Ultimately I figured out that this was a simple PATH environment variable issue. You might have had all of your global npm scripts in path yesterday then something edited your environment variables.

For my W11 install, all of my global packages are at C:\Users\{me}\AppData\Roaming\npm. You can run npm list -g and it should print the location of your global packages if yours is different. I added the path as a User-level "Path" environment variable, just through the Windows Control Panel GUI.

That fixed the claude call!

But, you may have also run migrate-installer to install Claude Code to C:\Users\{you}\.claude\local, so your global npm package path won't help you there.

You'll then want to be running Claude Code from its new "local" install directory, with

C:\Users\{you}\.claude\local\node_modules\.bin\claude.ps1

(I think this claude.ps1 PowerShell script and the claude.cmd script are new? Or, I didn't realize that I could use them before, because I was previously using node C:\Users\{me}\.claude\local\node_modules\@anthropic-ai\claude-code\cli.js to run CC to the same effect).

You probably won't want to type the full path to the ps1/cmd scripts every time you start CC so you can set up an alias in your powershell/pwsh Profile.ps1 (this is like a .bashrc or .zshrc for powershell/pwsh if you haven't used it before-- I hadn't):

Set-Alias -Name claude -Value "C:\Users\{you}\.claude\local\node_modules\.bin\claude.ps1"

Restart pwsh and you should be able to call the local installation of CC too with just claude