mkdir /tmp/fallow-perf-repro && cd /tmp/fallow-perf-repro
````bash
cat > gen-monorepo.cjs <<'GEN_EOF'
#!/usr/bin/env node
const fs=require('node:fs'),path=require('node:path'),cp=require('node:child_process');
function arg(n,d){const i=process.argv.indexOf(n);if(i===-1)return d;const v=process.argv[i+1];return v===undefined?true:v;}
const N_WS=parseInt(arg('--workspaces','20'),10),FILES_PER_WS=parseInt(arg('--files-per-ws','50'),10),ROOT=path.resolve(arg('--root','.')),IMPORTS_PER_FILE=parseInt(arg('--imports-per-file','3'),10),CROSS_WS=parseInt(arg('--cross-ws-imports','0'),10),COMMITS=parseInt(arg('--commits','0'),10),NEST_DEPTH=parseInt(arg('--nest-depth','0'),10),DUPE_BLOCKS=parseInt(arg('--dupe-blocks','0'),10),DUPE_BLOCK_LINES=parseInt(arg('--dupe-block-lines','30'),10),DUPE_VARIANTS=parseInt(arg('--dupe-variants','50'),10);
const COMMIT_DIST=String(arg('--commit-distribution','power-law')),BARREL_DEPTH=parseInt(arg('--barrel-depth','0'),10),TSCONFIG_PATHS=parseInt(arg('--tsconfig-paths','0'),10);
const PLUGINS=String(arg('--plugins','typescript,@nx/workspace,eslint')).split(',').filter(Boolean);
const PV={vite:'5.4.10',vitest:'1.6.1',jest:'29.7.0','@storybook/react':'8.4.0','@nx/workspace':'20.0.0','@angular/core':'18.2.0',next:'14.2.18',playwright:'1.48.0',cypress:'13.15.0',eslint:'9.13.0',tailwindcss:'3.4.14',react:'18.3.1','react-router':'6.27.0',remix:'1.19.3',gatsby:'5.13.7',nuxt:'3.13.2',astro:'4.16.0',rollup:'4.24.0',webpack:'5.95.0',parcel:'2.12.0',typescript:'5.6.3'};
const PC={vite:['vite.config.ts','export default { plugins: [] };\n'],vitest:['vitest.config.ts','export default { test: { globals: true } };\n'],jest:['jest.config.js','module.exports = { testEnvironment: "node" };\n'],next:['next.config.js','module.exports = {};\n'],playwright:['playwright.config.ts','export default { testDir: "./e2e" };\n'],eslint:['.eslintrc.cjs','module.exports = { root: false, rules: {} };\n'],tailwindcss:['tailwind.config.js','module.exports = { content: ["./src/**/*.{ts,tsx}"] };\n'],remix:['remix.config.js','module.exports = { ignoredRouteFiles: ["**/.*"] };\n'],gatsby:['gatsby-config.ts','export default { plugins: [] };\n'],rollup:['rollup.config.js','export default { input: "src/index.ts", output: { file: "dist/index.js" } };\n'],webpack:['webpack.config.js','module.exports = { entry: "./src/index.ts" };\n'],parcel:['.parcelrc','{ "extends": "@parcel/config-default" }\n']};
function mk(p){fs.mkdirSync(p,{recursive:true});}
function w(p,b){mk(path.dirname(p));fs.writeFileSync(p,b);}
function wsPkg(i){const d={};for(const p of PLUGINS) d[p]=PV[p]||'0.0.0';return{name:`@repro/pkg-${String(i).padStart(3,'0')}`,version:'0.0.0',private:true,main:'src/index.ts',types:'src/index.ts',dependencies:d};}
