stack/packages/conversation/tests/turns.test.mjs

// CHAT-03 §3 turns, dispatch and Interrupt (#1507): N1–N25 on the in-process
// fake engine. Unsealed-extension effects are simulated by the fake; no real
// extension loads (the binding would refuse it, N24).

import { test, after } from "node:test";
import assert from "node:assert/strict";
import { PassThrough } from "node:stream";
import { join } from "node:path";
import { Controller, TEST_ENGINE, REPO_ROOT, HANDLED_WITHOUT_RUN, ACK_WITHOUT_START, NO_TURN, RUN_OVERLAP, TRANSPORT_UNKNOWN } from "../src/controller.mjs";
import { AUTHORITY } from "../src/cohort.mjs";
import { FixtureVerifier, sha256 } from "../src/records.mjs";
import { ENGINE_ENV, PI_BIN, SEAL_FLAGS, UNSEALED_ENGINE, checkSeal } from "../src/pi-pin.mjs";
import { LineSplitter, encodeLine, parseLine } from "../src/framing.mjs";
import { BUSY_ERROR, FakeLauncher, FakePi } from "./fake-pi.mjs";
import { fixture, started, receiptState, outcomeUnknownPush, sessionText, cleanupAll, tick, noUnits, FAST } from "./harness.mjs";

after(() => cleanupAll());

// Records every proof the controller posts, so a test can see that no
// turnProof other than `turnState: interrupted` was ever produced (mutant 32).
class SpyVerifier extends FixtureVerifier {
  constructor() {
    super({ authorities: [AUTHORITY] });
    this.posted = [];
  }
  post(p) {
    this.posted.push(structuredClone(p));
    return super.post(p);
  }
}

async function until(pred, ms = 4000, what = "condition") {
  const end = Date.now() + ms;
  while (!pred()) {
    if (Date.now() > end) throw new Error(`timed out waiting for ${what}`);
    await tick(5);
  }
}

const cmds = (engine, type) => engine.commands.filter((c) => c.type === type);
const stopEvidence = (ctrl, id) => ctrl.evidence.stops.filter((e) => e.stop === id);
const lastStopEvidence = (ctrl, id) => stopEvidence(ctrl, id).at(-1) ?? null;
const signals = (ctrl) => ctrl.evidence.overlaps.map((o) => o.signal);
const reconciled = (ctrl, id) => ctrl.events.some((e) => e.type === "reconciled" && e.stop === id);
const turnProofs = (v) => v.posted.filter((p) => p.kind === "turnProof");

async function setup(opts = {}) {
  const verifier = new SpyVerifier();
  const h = await started({ verifier, ...opts });
  return { ...h, verifier };
}

// Admits a prompt and returns its receipt id.
async function prompt(h, text = "do the thing") {
  const r = await h.client.prompt(text);
  assert.equal(r.outcome, "admitted", JSON.stringify(r));
  return r.receipt.id;
}

// A Mosaic run held at step `p1` with its receipt `working`.
async function heldRun(h, rest = [{ text: "never", stop: "stop" }]) {
  h.engine.script([{ pause: "p1" }, ...rest]);
  h.engine.arm("p1");
  const id = await prompt(h);
  await receiptState(h.client, id, "working");
  await h.engine.waitPaused("p1");
  return id;
}

async function interrupt(h) {
  const r = await h.client.interrupt();
  assert.equal(r.outcome, "interrupt-fenced", JSON.stringify(r));
  return r.stop.id;
}

async function stopSettled(h, id) {
  await until(() => {
    const s = h.ctrl.stops.get(id);
    return s && (s.state === "uncertain" || s.state === "turn-interrupted" || s.state === "superseded");
  }, 8000, `stop ${id} to settle`);
  return h.ctrl.stops.get(id);
}

// The stop is uncertain: no reconciled, prompts refuse, force stop works.
async function assertUncertainStop(h, stopId, outcome) {
  const s = await stopSettled(h, stopId);
  assert.equal(s.state, "uncertain");
  assert.equal(lastStopEvidence(h.ctrl, stopId)?.outcome, outcome);
  assert.equal(reconciled(h.ctrl, stopId), false);
  assert.equal(h.ctrl.binding.admission, "closed");
  assert.ok(turnProofs(h.verifier).every((p) => p.turnState === "interrupted"), "no other turnState is ever written");
  assert.ok(!turnProofs(h.verifier).some((p) => p.stop === stopId), "no turnProof for an uncertain stop");
  const before = h.engine.bytes().length;
  const p = await h.client.prompt("again");
  assert.equal(p.refusal, "fenced");
  assert.equal(h.engine.bytes().length, before, "a refused prompt writes no engine bytes");
  const fs = await h.client.confirmed("force-stop");
  assert.equal(fs.outcome, "force-stop-fenced", JSON.stringify(fs));
  await until(() => h.ctrl.binding.state === "stopped", 4000, "force stop");
}

test("N25: ordinary Interrupt reconciles; a non-empty queue_update in the window is O5", async () => {
  const h = await setup();
  try {
    const id = await heldRun(h);
    const stopId = await interrupt(h);
    await until(() => reconciled(h.ctrl, stopId), 6000, "reconciled");
    assert.deepEqual(signals(h.ctrl), [], "Pi's empty queue_update before each clear response is no signal");
    const s = h.ctrl.stops.get(stopId);
    assert.equal(s.state, "turn-interrupted");
    assert.equal(s.nativeQueue, "cleared");
    assert.equal((await receiptState(h.client, id, "failed")).reasonCode, "interrupted");
    // Each clear_queue answered after Pi's empty queue_update.
    const clears = cmds(h.engine, "clear_queue");
    assert.equal(clears.length, 2, "the interrupt clear and the post-settle clear");
    const types = h.engine.sent.map((l) => JSON.parse(l)).map((v) => (v.type === "response" ? `response:${v.command}` : v.type));
    for (let i = 0; i < types.length; i++) if (types[i] === "response:clear_queue") assert.equal(types[i - 1], "queue_update");
    assert.equal(h.ctrl.binding.admission, "open");
    const next = await h.client.prompt("next");
    assert.equal(next.outcome, "admitted");
    await receiptState(h.client, next.receipt.id, "finished");
  } finally {
    await h.close();
  }
  // The same window with a non-empty queue_update.
  const h2 = await setup();
  try {
    await heldRun(h2);
    h2.engine.arm("clear");
    const stopId = await interrupt(h2);
    await h2.engine.waitPaused("clear");
    h2.engine.queue("steer", "slipped in");
    h2.engine.resume("clear");
    const s = await stopSettled(h2, stopId);
    assert.equal(s.state, "uncertain");
    assert.ok(signals(h2.ctrl).includes("O5"));
    assert.equal(reconciled(h2.ctrl, stopId), false);
  } finally {
    await h2.close();
  }
});

