With the built-in SSH server, closing the client connection cancelled
the `gitea serv` process tree. go-git based clients close it right after
the push report, so post-receive was killed and branches, pull requests,
webhooks and Actions were not updated.
The command now runs under the server's hammer context like with
OpenSSH, where it ends once its pipes close or at shutdown.
Migrate away from this thin ssh wrapper module while adding more test
coverage.
Removes `sessionPartial`, which hand-copied the layout of a private
`gliderlabs/ssh` struct and reinterpreted a pointer to it via
`reflect.UnsafePointer` to reach the permissions of the authenticated
connection. The layout is unchecked, so an upstream field reorder would
mismatch silently.
The builtin server only needs the session channel with `exec` and
`shell`. Serving those on `x/crypto` drops the hack and the dependency,
since `PublicKeyCallback` returns permissions per key and `x/crypto`
assigns them only after verifying the signature.
Two benign behavior changes:
1. Internal session handler errors report exit status 1 rather than 0,
so a client no longer reads a failure as success.
1. An unusable host key is fatal at startup instead of being replaced by
an ephemeral one that would trigger an error at the client.
silverwind