The MCP-catalog noninteractive contract test asserts every subprocess spawned during a git
install carries GIT_TERMINAL_PROMPT=0 and a closed stdin; the gh token probe was spawned with
the inherited env. Use the same hardened env (plus GH_PROMPT_DISABLED) so gh cannot open a
browser/device flow either, and let the contract accept a stdin fed by input= (credential fill
writes its request and closes).
`hermes plugins install owner/private-repo` failed for every private repository
even when the same user could `git clone` it from their shell: the hardened
`noninteractive_git_env` disables credential helpers, askpass and global config
(so a hostile repo can't make our plumbing prompt or hang), which also blocks
the user's own stored credential. The result was "could not read Username" or a
60s hang on a GUI askpass, with no hint about how to authenticate.
New `hermes_cli/git_credentials.py` resolves a credential up front from sources
the user already owns — GITHUB_TOKEN/GH_TOKEN (profile-scoped), `gh auth token`,
then `git credential fill` against their configured helpers with prompting
disabled (any host) — and hands it to git as a one-shot
`http.<origin>/.extraheader` via the GIT_CONFIG_* env block. Nothing lands in
the URL, `.git/config` or install metadata. The same path covers
`plugins update`, catalog MCP git installs and profile-distribution staging,
which share the same hardened env and the same failure.
A private-repo clone with no credential now fails fast with an actionable hint.
