fix: keep stderr after the report it closes

verify.py --emulator fbneo --strict > log 2>&1 put the ERROR verdict on
the first line of the log: redirected, stdout is block-buffered and
stderr is not, and run_cli flushed stdout only after main returned.
run_cli now sets stdout to line buffering, so every tool it runs keeps
the two streams in the order they were written.

scripts/common.py

@@ -3676,6 +3676,13 @@ def run_cli(main: Callable[[], int | None]) -> None:
     for name in ("SIGTERM", "SIGHUP"):
         if hasattr(signal, name):
             signal.signal(getattr(signal, name), _exit_on_signal)
+    # Redirected, stdout is block-buffered and stderr is not: the --strict
+    # verdict landed on the first line of the log, before the report it
+    # closes. Line buffering keeps the two in the order they were written.
+    # A stream a caller swapped in (a test's StringIO) has nothing to set.
+    reconfigure = getattr(sys.stdout, "reconfigure", None)
+    if reconfigure is not None:
+        reconfigure(line_buffering=True)
     try:
         code = main()
         sys.stdout.flush()

tests/test_tool_messages.py

@@ -147,6 +147,31 @@ class ADamagedProfileNamesItself(unittest.TestCase):
         self.assertFalse(issubclass(common.SourceUnreadable, FileNotFoundError))
 
 
+class TheVerdictClosesARedirectedReport(unittest.TestCase):
+    """`verify.py --emulator fbneo --strict > log 2>&1` put the --strict
+    ERROR on the first line of the log: stdout redirected is block-buffered,
+    stderr is not, and the report it closes came after."""
+
+    def test_stderr_stays_after_what_stdout_wrote_first(self):
+        program = (
+            "import sys\n"
+            "sys.path.insert(0, 'scripts')\n"
+            "from common import run_cli\n"
+            "def main():\n"
+            "    print('report')\n"
+            "    print('ERROR: verdict', file=sys.stderr)\n"
+            "    return 1\n"
+            "run_cli(main)\n"
+        )
+        env = {k: v for k, v in os.environ.items() if k != "PYTHONUNBUFFERED"}
+        proc = subprocess.run(
+            [sys.executable, "-c", program], cwd=REPO_ROOT, stdout=subprocess.PIPE,
+            stderr=subprocess.STDOUT, text=True, timeout=60, check=False, env=env,
+        )
+        self.assertEqual(proc.returncode, 1)
+        self.assertEqual(proc.stdout.splitlines(), ["report", "ERROR: verdict"])
+
+
 class AMistypedTargetAcrossAllPlatforms(unittest.TestCase):
     """`verify --all --target swich` ended on "no platform has it" after 17
     INFO lines, two of which held the suggestion."""