perf(cli): add --prefer-offline to npm install during update (#39267)

Re-derivation of PR #39399 onto current main: pass --prefer-offline to
the web-UI workspace install (both silent and verbose arms of
_install_web_deps) and to the update-time Node dependency refresh in
_update_node_dependencies, so npm reuses its local cache instead of
re-fetching metadata. Test expectations updated to match, mirroring the
PR's own test-update commit.

hermes_cli/main.py

@@ -5710,7 +5710,7 @@ def _do_build_web_ui(web_dir: Path, *, fatal: bool = False) -> bool:
         return _run_npm_install_deterministic(
             npm,
             npm_cwd,
-            extra_args=(*npm_workspace_args, "--silent") if silent else npm_workspace_args,
+            extra_args=(*npm_workspace_args, "--silent", "--prefer-offline") if silent else (*npm_workspace_args, "--prefer-offline"),
             env=build_env,
         )
 

hermes_cli/update_cmd.py

@@ -2089,7 +2089,7 @@ def _update_node_dependencies() -> list[str]:
         print("    deps). Fix npm and re-run `hermes update`.")
         return list(labels)
 
-    extra_args = ["--no-fund", "--no-audit", "--progress=false"]
+    extra_args = ["--no-fund", "--no-audit", "--prefer-offline", "--progress=false"]
 
     from hermes_constants import with_hermes_node_path
 

tests/hermes_cli/test_web_ui_build.py

@@ -150,7 +150,7 @@ class TestBuildWebUISkipsWhenFresh:
         assert result is True
         args, kwargs = mock_run.call_args
         assert "--workspace" not in args[0]
-        assert args[0] == ["/usr/bin/npm", "ci", "--include=dev", "--silent"]
+        assert args[0] == ["/usr/bin/npm", "ci", "--include=dev", "--silent", "--prefer-offline"]
         assert kwargs["cwd"] == web_dir
 
     def test_web_build_uses_idle_timeout_helper(self, tmp_path):