feat: pivot Codectx to NixOS context checkpoints

.codectx/nix.example.toml

@@ -0,0 +1,25 @@
+id = "NX-0001"
+target = ".#nixosConfigurations.example.config.system.build.toplevel"
+flake_lock_path = "flake.lock"
+baseline = "main"
+
+expected_paths = [
+  "hosts/example/**",
+]
+
+supporting_paths = [
+  "flake.nix",
+  "flake.lock",
+  "modules/**",
+  "tests/**",
+]
+
+constraints = [
+  "preserve remote access",
+  "do not activate a system that has not been built and reviewed",
+]
+
+checks = [
+  "nix flake check",
+  "nix build .#nixosConfigurations.example.config.system.build.toplevel",
+]

.github/workflows/proof.yml

@@ -36,6 +36,3 @@ jobs:
 
       - name: CLI help
         run: cargo run -p codectx-cli --bin codectx -- --help
-
-      - name: Demo
-        run: bash scripts/demo.sh

.gitignore

@@ -14,6 +14,8 @@ target
 # RustRover / JetBrains local config
 #.idea/
 
-# Local Codectx projections
+# Local Codectx state
 /.codectx/focus.toml
 /.codectx/handoffs/
+/.codectx/nix.toml
+/.codectx/checkpoints/