test("N1: an extension's follow-up queued after the fence is cleared before any abort; O5, Unknown", async () => {
  const h = await setup();
  try {
    const id = await heldRun(h);
    h.engine.arm("clear");
    const stopId = await interrupt(h);
    // The clear_queue is in Pi's hands but not yet run; the extension queues.
    await h.engine.waitPaused("clear");
    h.engine.queue("followUp", "external item");
    h.engine.resume("clear");
    const s = await stopSettled(h, stopId);
    const order = h.engine.commands.map((c) => c.type).filter((t) => t === "clear_queue" || t === "abort");
    assert.equal(order[0], "clear_queue");
    assert.equal(cmds(h.engine, "abort").length, 0, "a non-empty clear stops before abort");
    assert.equal(h.engine.runs.length, 1);
    assert.ok(!h.engine.sent.some((l) => l.includes("external item") && l.includes('"message_start"')), "the follow-up never ran");
    assert.ok(signals(h.ctrl).filter((x) => x === "O5").length >= 2, "the queue_update and the non-empty clear");
    assert.equal(s.state, "uncertain");
    assert.equal(s.nativeQueue, "unknown", "a non-empty clear leaves the native queue unknown");
    assert.equal(lastStopEvidence(h.ctrl, stopId).outcome, "unknown");
    const digest = sha256("external item");
    assert.ok(h.ctrl.evidence.overlaps.some((o) => o.removed?.some((r) => r.digest === digest && r.bytes === 13)), "evidence holds the item's digest and size");
    assert.equal(h.client.receipt(id).state, "working");
    await until(() => outcomeUnknownPush(h.client, id), 2000, "the receipt shown as outcome unknown");
    assert.equal(outcomeUnknownPush(h.client, id).reason, RUN_OVERLAP);
    assert.ok(!JSON.stringify(h.ctrl.receipts.get(id)).includes("external item"), "the removed item is never attributed to the request");
    assert.equal(cmds(h.engine, "prompt").length, 1, "nothing is resent");
    await assertUncertainStop(h, stopId, "unknown");
  } finally {
    await h.close();
  }
});

test("N1: a follow-up queued before the fence is O5 at once; the Interrupt refuses fenced", async () => {
  const h = await setup();
  try {
    await heldRun(h);
    h.engine.queue("followUp", "early");
    await until(() => h.ctrl.binding.state === "uncertain", 2000, "uncertain");
    const r = await h.client.interrupt();
    assert.equal(r.refusal, "fenced");
    assert.equal(h.ctrl.stops.size, 0);
  } finally {
    await h.close();
  }
});

test("N2: with abort first, the fake runs the external item (the ordering guard has teeth)", async () => {
  // The mutant's order, driven straight at the fake: abort before clear.
  const drive = async (order) => {
    const input = new PassThrough(), output = new PassThrough();
    const fake = new FakePi({ input, output });
    const lines = [];
    output.on("data", (c) => lines.push(...c.toString().split("\n").filter(Boolean).map((l) => JSON.parse(l))));
    fake.script([{ pause: "p1" }, { text: "x" }]);
    fake.arm("p1");
    input.write(encodeLine({ id: "p", type: "prompt", message: "mosaic" }));
    await fake.waitPaused("p1");
    fake.queue("followUp", "external item");
    for (const [i, type] of order.entries()) {
      input.write(encodeLine({ id: `c${i}`, type }));
      await until(() => lines.some((v) => v.id === `c${i}`));
    }
    await fake.waitIdle();
    return lines.some((v) => v.type === "message_start" && v.message?.role === "user" && v.message.content?.[0]?.text === "external item");
  };
  assert.equal(await drive(["abort", "clear_queue"]), true, "abort first continues the queued item in the same run");
  assert.equal(await drive(["clear_queue", "abort"]), false, "clear first removes it");
});

test("N3: the fence lands in preflight, preflight errors, no run: failed, No run, uncertain", async () => {
  const h = await setup();
  try {
    h.engine.arm("915");
    h.engine.plan({ error: "auth check failed", at: "915" });
    const id = await prompt(h);
    await h.engine.waitPaused("915");
    await receiptState(h.client, id, "dispatched");
    const stopId = await interrupt(h);
    await until(() => cmds(h.engine, "abort").length === 1, 3000, "abort");
    h.engine.resume("915");
    const r = await receiptState(h.client, id, "failed");
    assert.equal(r.reasonCode, null);
    assert.ok(h.client.pushes.some((p) => p.kind === "receipt" && p.receipt.id === id && p.nativeError === "auth check failed"), "native error kept");
    assert.equal(h.engine.runs.length, 0);
    await assertUncertainStop(h, stopId, "no-run");
  } finally {
    await h.close();
  }
});

test("N4: the ack arrives after the first abort and a run starts: clear and abort again; Interrupted", async () => {
  const h = await setup();
  try {
    h.engine.arm("915");
    h.engine.script([{ pause: "p1" }, { text: "never" }]);
    h.engine.arm("p1");
    const id = await prompt(h);
    await h.engine.waitPaused("915");
    const stopId = await interrupt(h);
    await until(() => cmds(h.engine, "abort").length === 1, 3000, "first abort");
    h.engine.resume("915");
    await until(() => reconciled(h.ctrl, stopId), 8000, "reconciled");
    assert.equal(cmds(h.engine, "abort").length, 2, "a second abort for the late run");
    assert.equal(cmds(h.engine, "clear_queue").length, 3, "two interrupt clears and the post-settle clear");
    const r = await receiptState(h.client, id, "failed");
    assert.equal(r.reasonCode, "interrupted");
    assert.equal(h.ctrl.stops.get(stopId).state, "turn-interrupted");
    assert.equal(turnProofs(h.verifier).at(-1).turnState, "interrupted");
    assert.equal(h.ctrl.binding.admission, "open");
  } finally {
    await h.close();
  }
});

