swarm-ui: a builds page for the swarm builder's runs, and the status links to it

/builds lists the builder's recent builds newest first, one card each with how
it ended, and opens a failed build's nix tail. /builds?run=<id> opens that
build's card and scrolls to it. The swarm-builder commit status now links
there instead of to the raw JSON record.

frontend/packages/swarm-ui/test/builds-types.test.mjs

@@ -0,0 +1,51 @@
+// The builds page's `?run=` link and what each outcome's card shows. Run by
+// `npm test`, which Node runs with its built-in test runner and type
+// stripping, so the `.ts` module is imported as it is.
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import { bodyText, wantedRun } from "../src/pages/builds/builds-types.ts";
+
+const base = {
+  id: "atlas-abc-1",
+  repo: "agent-configs/atlas",
+  pr: 3,
+  head_sha: "abcdef0123456789",
+  started_unix: 100,
+  finished_unix: 160,
+};
+
+test("a ?run= link names the run it carries", () => {
+  assert.equal(wantedRun("?run=atlas-abc-1"), "atlas-abc-1");
+  assert.equal(wantedRun("run=atlas-abc-1&x=1"), "atlas-abc-1");
+});
+
+test("no run, or an empty one, names none", () => {
+  assert.equal(wantedRun(""), null);
+  assert.equal(wantedRun("?x=1"), null);
+  assert.equal(wantedRun("?run="), null);
+});
+
+test("a failed build shows what nix printed, as it was printed", () => {
+  const body = bodyText({ ...base, outcome: "failed", error_tail: "error: x" });
+  assert.deepEqual(body, {
+    label: "what nix printed",
+    text: "error: x",
+    preformatted: true,
+  });
+});
+
+test("a built one shows its closure, an errored one its reason", () => {
+  assert.equal(
+    bodyText({ ...base, outcome: "built", out_path: "/nix/store/x" })?.text,
+    "/nix/store/x",
+  );
+  assert.equal(
+    bodyText({ ...base, outcome: "error", detail: "no node" })?.text,
+    "no node",
+  );
+});
+
+test("a run with no text for its outcome shows no body", () => {
+  assert.equal(bodyText({ ...base, outcome: "failed" }), null);
+  assert.equal(bodyText({ ...base, outcome: "built", error_tail: "x" }), null);
+});