diff --git a/lib/archeflow-rollback.sh b/lib/archeflow-rollback.sh
index 7a793e1..50fec3a 100755
--- a/lib/archeflow-rollback.sh
+++ b/lib/archeflow-rollback.sh
@@ -1,26 +1,67 @@
 #!/usr/bin/env bash
-# archeflow-rollback.sh — Auto-revert a merge that fails post-merge tests.
+# archeflow-rollback.sh — Auto-revert a merge that fails post-merge tests,
+# or roll back to a specific PDCA phase boundary.
 #
-# Usage: archeflow-rollback.sh <run_id> [--test-cmd <cmd>]
+# Usage:
+#   archeflow-rollback.sh <run_id> [--test-cmd <cmd>]       # Post-merge test + revert
+#   archeflow-rollback.sh <run_id> --to <phase>             # Roll back to phase boundary
 #
-# If --test-cmd not provided, reads test_command from .archeflow/config.yaml.
-# Returns 0 if tests pass, 1 if tests fail (merge reverted).
+# --to <phase>: Roll back to the given phase boundary (plan, do, or check).
+#   Delegates to archeflow-git.sh rollback and emits a decision event.
+#
+# If --test-cmd not provided (and --to not used), reads test_command from .archeflow/config.yaml.
+# Returns 0 if tests pass (or rollback succeeds), 1 if tests fail (merge reverted).
 
 set -euo pipefail
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
-RUN_ID="${1:?Usage: archeflow-rollback.sh <run_id> [--test-cmd <cmd>]}"
+RUN_ID="${1:?Usage: archeflow-rollback.sh <run_id> [--test-cmd <cmd>] [--to <phase>]}"
 shift
 
-# Parse optional --test-cmd
+# Parse options
 TEST_CMD=""
+TARGET_PHASE=""
 while [[ $# -gt 0 ]]; do
   case "$1" in
     --test-cmd) TEST_CMD="$2"; shift 2 ;;
+    --to) TARGET_PHASE="$2"; shift 2 ;;
     *) echo "Unknown option: $1" >&2; exit 2 ;;
   esac
 done
 
+# --- Phase rollback mode ---
+if [[ -n "$TARGET_PHASE" ]]; then
+  # Validate phase name
+  case "$TARGET_PHASE" in
+    plan|do|check) ;;
+    *)
+      echo "ERROR: Invalid phase '$TARGET_PHASE'. Must be one of: plan, do, check" >&2
+      exit 2
+      ;;
+  esac
+
+  echo "Rolling back run $RUN_ID to phase boundary: $TARGET_PHASE"
+
+  # Delegate to archeflow-git.sh
+  if [[ ! -x "$SCRIPT_DIR/archeflow-git.sh" ]]; then
+    echo "ERROR: archeflow-git.sh not found or not executable" >&2
+    exit 1
+  fi
+
+  "$SCRIPT_DIR/archeflow-git.sh" rollback "$RUN_ID" --to "$TARGET_PHASE"
+
+  # Emit decision event
+  if [[ -x "$SCRIPT_DIR/archeflow-event.sh" ]]; then
+    "$SCRIPT_DIR/archeflow-event.sh" "$RUN_ID" decision act "" \
+      "{\"what\":\"phase_rollback\",\"chosen\":\"rollback_to_${TARGET_PHASE}\",\"rationale\":\"user requested rollback to ${TARGET_PHASE} phase boundary\"}" ""
+  fi
+
+  echo "Rollback to $TARGET_PHASE complete for run $RUN_ID."
+  exit 0
+fi
+
+# --- Post-merge test mode ---
+
 # Read test_command from config if not provided
 if [[ -z "$TEST_CMD" ]]; then
   if [[ -f ".archeflow/config.yaml" ]]; then