fix(runner): resolve exported ACP package manifests

packages/paperclip-runner/src/drivers/acpx/installation-integrity.test.ts

@@ -82,8 +82,13 @@ describe("ACPX installation integrity", () => {
     await mkdir(nestedDependencyDirectory, { recursive: true });
     await writeFile(
       nestedDependencyPackageJson,
-      JSON.stringify({ name: "qualified-dependency", version: "1.0.0" }),
+      JSON.stringify({
+        name: "qualified-dependency",
+        version: "1.0.0",
+        exports: "./index.js",
+      }),
     );
+    await writeFile(join(nestedDependencyDirectory, "index.js"), "export {};");
     expect(
       createAcpxPackageJsonResolver(root)(
         "qualified-dependency",
@@ -549,6 +554,18 @@ describe("ACPX installation integrity", () => {
     );
   });
 
+  it.runIf(process.platform === "linux" && process.arch === "x64")(
+    "resolves and pins the installed Claude ACP dependency graph",
+    async () => {
+      const profile = resolveQualifiedAcpxProfile("claude", "claude-sonnet-5");
+      const installation = await verifyQualifiedAcpxInstallation(profile);
+      expect(installation.agentServerPackageJsonPath).toContain(
+        "/@agentclientprotocol/claude-agent-acp/package.json",
+      );
+      await (await installation.openCommand()).close();
+    },
+  );
+
   it.runIf(process.platform === "linux" && process.arch === "x64")(
     "resolves and pins the qualified Codex native runtime through its transitive packages",
     async () => {

packages/paperclip-runner/src/drivers/acpx/installation-integrity.ts

@@ -295,7 +295,7 @@ export function createAcpxPackageJsonResolver(
       );
     }
     const packageJsonPath = realpathSync(
-      createRequire(canonicalIssuer).resolve(`${packageName}/package.json`),
+      resolvePackageJsonFromIssuer(packageName, canonicalIssuer),
     );
     if (!pathIsInside(canonicalNodeModules, packageJsonPath)) {
       throw new Error(
@@ -306,6 +306,44 @@ export function createAcpxPackageJsonResolver(
   };
 }
 
+function resolvePackageJsonFromIssuer(
+  packageName: string,
+  issuerPackageJsonPath: string,
+): string {
+  const issuerRequire = createRequire(issuerPackageJsonPath);
+  try {
+    return issuerRequire.resolve(`${packageName}/package.json`);
+  } catch (error) {
+    if (
+      (error as NodeJS.ErrnoException).code !== "ERR_PACKAGE_PATH_NOT_EXPORTED"
+    )
+      throw error;
+  }
+
+  const packageSegments = packageName.split("/");
+  if (
+    packageSegments.length < 1 ||
+    packageSegments.length > 2 ||
+    packageSegments.some((segment) => segment.length === 0)
+  ) {
+    throw new Error(`ACPX provider package name is invalid: ${packageName}`);
+  }
+  let directory = dirname(realpathSync(issuerRequire.resolve(packageName)));
+  for (let count = 0; count < MAX_DEPENDENCY_ANCESTORS; count += 1) {
+    const matchesPackage =
+      basename(directory) === packageSegments.at(-1) &&
+      (packageSegments.length === 1 ||
+        basename(dirname(directory)) === packageSegments[0]);
+    if (matchesPackage) return resolve(directory, "package.json");
+    const parent = dirname(directory);
+    if (parent === directory) break;
+    directory = parent;
+  }
+  throw new Error(
+    `ACPX provider package manifest could not be located for ${packageName}`,
+  );
+}
+
 function pathIsInside(root: string, candidate: string): boolean {
   const candidateRelativePath = relative(root, candidate);
   return (