What this error means
completionSource(bin, shell) can generate adapters only for bash, elvish, fish, nushell, powershell, and zsh. Passing another value from JavaScript, configuration, or a type assertion raises this error. The original value is stored in details.shell.
How to fix it
Normalize the shell name to a supported lowercase value and reject unknown input in custom integrations. On Windows, the valid value is powershell, not pwsh or cmd. For the standard installation flow, use the commands in Shell completion directly.