diff --git a/rvctl.py b/rvctl.py
index 292ad3d..7d7219d 100755
--- a/rvctl.py
+++ b/rvctl.py
@@ -3352,6 +3352,28 @@ def current_user_slug() -> str:
     return slug_value(os.environ.get("USER") or home_dir.name or f"uid{os.getuid()}", "user name")
 
 
+def display_user_slug(raw_user: str) -> str:
+    match = re.fullmatch(r"u(\d+)", raw_user)
+    if match:
+        return f"u{int(match.group(1)):02d}"
+    return raw_user
+
+
+def runtime_name_slug(raw_value: str, field_name: str) -> str:
+    slug = re.sub(r"[^a-z0-9]+", "_", raw_value.strip().lower()).strip("_")
+    if not slug:
+        raise SystemExit(f"Invalid {field_name}: {raw_value!r}")
+    return slug
+
+
+def runtime_name(user_name: str, profile: str, selector: str, window_name: str) -> str:
+    selector_parts = selector.split("/")
+    name_parts = [display_user_slug(user_name), profile]
+    name_parts.extend(runtime_name_slug(part, "card selector") for part in selector_parts)
+    name_parts.append(runtime_name_slug(window_name, "tmux window name"))
+    return "_".join(name_parts)
+
+
 def build_container_command(
     config: WorkspaceConfig,
     selector: str,
@@ -3373,13 +3395,10 @@ def build_container_command(
 
     home_dir = Path(os.environ.get("HOME") or str(Path.home()))
     card_path_text = str(card_path)
-    selector_slug = slug_value(selector.replace("/", "-"), "card selector")
-    window_slug = slug_value(window_name, "tmux window name")
     user_name = current_user_slug()
     host_uid = str(os.getuid())
     host_gid = str(os.getgid())
-    container_name_parts = [selector_slug, window_slug, profile, user_name]
-    container_name = "-".join(container_name_parts)
+    container_name = runtime_name(user_name, profile, selector, window_name)
     shell_rcfile = tool_root / "configs" / "rv-shell.bashrc"
     env_parts = [
         f"WORKSPACE_ROOT={shlex.quote(str(config.workspace_root))}",
@@ -3464,7 +3483,7 @@ def run_tmux_container(config: WorkspaceConfig, args: argparse.Namespace) -> Non
 
     profile = normalize_env_profile(args.profile)
     user_name = current_user_slug()
-    default_session_name = f"rvctl-{user_name}-{slug_value(selector.replace('/', '-'), 'card selector')}-{profile}"
+    default_session_name = runtime_name(user_name, profile, selector, args.window or config.defaults.get("tmux_window", "rv"))
     session_name = args.session or default_session_name
     window_name = args.window or config.defaults.get("tmux_window", "rv")
     instance = args.instance or config.defaults.get("instance", "shell")