mesh-build-node: emit a package that builds before its tests, so tests importing its own output find it (issue 1869, part of issue 1309's run step)

A package with a build or prepare script and a tsconfig.json is built with tsc -p . in the
shut-off run step, at both levels, instead of the --noEmit type-check; the fetch's
--ignore-scripts never runs those scripts. mesh-sdk's tests import ../dist and failed
ERR_MODULE_NOT_FOUND. The result names the step build.

modules/mesh-build-node/cmd/mesh-build-node/build_integration_test.go

@@ -89,3 +89,28 @@ func TestTheFixturePassesTheUnitLevel(t *testing.T) {
 		t.Errorf("result = %+v", r)
 	}
 }
+
+// Issue 1869: a package whose test imports its own build output (as mesh-sdk's do) passes the unit level: the test step
+// emits it with the real tsc, shut off, before the test script runs.
+func TestAPackageWhoseTestsImportItsBuildPassesTheUnitLevel(t *testing.T) {
+	if _, err := exec.LookPath("bwrap"); err != nil {
+		t.Skip("NOT RUN: no bubblewrap installed where this check runs; every build node has it (the module declares it)")
+	}
+	m, work := realMachine(t)
+	for p, body := range map[string]string{
+		"modules/p/package.json":  `{"name":"p","type":"module","scripts":{"build":"tsc","test":"node --test test/a.test.mjs","prepare":"tsc"}}`,
+		"modules/p/tsconfig.json": `{"compilerOptions":{"module":"NodeNext","moduleResolution":"NodeNext","target":"ES2022","outDir":"dist","rootDir":"src"},"include":["src"]}`,
+		"modules/p/src/index.ts":  "export const answer: number = 42;\n",
+		"modules/p/test/a.test.mjs": "import { test } from 'node:test';\nimport assert from 'node:assert';\nimport { answer } from '../dist/index.js';\n" +
+			"test('the build is there', () => assert.equal(answer, 42));\n",
+	} {
+		write(t, filepath.Join(work, "w1", "tree", filepath.FromSlash(p)), body, 0o644)
+	}
+	out, err := m.test(context.Background(), map[string]any{"workspace": "w1", "module": "modules/p", "level": "unit"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if r := out.(*TestResult); !r.Passed || !slices.Equal(r.Ran, []string{"build", "test"}) {
+		t.Errorf("result = %+v", r)
+	}
+}