test("N5: an input handler takes the prompt: ack, no run, delivery-unknown handled-without-run", async () => {
  const h = await setup();
  try {
    h.engine.plan({ handled: true });
    const id = await prompt(h);
    const r = await receiptState(h.client, id, "delivery-unknown");
    assert.equal(r.reasonCode, HANDLED_WITHOUT_RUN);
    assert.ok(!h.client.pushes.some((p) => p.kind === "receipt" && p.receipt.id === id && ["working", "finished"].includes(p.receipt.state)));
    await tick(100);
    assert.equal(cmds(h.engine, "prompt").length, 1, "nothing is resent");
    assert.equal(h.engine.runs.length, 0);
    assert.equal(h.ctrl.binding.admission, "open");
  } finally {
    await h.close();
  }
});

test("N6: an extension queues between clear_queue and abort: O5 and O6, Unknown", async () => {
  const h = await setup();
  try {
    const id = await heldRun(h);
    h.engine.arm("abort");
    const stopId = await interrupt(h);
    await h.engine.waitPaused("abort");
    h.engine.queue("followUp", "between");
    h.engine.resume("abort");
    const s = await stopSettled(h, stopId);
    assert.ok(signals(h.ctrl).includes("O5"));
    assert.ok(signals(h.ctrl).includes("O6"), "abort continued the queued item in the same run");
    assert.equal(h.engine.runs.length, 1);
    assert.equal(s.state, "uncertain");
    assert.equal(h.client.receipt(id).state, "working");
    await until(() => outcomeUnknownPush(h.client, id), 2000, "outcome unknown");
    assert.equal(outcomeUnknownPush(h.client, id).reason, RUN_OVERLAP);
    await assertUncertainStop(h, stopId, "unknown");
  } finally {
    await h.close();
  }
});

test("N7: clear_queue times out: no abort, nativeQueue unknown, force stop still ends it", async () => {
  const h = await setup();
  try {
    const id = await heldRun(h);
    h.engine.dropResponse("clear_queue");
    const stopId = await interrupt(h);
    const s = await stopSettled(h, stopId);
    assert.equal(cmds(h.engine, "abort").length, 0, "abort would run whatever is queued");
    assert.equal(s.nativeQueue, "unknown");
    assert.equal(s.state, "uncertain");
    assert.equal(h.ctrl.binding.state, "uncertain");
    assert.equal(h.client.receipt(id).state, "working");
    await until(() => outcomeUnknownPush(h.client, id), 2000, "outcome unknown");
    assert.equal(outcomeUnknownPush(h.client, id).reason, TRANSPORT_UNKNOWN);
    assert.equal(lastStopEvidence(h.ctrl, stopId).outcome, "unknown");
    const fs = await h.client.confirmed("force-stop");
    assert.equal(fs.outcome, "force-stop-fenced");
    await until(() => h.ctrl.binding.state === "stopped", 4000, "force stop");
  } finally {
    await h.close();
  }
});

test("N7: clear_queue answers an error: no abort, nativeQueue unknown, the link not poisoned", async () => {
  // An error response is the one clear failure that leaves the link
  // unpoisoned, so nothing but rule 2 keeps the abort off the pipe.
  const h = await setup();
  try {
    const id = await heldRun(h);
    h.engine.failResponse("clear_queue");
    const stopId = await interrupt(h);
    const s = await stopSettled(h, stopId);
    assert.equal(h.ctrl.exec.link.poisoned, null);
    assert.equal(cmds(h.engine, "abort").length, 0, "abort would run whatever is queued");
    assert.equal(s.nativeQueue, "unknown");
    assert.equal(s.state, "uncertain");
    assert.equal(h.client.receipt(id).state, "working");
  } finally {
    await h.close();
  }
});

test("N8: an extension prompt starts a run during Mosaic preflight; the losing settle is O3", async () => {
  const h = await setup();
  try {
    h.engine.arm("915");
    const id = await prompt(h);
    await h.engine.waitPaused("915");
    // The order: Mosaic ack, the other run's agent_start and user
    // message_start, then the losing Mosaic prompt's agent_settled.
    h.engine.arm("run-start");
    h.engine.arm("state");
    h.engine.resume("915");
    await h.engine.waitPaused("run-start");
    await h.engine.waitPaused("state");
    h.engine.arm("ext-hold");
    void h.engine.extensionPrompt({ text: "from an extension", steps: [{ pause: "ext-hold" }, { text: "ext done" }] });
    await h.engine.waitPaused("ext-hold");
    await receiptState(h.client, id, "working");
    h.engine.resume("run-start");
    await until(() => signals(h.ctrl).includes("O3"), 2000, "O3");
    h.engine.resume("state");
    h.engine.resume("ext-hold");
    await h.engine.waitIdle();
    await tick(50);
    const wire = h.engine.sent.map((l) => JSON.parse(l)).filter((v) => v.type !== "message_update");
    const ack = wire.findIndex((v) => v.type === "response" && v.command === "prompt");
    const start = wire.findIndex((v, i) => i > ack && v.type === "agent_start");
    const user = wire.findIndex((v, i) => i > start && v.type === "message_start" && v.message.role === "user");
    const settle = wire.findIndex((v, i) => i > user && v.type === "agent_settled");
    assert.ok(ack >= 0 && ack < start && start < user && user < settle, "the pinned wire order");
    assert.equal(h.client.receipt(id).state, "working", "never finished or failed");
    await until(() => outcomeUnknownPush(h.client, id), 2000, "outcome unknown");
    assert.equal(outcomeUnknownPush(h.client, id).reason, RUN_OVERLAP);
    assert.equal(h.ctrl.binding.state, "uncertain");
    assert.equal(h.ctrl.binding.admission, "closed");
    assert.equal(cmds(h.engine, "prompt").length, 1, "nothing resent");
  } finally {
    await h.close();
  }
});

test("N9: a run that started before the fence and ends aborted: failed interrupted, Interrupted", async () => {
  const h = await setup();
  try {
    const id = await heldRun(h);
    const stopId = await interrupt(h);
    await until(() => reconciled(h.ctrl, stopId), 6000, "reconciled");
    const r = await receiptState(h.client, id, "failed");
    assert.equal(r.reasonCode, "interrupted");
    assert.ok(h.client.pushes.some((p) => p.kind === "receipt" && p.receipt.id === id && p.stop === stopId), "evidence links the stop");
    assert.equal(lastStopEvidence(h.ctrl, stopId).outcome, "interrupted");
    assert.equal(turnProofs(h.verifier).at(-1).turnState, "interrupted");
  } finally {
    await h.close();
  }
});

