Switch Docker to rootful after the rootless setup broke in practice

Rootless Docker's per-user systemd unit didn't start in a session
that was already logged in before a switch, and DOCKER_HOST only
reaches freshly-started shells -- both bit Tom immediately (docker
run failed against the default rootful socket path, which never
existed under rootless). virtualisation.docker.enable = true now
runs dockerd as a standard root system service, started at boot;
tom joins the docker group for sudo-less access. Trades rootless's
isolation guarantee for reliability on a long-lived desktop session.

Archives switch-docker-rootful and syncs the container-runtime
capability's requirements and Purpose text to match.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HngxrvqEzq8oBEBDtrYJyB

1 files changed, 25 insertions, 0 deletions

diff --git a/openspec/changes/archive/2026-09-24-switch-docker-rootful/specs/container-runtime/spec.md b/openspec/changes/archive/2026-09-24-switch-docker-rootful/specs/container-runtime/spec.md
new file mode 100644
index 0000000..7edb25d
--- /dev/null
+++ b/openspec/changes/archive/2026-09-24-switch-docker-rootful/specs/container-runtime/spec.md
@@ -0,0 +1,25 @@
+## REMOVED Requirements
+
+### Requirement: A rootless Docker daemon runs on every NixOS host
+**Reason**: Switched to a standard rootful Docker daemon — the rootless per-user systemd service didn't reliably start in already-logged-in sessions, causing real `docker` CLI failures in practice.
+**Migration**: Replaced by "A Docker daemon runs on every NixOS host" below.
+
+### Requirement: The Docker CLI connects to the rootless daemon without manual configuration
+**Reason**: Rootful Docker uses the standard system-wide socket path and `docker`-group membership instead of a per-session `DOCKER_HOST` export, so this requirement no longer applies.
+**Migration**: Replaced by "The user account has access to the Docker socket" below.
+
+## ADDED Requirements
+
+### Requirement: A Docker daemon runs on every NixOS host
+Every NixOS host built from this flake's shared system module SHALL run a Docker daemon as a system-level service, started at boot rather than tied to a user login session, without requiring per-host opt-in.
+
+#### Scenario: Daemon available after boot
+- **WHEN** a NixOS host built from this flake's shared system module finishes booting
+- **THEN** a Docker daemon is running as a system service, independent of whether any user has logged in
+
+### Requirement: The user account has access to the Docker socket
+The user account provisioned on a NixOS host built from this flake's shared system module SHALL be a member of the group that grants access to the Docker daemon's socket, so Docker CLI commands work without `sudo` or manual connection configuration.
+
+#### Scenario: Docker command works without sudo
+- **WHEN** the provisioned user runs a `docker` CLI command on a NixOS host built from this flake's shared system module
+- **THEN** the command reaches the daemon and executes, without requiring `sudo` or any manually exported connection configuration