Propose GNOME desktop for NixOS hosts

Planning artifacts only (proposal, spec, design, tasks) — GDM+GNOME,
NetworkManager, PipeWire, and CUPS+Avahi printing, applied
unconditionally to every NixOS host via modules/nixos/common.nix. Not
yet implemented.

1 files changed, 33 insertions, 0 deletions

diff --git a/openspec/changes/add-gnome-desktop/specs/gnome-desktop/spec.md b/openspec/changes/add-gnome-desktop/specs/gnome-desktop/spec.md
new file mode 100644
index 0000000..ee932c2
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+## Purpose
+
+Provides a working GNOME desktop environment, including login, networking, audio, and printing, on every NixOS host built from this flake.
+
+## ADDED Requirements
+
+### Requirement: GNOME is the default desktop on every NixOS host
+Every NixOS host built from this flake's shared system module SHALL boot into a GNOME desktop session via a graphical login manager, without requiring per-host opt-in.
+
+#### Scenario: Graphical login is available after boot
+- **WHEN** a NixOS host built from this flake's shared system module finishes booting
+- **THEN** a graphical login manager is presented, and selecting the default session starts a GNOME desktop
+
+### Requirement: Desktop networking is functional
+The desktop environment SHALL provide working network configuration through its own UI, not require a separate manual networking setup step.
+
+#### Scenario: Network settings are usable from the desktop
+- **WHEN** a user opens the desktop's network configuration UI
+- **THEN** available networks can be viewed and configured without additional manual setup outside the desktop environment
+
+### Requirement: Desktop audio is functional
+The desktop environment SHALL provide working audio output and input, including compatibility with applications expecting a PulseAudio-compatible audio server.
+
+#### Scenario: Audio applications can play sound
+- **WHEN** an application on the desktop attempts to play or capture audio
+- **THEN** the audio server is running and available to handle the request
+
+### Requirement: Printing is supported and printers are discoverable
+The desktop environment SHALL support printing to CUPS-compatible printers, and SHALL be able to discover network printers automatically without requiring the firewall to be manually reconfigured.
+
+#### Scenario: A network printer is discoverable
+- **WHEN** a network printer advertises itself on the local network
+- **THEN** it can be discovered and configured for printing without the host's firewall blocking the discovery traffic