why

Stagehand unconditionally injected --site-per-process when launching local Chromium. That explicit switch overrides --disable-features=site-per-process and defeats --renderer-process-limit on multi-origin workloads, causing renderer pools to grow unbounded and leading to memory pressure/OOM kills under container limits.

The duplicate injection in v3.ts was already removed in #2127; this removes the remaining copy in launch/local.ts.

what changed

• Dropped --site-per-process from STAGEHAND_DEFAULT_FLAGS in packages/core/lib/v3/launch/local.ts
• Dropped the same flag from packages/evals/core/targets/localChrome.ts
• Added regression tests in launch-local-ignore-default-args.test.ts
• Added a patch changeset for @browserbasehq/stagehand

test plan

• pnpm --filter @browserbasehq/stagehand exec vitest run dist/esm/tests/unit/launch-local-ignore-default-args.test.js (13/13 passed)
• Live Chrome launch: parent argv has no standalone --site-per-process; user disable/cap flags present
• Full multi-origin SPA repro: renderer count stays near configured --renderer-process-limit

---

Summary by cubic

Stop injecting --site-per-process into local Chromium launches. This lets user flags like --disable-features=site-per-process and --renderer-process-limit work and prevents runaway renderer counts.

• Bug Fixes
  • Removed the flag from packages/core/lib/v3/launch/local.ts and packages/evals/core/targets/localChrome.ts.
  • Added regression tests in packages/core/tests/unit/launch-local-ignore-default-args.test.ts (includes opt-in via args).
  • Added a patch changeset for @browserbasehq/stagehand.

Fixes #2193