// Lead decision 34: only the controller's abort produces `aborted`. Mutant
// r2-D34 (turns.mjs drops the aborted-without-stop overlap) fails here.
test("N9: decision 34: a run that ends aborted with no stop in progress: aborted-without-stop, uncertain, outcome unknown", async () => {
  const h = await setup();
  try {
    h.engine.script([{ text: "", stop: "aborted", errorMessage: "Request was aborted" }]);
    const id = await prompt(h);
    await until(() => signals(h.ctrl).includes("aborted-without-stop"), 4000, "the overlap");
    assert.equal(h.ctrl.stops.size, 0);
    assert.equal(h.ctrl.binding.state, "uncertain");
    assert.equal(h.ctrl.binding.admission, "closed");
    await until(() => outcomeUnknownPush(h.client, id), 2000, "outcome unknown");
    assert.equal(outcomeUnknownPush(h.client, id).reason, RUN_OVERLAP);
    assert.notEqual(h.client.receipt(id).state, "failed");
    assert.equal(turnProofs(h.verifier).length, 0);
  } finally {
    await h.close();
  }
});

// n1: the fence alone doesn't link an `aborted`; an abort must have been
// written in the stop's chain. Mutant r2-n1 (link to any stop in progress)
// fails here.
test("N9: an aborted that lands after the fence but before any abort is written: aborted-without-stop, Unknown", async () => {
  const h = await setup();
  try {
    const id = await heldRun(h, [{ text: "", stop: "aborted", errorMessage: "Request was aborted" }]);
    h.engine.arm("clear");
    const stopId = await interrupt(h);
    await h.engine.waitPaused("clear");
    h.engine.resume("p1");
    await until(() => signals(h.ctrl).includes("aborted-without-stop"), 4000, "the overlap");
    h.engine.resume("clear");
    assert.equal(cmds(h.engine, "abort").length, 0, "no abort was written");
    assert.notEqual(h.client.receipt(id).state, "failed");
    await until(() => outcomeUnknownPush(h.client, id), 2000, "outcome unknown");
    await assertUncertainStop(h, stopId, "unknown");
  } finally {
    await h.close();
  }
});

// N10: the fake's own behaviour, against pinned Pi's (agent-session.js
// 821–949, rpc-mode.js 298–335). Mutant 28 (a fake that queues a Mosaic
// prompt while streaming) fails here.
function rawFake(opts = {}) {
  const input = new PassThrough(), output = new PassThrough();
  const fake = new FakePi({ input, output, ...opts });
  const lines = [];
  output.pipe(new PassThrough()).on("data", () => {});
  const splitter = new LineSplitter((l) => lines.push(parseLine(l).value));
  output.on("data", (c) => splitter.push(c));
  let n = 0;
  const send = (type, fields = {}) => {
    const id = `r${++n}`;
    input.write(encodeLine({ id, type, ...fields }));
    return id;
  };
  const response = (id) => until(() => lines.some((v) => v.type === "response" && v.id === id)).then(() => lines.find((v) => v.type === "response" && v.id === id));
  return { fake, lines, send, response };
}

test("N10: fake conformance", async () => {
  // Acks before running; agent_settled from a finally; several agent_start …
  // agent_end pairs in one run.
  {
    const f = rawFake();
    f.fake.script([{ continue: true }, { text: "ok", stop: "stop" }]);
    const id = f.send("prompt", { message: "a" });
    await until(() => f.lines.some((v) => v.type === "agent_settled"));
    const types = f.lines.map((v) => v.type);
    const ack = f.lines.findIndex((v) => v.type === "response" && v.id === id);
    assert.ok(ack >= 0 && ack < types.indexOf("agent_start"), "ack before the run");
    assert.equal(types.filter((t) => t === "agent_start").length, 2);
    assert.equal(types.filter((t) => t === "agent_settled").length, 1);
    assert.equal(types.at(-1), "agent_settled");
  }
  // A failing run still settles (finally).
  {
    const f = rawFake();
    f.fake.script([{ failBeforeUser: "boom" }]);
    f.send("prompt", { message: "a" });
    await until(() => f.lines.some((v) => v.type === "agent_settled"));
    assert.ok(!f.lines.some((v) => v.type === "message_start" && v.message.role === "user"));
  }
  // A prompt while streaming throws (no streamingBehavior); it is never
  // queued.
  {
    const f = rawFake();
    f.fake.script([{ pause: "p1" }, { text: "x" }]);
    f.fake.arm("p1");
    f.send("prompt", { message: "first" });
    await f.fake.waitPaused("p1");
    const before = f.lines.length;
    const r = await f.response(f.send("prompt", { message: "second" }));
    assert.equal(r.success, false);
    assert.equal(r.error, BUSY_ERROR);
    assert.ok(!f.lines.slice(before).some((v) => v.type === "queue_update"), "no queue_update: the prompt was not queued");
    assert.equal(f.fake.steering.length + f.fake.followUp.length + f.fake.agentQueue.length + f.fake.nextTurn.length, 0);
    f.fake.resume("p1");
    await f.fake.waitIdle();
    assert.equal(f.fake.runs.length, 1);
    assert.ok(!f.lines.some((v) => v.type === "message_start" && v.message.content?.[0]?.text === "second"), "the second prompt never ran");
  }
  // Pauses at 843, 895 and 915, between the line-860 check and the run start:
  // no ack until all three pass.
  {
    const f = rawFake();
    for (const p of ["843", "895", "915"]) f.fake.arm(p);
    const id = f.send("prompt", { message: "a" });
    for (const p of ["843", "895", "915"]) {
      await f.fake.waitPaused(p);
      assert.ok(!f.lines.some((v) => v.id === id), `no ack while paused at ${p}`);
      f.fake.resume(p);
    }
    await f.response(id);
    await f.fake.waitIdle();
  }
  // A colliding prompt (past line 860 before the other run started) is
  // acked, its throw swallowed, it settles with no agent_start, and leaves
  // isStreaming false while the other run goes on.
  {
    const f = rawFake();
    f.fake.script([{ pause: "p1" }, { text: "x" }]);
    f.fake.arm("p1");
    f.fake.arm("run-start");
    const a = f.send("prompt", { message: "A" });
    await f.fake.waitPaused("run-start");
    await f.response(a);
    f.fake.arm("915");
    const b = f.send("prompt", { message: "B" });
    await f.fake.waitPaused("915");
    f.fake.resume("run-start");
    await f.fake.waitPaused("p1");
    const mark = f.lines.length;
    f.fake.resume("915");
    const rb = await f.response(b);
    assert.equal(rb.success, true, "the colliding prompt is acked");
    await until(() => f.lines.slice(mark).some((v) => v.type === "agent_settled"));
    assert.ok(!f.lines.slice(mark).some((v) => v.type === "agent_start"), "no agent_start for the loser");
    const st = await f.response(f.send("get_state"));
    assert.equal(st.data.isStreaming, false, "isStreaming false while the other run goes on");
    assert.ok(f.fake.run, "the other run is still going");
    f.fake.resume("p1");
    await f.fake.waitIdle();
  }
  // clear_queue: an empty queue_update before its response; returns steer and
  // follow-up only; drops agent-level custom messages; keeps nextTurn.
  {
    const f = rawFake();
    f.fake.queue("steer", "s");
    f.fake.queue("followUp", "f");
    f.fake.queue("agent", "custom");
    f.fake.queue("nextTurn", "nt");
    const mark = f.lines.length;
    const id = f.send("clear_queue");
    const r = await f.response(id);
    const window = f.lines.slice(mark);
    const at = window.findIndex((v) => v.id === id);
    assert.deepEqual(window[at - 1], { type: "queue_update", steering: [], followUp: [] });
    assert.deepEqual(r.data, { steering: ["s"], followUp: ["f"] });
    assert.equal(f.fake.agentQueue.length, 0, "agent-level custom messages are dropped, not returned");
    assert.equal(f.fake.nextTurn.length, 1, "nextTurn survives the clear");
  }
});

