fix: search past a folder this user cannot open

One closed folder under HOME (~/.config/EmuDeck at 000) made the whole
detection return nothing: a RetroArch whose retroarch.cfg was readable
was lost and the run fell back to a folder it does not read. Every
detection probe now goes through _exists, _is_dir or _is_file, which
count a refused place as absent, name the closed folder once, and let
the other probes go on. The decorator stays as the last net.

The refusal is an unsearched event before detect. The interface keeps
the line above the list of setups. At HOME or a drive root A goes into
a visible subfolder, never a card or drive row nor .cache, and with
none it stays on Use this folder and says where it is. A default folder
taken because the platform was not found is no longer called detected.

tests/test_install_experience.py

@@ -665,6 +665,84 @@ class AHomeThisUserCannotOpen(unittest.TestCase):
         self.assertIn(f"Could not look for setups: this user cannot open {home}",
                       runs["detected"].stderr)
 
+    @unittest.skipIf(os.name == "nt" or os.geteuid() == 0,
+                     "a folder without search permission is POSIX")
+    def test_an_assumed_folder_is_not_called_detected(self):
+        """The refusal ended "than the one detected here" for the built-in
+        default taken because RetroArch was not detected."""
+        with FakeRepository() as repo:
+            home = repo.root / "home"
+            home.mkdir()
+            env = {**repo.env(), "HOME": str(home), "RETROBIOS_OS": "linux"}
+            os.chmod(home, 0o000)
+            try:
+                proc = subprocess.run(
+                    [sys.executable, str(REPO_ROOT / "install.py"), "--check",
+                     "--no-input", "--platform", "retroarch"],
+                    env=env, capture_output=True, text=True, timeout=60,
+                    stdin=subprocess.DEVNULL)
+            finally:
+                os.chmod(home, 0o755)
+        self.assertEqual(proc.returncode, 1, proc.stdout + proc.stderr)
+        said = " ".join(proc.stderr.split())
+        self.assertNotIn("the one detected here", said)
+        self.assertIn("than the one taken as RetroArch's default, RetroArch not being "
+                      "found here (name another with --dest).", said)
+
+
+class APartlyClosedHome(unittest.TestCase):
+    """~/.config/EmuDeck at 000 (a sudo run leaves it owned by root) made
+    detection return nothing: the readable retroarch.cfg beside it was
+    never read, and the run fell back to ~/.config/retroarch/system, a
+    folder that RetroArch does not read."""
+
+    @unittest.skipIf(os.name == "nt" or os.geteuid() == 0,
+                     "a folder without search permission is POSIX")
+    def test_retroarch_is_found_past_the_closed_folder(self):
+        with FakeRepository() as repo:
+            home = repo.root / "home"
+            closed = home / ".config" / "EmuDeck"
+            closed.mkdir(parents=True)
+            cfg = home / ".config" / "retroarch" / "retroarch.cfg"
+            cfg.parent.mkdir()
+            system = repo.root / "elsewhere" / "system"
+            system.mkdir(parents=True)
+            cfg.write_text(f'system_directory = "{system}"\n')
+            env = {**repo.env(), "HOME": str(home), "RETROBIOS_OS": "linux"}
+            runs = {}
+            os.chmod(closed, 0o000)
+            try:
+                for name, extra in (("detected", []),
+                                    ("named", ["--platform", "retroarch"]),
+                                    ("events", ["--events"])):
+                    runs[name] = subprocess.run(
+                        [sys.executable, str(REPO_ROOT / "install.py"), "--check",
+                         "--no-input", *extra],
+                        env=env, capture_output=True, text=True, timeout=60,
+                        stdin=subprocess.DEVNULL)
+            finally:
+                os.chmod(closed, 0o755)
+        refusal = (f"Could not look for setups: this user cannot open {closed} "
+                   "(Permission denied)")
+        for name, proc in runs.items():
+            with self.subTest(run=name):
+                self.assertNotIn("Traceback", proc.stderr)
+                self.assertEqual(" ".join(proc.stderr.split()).count(refusal), 1,
+                                 proc.stderr)
+                self.assertNotIn(str(home / ".config" / "retroarch" / "system"),
+                                 proc.stdout + proc.stderr)
+        self.assertIn(f"Found RetroArch at {system}", runs["detected"].stdout)
+        self.assertIn("0/5 present", runs["named"].stdout)
+        self.assertNotIn("not detected", runs["named"].stdout)
+        events = [json.loads(line) for line in runs["events"].stdout.splitlines()]
+        kinds = [event["event"] for event in events]
+        self.assertLess(kinds.index("unsearched"), kinds.index("detect"))
+        unsearched = events[kinds.index("unsearched")]
+        self.assertEqual((unsearched["folder"], unsearched["reason"]),
+                         (str(closed), "Permission denied"))
+        detect = events[kinds.index("detect")]
+        self.assertEqual([entry["bios_dir"] for entry in detect["platforms"]], [str(system)])
+
 
 class OutputToAFileAsksNothing(unittest.TestCase):
     """`install.py > log.txt` at a terminal: the menu went into the file