fix: resumeStopped reads /proc on Linux, keeps ps for macOS

The stop check no longer needs a ps binary on Linux. A missing /proc entry
(the child was already reaped) loops to the exit check instead of failing.

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

test/cso-snapshot-state.test.ts

@@ -8,7 +8,7 @@ function repo(){const p=tmp();git(p,'init','-q');git(p,'config','user.email','fi
 async function waitForPath(file:string,timeout=5000):Promise<void>{const deadline=Date.now()+timeout;while(!fs.existsSync(file)){if(Date.now()>=deadline)throw new Error(`Timed out waiting for ${path.basename(file)}`);await Bun.sleep(5);}}
 function childExit(child:ReturnType<typeof spawn>,timeout=5000):Promise<number|null>{return new Promise((resolve,reject)=>{if(child.exitCode!==null){resolve(child.exitCode);return;}const timer=setTimeout(()=>reject(new Error(`Child ${child.pid} did not exit`)),timeout);child.once('error',error=>{clearTimeout(timer);reject(error);});child.once('close',code=>{clearTimeout(timer);resolve(code);});});}
 function stopChildren(children:Array<ReturnType<typeof spawn>>):void{for(const child of children){if(!child.pid||child.exitCode!==null)continue;try{process.kill(child.pid,'SIGCONT');}catch{}try{process.kill(child.pid,'SIGKILL');}catch{}}}
-async function resumeStopped(child:ReturnType<typeof spawn>,timeout=2000):Promise<void>{const deadline=Date.now()+timeout;for(;;){if(child.exitCode!==null||child.signalCode!==null)throw new Error(`Child ${child.pid} exited (${child.exitCode??child.signalCode}) after marking its pause, before it stopped`);const ps=spawnSync('ps',['-o','stat=','-p',String(child.pid)],{encoding:'utf8',timeout:2000});if(ps.error)throw new Error(`Child ${child.pid} stop check failed: ${ps.error.message}`);if((ps.stdout??'').trim()[0]==='T')break;if(Date.now()>=deadline)throw new Error(`Child ${child.pid} marked its pause but never stopped`);await Bun.sleep(5);}process.kill(child.pid!,'SIGCONT');}
+async function resumeStopped(child:ReturnType<typeof spawn>,timeout=2000):Promise<void>{const deadline=Date.now()+timeout;for(;;){if(child.exitCode!==null||child.signalCode!==null)throw new Error(`Child ${child.pid} exited (${child.exitCode??child.signalCode}) after marking its pause, before it stopped`);let state='';if(process.platform==='linux'){try{const stat=fs.readFileSync(`/proc/${child.pid}/stat`,'utf8');state=stat.slice(stat.lastIndexOf(')')+2);}catch(error){if((error as NodeJS.ErrnoException).code!=='ENOENT')throw new Error(`Child ${child.pid} stop check failed: ${(error as Error).message}`);}}else{const ps=spawnSync('ps',['-o','stat=','-p',String(child.pid)],{encoding:'utf8',timeout:2000});if(ps.error)throw new Error(`Child ${child.pid} stop check failed: ${ps.error.message}`);state=(ps.stdout??'').trim();}if(state[0]==='T')break;if(Date.now()>=deadline)throw new Error(`Child ${child.pid} marked its pause but never stopped`);await Bun.sleep(5);}process.kill(child.pid!,'SIGCONT');}
 function leaseContenderSource():string{return `import fs from 'node:fs';import * as fsModule from 'node:fs';import * as cryptoModule from 'node:crypto';import path from 'node:path';import {spyOn} from 'bun:test';
 const dir=process.env.RACE_DIR!,barrier=process.env.BARRIER!,id=process.env.RACE_ID!,mode=process.env.RACE_MODE??'normal',token=process.env.RACE_TOKEN,leases=path.join(dir,'.mutation-lock-leases'),wait=new Int32Array(new SharedArrayBuffer(4));let triggered=false;
 const write=fs.writeFileSync.bind(fs),mark=(name,value='ready')=>write(path.join(barrier,name),value,{flag:'wx'}),waitFor=(name)=>{const deadline=Date.now()+5000;while(!fs.existsSync(path.join(barrier,name))){if(Date.now()>=deadline)throw new Error('barrier timeout: '+name);Atomics.wait(wait,0,0,1);}};