test(cli): cover the dsh built-bin non-TTY refusal

Removing the dsh-tui-demo bin dropped the only test of the TUI's piped-launch
refusal. Add apps/cli/tests/built-bin.e2e.ts (apps/*/tests added to the e2e
vitest include) running the built lib/bin.js under plain Node with piped stdio,
and point the refusal message at `dsh -p "task"` for automation.

apps/cli/src/tui.ts

@@ -53,7 +53,9 @@ export async function runTui(config: string | undefined, resumeSessionId: string
   // is logged per-entry rather than rethrown, so a piped launch would
   // otherwise settle into an idle UI-less process instead of exiting nonzero.
   if (!process.stdin.isTTY || !process.stdout.isTTY) {
-    process.stderr.write(`${NAME}: the TUI requires stdin and stdout to be interactive TTYs\n`)
+    process.stderr.write(
+      `${NAME}: the TUI requires stdin and stdout to be interactive TTYs; use \`${NAME} -p "task"\` for pipes and automation\n`,
+    )
     process.exit(1)
   }
   installFailLoud(NAME)

apps/cli/tests/built-bin.e2e.ts

@@ -0,0 +1,54 @@
+import { spawn } from 'node:child_process'
+import { existsSync } from 'node:fs'
+import { join } from 'node:path'
+import { fileURLToPath } from 'node:url'
+import { describe, expect, it } from 'vitest'
+
+/**
+ * Published-entry smoke for the `dsh` bin: run the built `lib/bin.js` under
+ * plain Node (no tsx) with PIPED stdio and assert the TUI refuses to boot.
+ * `dsh` is the sole terminal front door; the TUI owns no non-TTY fallback, so a
+ * piped launch must exit nonzero with a stderr pointer at the one-shot `-p`
+ * mode. The guard fires inside `runTui` BEFORE the Loader resolves the config
+ * tree — a compose-time throw inside the tree is logged per-entry, not
+ * rethrown, so without this guard a piped launch would settle into an idle
+ * UI-less process. The bin resolves its workspace deps through the repo's
+ * node_modules, so no external consumer is assembled; missing-config fail-loud
+ * and full-boot coverage for the shared dsh-app-boot glue live in cli-demo's
+ * built-bin suite, and interactive TTY behavior is PTY-covered by
+ * examples/tui-agent. Skips before the bin is built.
+ */
+
+const repoRoot = fileURLToPath(new URL('../../../', import.meta.url))
+const dshBin = join(repoRoot, 'apps/cli/lib/bin.js')
+
+/** Run the built bin with PIPED stdio; resolve with output + exit code. */
+function runBuiltBin(): Promise<{ stdout: string; code: number; stderr: string }> {
+  return new Promise((resolve, reject) => {
+    const child = spawn(process.execPath, [dshBin], { stdio: ['pipe', 'pipe', 'pipe'] })
+    let stdout = ''
+    let stderr = ''
+    child.stdout.setEncoding('utf8')
+    child.stdout.on('data', (c: string) => { stdout += c })
+    child.stderr.setEncoding('utf8')
+    child.stderr.on('data', (c: string) => { stderr += c })
+    const timer = setTimeout(() => {
+      child.kill('SIGKILL')
+      reject(new Error(`dsh built bin did not exit within 25s. stdout:\n${stdout}\nstderr:\n${stderr}`))
+    }, 25_000)
+    child.on('exit', (code) => { clearTimeout(timer); resolve({ stdout, code: code ?? -1, stderr }) })
+    child.on('error', (err) => { clearTimeout(timer); reject(err) })
+    child.stdin.end()
+  })
+}
+
+describe.skipIf(!existsSync(dshBin))('dsh BUILT bin (node lib/bin.js, no tsx)', () => {
+  it('refuses pipes LOUD (non-zero exit + stderr) before booting the Loader', async () => {
+    const { stdout, code, stderr } = await runBuiltBin()
+    expect(code).not.toBe(0)
+    expect(stderr).toContain('requires stdin and stdout to be interactive TTYs')
+    expect(stderr).toContain('dsh -p')
+    // The refusal happens before any plugin mounts: stdout stays silent.
+    expect(stdout).toBe('')
+  }, 30_000)
+})