test("N11: the run fails before any user message_start: delivery-unknown ack-without-start, never failed", async () => {
  const h = await setup();
  try {
    const before = sessionText(h.fx);
    h.engine.script([{ failBeforeUser: "provider refused" }]);
    const id = await prompt(h);
    const r = await receiptState(h.client, id, "delivery-unknown");
    assert.equal(r.reasonCode, ACK_WITHOUT_START);
    assert.ok(!h.client.pushes.some((p) => p.kind === "receipt" && p.receipt.id === id && p.receipt.state === "failed"));
    const added = sessionText(h.fx).slice(before.length).split("\n").filter(Boolean).map((l) => JSON.parse(l));
    assert.ok(!added.some((e) => e.message?.role === "user"), "the session gains no user entry");
    assert.equal(cmds(h.engine, "prompt").length, 1);
  } finally {
    await h.close();
  }
  // The same schedule with the failure line unparseable.
  const h2 = await setup();
  try {
    h2.engine.script([{ failBeforeUser: "x", raw: "{not json\n" }]);
    const id = await prompt(h2);
    const r = await receiptState(h2.client, id, "delivery-unknown");
    assert.equal(r.reasonCode, TRANSPORT_UNKNOWN);
    assert.equal(h2.ctrl.binding.state, "uncertain");
  } finally {
    await h2.close();
  }
});

test("N12: input that starts a run after the final empty clear is O1 and not part of the stop's proof", async () => {
  const h = await setup();
  try {
    await heldRun(h);
    const stopId = await interrupt(h);
    await until(() => reconciled(h.ctrl, stopId), 6000, "reconciled");
    const ev = lastStopEvidence(h.ctrl, stopId);
    const lastClear = ev.clears.at(-1);
    const proof = turnProofs(h.verifier).find((p) => p.stop === stopId);
    assert.equal(proof.observedAt, lastClear.at, "the stop records the final clear's observedAt");
    void h.engine.extensionPrompt({ text: "late" });
    await until(() => signals(h.ctrl).includes("O1"), 2000, "O1");
    const o1 = h.ctrl.evidence.overlaps.find((o) => o.signal === "O1");
    assert.equal(o1.why, "no slot held");
    assert.ok(o1.idx > lastClear.idx, "the run came after the proof's observation");
    assert.equal(h.ctrl.binding.state, "uncertain");
    assert.equal(h.ctrl.binding.admission, "closed");
    assert.equal(h.ctrl.stops.get(stopId).state, "turn-interrupted", "the stopped turn's proof is unchanged");
  } finally {
    await h.close();
  }
});

test("N13: agent_start with no slot held is O1; a later prompt refuses with zero engine bytes", async () => {
  const h = await setup();
  try {
    h.engine.emit({ type: "agent_start" });
    await until(() => signals(h.ctrl).includes("O1"), 2000, "O1");
    assert.equal(h.ctrl.binding.state, "uncertain");
    assert.equal(h.ctrl.binding.admission, "closed");
    assert.ok(h.ctrl.evidence.uncertain.some((u) => u.reason === RUN_OVERLAP));
    const before = h.engine.bytes().length;
    const r = await h.client.prompt("after");
    assert.equal(r.refusal, "fenced");
    await tick(50);
    assert.equal(h.engine.bytes().length, before);
  } finally {
    await h.close();
  }
});

test("N14: the run completes while clear_queue is in flight: finished, Completed first, uncertain", async () => {
  const h = await setup();
  try {
    const id = await heldRun(h, [{ text: "done", stop: "stop" }]);
    h.engine.arm("clear");
    const stopId = await interrupt(h);
    await h.engine.waitPaused("clear");
    h.engine.resume("p1");
    await receiptState(h.client, id, "finished");
    h.engine.resume("clear");
    await stopSettled(h, stopId);
    assert.equal(cmds(h.engine, "abort").length, 1, "the abort reached an idle engine");
    assert.ok(lastStopEvidence(h.ctrl, stopId).clears.every((c) => c.empty));
    assert.equal(h.client.receipt(id).state, "finished", "never relabelled interrupted");
    assert.equal(h.client.receipt(id).reasonCode, null);
    await assertUncertainStop(h, stopId, "completed-first");
  } finally {
    await h.close();
  }
});

test("N14: the run completes after the abort is written, before Pi applies it: finished, never relabelled", async () => {
  const h = await setup();
  try {
    const id = await heldRun(h, [{ text: "done", stop: "stop" }]);
    h.engine.arm("abort");
    const stopId = await interrupt(h);
    await h.engine.waitPaused("abort");
    h.engine.resume("p1");
    await receiptState(h.client, id, "finished");
    h.engine.resume("abort");
    await stopSettled(h, stopId);
    assert.equal(cmds(h.engine, "abort").length, 1);
    assert.equal(h.client.receipt(id).state, "finished", "a run that ended stop is never relabelled interrupted");
    assert.equal(h.client.receipt(id).reasonCode, null);
    await assertUncertainStop(h, stopId, "completed-first");
  } finally {
    await h.close();
  }
});

