diff --git a/hermes_cli/profiles.py b/hermes_cli/profiles.py
index c21b5319dd..8ee6d18850 100644
--- a/hermes_cli/profiles.py
+++ b/hermes_cli/profiles.py
@@ -294,10 +294,21 @@ def normalize_profile_name(name: str) -> str:
     case-insensitively. Dashboards/tools may pass title-cased labels — normalize before
     validation, assignment, and subprocess spawn.
 
-    Named profiles are stored lowercase under ``profiles/<id>/``. See #18498.
+    Named profiles are stored lowercase under ``profiles/<id>/``. The special
+    alias ``default`` is matched case-insensitively (``Default`` → ``default``).
+    Dashboards and tools may pass title-cased display labels; normalize before
+    validation, assignment, and subprocess spawn (see issue #18498).
+
+    Raises ``ValueError`` for non-string input: a numeric profile id (e.g. a
+    DB row id or a falsy sentinel) silently coerced via ``str()`` becomes a
+    real on-disk profile directory (``profiles/0/``, #88842). Callers that
+    hold a numeric id must resolve it to an actual profile name first.
     """
     if not isinstance(name, str):
-        name = str(name)
+        raise ValueError(
+            "profile name must be a string, got "
+            f"{type(name).__name__}: {name!r}"
+        )
     stripped = name.strip()
     if not stripped:
         raise ValueError("profile name cannot be empty")
diff --git a/tests/hermes_cli/test_profiles.py b/tests/hermes_cli/test_profiles.py
index 035dbd8311..95281c20cc 100644
--- a/tests/hermes_cli/test_profiles.py
+++ b/tests/hermes_cli/test_profiles.py
@@ -75,6 +75,21 @@ class TestNormalizeProfileName:
         assert normalize_profile_name("Jules") == "jules"
         assert normalize_profile_name("  Librarian ") == "librarian"
 
+    def test_non_string_name_rejected(self):
+        # A numeric profile id (DB row id / falsy sentinel) must not be
+        # silently coerced into a real on-disk profile directory (#88842).
+        with pytest.raises(ValueError):
+            normalize_profile_name(0)
+        with pytest.raises(ValueError):
+            normalize_profile_name(None)
+        with pytest.raises(ValueError):
+            normalize_profile_name(42)
+
+    def test_literal_zero_string_is_a_valid_explicit_name(self):
+        # A literal "0" typed by the user is a legal profile id; only the
+        # non-string coercion created the phantom profile.
+        assert normalize_profile_name("0") == "0"
+
 
 class TestValidateProfileName:
     """Tests for validate_profile_name()."""