ci(nix): re-enable Nix builds now that nixpkgs has Plasma 6.6

nixpkgs-unstable includes the full Plasma 6.6 stack (LayerShellQt 6.6,
KWin 6.6) since PR NixOS/nixpkgs#479797 merged Feb 17, 2026.

- Re-enable Nix flake CI (x86_64 + aarch64)
- Re-enable Nix release build and include plasmazones.nix in assets
- Re-enable weekly flake.lock update workflow
- Add build-nix to release job dependencies

Co-Authored-By: claude-flow <ruv@ruv.net>

Author: fuddlesworth

.github/workflows/ci.yml

@@ -56,10 +56,9 @@ jobs:
           find install -type f | head -50
 
   # ═══════════════════════════════════════════════════════════════════════════
-  # Nix Flake CI (x86_64 + aarch64) — disabled until nixpkgs has Plasma 6.6 stack
+  # Nix Flake CI (x86_64 + aarch64)
   # ═══════════════════════════════════════════════════════════════════════════
   nix:
-    if: false
     name: Nix (${{ matrix.system }})
     strategy:
       fail-fast: false

.github/workflows/release.yml

@@ -346,10 +346,9 @@ jobs:
           retention-days: 30
 
   # ═══════════════════════════════════════════════════════════════════════════
-  # Verify Nix Build — disabled until nixpkgs has Plasma 6.6 stack
+  # Verify Nix Build
   # ═══════════════════════════════════════════════════════════════════════════
   build-nix:
-    if: false
     name: Verify Nix Build
     needs: version
     runs-on: ubuntu-latest
@@ -443,7 +442,7 @@ jobs:
   # ═══════════════════════════════════════════════════════════════════════════
   release:
     name: Create GitHub Release
-    needs: [version, build-rpm, build-arch, build-generic]
+    needs: [version, build-rpm, build-arch, build-generic, build-nix]
     runs-on: ubuntu-latest
 
     steps:
@@ -547,6 +546,7 @@ jobs:
             artifacts/**/*.rpm
             artifacts/**/*.pkg.tar.zst
             artifacts/**/*linux-x86_64.tar.gz
+            artifacts/**/*.nix
           generate_release_notes: false
           make_latest: true
 

.github/workflows/update-flake-lock.yml

@@ -1,5 +1,4 @@
 # Auto-update flake.lock weekly to keep nixpkgs fresh
-# Disabled until Nix CI/builds are re-enabled (Plasma 6.6 stack in nixpkgs).
 # SPDX-License-Identifier: GPL-3.0-or-later
 
 name: Update flake.lock
@@ -15,7 +14,6 @@ permissions:
 
 jobs:
   update:
-    if: false
     name: Update flake.lock
     runs-on: ubuntu-latest
 

packaging/nix/package.nix

@@ -2,9 +2,7 @@
 # SPDX-License-Identifier: GPL-3.0-or-later
 #
 # Requires Plasma 6.6+ (KF6 6.6, Qt 6.6, LayerShellQt 6.6, KWin 6.6).
-# You must use nixpkgs that provides the full Plasma 6.6 stack (LayerShellQt 6.6,
-# KWin 6.6). nixos-unstable or a newer channel will have this once KDE 6.6 is
-# merged; until then the build will fail with the assertion below.
+# nixos-unstable has the full Plasma 6.6 stack since Feb 2026 (nixpkgs PR #479797).
 #
 # Usage:
 #   plasmazones = pkgs.callPackage ./packaging/nix/package.nix {