test("N15: the fence lands in preflight, then an input handler takes it: handled-without-run, No run", async () => {
  const h = await setup();
  try {
    h.engine.arm("843");
    h.engine.plan({ handled: true });
    const id = await prompt(h);
    await h.engine.waitPaused("843");
    const stopId = await interrupt(h);
    await until(() => cmds(h.engine, "abort").length === 1, 3000, "abort");
    h.engine.resume("843");
    const r = await receiptState(h.client, id, "delivery-unknown");
    assert.equal(r.reasonCode, HANDLED_WITHOUT_RUN);
    await stopSettled(h, stopId);
    assert.equal(cmds(h.engine, "abort").length, 1, "no second abort");
    assert.equal(cmds(h.engine, "clear_queue").length, 1, "no second clear");
    await assertUncertainStop(h, stopId, "no-run");
  } finally {
    await h.close();
  }
});

test("N16: Interrupt with no slot and no run refuses no-turn: no stop, no bytes, admission open", async () => {
  const h = await setup();
  try {
    const before = h.engine.bytes().length;
    const r = await h.client.interrupt();
    assert.equal(r.refusal, NO_TURN);
    assert.deepEqual(r.effect, { dispatchRefused: null });
    assert.equal(h.ctrl.stops.size, 0);
    assert.equal(h.ctrl.binding.stop, null);
    assert.equal(h.engine.bytes().length, before);
    assert.equal(h.ctrl.binding.admission, "open");
    const p = await h.client.prompt("next");
    assert.equal(p.outcome, "admitted");
    await receiptState(h.client, p.receipt.id, "finished");
  } finally {
    await h.close();
  }
});

test("N17: the run fails on its own during the exchange: failed, Failed on its own", async () => {
  const h = await setup();
  try {
    const id = await heldRun(h, [{ text: "", stop: "error", errorMessage: "model error" }]);
    h.engine.arm("clear");
    const stopId = await interrupt(h);
    await h.engine.waitPaused("clear");
    h.engine.resume("p1");
    const r = await receiptState(h.client, id, "failed");
    assert.equal(r.reasonCode, null);
    h.engine.resume("clear");
    await assertUncertainStop(h, stopId, "failed-on-its-own");
  } finally {
    await h.close();
  }
});

test("N18: no final assistant message_end, or a lost line: working stays working; before working, transport-unknown", async () => {
  // No final assistant message during the exchange.
  {
    const h = await setup();
    try {
      const id = await heldRun(h, [{ text: "partial", final: false }]);
      h.engine.arm("clear");
      const stopId = await interrupt(h);
      await h.engine.waitPaused("clear");
      h.engine.resume("p1");
      await until(() => outcomeUnknownPush(h.client, id), 2000, "outcome unknown");
      h.engine.resume("clear");
      const s = await stopSettled(h, stopId);
      assert.equal(s.state, "uncertain");
      assert.equal(h.client.receipt(id).state, "working");
      assert.equal(lastStopEvidence(h.ctrl, stopId).outcome, "unknown");
      assert.equal(h.ctrl.binding.state, "uncertain");
    } finally {
      await h.close();
    }
  }
  // A lost (unparseable) line after working never moves it back.
  {
    const h = await setup();
    try {
      const id = await heldRun(h, [{ raw: "{lost\n" }, { text: "x" }]);
      h.engine.resume("p1");
      await until(() => outcomeUnknownPush(h.client, id), 2000, "outcome unknown");
      await tick(50);
      assert.equal(h.client.receipt(id).state, "working");
      assert.equal(outcomeUnknownPush(h.client, id).reason, TRANSPORT_UNKNOWN);
      assert.ok(!h.client.pushes.some((p) => p.kind === "receipt" && p.receipt.id === id && p.receipt.state === "delivery-unknown"));
    } finally {
      await h.close();
    }
  }
  // A lost line before working.
  {
    const h = await setup();
    try {
      h.engine.arm("run-start");
      h.engine.arm("state");
      const id = await prompt(h);
      await h.engine.waitPaused("run-start");
      await receiptState(h.client, id, "acknowledged");
      h.engine.raw("{lost\n");
      const r = await receiptState(h.client, id, "delivery-unknown");
      assert.equal(r.reasonCode, TRANSPORT_UNKNOWN);
      h.engine.resume("state");
      h.engine.resume("run-start");
    } finally {
      await h.close();
    }
  }
});

test("N19: a losing extension prompt settles inside the Mosaic run before its user message: O3, run-overlap", async () => {
  const h = await setup();
  try {
    h.engine.arm("ext:915");
    void h.engine.extensionPrompt({ text: "loser" });
    await h.engine.waitPaused("ext:915");
    h.engine.arm("after-start");
    const id = await prompt(h);
    await h.engine.waitPaused("after-start");
    await receiptState(h.client, id, "acknowledged");
    h.engine.resume("ext:915");
    await until(() => signals(h.ctrl).includes("O3"), 2000, "O3");
    h.engine.resume("after-start");
    await h.engine.waitIdle();
    const r = await receiptState(h.client, id, "delivery-unknown");
    assert.equal(r.reasonCode, RUN_OVERLAP, "never failed ack-without-start");
    await tick(50);
    assert.equal(h.client.receipt(id).state, "delivery-unknown");
    assert.equal(h.ctrl.binding.state, "uncertain");
  } finally {
    await h.close();
  }
  // Before the Mosaic agent_start: O4.
  const h2 = await setup();
  try {
    h2.engine.arm("run-start");
    h2.engine.arm("state");
    const id = await prompt(h2);
    await h2.engine.waitPaused("run-start");
    await h2.engine.waitPaused("state");
    h2.engine.emit({ type: "agent_settled" });
    await until(() => signals(h2.ctrl).includes("O4"), 2000, "O4");
    const r = await receiptState(h2.client, id, "delivery-unknown");
    assert.equal(r.reasonCode, RUN_OVERLAP);
    h2.engine.resume("state");
    h2.engine.resume("run-start");
    await h2.engine.waitIdle();
    await tick(50);
    assert.equal(h2.client.receipt(id).state, "delivery-unknown");
    assert.equal(h2.ctrl.binding.state, "uncertain");
  } finally {
    await h2.close();
  }
});

