fix(javascript): scope Next package admission by container identity

src/application/javascript/JavaScriptNextAppContext.test.ts

@@ -15,6 +15,30 @@ const file = (path: string, text = ""): JavaScriptArtifactFile => ({
   text: { included: true, value: text },
 });
 
+it("keeps package applicability and its root cache scoped to the source container", () => {
+  const manifest = file("package.json", '{"dependencies":{"next":"16.4.2"}}');
+  const foreign = {
+    ...file("package.json", '{"name":"plain"}'),
+    container_sha256: "c".repeat(64),
+  };
+  const page = file("app/page.js");
+  const foreignPage = { ...page, container_sha256: foreign.container_sha256 };
+  const context = createJavaScriptNextAppContext(
+    [manifest, foreign, page, foreignPage],
+    new JavaScriptJsonDocuments(),
+    new Set(["app"]),
+  );
+  expect(context(page)).toMatchObject({
+    kind: "app-directory",
+    package: { container_sha256: manifest.container_sha256 },
+  });
+  expect(context(foreignPage)).toMatchObject({
+    kind: "unknown",
+    package: { container_sha256: foreign.container_sha256 },
+  });
+  expect(context(page).kind).toBe("app-directory");
+});
+
 it("uses the nearest declared Next package and root directory precedence", () => {
   const files = [
     file("package.json", '{"dependencies":{"next":"16.4.2"}}'),

src/application/javascript/JavaScriptNextAppContext.ts

@@ -2,6 +2,7 @@ import { posix } from "node:path";
 
 import type { JavaScriptArtifactFile } from "../../domain/javascript/javascriptArtifactFiles.js";
 import type { NextAppSourceContext } from "../../domain/javascript/javascriptRoutePaths.js";
+import { compositeKey } from "../../domain/unicodeCodePointOrder.js";
 import type { JavaScriptJsonDocuments } from "./JavaScriptJsonDocuments.js";
 
 /** Package declarations and inventoried directories own source-router applicability. */
@@ -15,7 +16,10 @@ export const createJavaScriptNextAppContext = (
   const packages = new Map(
     files
       .filter(({ kind }) => kind === "package-json")
-      .map((file) => [posix.dirname(file.path), file]),
+      .map((file) => [
+        compositeKey([file.container_sha256, posix.dirname(file.path)]),
+        file,
+      ]),
   );
   const roots = new Map<JavaScriptArtifactFile, string | null>();
   return (file) => {
@@ -24,11 +28,10 @@ export const createJavaScriptNextAppContext = (
       ;
       directory = posix.dirname(directory)
     ) {
-      const manifest = packages.get(directory);
-      if (
-        manifest !== undefined &&
-        manifest.container_sha256 === file.container_sha256
-      ) {
+      const manifest = packages.get(
+        compositeKey([file.container_sha256, directory]),
+      );
+      if (manifest !== undefined) {
         const identity = {
           path: manifest.path,
           sha256: manifest.sha256,