Keep an explicit null act fault instead of the requested fault

CHANGELOG.md

@@ -13,6 +13,9 @@ project adheres to [Semantic Versioning](https://semver.org/).
 - Playwright setup note in the Quick start section of `README.md`.
 
 ### Fixed
+- An act result that explicitly reports `fault: null` is stored as null. The
+  report used to replace that null with the requested fault, so a cleared
+  fault was recorded as `duplicate` when `--fault duplicate` was passed.
 - The integrator example now removes its scratch directory when decide fails
   or policy refuses the response. `process.exit` skipped the cleanup, so each
   failed run left an `aas-integrator-` directory behind.

bin/aas.mjs

@@ -1696,7 +1696,7 @@ export async function runDemo(args = [], options = {}) {
       status: stages.act.status,
       outcome,
       state: act.raw?.state ?? null,
-      fault: act.raw?.fault ?? fault,
+      fault: act.raw && Object.hasOwn(act.raw, "fault") ? act.raw.fault : fault,
       action_id: act.raw?.action_id ?? null,
       assurance_mode: act.raw?.assurance_mode ?? null,
       bundle_verification: act.raw?.bundle_verification ?? null,

test/stack.test.mjs

@@ -1813,6 +1813,20 @@ test("demo rejects an unknown domain before running any stage", async () => {
   assert.equal(rejected.exitCode, 2);
 });
 
+test("an explicit null act fault stays null instead of becoming the requested fault", async () => {
+  const outputRoot = tempRoot();
+  const cleared = await runDemo(["--fault", "duplicate"], stubOptions(outputRoot, {
+    runId: "null-fault",
+    runActFn: async () => ({ ok: true, raw: { outcome: "settled", state: "CLOSED", fault: null, action_id: "act-null" }, status: 0 }),
+  }));
+  assert.equal(cleared.report.stages.act.fault, null);
+  const omitted = await runDemo(["--fault", "duplicate"], stubOptions(outputRoot, {
+    runId: "omitted-fault",
+    runActFn: async () => ({ ok: true, raw: { outcome: "settled", state: "CLOSED", action_id: "act-omit" }, status: 0 }),
+  }));
+  assert.equal(omitted.report.stages.act.fault, "duplicate");
+});
+
 test("runAct targets the requested rail demo domain", () => {
   const seen = [];
   const runner = (bin, args) => {