diff --git a/scripts/extract.sh b/scripts/extract.sh
new file mode 100644
index 0000000..212a29a
--- /dev/null
+++ b/scripts/extract.sh
@@ -0,0 +1,70 @@
+#!/usr/bin/env bash
+# Reverse sync: show diff between consumer-file and brain template, optionally apply
+#
+# Usage: extract.sh --source=<consumer-path> --file=<relative-path> [--dry-run]
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+source "$SCRIPT_DIR/lib/common.sh"
+
+BRAIN_ROOT="${BRAIN_ROOT:-$(cd "$SCRIPT_DIR/.." && pwd)}"
+
+source_dir=""
+file=""
+dry_run=0
+
+while [ $# -gt 0 ]; do
+    case "$1" in
+        --source=*) source_dir="${1#--source=}" ;;
+        --file=*) file="${1#--file=}" ;;
+        --dry-run) dry_run=1 ;;
+        *) log_error "Unknown: $1"; exit 1 ;;
+    esac
+    shift
+done
+
+[ -n "$source_dir" ] || { log_error "--source required"; exit 1; }
+[ -n "$file" ] || { log_error "--file required"; exit 1; }
+
+consumer_file="$source_dir/$file"
+[ -f "$consumer_file" ] || { log_error "Not found: $consumer_file"; exit 1; }
+
+# Find brain template (try with and without .template suffix)
+brain_file=""
+if [ -f "$BRAIN_ROOT/project-files/$file.template" ]; then
+    brain_file="$BRAIN_ROOT/project-files/$file.template"
+elif [ -f "$BRAIN_ROOT/project-files/$file" ]; then
+    brain_file="$BRAIN_ROOT/project-files/$file"
+else
+    log_error "Brain template not found for: $file"
+    exit 1
+fi
+
+log_info "Comparing $consumer_file <-> $brain_file"
+if diff -q "$brain_file" "$consumer_file" >/dev/null; then
+    log_info "Identical, no changes needed"
+    exit 0
+fi
+
+log_warn "Files differ:"
+diff -u "$brain_file" "$consumer_file" || true
+
+if [ "$dry_run" -eq 1 ]; then
+    exit 2
+fi
+
+# Interactive prompt
+printf "Action [a]pply / [r]eject / [q]uit: " >&2
+read -r action
+case "$action" in
+    a|apply)
+        cp "$consumer_file" "$brain_file"
+        log_info "Applied. Don't forget to commit brain repo + bump version."
+        ;;
+    r|reject)
+        log_info "Rejected. Brain template unchanged."
+        ;;
+    *)
+        log_info "Quit. No changes."
+        ;;
+esac
diff --git a/scripts/tests/extract-test.sh b/scripts/tests/extract-test.sh
new file mode 100644
index 0000000..6074071
--- /dev/null
+++ b/scripts/tests/extract-test.sh
@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+set -u
+SCRIPT_DIR="$(cd "$(dirname "$0")/.." && pwd)"
+source "$SCRIPT_DIR/lib/common.sh"
+
+FAILURES=0
+assert_eq() {
+    if [ "$1" = "$2" ]; then echo "PASS: $3"; else echo "FAIL: $3 (expected '$1', got '$2')"; FAILURES=$((FAILURES + 1)); fi
+}
+
+# Test: identical content → exit 0 (no diff)
+tmpdir=$(mktemp -d)
+brain="$tmpdir/brain"
+consumer="$tmpdir/consumer"
+mkdir -p "$brain/project-files" "$consumer"
+echo "same content" > "$brain/project-files/CLAUDE.md.template"
+echo "same content" > "$consumer/CLAUDE.md"
+
+BRAIN_ROOT="$brain" bash "$SCRIPT_DIR/extract.sh" --source="$consumer" --file=CLAUDE.md --dry-run >/dev/null 2>&1
+assert_eq "0" "$?" "identical content returns exit 0"
+
+# Test: different content → exit non-zero
+echo "consumer different" > "$consumer/CLAUDE.md"
+BRAIN_ROOT="$brain" bash "$SCRIPT_DIR/extract.sh" --source="$consumer" --file=CLAUDE.md --dry-run >/dev/null 2>&1
+result=$?
+[ "$result" -ne 0 ] && assert_eq "0" "0" "different content returns non-zero" || assert_eq "0" "1" "different content returns non-zero"
+
+rm -rf "$tmpdir"
+
+echo "---"
+echo "Failures: $FAILURES"
+exit $FAILURES