Add uv and a rootless Docker runtime on NixOS hosts

uv joins the CLI package list. Docker's daemon is now actually managed
on NixOS hosts too, in rootless mode (per-user systemd service, no
docker-group root-equivalent access), rather than leaving the runtime
entirely externally-managed as before -- the already-installed docker
CLI picks it up automatically via DOCKER_HOST. This is a documented,
narrow exception to developer-environment's client-only tools policy;
kubectl and awscli2 remain unaffected.

Archives add-uv-and-docker-runtime and syncs the new container-runtime
capability plus the narrowed developer-environment requirement into
the main specs.

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

1 files changed, 6 insertions, 2 deletions

diff --git a/openspec/specs/developer-environment/spec.md b/openspec/specs/developer-environment/spec.md
index 374f098..bcdc3e4 100644
--- a/openspec/specs/developer-environment/spec.md
+++ b/openspec/specs/developer-environment/spec.md
@@ -12,12 +12,16 @@ The shared home-manager profile SHALL include the user's evidenced most-used CLI
 - **THEN** the provisioned developer CLI tools are available on `PATH` without any additional manual installation step
 
 ### Requirement: Container and cloud tools are client-only
-Container and cloud-related packages provisioned by this capability SHALL provide client/CLI functionality only; they SHALL NOT attempt to provide or manage the underlying runtime or service (e.g. a container engine or cloud account).
+Container and cloud-related packages provisioned by this capability SHALL provide client/CLI functionality only; they SHALL NOT attempt to provide or manage the underlying runtime or service (e.g. a Kubernetes cluster or cloud account), with one exception: Docker's runtime is managed on NixOS hosts by the separate `container-runtime` capability. Outside of NixOS hosts, and for every other tool (`kubectl`, `awscli2`), no corresponding runtime or account is installed or managed.
 
 #### Scenario: No runtime is installed or managed
-- **WHEN** a container or cloud CLI tool is provisioned by the shared home profile
+- **WHEN** a container or cloud CLI tool other than Docker is provisioned by the shared home profile
 - **THEN** no corresponding daemon, virtual machine, or account configuration is installed or managed by this capability — the tool simply connects to whatever runtime or account is already configured on the system
 
+#### Scenario: Docker's runtime is the documented exception on NixOS
+- **WHEN** the Docker CLI is provisioned by the shared home profile on a NixOS host built from this flake's shared system module
+- **THEN** a Docker runtime is available via the separate `container-runtime` capability, rather than being left entirely unmanaged
+
 ### Requirement: Shell and prompt configuration defers to the user's personal dotfiles
 Where the user's personal dotfiles repository already owns a piece of shell or prompt configuration, the shared home profile SHALL provide only the underlying package, not a competing managed configuration for that same file.