diff --git a/setup b/setup
index 275236cd3..3d1eec386 100755
--- a/setup
+++ b/setup
@@ -748,8 +748,9 @@ create_agents_sidecar() {
   local agents_gstack="$repo_root/.agents/skills/gstack"
   mkdir -p "$agents_gstack"
 
-  # Sidecar directories that skills reference at runtime
-  for asset in bin browse review qa; do
+  # Sidecar directories that skills reference at runtime. bin scripts import
+  # shared modules via ../lib, so bin and lib must always travel together.
+  for asset in bin lib browse review qa; do
     local src="$SOURCE_GSTACK_DIR/$asset"
     local dst="$agents_gstack/$asset"
     if [ -d "$src" ] || [ -f "$src" ]; then
@@ -796,6 +797,9 @@ create_codex_runtime_root() {
   if [ -d "$gstack_dir/bin" ]; then
     _link_or_copy "$gstack_dir/bin" "$codex_gstack/bin"
   fi
+  if [ -d "$gstack_dir/lib" ]; then
+    _link_or_copy "$gstack_dir/lib" "$codex_gstack/lib"
+  fi
   if [ -d "$gstack_dir/browse/dist" ]; then
     _link_or_copy "$gstack_dir/browse/dist" "$codex_gstack/browse/dist"
   fi
@@ -836,6 +840,9 @@ create_factory_runtime_root() {
   if [ -d "$gstack_dir/bin" ]; then
     _link_or_copy "$gstack_dir/bin" "$factory_gstack/bin"
   fi
+  if [ -d "$gstack_dir/lib" ]; then
+    _link_or_copy "$gstack_dir/lib" "$factory_gstack/lib"
+  fi
   if [ -d "$gstack_dir/browse/dist" ]; then
     _link_or_copy "$gstack_dir/browse/dist" "$factory_gstack/browse/dist"
   fi
@@ -874,6 +881,9 @@ create_opencode_runtime_root() {
   if [ -d "$gstack_dir/bin" ]; then
     _link_or_copy "$gstack_dir/bin" "$opencode_gstack/bin"
   fi
+  if [ -d "$gstack_dir/lib" ]; then
+    _link_or_copy "$gstack_dir/lib" "$opencode_gstack/lib"
+  fi
   if [ -d "$gstack_dir/browse/dist" ]; then
     _link_or_copy "$gstack_dir/browse/dist" "$opencode_gstack/browse/dist"
   fi
@@ -1115,6 +1125,7 @@ if [ "$INSTALL_KIRO" -eq 1 ]; then
   [ -L "$KIRO_GSTACK" ] && rm -f "$KIRO_GSTACK"
   mkdir -p "$KIRO_GSTACK" "$KIRO_GSTACK/browse" "$KIRO_GSTACK/gstack-upgrade" "$KIRO_GSTACK/review"
   _link_or_copy "$SOURCE_GSTACK_DIR/bin" "$KIRO_GSTACK/bin"
+  _link_or_copy "$SOURCE_GSTACK_DIR/lib" "$KIRO_GSTACK/lib"
   _link_or_copy "$SOURCE_GSTACK_DIR/browse/dist" "$KIRO_GSTACK/browse/dist"
   _link_or_copy "$SOURCE_GSTACK_DIR/browse/bin" "$KIRO_GSTACK/browse/bin"
   # ETHOS.md — referenced by "Search Before Building" in all skill preambles
diff --git a/test/gen-skill-docs.test.ts b/test/gen-skill-docs.test.ts
index 2fb783ffd..bc9c1b29b 100644
--- a/test/gen-skill-docs.test.ts
+++ b/test/gen-skill-docs.test.ts
@@ -2406,6 +2406,7 @@ describe('setup script validation', () => {
     expect(setupContent).toContain('kiro-cli');
     expect(setupContent).toContain('KIRO_SKILLS=');
     expect(setupContent).toContain('~/.kiro/skills/gstack');
+    expect(setupContent).toContain('$KIRO_GSTACK/lib');
   });
 
   test('setup supports --host opencode with install section and OpenCode skill path vars', () => {
@@ -2421,14 +2422,16 @@ describe('setup script validation', () => {
     expect(setupContent).toContain('qa/templates');
     expect(setupContent).toContain('qa/references');
     expect(setupContent).toContain('dx-hall-of-fame.md');
+    expect(setupContent).toContain('$opencode_gstack/lib');
   });
 
   test('create_agents_sidecar links runtime assets', () => {
-    // Sidecar must link bin, browse, review, qa
+    // Sidecar must link bin with its shared lib modules, plus browse, review, qa
     const fnStart = setupContent.indexOf('create_agents_sidecar()');
     const fnEnd = setupContent.indexOf('}', setupContent.indexOf('done', fnStart));
     const fnBody = setupContent.slice(fnStart, fnEnd);
     expect(fnBody).toContain('bin');
+    expect(fnBody).toContain('lib');
     expect(fnBody).toContain('browse');
     expect(fnBody).toContain('review');
     expect(fnBody).toContain('qa');
@@ -2439,6 +2442,7 @@ describe('setup script validation', () => {
     const fnEnd = setupContent.indexOf('}', setupContent.indexOf('done', setupContent.indexOf('review/', fnStart)));
     const fnBody = setupContent.slice(fnStart, fnEnd);
     expect(fnBody).toContain('gstack/SKILL.md');
+    expect(fnBody).toContain('$codex_gstack/lib');
     expect(fnBody).toContain('browse/dist');
     expect(fnBody).toContain('browse/bin');
     expect(fnBody).toContain('gstack-upgrade/SKILL.md');
@@ -2450,6 +2454,14 @@ describe('setup script validation', () => {
     expect(fnBody).not.toContain('_link_or_copy "$gstack_dir" "$codex_gstack"');
   });
 
+  test('create_factory_runtime_root links shared lib modules beside bin', () => {
+    const fnStart = setupContent.indexOf('create_factory_runtime_root()');
+    const fnEnd = setupContent.indexOf('create_opencode_runtime_root()', fnStart);
+    const fnBody = setupContent.slice(fnStart, fnEnd);
+    expect(fnBody).toContain('$factory_gstack/bin');
+    expect(fnBody).toContain('$factory_gstack/lib');
+  });
+
   test('direct Codex installs are migrated out of ~/.codex/skills/gstack', () => {
     expect(setupContent).toContain('migrate_direct_codex_install');
     expect(setupContent).toContain('$HOME/.gstack/repos/gstack');