fix(lib,install): update locking doc to SQLite transaction, cache NFS check, verify PyYAML

deploy/install.sh

@@ -42,6 +42,14 @@ else
   exit 1
 fi
 
+# Verify PyYAML (needed by system python3 for atomic state writes)
+if ! python3 -c "import yaml" &>/dev/null; then
+  echo "❌ Error: 'PyYAML' is not installed in the system python3. Please install it first" >&2
+  echo "   (e.g., 'pip3 install PyYAML' or 'sudo apt-get install python3-yaml')." >&2
+  exit 1
+fi
+echo "✅ PyYAML (system dependency) detected."
+
 # --- 2. Workspace Setup ---
 mkdir -p "$TARGET_DIR"
 cd "$TARGET_DIR"
@@ -79,7 +87,7 @@ if command -v df &>/dev/null && command -v mount &>/dev/null; then
   if [ -n "$MOUNTPOINT" ]; then
     if mount | grep -q "$MOUNTPOINT.*nfs\|$MOUNTPOINT.*cifs\|$MOUNTPOINT.*fuse.sshfs"; then
       echo "⚠️  WARNING: Target directory is on a network filesystem (NFS/CIFS/SSHFS)."
-      echo "   File locks (fcntl.flock) are UNRELIABLE on network storage."
+      echo "   SQLite WAL journaling and file locks are UNRELIABLE on network storage."
       echo "   The sqlite3 registry will fall back to 'DELETE' journaling instead of WAL."
     else
       echo "✅ File system supports WAL (Local storage detected)."