When attempting to run a client-side command registered via Fabric API's ClientCommandRegistrationCallback via ClickEvent.RUN_COMMAND in a chat message, the command is reported to be unrecognized.

I've created a mod to quickly reproduce the issue: https://github.com/unilock/CommandTest (download)

In a singleplayer world, attempt the following commands:

1. /ctest (client-side command). The command should return "ctest complete!"
2. /stest (server-side command). The command should return "stest complete!"
3. /tellraw @s {"text":"ctest (click here)","clickEvent":{"action":"run_command","value":"/ctest"}}, then click on "ctest (click here)". An "unknown or incomplete command" error should be thrown, which is the issue in question.
4. /tellraw @s {"text":"stest (click here)","clickEvent":{"action":"run_command","value":"/stest"}}, then click on "stest (click here)". The command should return "stest complete!"

This was a NeoForge bug, fixed with v21.1.178 (neoforged/NeoForge#2323)