ci: retry browser bundle sharding with six Playwright workers

Restore three Rollup processes on the existing bundle runner to measure their effect alongside the current test parallelism.

Co-Authored-By: GPT-6 <codex@openai.com>

Author: nicohrubec

packages/browser/package.json

@@ -52,7 +52,10 @@
   "scripts": {
     "build": "run-p build:transpile build:bundle build:types",
     "build:dev": "run-p build:transpile build:types",
-    "build:bundle": "rollup -c rollup.bundle.config.mjs",
+    "build:bundle": "run-p build:bundle:shard:*",
+    "build:bundle:shard:1": "rollup -c rollup.bundle.config.mjs --configShard=1",
+    "build:bundle:shard:2": "rollup -c rollup.bundle.config.mjs --configShard=2",
+    "build:bundle:shard:3": "rollup -c rollup.bundle.config.mjs --configShard=3",
     "build:transpile": "rollup -c rollup.npm.config.mjs",
     "build:types": "tsc -p tsconfig.types.json",
     "build:watch": "run-p build:transpile:watch build:bundle:watch",

packages/browser/rollup.bundle.config.mjs

@@ -157,4 +157,16 @@ builds.push(
   ...makeBundleConfigVariants(tracingReplayFeedbackLogsMetricsBaseBundleConfig),
 );
 
-export default builds;
+export default ({ configShard } = {}) => {
+  if (configShard === undefined) {
+    return builds;
+  }
+
+  const shard = Number(configShard);
+
+  if (![1, 2, 3].includes(shard)) {
+    throw new Error('configShard must be 1, 2, or 3');
+  }
+
+  return builds.filter((_, index) => Math.floor(index / 3) % 3 === shard - 1);
+};