Adds a pinned x86_64 Linux Nix package and development shell, example configurations, and README quickstarts for both transports. The installed binary supplies Git/SSH at runtime. Documentation distinguishes one-shot Git listen, continuous Git watch and continuous space listen, and records at-least-once delivery, trust boundaries and baseline preservation.
Product fa1fab5056f8b61fb9a53890b96a850bb6a1c394 targets reviewed M3 #10; tests are stacked in #12. The active spike/fake fixtures remain because existing gates use them. No message behavior or test was removed.
Exact combined tip a2129015ec63581d9900aba6ec2e60b7ac95b3b4 on b1 passed the Nix build (including the full CLI suite), 14 uncached CLI tests, one spike test and fixture build through the pinned development shell. Package /nix/store/w3axbpskp8ljf2idaqkpq2ywbbkzxl1r-agent-messenger-0.1.0 passed the empty-PATH Git smoke test and literal README Git commands. Fresh m4builder0740 identities passed the existing real-space driver through that installed package: exact delivery, unrelated filtering, nonmember refusal, forged-mark refusal, unmarked replay, durable marks, post-mark restart, new-message liveness, SAP ack and history. No skips.
Venue: default/agent-messenger-testing, 100.65.109.30; Nix generation 4r2nn49a1jpkm3f2y6p9m9aalnxxp906, reviewed Nix tree 9c76135 / equivalent landed d5e583d; Habitat/SAP 242714e. No persistent configuration changed. Previous m3builderfinal fixture restored and M4-only mappings removed. Human merge only.