diff --git a/.claude-plugin/marketplace.json b/.claude-plugin/marketplace.json
index 0540187..08bb3d6 100644
--- a/.claude-plugin/marketplace.json
+++ b/.claude-plugin/marketplace.json
@@ -10,7 +10,7 @@
       "name": "agent-loop",
       "source": "./",
       "description": "Autonomous generator-evaluator agent loop for long-running coding tasks. Plan interactively, then execute with full visibility.",
-      "version": "0.9.0",
+      "version": "0.10.0",
       "author": {
         "name": "Sheldon"
       },
diff --git a/.claude-plugin/plugin.json b/.claude-plugin/plugin.json
index b4b1971..b446e57 100644
--- a/.claude-plugin/plugin.json
+++ b/.claude-plugin/plugin.json
@@ -1,6 +1,6 @@
 {
   "name": "agent-loop",
-  "version": "0.9.0",
+  "version": "0.10.0",
   "description": "Autonomous generator-evaluator agent loop for long-running coding tasks. Run /agent-loop:run to start.",
   "author": {
     "name": "Sheldon"
diff --git a/setup.sh b/setup.sh
index 1e05fa9..7eebcec 100755
--- a/setup.sh
+++ b/setup.sh
@@ -10,10 +10,17 @@
 
 set -euo pipefail
 
+# --- Parse arguments ---
+UPDATE_ONLY=false
 MODE="${1:-implement}"
 
+if [ "$MODE" = "--update" ]; then
+    UPDATE_ONLY=true
+    MODE="${2:-implement}"  # mode not used in update, but keep arg parsing clean
+fi
+
 # --- Validate mode ---
-if [[ ! "$MODE" =~ ^(implement|explore|fix)$ ]]; then
+if [ "$UPDATE_ONLY" = false ] && [[ ! "$MODE" =~ ^(implement|explore|fix)$ ]]; then
     echo "[setup] ERROR: Invalid mode '$MODE'. Must be: implement, explore, fix"
     exit 1
 fi
@@ -45,6 +52,37 @@ fi
 
 echo "[setup] Harness source: $HARNESS_SRC"
 
+# Read plugin version from source
+PLUGIN_VERSION=""
+if [ -f "$HARNESS_SRC/.claude-plugin/plugin.json" ]; then
+    if command -v jq &>/dev/null; then
+        PLUGIN_VERSION=$(jq -r '.version // empty' "$HARNESS_SRC/.claude-plugin/plugin.json" 2>/dev/null)
+    elif command -v python3 &>/dev/null; then
+        PLUGIN_VERSION=$(python3 -c "import json; print(json.load(open('$HARNESS_SRC/.claude-plugin/plugin.json')).get('version',''),end='')" 2>/dev/null)
+    fi
+fi
+
+# --- Update-only mode: refresh harness files without touching run state ---
+if [ "$UPDATE_ONLY" = true ]; then
+    LOOP_DIR="$(pwd)/.loop"
+    if [ ! -d "$LOOP_DIR" ]; then
+        echo "[setup] ERROR: No .loop/ directory found. Run setup first."
+        exit 1
+    fi
+
+    echo "[setup] Updating harness files..."
+    cp -r "$HARNESS_SRC/prompts"    "$LOOP_DIR/"
+    cp -r "$HARNESS_SRC/templates"  "$LOOP_DIR/"
+    cp -r "$HARNESS_SRC/lib"        "$LOOP_DIR/"
+    cp    "$HARNESS_SRC/loop.sh"    "$LOOP_DIR/"
+    chmod +x "$LOOP_DIR/loop.sh"
+
+    [ -n "$PLUGIN_VERSION" ] && echo "$PLUGIN_VERSION" > "$LOOP_DIR/.harness-version"
+
+    echo "[setup] Harness updated to ${PLUGIN_VERSION:-unknown}. Run state (prd.json, contracts, config.json) unchanged."
+    exit 0
+fi
+
 # --- Ensure git repo exists ---
 if ! git rev-parse --git-dir &>/dev/null; then
     echo "[setup] No git repo found. Initializing..."
@@ -79,6 +117,9 @@ cp -r "$HARNESS_SRC/lib"        "$LOOP_DIR/"
 cp    "$HARNESS_SRC/loop.sh"    "$LOOP_DIR/"
 chmod +x "$LOOP_DIR/loop.sh"
 
+# Stamp harness version
+[ -n "$PLUGIN_VERSION" ] && echo "$PLUGIN_VERSION" > "$LOOP_DIR/.harness-version"
+
 # Verify critical files
 for f in prompts/generator/_base.md prompts/evaluator/_base.md templates/progress.md.template lib/state.sh loop.sh; do
     if [ ! -f "$LOOP_DIR/$f" ]; then
@@ -99,6 +140,7 @@ triage/
 archive/
 .archive-staging/
 .last-branch
+.harness-version
 .loop.lock
 GITIGNORE
 
diff --git a/skills/run/SKILL.md b/skills/run/SKILL.md
index 142d0ff..6bfb9bc 100644
--- a/skills/run/SKILL.md
+++ b/skills/run/SKILL.md
@@ -20,7 +20,7 @@ Follow this sequence. Each phase checks what exists and skips if already done.
 
 ---
 
-## Phase 1: Scaffold (if needed)
+## Phase 1: Scaffold or Update Harness
 
 Check if `.loop/config.json` exists.
 
@@ -36,7 +36,23 @@ bash "$(ls -d ~/.claude/plugins/cache/agent-loop/agent-loop/*/setup.sh 2>/dev/nu
 
 Show the output. If setup fails, stop.
 
-**If it already exists**, skip to Phase 2.
+**If it already exists**, check if the harness files need updating. Compare the installed harness version against the plugin version:
+
+```bash
+INSTALLED=$(cat .loop/.harness-version 2>/dev/null || echo "unknown")
+PLUGIN=$(jq -r '.version // empty' "$(ls -d ~/.claude/plugins/cache/agent-loop/agent-loop/*/.claude-plugin/plugin.json 2>/dev/null | tail -1)" 2>/dev/null || echo "unknown")
+echo "installed=$INSTALLED plugin=$PLUGIN"
+```
+
+If the versions differ (or installed is "unknown"), update the harness files:
+
+```bash
+bash "$(ls -d ~/.claude/plugins/cache/agent-loop/agent-loop/*/setup.sh 2>/dev/null | tail -1)" --update
+```
+
+Tell the user: *"Updated harness files to v{version}."* Then continue to Phase 2.
+
+If versions match, skip to Phase 2.
 
 ---