test(ship): the PR check precedes the Greptile dispatch, and each skip names its reason

Runs Step 10's generated check against stub gh for gh missing, not logged
in, a non-GitHub remote, no PR, a failed lookup and an existing PR. Fails on
the previous text (which printed PR: unknown and dispatched).

Co-authored-by: dgrant <dgrant@users.noreply.github.com>

test/ship-greptile-pr-check.test.ts

@@ -0,0 +1,54 @@
+/**
+ * /ship Step 10 (CEO-19, ENG-1): the PR check runs before the Greptile triage
+ * dispatch, and every outcome except an existing PR skips the dispatch with
+ * its reason. The check block is executed from the generated section against
+ * stub `gh` binaries.
+ */
+import { afterAll, describe, expect, test } from 'bun:test';
+import { spawnSync } from 'child_process';
+import * as fs from 'fs';
+import * as os from 'os';
+import * as path from 'path';
+
+const ROOT = path.resolve(import.meta.dir, '..');
+const SECTION = fs.readFileSync(path.join(ROOT, 'ship/sections/greptile.md'), 'utf8');
+const CHECK = SECTION.match(/```bash\n([\s\S]*?)\n```/)![1];
+const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-ship-greptile-'));
+afterAll(() => fs.rmSync(tmp, { recursive: true, force: true }));
+
+/** Run the check with a PATH holding only `head` and, unless null, a stub gh. */
+function check(gh: string | null): string {
+  const bin = fs.mkdtempSync(path.join(tmp, 'bin-'));
+  fs.symlinkSync(Bun.which('head')!, path.join(bin, 'head'));
+  if (gh !== null) fs.writeFileSync(path.join(bin, 'gh'), `#!${Bun.which('bash')}\n${gh}\n`, { mode: 0o755 });
+  const r = spawnSync(Bun.which('bash')!, ['-c', CHECK], { cwd: tmp, encoding: 'utf8', timeout: 10_000, env: { PATH: bin } });
+  expect(r.status, r.stderr).toBe(0);
+  return r.stdout.trim();
+}
+
+describe('/ship Step 10 Greptile PR check', () => {
+  test('the PR check precedes the dispatch, and only an existing PR dispatches', () => {
+    const checkIdx = SECTION.indexOf('gh pr view --json number');
+    const dispatchIdx = SECTION.indexOf('Dispatch a subagent through Agent');
+    expect(checkIdx).toBeGreaterThan(-1);
+    expect(dispatchIdx).toBeGreaterThan(checkIdx);
+    const between = SECTION.slice(checkIdx, dispatchIdx);
+    expect(between).toContain('Only `PR: exists` dispatches.');
+    expect(between).toContain('"Greptile: not run (<reason>); runs on the PR once it exists"');
+    expect(SECTION).not.toContain('PR: unknown');
+  });
+
+  const ok = 'exit 0';
+  const cases: Array<[string, string | null, string]> = [
+    ['gh missing', null, 'PR: skip (gh not installed)'],
+    ['gh not logged in', `[ "$1" = auth ] && { echo "You are not logged into any GitHub hosts." >&2; exit 1; }; ${ok}`, 'PR: skip (gh not logged in)'],
+    ['non-GitHub remote', `[ "$1" = repo ] && { echo "none of the git remotes configured for this repository point to a known GitHub host" >&2; exit 1; }; ${ok}`,
+      'PR: skip (not a GitHub remote: none of the git remotes configured for this repository point to a known GitHub host)'],
+    ['no PR yet', `[ "$1" = pr ] && { echo 'no pull requests found for branch "feat"' >&2; exit 1; }; ${ok}`, 'PR: skip (no PR yet)'],
+    ['other lookup error', `[ "$1" = pr ] && { printf 'HTTP 502: bad gateway\\nretry later\\n' >&2; exit 1; }; ${ok}`, 'PR: skip (PR lookup failed: HTTP 502: bad gateway)'],
+    ['PR exists', `[ "$1" = pr ] && { echo 12; exit 0; }; ${ok}`, 'PR: exists'],
+  ];
+  for (const [name, gh, expected] of cases) {
+    test(name, () => expect(check(gh)).toBe(expected));
+  }
+});