Prove the board says what a person opened it for

A machine is given a declaration it cannot apply, and the board names it,
says 'failed' rather than 'error', and shows the host's own words about what it
could not do — a board that said only 'failed' would send a person to ask the
thing they opened the board to avoid asking.

And it agrees with the command, from the same read: two answers to 'which
machine is broken' would be worse than either alone. Reading it changes
nothing.

test/integration/mesh.test.ts

@@ -1109,3 +1109,73 @@ test("a new commit reaches a machine that is already running the old one", {
   assert.doesNotMatch(after, /delivered.*<.*[0-9a-f]{8}/,
     `the module is still reported as behind after catching up:\n${after}`);
 });
+
+test("the board names the machine that is not doing what it was told", {
+  skip, timeout: 900_000,
+}, async () => {
+  // novox/hq 03-DESIGN/01-to-be/11-a-board.md. The board being replaced reads every context's
+  // database directly; this one asks the same questions through the same functions the commands
+  // use, and holds nothing. So the check is that what it says matches what the mesh says, and
+  // that it says the thing a person opened it for.
+  await must("anchor", `printf %s '{"module":"board","version":"1",` +
+    `"listens":[{"port":8090,"from":"mesh","why":"the board"}],` +
+    `"resources":[]}' > /tmp/board.json`);
+  await must("anchor", `docker cp /tmp/board.json mesh-control:/board.json`);
+  await mesh("module add /board.json");
+
+  // Served from the control plane's own container, reading the mesh on every request.
+  await must("anchor", `docker exec -d mesh-control /mesh-control board --listen 0.0.0.0:8090`);
+  await new Promise((r) => setTimeout(r, 3000));
+
+  const read = async (path: string) =>
+    await on("anchor", `curl -sf http://127.0.0.1:8090${path}`, 30_000);
+
+  let up = false;
+  let said = { out: "", ok: false };
+  for (let i = 0; i < 15 && !up; i++) {
+    said = await read("/");
+    up = said.ok;
+    if (!up) await new Promise((r) => setTimeout(r, 2000));
+  }
+  assert.ok(up, `the board does not answer:\n${said.out}`);
+
+  // Something a person opened it for: give a machine a declaration it cannot apply.
+  await must("anchor", `printf %s '{"module":"impossible","version":"1",` +
+    `"resources":[{"id":"nowhere","type":"file","path":"/does/not/exist/at/all/file",` +
+    `"content":"x","mode":"0644"}]}' > /tmp/impossible.json`);
+  await must("anchor", `docker cp /tmp/impossible.json mesh-control:/impossible.json`);
+  await mesh("module add /impossible.json");
+  await mesh("assign laptop impossible");
+  await mesh("push laptop");
+
+  let named = false;
+  let page = "";
+  for (let i = 0; i < 20 && !named; i++) {
+    page = (await read("/")).out;
+    named = page.includes("laptop") && page.includes(">failed<");
+    if (!named) await new Promise((r) => setTimeout(r, 3000));
+  }
+  assert.ok(named, `the board does not name the machine that failed:\n${page}`);
+
+  // The host's own words, which say exactly what it could not do. A board that said only
+  // "failed" would make a person go and ask the thing they opened the board to avoid asking.
+  assert.match(page, /nowhere/, `the board does not say what failed:\n${page}`);
+
+  // It agrees with the command, because both read the same thing. Two answers to "which machine
+  // is broken" is worse than either alone.
+  const asJSON = JSON.parse((await read("/mesh.json")).out);
+  assert.equal(asJSON.wrong[0].node, "laptop", `the page and the JSON disagree: ${JSON.stringify(asJSON)}`);
+  assert.equal(asJSON.wrong[0].outcome, "failed");
+
+  const fromCommand = JSON.parse(await mesh("status --json"));
+  assert.deepEqual(asJSON.wrong, fromCommand.wrong,
+    "the board and the command disagree about which machine is broken");
+
+  // And it changes nothing: the mesh is exactly as it was after being read.
+  const before = await mesh("status");
+  await read("/");
+  assert.equal(await mesh("status"), before, "reading the board changed the mesh");
+
+  await mesh("unassign laptop impossible");
+  await mesh("push laptop");
+});