test("N20: an extension triggerTurn during Mosaic preflight starts first; while streaming it queues with no signal", async () => {
  const h = await setup();
  try {
    h.engine.arm("915");
    const id = await prompt(h);
    await h.engine.waitPaused("915");
    h.engine.arm("ext-hold");
    void h.engine.extensionPrompt({ text: "timer", preflight: false, steps: [{ pause: "ext-hold" }, { text: "t" }] });
    await h.engine.waitPaused("ext-hold");
    await until(() => signals(h.ctrl).includes("O1"), 2000, "O1");
    h.engine.resume("915");
    h.engine.resume("ext-hold");
    await h.engine.waitIdle();
    const r = await receiptState(h.client, id, "delivery-unknown");
    assert.equal(r.reasonCode, RUN_OVERLAP);
    await tick(50);
    assert.ok(!h.client.pushes.some((p) => p.kind === "receipt" && p.receipt.id === id && ["finished", "failed"].includes(p.receipt.state)), "never finished or failed");
    assert.equal(h.ctrl.binding.state, "uncertain");
  } finally {
    await h.close();
  }
  // While the Mosaic run streams: queued straight into the agent, no signal.
  const h2 = await setup();
  try {
    const id = await heldRun(h2, [{ text: "done", stop: "stop" }]);
    const q = await h2.engine.extensionPrompt({ text: "timer", preflight: false });
    assert.deepEqual(q, { queued: true });
    h2.engine.resume("p1");
    await receiptState(h2.client, id, "finished");
    assert.deepEqual(signals(h2.ctrl), [], "Limit 7: no signal fires");
    assert.ok(h2.engine.sent.some((l) => l.includes('"customType":"fake"') && l.includes("timer")), "the custom message ran inside the Mosaic run");
  } finally {
    await h2.close();
  }
});

test("N21: a losing settle after the receipt settled finished is O2; the receipt stays finished", async () => {
  const h = await setup();
  try {
    const id = await prompt(h);
    await receiptState(h.client, id, "finished");
    h.engine.emit({ type: "agent_settled" });
    await until(() => signals(h.ctrl).includes("O2"), 2000, "O2");
    assert.equal(h.client.receipt(id).state, "finished");
    const o2 = h.ctrl.evidence.overlaps.find((o) => o.signal === "O2");
    assert.equal(o2.request, h.ctrl.receipts.get(id).request, "evidence records the overlap against it");
    assert.equal(h.ctrl.binding.state, "uncertain");
    assert.equal(h.ctrl.binding.admission, "closed");
    assert.ok(h.ctrl.evidence.uncertain.some((u) => u.reason === RUN_OVERLAP));
  } finally {
    await h.close();
  }
});

test("N22: an agent-level custom message is dropped by the clear with no signal; evidence names the seal", async () => {
  const h = await setup();
  try {
    await heldRun(h);
    h.engine.queue("agent", "custom from an extension");
    const stopId = await interrupt(h);
    await until(() => reconciled(h.ctrl, stopId), 6000, "reconciled");
    assert.deepEqual(signals(h.ctrl), [], "Limit 7: no signal fires");
    assert.equal(h.engine.agentQueue.length, 0);
    assert.ok(!h.engine.sent.some((l) => l.includes("custom from an extension")), "the item is gone, never run");
    const ev = lastStopEvidence(h.ctrl, stopId);
    assert.equal(ev.agentLevelQueues, "unobservable");
    assert.match(ev.queueBasis, /^seal:/);
    assert.ok(!JSON.stringify(ev).includes("nothing removed"));
  } finally {
    await h.close();
  }
});

test("N23: a nextTurn message survives clear and abort and attaches to the next prompt, with no signal", async () => {
  const h = await setup();
  try {
    await heldRun(h);
    h.engine.queue("nextTurn", "rides along");
    const stopId = await interrupt(h);
    await until(() => reconciled(h.ctrl, stopId), 6000, "reconciled");
    assert.equal(h.engine.nextTurn.length, 1, "it survived");
    const p = await h.client.prompt("next");
    await receiptState(h.client, p.receipt.id, "finished");
    assert.equal(h.engine.nextTurn.length, 0);
    assert.ok(h.engine.sent.some((l) => l.includes("rides along") && l.includes('"message_start"')), "it attached to the next prompt");
    assert.deepEqual(signals(h.ctrl), [], "Limit 7: no signal fires");
  } finally {
    await h.close();
  }
});

test("N24: the seal is an allow-list: --extension, a missing --no-* flag, a second --mode or --session, a session or output flag, or a stray word refuses unsealed-engine; no engine starts", async () => {
  const fx = fixture();
  const outside = join(fx.base, "outside", "proj", ".pi", "state", "other", "sessions", "s1.jsonl");
  for (const extraArgs of [
    ["--extension", "./ext.ts"], ["--extension=npm:some-ext"], ["-e", "git:github.com/x/y"], ["--extension", "npm:@scope/pkg"],
    // Pi keeps the last --session and the last --mode (cli/args.js).
    ["--session", outside], ["--mode", "json"], ["--mode", "text"], ["--mode", "rpc"],
    ["--no-session"], ["--session-dir", fx.base], ["--session-id", "x"], ["--fork", fx.sessionFile], ["--continue"], ["-c"], ["--resume"],
    ["--print"], ["-p"], ["--export", join(fx.base, "out.html")], ["--prompt-template", "x"], ["--approve"], ["--no-extensions"],
    // A bare word is a prompt, an @ word a file.
    ["hello"], ["@notes.md"],
    // Allowed options: once each, one plain value.
    ["--model", "a", "--model", "b"], ["--model"], ["--model", "--mode"], ["--thinking", "-x"], ["--provider", "@p"], ["--model=other"],
  ]) {
    const launcher = new FakeLauncher();
    assert.throws(
      () => new Controller({ fixtureRoot: fx.base, claimRoot: fx.claimRoot, socketDir: fx.socketDir, sessionFile: fx.sessionFile, seat: fx.seat, launcher, units: noUnits, timeouts: FAST, engine: { extraArgs } }),
      (e) => e.code === UNSEALED_ENGINE,
      JSON.stringify(extraArgs),
    );
    assert.equal(launcher.launches.length, 0);
  }
  {
    const launcher = new FakeLauncher();
    assert.throws(
      () => new Controller({ fixtureRoot: fx.base, claimRoot: fx.claimRoot, socketDir: fx.socketDir, sessionFile: fx.sessionFile, seat: fx.seat, launcher, units: noUnits, engine: { preArgs: ["cli.js", "--extension", "x"] } }),
      (e) => e.code === UNSEALED_ENGINE,
    );
  }
  for (const engine of [{ extraArgs: "--model x" }, { extraArgs: 3 }, { preArgs: "cli.js" }]) {
    assert.throws(
      () => new Controller({ fixtureRoot: fx.base, claimRoot: fx.claimRoot, socketDir: fx.socketDir, sessionFile: fx.sessionFile, seat: fx.seat, launcher: new FakeLauncher(), units: noUnits, engine }),
      (e) => e.code === UNSEALED_ENGINE,
      JSON.stringify(engine),
    );
  }
  // The controller always builds the prefix itself, so a missing flag, a
  // reordered prefix or a relative session path is reachable only through
  // checkSeal, which bind runs on the argv.
  for (const flag of SEAL_FLAGS) {
    const args = ["--mode", "rpc", ...SEAL_FLAGS.filter((f) => f !== flag), "--session", fx.sessionFile];
    assert.throws(() => checkSeal(args), (e) => e.code === UNSEALED_ENGINE, flag);
  }
  for (const args of [
    ["--mode", "rpc", "--session", fx.sessionFile, ...SEAL_FLAGS],
    ["--mode", "json", ...SEAL_FLAGS, "--session", fx.sessionFile],
    ["--mode", "rpc", ...SEAL_FLAGS, "--session", "s1.jsonl"],
    ["--mode", "rpc", ...SEAL_FLAGS, "--session"],
  ]) {
    assert.throws(() => checkSeal(args), (e) => e.code === UNSEALED_ENGINE, JSON.stringify(args));
  }
  assert.equal(checkSeal(["--mode", "rpc", ...SEAL_FLAGS, "--session", fx.sessionFile, "--model", "m", "--provider", "p", "--thinking", "off"]), true);
  // The argv a real bind launches carries every seal flag and no --extension.
  const h = await started({ fx: fixture() });
  try {
    const args = h.launcher.launches[0].args;
    for (const flag of SEAL_FLAGS) assert.ok(args.includes(flag), flag);
    assert.ok(!args.some((a) => a === "-e" || a.startsWith("--extension")));
    assert.deepEqual(h.engine.argv.slice(0, 2), ["--mode", "rpc"]);
  } finally {
    await h.close();
  }
});

