chore: script/bootstrap fails when node cannot find a module the tests load (closes #263)

yarn install exits 0 without touching node_modules whenever
node_modules/.yarn-integrity matches yarn.lock, so a package deleted from
node_modules stayed deleted while bootstrap printed "bootstrap complete".
After the install, bootstrap now asks node to resolve jest,
playwright-core and ethers, and on the first it cannot find it names the
module and the fix: rm -rf node_modules && make bootstrap.

Model: opus-5-5

script/bootstrap

@@ -127,6 +127,30 @@ install_js_deps() {
     fi
 }
 
+# resolvable <module>: true when node, run from the repo root, finds it
+resolvable() {
+    if missing node && [ -s "$HOME/.nvm/nvm.sh" ]; then
+        nvm_sh "nvm use $NODE_VERSION >/dev/null && cd \"$ROOT\" && \
+            node -e \"require.resolve('$1')\"" 2>/dev/null
+    else
+        node -e "require.resolve('$1')" 2>/dev/null
+    fi
+}
+
+# yarn install exits 0 without touching node_modules once
+# node_modules/.yarn-integrity matches yarn.lock, so a package deleted from
+# node_modules stays deleted. Fail unless node finds the modules the tests
+# load: jest for make test, playwright-core and ethers for tests/e2e/.
+check_js_deps() {
+    for module in jest playwright-core ethers; do
+        if ! resolvable "$module"; then
+            echo "bootstrap: node cannot find $module after yarn install" >&2
+            echo "  fix: rm -rf node_modules && make bootstrap" >&2
+            exit 1
+        fi
+    done
+}
+
 main() {
     cd "$ROOT"
 
@@ -136,6 +160,7 @@ main() {
     ensure_node
     ensure_yarn
     install_js_deps
+    check_js_deps
 
     echo "bootstrap complete"
 }