refactor: share loader smoke harness

packages/support/loader-smoke/tests/fixtures/fail.ts

@@ -0,0 +1,4 @@
+/** Non-zero subprocess fixture for the Loader-smoke harness. */
+
+console.error('fixture failed')
+process.exitCode = 7

packages/support/loader-smoke/tests/fixtures/hang.ts

@@ -0,0 +1,4 @@
+/** Deadline subprocess fixture for the Loader-smoke harness. */
+
+console.log('fixture hanging')
+setInterval(() => {}, 1_000)

packages/support/loader-smoke/tests/fixtures/success.ts

@@ -0,0 +1,16 @@
+/** Successful subprocess fixture for the Loader-smoke harness. */
+
+let input = ''
+process.stdin.setEncoding('utf8')
+process.stdin.on('data', (chunk: string) => { input += chunk })
+process.stdin.on('end', () => {
+  console.log(JSON.stringify({
+    configPath: process.argv[2],
+    cwd: process.cwd(),
+    dshHome: process.env.DSH_HOME,
+    agentsHome: process.env.DSH_AGENTS_HOME,
+    marker: process.env.LOADER_SMOKE_MARKER,
+    input,
+  }))
+  console.error('fixture stderr')
+})