diff --git a/hermes_cli/main.py b/hermes_cli/main.py
index d442e138f..21d544d87 100644
--- a/hermes_cli/main.py
+++ b/hermes_cli/main.py
@@ -725,9 +725,18 @@ def _print_tui_exit_summary(session_id: Optional[str]) -> None:
     )
 
 
-def _tui_deps_ready(root: Path) -> bool:
-    """Nix and local dev both need file: workspace @hermes/ink under node_modules."""
-    return (root / "node_modules" / "@hermes" / "ink" / "package.json").is_file()
+def _tui_need_npm_install(root: Path) -> bool:
+    """True when @hermes/ink is missing or node_modules is behind package-lock.json (post-pull)."""
+    ink = root / "node_modules" / "@hermes" / "ink" / "package.json"
+    if not ink.is_file():
+        return True
+    lock = root / "package-lock.json"
+    if not lock.is_file():
+        return False
+    marker = root / "node_modules" / ".package-lock.json"
+    if not marker.is_file():
+        return True
+    return lock.stat().st_mtime > marker.stat().st_mtime
 
 
 def _find_bundled_tui(tui_dir: Path) -> Optional[Path]:
@@ -735,9 +744,9 @@ def _find_bundled_tui(tui_dir: Path) -> Optional[Path]:
     env = os.environ.get("HERMES_TUI_DIR")
     if env:
         p = Path(env)
-        if (p / "dist" / "entry.js").exists() and _tui_deps_ready(p):
+        if (p / "dist" / "entry.js").exists() and not _tui_need_npm_install(p):
             return p
-    if (tui_dir / "dist" / "entry.js").exists() and _tui_deps_ready(tui_dir):
+    if (tui_dir / "dist" / "entry.js").exists() and not _tui_need_npm_install(tui_dir):
         return tui_dir
     return None
 
@@ -794,12 +803,12 @@ def _make_tui_argv(tui_dir: Path, tui_dev: bool) -> tuple[list[str], Path]:
         ext_dir = os.environ.get("HERMES_TUI_DIR")
         if ext_dir:
             p = Path(ext_dir)
-            if (p / "dist" / "entry.js").exists() and _tui_deps_ready(p):
+            if (p / "dist" / "entry.js").exists() and not _tui_need_npm_install(p):
                 node = _node_bin("node")
                 return [node, str(p / "dist" / "entry.js")], p
 
     npm = _node_bin("npm")
-    if not _tui_deps_ready(tui_dir):
+    if _tui_need_npm_install(tui_dir):
         print("Installing TUI dependencies…")
         result = subprocess.run(
             [npm, "install", "--silent", "--no-fund", "--no-audit", "--progress=false"],
diff --git a/tests/hermes_cli/test_tui_npm_install.py b/tests/hermes_cli/test_tui_npm_install.py
new file mode 100644
index 000000000..3f3191ccf
--- /dev/null
+++ b/tests/hermes_cli/test_tui_npm_install.py
@@ -0,0 +1,53 @@
+"""_tui_need_npm_install: auto npm when lockfile ahead of node_modules."""
+
+import os
+from pathlib import Path
+
+import pytest
+
+
+@pytest.fixture
+def main_mod():
+    import hermes_cli.main as m
+
+    return m
+
+
+def _touch_ink(root: Path) -> None:
+    ink = root / "node_modules" / "@hermes" / "ink" / "package.json"
+    ink.parent.mkdir(parents=True, exist_ok=True)
+    ink.write_text("{}")
+
+
+def test_need_install_when_ink_missing(tmp_path: Path, main_mod) -> None:
+    (tmp_path / "package-lock.json").write_text("{}")
+    assert main_mod._tui_need_npm_install(tmp_path) is True
+
+
+def test_need_install_when_lock_newer_than_marker(tmp_path: Path, main_mod) -> None:
+    _touch_ink(tmp_path)
+    (tmp_path / "package-lock.json").write_text("{}")
+    (tmp_path / "node_modules" / ".package-lock.json").write_text("{}")
+    os.utime(tmp_path / "package-lock.json", (200, 200))
+    os.utime(tmp_path / "node_modules" / ".package-lock.json", (100, 100))
+    assert main_mod._tui_need_npm_install(tmp_path) is True
+
+
+def test_no_install_when_lock_older_than_marker(tmp_path: Path, main_mod) -> None:
+    _touch_ink(tmp_path)
+    (tmp_path / "package-lock.json").write_text("{}")
+    (tmp_path / "node_modules" / ".package-lock.json").write_text("{}")
+    os.utime(tmp_path / "package-lock.json", (100, 100))
+    os.utime(tmp_path / "node_modules" / ".package-lock.json", (200, 200))
+    assert main_mod._tui_need_npm_install(tmp_path) is False
+
+
+def test_need_install_when_marker_missing(tmp_path: Path, main_mod) -> None:
+    _touch_ink(tmp_path)
+    (tmp_path / "package-lock.json").write_text("{}")
+    assert main_mod._tui_need_npm_install(tmp_path) is True
+
+
+def test_no_install_without_lockfile_when_ink_present(tmp_path: Path, main_mod) -> None:
+    _touch_ink(tmp_path)
+    assert main_mod._tui_need_npm_install(tmp_path) is False