Configuration identity for one decoded host installation.
The digest is SHA-256 over "ptc.installation-config.v1\0", the
big-endian u64 byte length, and a TJCS projection of the complete
install.<alias> declaration after ordinary host decoding. A matching
digest means the same normalized installation declaration was selected. It
does not prove that a local process, remote endpoint, credential, filesystem
path, or server still grants the same effective authority.
The projection applies schema defaults by hashing the decoded installation
map, omits installation_revision and the digest field itself, and never
includes the alias name, resolved credential bytes, ambient environment
values, remote or discovered server state, or machine-local resolved paths.
Credential binding names and environment variable names remain. Unknown
structs fail closed. Set-valued declaration fields such as accepts_data
and OAuth redirect_uris are ordered canonically before encoding, so author
order is not configuration drift. Ordered lists such as transport args
and HTTP auth keep their written sequence.