test("N24b: the seal covers the engine command and environment: config can't name either, the env is built from names, and a mutated command is refused at bind", async () => {
  const fx = fixture();
  const make = (extra) => new Controller({ fixtureRoot: fx.base, claimRoot: fx.claimRoot, socketDir: fx.socketDir, sessionFile: fx.sessionFile, seat: fx.seat, launcher: new FakeLauncher(), units: noUnits, timeouts: FAST, ...extra });
  // The plain engine option takes extraArgs, cwd and envKeys; the command,
  // pre-arguments and environment are the controller's (I3, #1507).
  for (const engine of [{ command: "/bin/sh" }, { preArgs: [join(REPO_ROOT, PI_BIN)] }, { command: process.execPath, preArgs: [join(REPO_ROOT, PI_BIN), "--extension", "x"] }, { env: {} }, { env: process.env }, null, [], "pi"]) {
    assert.throws(() => make({ engine }), (e) => e.code === UNSEALED_ENGINE, JSON.stringify(engine));
  }
  // A configuration is JSON, which can't carry the symbol-keyed test engine.
  const parsed = JSON.parse(JSON.stringify({ engine: { cwd: fx.proj }, [TEST_ENGINE]: { command: "/bin/sh", preArgs: [], env: {} } }));
  assert.equal(Object.getOwnPropertySymbols(parsed).length, 0);
  // envKeys may name provider credentials only.
  for (const envKeys of [["NODE_OPTIONS"], ["LD_PRELOAD"], ["PI_PACKAGE_DIR"], ["BASH_ENV"], ["ZAI_API_KEY", "PATH"], ["zai_api_key"], ["_API_KEY"], [3], "ZAI_API_KEY"]) {
    assert.throws(() => make({ engine: { envKeys } }), (e) => e.code === UNSEALED_ENGINE, JSON.stringify(envKeys));
  }
  // The test engine is still sealed on its arguments.
  assert.throws(() => make({ [TEST_ENGINE]: { command: process.execPath, preArgs: ["fake.mjs", "-e", "x"], env: {} } }), (e) => e.code === UNSEALED_ENGINE);
  assert.throws(() => make({ [TEST_ENGINE]: { command: "", preArgs: [], env: {} } }), (e) => e.code === UNSEALED_ENGINE);

  // The launch: this Node, the pinned bin, and an environment of named keys
  // only, whatever the controller's own environment holds.
  const planted = { NODE_OPTIONS: "--require /tmp/x.cjs", LD_PRELOAD: "/tmp/x.so", PI_PACKAGE_DIR: "/tmp/pkg", ZAI_API_KEY: "zai-test-value", OTHER_API_KEY: "other-test-value" };
  const saved = Object.fromEntries(Object.keys(planted).map((k) => [k, process.env[k]]));
  Object.assign(process.env, planted);
  let h;
  try {
    h = await started({ fx: fixture(), engine: { envKeys: ["ZAI_API_KEY"] } });
  } finally {
    for (const [k, v] of Object.entries(saved)) if (v === undefined) delete process.env[k]; else process.env[k] = v;
  }
  try {
    const l = h.launcher.launches[0];
    assert.equal(l.command, process.execPath);
    assert.equal(l.args[0], join(REPO_ROOT, PI_BIN));
    assert.equal(l.env.ZAI_API_KEY, "zai-test-value");
    for (const k of Object.keys(l.env)) assert.ok(ENGINE_ENV.includes(k) || k === "ZAI_API_KEY", k);
    for (const k of ["NODE_OPTIONS", "LD_PRELOAD", "PI_PACKAGE_DIR", "OTHER_API_KEY"]) assert.equal(k in l.env, false, k);
    if (process.env.PATH) assert.equal(l.env.PATH, process.env.PATH);
  } finally {
    await h.close();
  }

  // A command changed after construction is refused at bind; nothing launches.
  const fx2 = fixture();
  const launcher = new FakeLauncher();
  const ctrl = new Controller({ fixtureRoot: fx2.base, claimRoot: fx2.claimRoot, socketDir: fx2.socketDir, sessionFile: fx2.sessionFile, seat: fx2.seat, launcher, units: noUnits, timeouts: FAST });
  // Closed in finally: a start that wrongly succeeds holds the socket open.
  try {
    ctrl.engine.command = "/bin/sh";
    await assert.rejects(ctrl.start(), (e) => e.code === UNSEALED_ENGINE);
    assert.equal(launcher.launches.length, 0);
    ctrl.engine.command = process.execPath;
    ctrl.engine.preArgs = [join(fx2.base, "cli.js")];
    await assert.rejects(ctrl.start(), (e) => e.code === UNSEALED_ENGINE);
    assert.equal(launcher.launches.length, 0);
  } finally {
    await ctrl.close().catch(() => {});
  }
});