Module keystore_proxy 

Node-side keystore proxy (was m4a_signer_proxy) (option A, specs/m4a-session-keys-2026-10-16.md).

The node holds NO m4a private keys. For each PTY session it keeps the session’s capability (issued by the hq-core signer) in its own memory and gives the PTY only a handle (M4A_SESSION_HANDLE) plus the nick. A handle is useless on its own: the proxy accepts a request on its UDS only if the kernel-reported peer (SO_PEERCRED) has the session’s uid and its pid is the session’s PTY root process or a descendant of it. A neighbour shell on the same node that steals the handle (env, /proc/<pid>/environ, a prompt injection) is refused, and nothing it could steal lets it sign: the capability never enters the PTY and the key never leaves hq-core.

Structs

LinuxProc

ProxyRequest

SignedReply

SignerProxy

UplinkCoreSigner

Core signer over the node-call channel (Noise over the uplink, opaque to C2; core takes the node id from the stream). Called from blocking threads only.

Enums

ProxyResponse

Refusal

Constants

HANDLE_ENV

SOCKET_ENV

Traits

CoreSigner

The hq-core signer as seen from the node (in production: a call over the C2 uplink).

ProcTree

Parent-pid lookup; /proc on Linux, injectable for tests.

Functions

request

Blocking client (what the session-side m4a tool does).

serve

Serve the proxy on a Unix socket (0600 dir/socket owned by the node user). One JSON line request per connection; peer identity comes from SO_PEERCRED, never from the request.