function body(wi,fi){const L=[];for(let k=1;k<=IMPORTS_PER_FILE;k++){const t=(fi+k)%FILES_PER_WS;if(t!==fi) L.push(`import { fn${t} } from "./mod-${t}";`);}for(let k=0;k<CROSS_WS&&N_WS>1;k++){const o=(wi+k+1)%N_WS;L.push(`import { fn0 as cross${k} } from "@repro/pkg-${String(o).padStart(3,'0')}";`);}if(TSCONFIG_PATHS>0&&N_WS>1){const a=(wi+fi)%Math.min(TSCONFIG_PATHS,N_WS);L.push(`import { fn0 as aliased } from "@repro/alias-${String(a).padStart(3,'0')}";`);}L.push('',`export function fn${fi}(input:number):number{`,'  let acc=input;','  if(acc>10) acc+=1; else acc-=1;','  for(let i=0;i<3;i++) acc*=2;','  return acc;','}',`export const CONST_${fi}=${fi};`);return L.join('\n')+'\n';}
function sub(fi){if(NEST_DEPTH<=0) return 'src';const s=['src'];let n=fi;for(let d=0;d<NEST_DEPTH;d++){s.push(`g${n%5}`);n=Math.floor(n/5);}return s.join('/');}
function rootIdx(){const L=[];if(BARREL_DEPTH>0&&NEST_DEPTH>0){for(let g=0;g<5;g++) L.push(`export * from "./g${g}";`);}else{for(let i=0;i<FILES_PER_WS;i++) L.push(`export * from "./mod-${i}";`);}return L.join('\n')+'\n';}
function nestedBarrels(wsRoot,files){if(BARREL_DEPTH<=0||NEST_DEPTH<=0) return [];const dirToFiles=new Map();for(const fp of files){const rel=path.relative(wsRoot,fp);const dir=path.dirname(rel);if(!dirToFiles.has(dir)) dirToFiles.set(dir,[]);dirToFiles.get(dir).push(path.basename(fp,'.ts'));}const allDirs=new Set();for(const dir of dirToFiles.keys()){const parts=dir.split('/');for(let i=1;i<=parts.length;i++){const sub=parts.slice(0,i).join('/');if(sub.startsWith('src')) allDirs.add(sub);}}const barrels=[];for(const dir of allDirs){const depth=dir.split('/').length-1;if(depth===0||depth>BARREL_DEPTH) continue;const lines=[];const mods=dirToFiles.get(dir)||[];for(const m of mods) lines.push(`export * from "./${m}";`);const childDirs=new Set();for(const otherDir of allDirs){if(otherDir.startsWith(dir+'/')&&otherDir.split('/').length===depth+2) childDirs.add(otherDir.split('/')[depth+1]);}for(const cd of childDirs) lines.push(`export * from "./${cd}";`);if(lines.length>0) barrels.push([path.join(wsRoot,dir,'index.ts'),lines.join('\n')+'\n']);}return barrels;}
function dupes(){const V=[];for(let v=0;v<DUPE_VARIANTS;v++){const L=[`// dupe-${v}`,`export class DupeBuilder${v}{`,`  private readonly tag='variant-${v}';`,'  private parts:string[]=[];','  add(p:string):this{this.parts.push(p);return this;}','  build():string{let acc=this.tag+":";for(const p of this.parts){if(p.length===0) continue;acc+=" | "+p.toLowerCase().trim();}return acc;}','  reset():this{this.parts.length=0;return this;}',`  static def${v}():DupeBuilder${v}{const b=new DupeBuilder${v}();b.add('a-${v}').add('b-${v}').add('c-${v}');return b;}`,'}'];while(L.length<DUPE_BLOCK_LINES-1) L.push(`// pad-${L.length}`);L.push('');V.push(L.join('\n')+'\n');}return V;}
