Add real-time progress feedback to multi-run simulations

Switch from exec() to spawn() for streaming stderr, add onProgress
callback to runner, and emit per-run progress lines from workers.
CI now shows live percentage, tick count, and era during long runs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/game-simulation/src/multirun.ts

@@ -1,4 +1,4 @@
-import { exec } from 'node:child_process';
+import { spawn } from 'node:child_process';
 import { writeFileSync } from 'node:fs';
 import { resolve as pathResolve, dirname } from 'node:path';
 import { fileURLToPath } from 'node:url';
@@ -74,20 +74,30 @@ interface WorkerResult {
 function spawnWorker(runId: number, seed: number): Promise<WorkerResult> {
   return new Promise((resolve, reject) => {
     const workerPath = new URL('./worker.ts', import.meta.url).pathname.replace(/^\/([A-Z]:)/, '$1');
-    const cmd = `npx tsx "${workerPath}" --strategy ${strategyName} --ticks ${totalTicks} --seed ${seed} --run-id ${runId}`;
-    exec(cmd, { maxBuffer: 200 * 1024 * 1024 }, (error, stdout, stderr) => {
-      if (stderr) process.stderr.write(stderr);
-      if (error) {
-        reject(new Error(`Run #${runId} (seed ${seed}) failed: ${error.message}`));
+    const tsxBin = pathResolve(__dirname, '..', 'node_modules', '.bin', 'tsx');
+    const child = spawn(tsxBin, [workerPath, '--strategy', strategyName, '--ticks', String(totalTicks), '--seed', String(seed), '--run-id', String(runId)], {
+      stdio: ['ignore', 'pipe', 'pipe'],
+    });
+
+    let stdout = '';
+    child.stdout.on('data', (chunk: Buffer) => { stdout += chunk; });
+    child.stderr.on('data', (chunk: Buffer) => { process.stderr.write(chunk); });
+
+    child.on('close', (code) => {
+      if (code !== 0) {
+        reject(new Error(`Run #${runId} (seed ${seed}) exited with code ${code}`));
         return;
       }
       try {
-        const result = JSON.parse(stdout) as WorkerResult;
-        resolve(result);
+        resolve(JSON.parse(stdout) as WorkerResult);
       } catch (e) {
         reject(new Error(`Run #${runId} (seed ${seed}) produced invalid JSON: ${(e as Error).message}`));
       }
     });
+
+    child.on('error', (err) => {
+      reject(new Error(`Run #${runId} (seed ${seed}) failed to spawn: ${err.message}`));
+    });
   });
 }