {
 
   const candidates = [
     // Built server: dist/backend/backend/plugins -> dist/plugins
+    // Source tree:  src/backend/plugins          -> plugins
+    // Both are three levels up, which is why there is one entry, not two.
     path.resolve(here, "../../../plugins"),
-    // Running from source under vitest/tsx: src/backend/plugins -> plugins
-    path.resolve(here, "../../../plugins"),
+    // Built server invoked from a nested layout: .../dist/backend/backend/plugins
     path.resolve(here, "../../../../plugins"),
   ];
 
@@ -46,8 +51,21 @@ export function getPluginDir(pluginId: string): string {
   return path.join(getPluginsDir(), pluginId);
 }
 
-export function getPluginBackendEntry(pluginDir: string): string {
-  return path.join(pluginDir, "backend", "index.mjs");
+/**
+ * The backend entry, from the manifest's own `backend` field.
+ *
+ * Bundled plugins still ship a hand-written backend/index.mjs, so that stays
+ * the fallback until A2 gives every plugin a real build.
+ */
+export function getPluginBackendEntry(
+  pluginDir: string,
+  manifest?: Pick<PluginManifest, "backend">,
+): string {
+  const legacy = path.join(pluginDir, "backend", "index.mjs");
+  if (!manifest?.backend || manifest.backend === DEFAULT_BACKEND_ENTRY) {
+    if (fs.existsSync(legacy)) return legacy;
+  }
+  return path.join(pluginDir, manifest?.backend ?? DEFAULT_BACKEND_ENTRY);
 }
 
 export function getPluginManifestPath(pluginDir: string): string {