diff --git a/flake.nix b/flake.nix
index 98ca3c7..e4e7271 100644
--- a/flake.nix
+++ b/flake.nix
@@ -100,7 +100,7 @@
             ./home/${name}
           ];
           extraSpecialArgs = {
-            inherit inputs outputs;
+            inherit inputs outputs self;
           };
         };
     in
diff --git a/home/common/features/mutable-file.nix b/home/common/features/mutable-file.nix
new file mode 100644
index 0000000..71e4992
--- /dev/null
+++ b/home/common/features/mutable-file.nix
@@ -0,0 +1,90 @@
+{
+  config,
+  lib,
+  pkgs,
+  self,
+  ...
+}:
+let
+  cfg = config.home.mutableFiles;
+  repoPath = config.home.mutableFilesRepoPath;
+  flakePrefix = self.outPath;
+
+  fileEntries = lib.attrsToList cfg;
+
+  toRepoPath = storePath: repoPath + lib.removePrefix flakePrefix (toString storePath);
+
+  checkScript = lib.concatMapStringsSep "\n" (
+    { name, value }:
+    let
+      target = "${config.home.homeDirectory}/${name}";
+      storePath = value.source;
+      originalPath = toRepoPath value.source;
+    in
+    ''
+      if [ -f "${target}" ] && ! ${lib.getExe' pkgs.diffutils "diff"} -q "${storePath}" "${target}" > /dev/null 2>&1; then
+        echo ""
+        echo "!! mutable file changed: ${name}"
+        echo "   To bring changes upstream:"
+        echo "   cp ${target} ${originalPath}"
+        echo ""
+        ${lib.getExe' pkgs.diffutils "diff"} -u "${storePath}" "${target}" || true
+        _mutable_changed=1
+      fi
+    ''
+  ) fileEntries;
+
+  copyScript = lib.concatMapStringsSep "\n" (
+    { name, value }:
+    let
+      target = "${config.home.homeDirectory}/${name}";
+      source = value.source;
+      dirName = builtins.dirOf target;
+    in
+    ''
+      mkdir -p "${dirName}"
+      cp -f "${source}" "${target}"
+      chmod ${if value.executable then "755" else "644"} "${target}"
+    ''
+  ) fileEntries;
+in
+{
+  options.home.mutableFilesRepoPath = lib.mkOption {
+    type = lib.types.str;
+    description = "Absolute path to the nixos-config repo on disk.";
+  };
+
+  options.home.mutableFiles = lib.mkOption {
+    type = lib.types.attrsOf (
+      lib.types.submodule {
+        options = {
+          source = lib.mkOption {
+            type = lib.types.path;
+            description = "Path to the source file.";
+          };
+          executable = lib.mkOption {
+            type = lib.types.bool;
+            default = false;
+            description = "Whether the file should be executable.";
+          };
+        };
+      }
+    );
+    default = { };
+    description = "Files to copy (not symlink) into the home directory, with change detection.";
+  };
+
+  config = lib.mkIf (cfg != { }) {
+    home.activation.mutableFiles = lib.hm.dag.entryAfter [ "writeBoundary" ] ''
+      _mutable_changed=0
+      ${checkScript}
+      if [ "$_mutable_changed" -eq 1 ]; then
+        echo ""
+        echo "!! Aborting: mutable files have been modified outside of nix."
+        echo "   Bring the changes upstream first, then re-run."
+        exit 1
+      fi
+      ${copyScript}
+    '';
+  };
+}
diff --git a/home/common/programs/claude/default.nix b/home/common/programs/claude/default.nix
index 6c407c2..3662f08 100644
--- a/home/common/programs/claude/default.nix
+++ b/home/common/programs/claude/default.nix
@@ -54,6 +54,6 @@
     source = ./statusline.sh;
     executable = true;
   };
-  home.file.".claude/settings.json".source = ./settings.json;
+  home.mutableFiles.".claude/settings.json".source = ./settings.json;
   home.file.".claude/CLAUDE.md".source = ./CLAUDE.md;
 }
diff --git a/home/common/programs/default.nix b/home/common/programs/default.nix
index 2cf5adc..9656fac 100644
--- a/home/common/programs/default.nix
+++ b/home/common/programs/default.nix
@@ -6,6 +6,7 @@
 }:
 {
   imports = [
+    ../features/mutable-file.nix
     ./zsh.nix
     ./neovim
     ./rust.nix
@@ -23,6 +24,8 @@
     ./ssh.nix
   ];
 
+  home.mutableFilesRepoPath = "/home/naps62/projects/nixos-config";
+
   programs = {
     home-manager.enable = true;
   };