refactor(cli): extract plugin install plan helper

src/cli/plugin-install-plan.ts

@@ -0,0 +1,54 @@
+import type { BundledPluginSource } from "../plugins/bundled-sources.js";
+import { PLUGIN_INSTALL_ERROR_CODE } from "../plugins/install.js";
+import { shortenHomePath } from "../utils.js";
+
+type BundledLookup = (params: {
+  kind: "pluginId" | "npmSpec";
+  value: string;
+}) => BundledPluginSource | undefined;
+
+function isBareNpmPackageName(spec: string): boolean {
+  const trimmed = spec.trim();
+  return /^[a-z0-9][a-z0-9-._~]*$/.test(trimmed);
+}
+
+export function resolveBundledInstallPlanBeforeNpm(params: {
+  rawSpec: string;
+  findBundledSource: BundledLookup;
+}): { bundledSource: BundledPluginSource; warning: string } | null {
+  if (!isBareNpmPackageName(params.rawSpec)) {
+    return null;
+  }
+  const bundledSource = params.findBundledSource({
+    kind: "pluginId",
+    value: params.rawSpec,
+  });
+  if (!bundledSource) {
+    return null;
+  }
+  return {
+    bundledSource,
+    warning: `Using bundled plugin "${bundledSource.pluginId}" from ${shortenHomePath(bundledSource.localPath)} for bare install spec "${params.rawSpec}". To install an npm package with the same name, use a scoped package name (for example @scope/${params.rawSpec}).`,
+  };
+}
+
+export function resolveBundledInstallPlanForNpmFailure(params: {
+  rawSpec: string;
+  code?: string;
+  findBundledSource: BundledLookup;
+}): { bundledSource: BundledPluginSource; warning: string } | null {
+  if (params.code !== PLUGIN_INSTALL_ERROR_CODE.NPM_PACKAGE_NOT_FOUND) {
+    return null;
+  }
+  const bundledSource = params.findBundledSource({
+    kind: "npmSpec",
+    value: params.rawSpec,
+  });
+  if (!bundledSource) {
+    return null;
+  }
+  return {
+    bundledSource,
+    warning: `npm package unavailable for ${params.rawSpec}; using bundled plugin at ${shortenHomePath(bundledSource.localPath)}.`,
+  };
+}