diff --git a/install.sh b/install.sh
index c8f69fe..48a9c4b 100755
--- a/install.sh
+++ b/install.sh
@@ -14,6 +14,23 @@ say() { printf '\033[1;36m[install]\033[0m %s\n' "$*"; }
 warn() { printf '\033[1;33m[warn]\033[0m %s\n' "$*"; }
 err() { printf '\033[1;31m[error]\033[0m %s\n' "$*" >&2; }
 
+# Backup a populated target directory to a timestamped sibling before clobber.
+# No-op if target is absent or contains no regular files (recursively). This
+# means freshly-mkdir'd scaffolds are NOT backed up — only real user content.
+# Only called on $AGENTS_DIR/_blocks, _templates, _assembler, $HOOKS_DIR,
+# $SKILLS_DIR — never on $KIT_DIR source.
+backup_dir() {
+  local target="$1"
+  [ -d "$target" ] || return 0
+  # No regular files anywhere under target → nothing worth preserving
+  if [ -z "$(find "$target" -type f -print -quit 2>/dev/null)" ]; then
+    return 0
+  fi
+  local backup="${target}.bak-$(date +%s)"
+  cp -a "$target" "$backup"
+  say "backed up existing $target to $backup"
+}
+
 # --- prerequisites ----------------------------------------------------------
 say "checking prerequisites"
 if ! command -v cargo >/dev/null 2>&1; then
@@ -44,6 +61,7 @@ mkdir -p \
 
 # --- copy blocks (overwrite ours; blocks are SSoT from kit) ----------------
 say "copying shared blocks -> $AGENTS_DIR/_blocks/"
+backup_dir "$AGENTS_DIR/_blocks"
 cp -f "$KIT_DIR/_blocks/"*.md "$AGENTS_DIR/_blocks/"
 
 # --- copy generic manifests, DO NOT overwrite user's existing manifests -----
@@ -63,11 +81,13 @@ say "  copied $copied, skipped $skipped (already present)"
 # --- copy template ---------------------------------------------------------
 if compgen -G "$KIT_DIR/_templates/*.template" >/dev/null; then
   say "copying specialist template"
+  backup_dir "$AGENTS_DIR/_templates"
   cp -f "$KIT_DIR/_templates/"*.template "$AGENTS_DIR/_templates/"
 fi
 
 # --- copy assembler source (always refresh) --------------------------------
 say "copying assembler source"
+backup_dir "$AGENTS_DIR/_assembler"
 cp -f "$KIT_DIR/_assembler/Cargo.toml" "$AGENTS_DIR/_assembler/"
 cp -f "$KIT_DIR/_assembler/src/"*.rs "$AGENTS_DIR/_assembler/src/"
 if [[ -f "$KIT_DIR/_assembler/.gitignore" ]]; then
@@ -76,6 +96,7 @@ fi
 
 # --- copy hooks (refresh; hooks are logic, not config) ---------------------
 say "copying hooks -> $HOOKS_DIR/"
+backup_dir "$HOOKS_DIR"
 for h in assemble-agents.sh assemble-validate.sh no-hand-edit-agents.sh; do
   cp -f "$KIT_DIR/hooks/$h" "$HOOKS_DIR/$h"
   chmod +x "$HOOKS_DIR/$h"
@@ -84,6 +105,7 @@ done
 # --- copy skills -----------------------------------------------------------
 if [[ -d "$KIT_DIR/skills" ]]; then
   say "copying skills"
+  backup_dir "$SKILLS_DIR"
   for skill_dir in "$KIT_DIR/skills/"*/; do
     [ -d "$skill_dir" ] || continue
     skill_name="$(basename "$skill_dir")"