diff --git a/.gitignore b/.gitignore
index 2a11342..5a7c210 100644
--- a/.gitignore
+++ b/.gitignore
@@ -25,3 +25,5 @@ yarn-error.log
 /.vscode/*
 !/.vscode/mcp.json
 /.zed
+.claude/settings.local.json
+**/.claude/settings.local.json
diff --git a/scripts/check-public-boundary.sh b/scripts/check-public-boundary.sh
index 7f1274b..d694c4f 100755
--- a/scripts/check-public-boundary.sh
+++ b/scripts/check-public-boundary.sh
@@ -6,6 +6,12 @@ cd "$root"
 
 status=0
 
+# Claude Code's personal local settings must never be tracked (.github#355).
+if git ls-files -z | tr '\0' '\n' | grep -E '(^|/)\.claude/settings\.local\.json$'; then
+  echo 'refused: tracked .claude/settings.local.json' >&2
+  exit 1
+fi
+
 pattern_from_hex() {
   local hex="$1"
   local output=""