feat(shell): deliver project skills through .agents

lib/mk-skills-shell-hook.nix

@@ -1,5 +1,6 @@
 # Builds a dev-shell shellHook that links a project's selected skills into its
-# own `.claude/skills/` as direct-child symlinks into the Nix store.
+# own `.agents/skills/` as direct-child symlinks into the Nix store, with
+# `.claude/skills` as a compatibility symlink when that path is free.
 skills:
 let
   storeDir = builtins.storeDir;
@@ -8,7 +9,7 @@ let
   );
 in
 ''
-  # Places this project's Nix-delivered skills into ./.claude/skills/ on shell
+  # Places this project's Nix-delivered skills into ./.agents/skills/ on shell
   # entry.
   # Each run first drops every direct-child symlink pointing into the store,
   # then relinks the current selection.
@@ -16,12 +17,26 @@ in
   # skills for free and needs no manifest.
   # A real (non-symlink) skill directory is a hand-authored, project-private
   # skill and is left untouched.
+  # When ./.claude/skills is free, it is kept as a compatibility symlink to the
+  # canonical ./.agents/skills directory so Claude Code sees the same skills.
   # The whole hook runs in a subshell so it leaks no names into the interactive
   # shell.
   (
-    _mkskills_dir=".claude/skills"
+    _mkskills_dir=".agents/skills"
     mkdir -p "$_mkskills_dir"
 
+    mkdir -p .claude
+    if [ ! -e .claude/skills ] && [ ! -L .claude/skills ]; then
+      ln -s ../.agents/skills .claude/skills
+    elif [ -L .claude/skills ]; then
+      case "$(readlink .claude/skills)" in
+        ../.agents/skills) : ;;
+        ${storeDir}/*) rm -f .claude/skills && ln -s ../.agents/skills .claude/skills ;;
+      esac
+    else
+      printf 'mkSkillsShellHook: leaving existing non-symlink .claude/skills in place; Claude Code compatibility link not installed\n' >&2
+    fi
+
     for _mkskills_entry in "$_mkskills_dir"/*; do
       [ -L "$_mkskills_entry" ] || continue
       case "$(readlink "$_mkskills_entry")" in