/help showing commands that players do not have permission for (Brigadier)

Expected behavior

When declaring a requirement (mainly a permission requirement) using an ArgumentBuilder from Brigadier using .requires(source -> source.getSender().hasPermission("plugin.permission")), it is expected that such a command, as it is not visible to the client, showing the red text saying that this command does not exist, should also not be visible using /help.

Observed/Actual behavior

Instead, when running /help, anybody can still see the command. This isn't necessarily a big problem, but it feels like unintended behavior.

Steps/models to reproduce

Defining a command like this:

package io.papermc.testplugin;

import io.papermc.paper.command.brigadier.Commands;
import io.papermc.paper.plugin.lifecycle.event.types.LifecycleEvents;
import org.bukkit.plugin.java.JavaPlugin;

public final class TestPlugin extends JavaPlugin {

    @Override
    public void onEnable() {
        this.getLifecycleManager().registerEventHandler(LifecycleEvents.COMMANDS,
            event -> event.registrar().register(Commands.literal("testcmd")
                .requires(sender -> sender.getSender().hasPermission("permission.test"))
                .build()
            ));
    }
}

We can view in-game, if not opped, that we do not have access to /testcmd, yet running /help testcmd runs fine, printing the expected help block.

Plugin and Datapack List

plugins
[13:22:30 INFO]: Server Plugins (1):
[13:22:30 INFO]: Paper Plugins:
[13:22:30 INFO]:  - Paper-Test-Plugin

datapack list
[13:22:34 INFO]: There are 3 data pack(s) enabled: [vanilla (built-in)], [file/bukkit (world)], [paper (built-in)]
[13:22:34 INFO]: There are no more data packs available

Paper version

Latest, up-to-date (dev) version, as I am currently running the actual Paper project using ./gradlew runDevServer. This behavior also occurs on production builds.

version
[13:22:54 INFO]: Checking version, please wait...
[13:22:54 INFO]: This server is running Paper version 1.21.4-DEV (2025-01-03T12:22:18Z) (Implementing API version 1.21.4-R0.1-SNAPSHOT)
You are running a development version without access to version information

Other

If I understood it correctly, the current logic goes through the HelpMap. There are three possible ways I can see this fixed:

1. The HelpMap is modified in order to account for requirements on command nodes
2. In Commands#register, we append new overloads for a permission value, which acts like a second "requirement", which is also tracked by the HelpMap in order to not show commands the user has no access to. This does not account for nodes with permission inside a command tree.
3. The Brigadier ArgumentBuilder gets appended with a .withPermission(String) method, which acts not only as a second requirement predicate, but also a value that the HelpMap can use.

Reproduce the reported permission-gated Brigadier command with the supplied TestPlugin example, then trace how HelpMap handles commands registered through Commands#register. Compare that path with the requirement predicate on the Brigadier ArgumentBuilder, and verify that /help testcmd is hidden for an unauthorized sender without breaking accessible commands.