diff --git a/hermes_cli/main.py b/hermes_cli/main.py
index 9d77124909..4abb7bf830 100644
--- a/hermes_cli/main.py
+++ b/hermes_cli/main.py
@@ -5767,7 +5767,25 @@ def _do_build_web_ui(web_dir: Path, *, fatal: bool = False) -> bool:
     # would pull in desktop on every web build. See #38772.
     # When web/ has its own package-lock.json, _workspace_root() returns
     # web_dir itself and --workspace would fail.  See #42973.
-    npm_workspace_args: tuple[str, ...] = () if npm_cwd == web_dir else ("--workspace", "web")
+    #
+    # When running from the workspace root, this must name the SAME closure
+    # as `hermes update`'s _update_node_dependencies() (ui-tui + web +
+    # --include-workspace-root): the helper prefers `npm ci`, which deletes
+    # node_modules before reifying the requested tree, so a narrower closure
+    # here silently prunes everything the update step just installed (root
+    # devDependencies and the ui-tui workspace) while still exiting 0 —
+    # and since the manifests digest was already recorded, later no-op
+    # updates skip the repair. See #43564/#64354.
+    npm_workspace_args: tuple[str, ...]
+    if npm_cwd == web_dir:
+        npm_workspace_args = ()
+    else:
+        npm_workspace_args = ("--workspace", "web", "--include-workspace-root")
+        # Prebuilt/partial checkouts can lack the ui-tui workspace; naming a
+        # missing workspace makes npm fail hard, so only include it when
+        # present (same guard as _update_node_dependencies()).
+        if (npm_cwd / "ui-tui" / "package.json").exists():
+            npm_workspace_args = ("--workspace", "ui-tui", *npm_workspace_args)
     if _is_termux_startup_environment():
         npm_cwd, npm_workspace_args = _termux_workspace_install_context(web_dir)
 
diff --git a/tests/hermes_cli/test_web_ui_build.py b/tests/hermes_cli/test_web_ui_build.py
index e12e9050c6..e5871e8d62 100644
--- a/tests/hermes_cli/test_web_ui_build.py
+++ b/tests/hermes_cli/test_web_ui_build.py
@@ -153,6 +153,59 @@ class TestBuildWebUISkipsWhenFresh:
         assert args[0] == ["/usr/bin/npm", "ci", "--include=dev", "--silent", "--prefer-offline"]
         assert kwargs["cwd"] == web_dir
 
+    def test_workspace_root_install_names_update_closure(self, tmp_path, monkeypatch):
+        """From the workspace root, _build_web_ui must install the SAME
+        closure as `hermes update` (ui-tui + web + --include-workspace-root).
+
+        The install helper prefers `npm ci`, which deletes node_modules before
+        reifying the requested tree — a narrower `--workspace web`-only pass
+        right after the update step silently pruned root devDependencies and
+        the ui-tui workspace while exiting 0. See #43564/#64354.
+        """
+        web_dir, _ = _make_web_dir(tmp_path)
+        # Root lockfile only => _workspace_root(web_dir) == tmp_path.
+        (tmp_path / "package-lock.json").write_text("{}", encoding="utf-8")
+        (tmp_path / "ui-tui").mkdir()
+        (tmp_path / "ui-tui" / "package.json").write_text("{}", encoding="utf-8")
+        monkeypatch.delenv("TERMUX_VERSION", raising=False)
+        monkeypatch.setenv("PREFIX", "/usr")
+
+        install_cp = __import__("subprocess").CompletedProcess([], 0, stdout="", stderr="")
+        build_cp = __import__("subprocess").CompletedProcess([], 0, stdout="", stderr="")
+        with patch("hermes_cli.main.shutil.which", return_value="/usr/bin/npm"), \
+             patch("hermes_cli.main.subprocess.run", return_value=install_cp) as mock_run, \
+             patch("hermes_cli.main._run_with_idle_timeout", return_value=build_cp):
+            result = _build_web_ui(web_dir)
+
+        assert result is True
+        args, kwargs = mock_run.call_args
+        cmd = args[0]
+        assert "--include-workspace-root" in cmd
+        assert cmd.count("--workspace") == 2
+        assert "ui-tui" in cmd and "web" in cmd
+        assert kwargs["cwd"] == tmp_path
+
+    def test_workspace_root_install_skips_missing_ui_tui(self, tmp_path, monkeypatch):
+        """A checkout without the ui-tui workspace must not name it — npm
+        fails hard on a --workspace that doesn't exist."""
+        web_dir, _ = _make_web_dir(tmp_path)
+        (tmp_path / "package-lock.json").write_text("{}", encoding="utf-8")
+        monkeypatch.delenv("TERMUX_VERSION", raising=False)
+        monkeypatch.setenv("PREFIX", "/usr")
+
+        install_cp = __import__("subprocess").CompletedProcess([], 0, stdout="", stderr="")
+        build_cp = __import__("subprocess").CompletedProcess([], 0, stdout="", stderr="")
+        with patch("hermes_cli.main.shutil.which", return_value="/usr/bin/npm"), \
+             patch("hermes_cli.main.subprocess.run", return_value=install_cp) as mock_run, \
+             patch("hermes_cli.main._run_with_idle_timeout", return_value=build_cp):
+            result = _build_web_ui(web_dir)
+
+        assert result is True
+        cmd = mock_run.call_args[0][0]
+        assert "ui-tui" not in cmd
+        assert "--include-workspace-root" in cmd
+        assert "web" in cmd
+
     def test_web_build_uses_idle_timeout_helper(self, tmp_path):
         """npm run build now goes through _run_with_idle_timeout (issue #33788).