login passphrase is correct but key pull fails

On a fresh, machine, the *****************************\* keys are the same.

Shouldn't this work since they need the same key?

```
➜ ~ GNUPGHOME=~/.keybase-gnupghome keybase login
warn: No config file found; tried '/Users/filippo/.config/keybase/config.json'
Your keybase username or email: filippo
Your keybase login passphrase: ******************************
- run scrypt [==================================] 100%
info: Made directory '/Users/filippo/.cache/keybase'
info: Updated file: /Users/filippo/.cache/keybase/session.json
info: Made directory '/Users/filippo/.config/keybase'
info: Updated file: /Users/filippo/.config/keybase/config.json
info: Creating temporary keyring dir: /Users/filippo/.cache/keybase/tmp_keyrings
- run scrypt [==================================] 100%
error: Signature mismatch or bad decryption key
➜ ~ GNUPGHOME=~/.keybase-gnupghome keybase login
Your keybase login passphrase (to pull your private key from the server): ******************************
- run scrypt [==================================] 100%
error: Signature mismatch or bad decryption key
```

Start by reproducing the reported `GNUPGHOME=~/.keybase-gnupghome keybase login` flow on a fresh machine, including both login prompts. Trace the temporary keyring, session.json, and config.json paths mentioned in the output to determine where the signature or decryption mismatch occurs. Done means the correct passphrase successfully completes the private-key pull, or the failure is explained with a documented prerequisite.

Written by the indexing model from the issue text.