feat: manage Seriatim source prerequisites

README.md

@@ -4,8 +4,8 @@ Installs the [Seriatim](https://gitea.maximumdirect.net/eric/seriatim)
 transcript processor from source. The role supports Ubuntu 26.04 on `amd64`
 and `arm64` hosts and is independently usable outside the D&D pipeline role.
 
-At this point the role defines and validates its public contract; binary
-installation is added by subsequent implementation work.
+The role manages its build dependencies and a root-owned source checkout. At
+this point binary installation is added by subsequent implementation work.
 
 ## Requirements
 
@@ -37,6 +37,18 @@ ansible-galaxy collection install -r collections/requirements.yml
 For development revisions, set both `seriatim_source_ref` and an honest
 `seriatim_build_version`. Released deployments should select immutable tags.
 
+When `seriatim_manage_build_dependencies` is enabled, the role installs Git
+and converges the classic Go Snap to `seriatim_go_snap_channel`. When disabled,
+both Git and the configured Go executable must already be available, and Go
+must be version 1.25 or newer.
+
+The checkout is authoritative: tracked changes and all untracked or ignored
+files beneath `seriatim_source_dir` are discarded during convergence. The
+repository URL may point to a private remote, but authentication must be
+provided independently through the managed host's Git configuration or SSH
+environment; this role does not manage credentials or accept unknown host
+keys.
+
 ## Static validation
 
 ```sh