function pickCommitTarget(c,total){if(COMMIT_DIST==='flat') return c%total;if(COMMIT_DIST==='hot-files'){const hot=Math.max(1,Math.floor(total*0.05));if((c*13)%10<8) return ((c*31)^(c*17))%hot;return hot+(c%(total-hot));}let s=(c+1)*2654435761>>>0;s^=s<<13;s>>>=0;s^=s>>>17;s^=s<<5;s>>>=0;const r=(s&0xffffffff)/0x100000000;return Math.floor(total*(1-r*r*r))%total;}
const WSP=String(arg('--workspace-parent','packages')),WP=String(arg('--workspace-pattern',`${WSP}/*`));
console.log(`[gen v2] ws=${N_WS} files/ws=${FILES_PER_WS} plugins=${PLUGINS.length} pat=${WP} nest=${NEST_DEPTH} barrel-depth=${BARREL_DEPTH} ts-paths=${TSCONFIG_PATHS} commit-dist=${COMMIT_DIST} dupes=${DUPE_BLOCKS}@${DUPE_BLOCK_LINES}L×${DUPE_VARIANTS}var commits=${COMMITS}`);
mk(ROOT);
w(path.join(ROOT,'package.json'),JSON.stringify({name:'fallow-perf-repro',version:'0.0.0',private:true,workspaces:[WP],devDependencies:{typescript:'5.0.0'}},null,2)+'\n');
const tsPaths={};if(TSCONFIG_PATHS>0){for(let i=0;i<TSCONFIG_PATHS;i++){const wi=i%N_WS;tsPaths[`@repro/alias-${String(i).padStart(3,'0')}`]=[`./${WSP.replace(/\/.*/,'')}/pkg-${String(wi).padStart(3,'0')}/src/index.ts`];tsPaths[`@repro/alias-${String(i).padStart(3,'0')}/*`]=[`./${WSP.replace(/\/.*/,'')}/pkg-${String(wi).padStart(3,'0')}/src/*`];}}
w(path.join(ROOT,'tsconfig.json'),JSON.stringify({compilerOptions:{target:'ES2022',module:'ESNext',moduleResolution:'Bundler',strict:false,baseUrl:'.',paths:tsPaths}},null,2)+'\n');
const all=[];
for(let wi=0;wi<N_WS;wi++){const r=path.join(ROOT,WSP.replace(/\/.*/,''),`pkg-${String(wi).padStart(3,'0')}`);w(path.join(r,'package.json'),JSON.stringify(wsPkg(wi),null,2)+'\n');w(path.join(r,'src','index.ts'),rootIdx());const wsFiles=[];for(let f=0;f<FILES_PER_WS;f++){const fp=path.join(r,sub(f),`mod-${f}.ts`);w(fp,body(wi,f));all.push(fp);wsFiles.push(fp);}for(const [bp,bc] of nestedBarrels(r,wsFiles)) w(bp,bc);for(const p of PLUGINS){const c=PC[p];if(c) w(path.join(r,c[0]),c[1]);}}
if(DUPE_BLOCKS>0){const V=dupes();console.log(`[gen v2] inject ${DUPE_BLOCKS} dupes...`);for(let i=0;i<DUPE_BLOCKS;i++){fs.appendFileSync(all[(i*7919)%all.length],`\n// dup-${i}\nexport namespace dupeNs${i} {\n${V[i%DUPE_VARIANTS]}}\n`);}}
if(COMMITS>0){console.log(`[gen v2] git init + ${COMMITS} commits (${COMMIT_DIST})...`);cp.execSync('git init -q',{cwd:ROOT,stdio:'inherit'});cp.execSync('git config user.email perf@example.com',{cwd:ROOT});cp.execSync('git config user.name "Perf Reproducer"',{cwd:ROOT});cp.execSync('git add -A',{cwd:ROOT,stdio:'inherit'});cp.execSync('git commit -q -m "initial"',{cwd:ROOT});for(let c=1;c<=COMMITS;c++){fs.appendFileSync(all[pickCommitTarget(c,all.length)],`// touch ${c}\n`);cp.execSync(`git -c user.email=perf${c%5}@example.com -c user.name="A${c%5}" commit -q -am "touch ${c}"`,{cwd:ROOT});if(c%500===0) console.log(`[gen v2]   ${c}/${COMMITS}`);}}
console.log(`[gen v2] done.`);
GEN_EOF