This is an adapted patch from the games/anki FreeBSD port.
https://github.com/freebsd/freebsd-ports/blob/109c3d4629b84972e660b689d169ac0761c1a519/games/anki/files/patch-build_runner_src_yarn.rs

The ebuild ships a ready-to-use node_modules tarball which does not require
sys-apps/yarn to be installed. Pre-built node_modules allows us to run JS tests.
* Don't add inputs that depend on the yarn:bin target. This saves us from
setting an extra environment variable.

Rework when nodejs.eclass (GitHub PR 33426) gets added to the tree?
The benefit of `yarn install --cache-folder .yarn --offline --ignore-scripts`
is the hackability of `.yarn` contents in src_prepare.
The drawback is that we lose JS tests since some npm test deps (which?) access
the network to update their dependency graph before building.

From: Lucio Sauer <watermanpaint@posteo.net>
--- a/build/ninja_gen/src/node.rs
+++ b/build/ninja_gen/src/node.rs
@@ -76,12 +76,11 @@ pub struct YarnInstall<'a> {
 
 impl BuildAction for YarnInstall<'_> {
     fn command(&self) -> &str {
-        "$runner yarn $yarn $out"
+        "$runner yarn $out"
     }
 
     fn files(&mut self, build: &mut impl build::FilesHandle) {
         build.add_inputs("", &self.package_json_and_lock);
-        build.add_inputs("yarn", inputs![":yarn:bin"]);
         build.add_outputs("out", vec!["node_modules/.marker"]);
         for (key, value) in &self.exports {
             let outputs: Vec<_> = value.iter().map(|o| format!("node_modules/{o}")).collect();
@@ -139,9 +138,7 @@ pub fn setup_node(
             );
             build.add_dependency("yarn:bin", inputs![path]);
         }
-        Err(_) => {
-            build.add_action("yarn", YarnSetup {})?;
-        }
+        Err(_) => ()
     };
 
     for binary in binary_exports {
--- a/build/runner/src/yarn.rs
+++ b/build/runner/src/yarn.rs
@@ -2,23 +2,18 @@
 // License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
 use std::path::Path;
-use std::process::Command;
 
 use clap::Args;
 
-use crate::run::run_command;
-
 #[derive(Args)]
 pub struct YarnArgs {
-    yarn_bin: String,
     stamp: String,
 }
 
 pub fn setup_yarn(args: YarnArgs) {
+    println!("Patch: Linking pre-built node_modules.");
     link_node_modules();
 
-    run_command(Command::new(&args.yarn_bin).arg("install"));
-
     std::fs::write(args.stamp, b"").unwrap();
 }