test: cover disabling --site-per-process default

[cyphercodes]

why

--site-per-process is a Stagehand local-browser default, so users need a reliable regression test that localBrowserLaunchOptions.ignoreDefaultArgs can remove it. Refs #2193.

what changed

Added unit coverage for launchLocalChrome verifying that ignoreDefaultArgs: ["--site-per-process"] removes the Stagehand default while preserving user-provided Chromium flags such as --disable-features=site-per-process,IsolateOrigins and --renderer-process-limit=6.

test plan

• pnpm --dir packages/core exec vitest run --config vitest.esm.config.mjs dist/esm/tests/unit/launch-local-ignore-default-args.test.js
• pnpm --filter @browserbasehq/stagehand run typecheck
• pnpm exec prettier --check packages/core/tests/unit/launch-local-ignore-default-args.test.ts

---

Summary by cubic

Adds a unit test to ensure localBrowserLaunchOptions.ignoreDefaultArgs: ['--site-per-process'] disables Stagehand’s --site-per-process default in local Chrome while preserving user flags (--disable-features=site-per-process,IsolateOrigins, --renderer-process-limit=6, --remote-allow-origins=*). Refs #2193.

^{Written for commit 8dd9cbf. Summary will update on new commits.}

[changeset-bot]

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Latest commit: 8dd9cbf

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[github-actions]

This PR is from an external contributor and must be approved by a stagehand team member with write access before CI can run.
Approving the latest commit mirrors it into an internal PR owned by the approver.
If new commits are pushed later, the internal PR stays open but is marked stale until someone approves the latest external commit and refreshes it.

[cubic-dev-ai]

No issues found across 1 file

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

Architecture diagram

sequenceDiagram
    participant Test as Unit Test
    participant ULC as launchLocalChrome()
    participant GetArgs as getLaunchArgs()
    participant Puppet as Puppeteer::launch()
    participant Chrome as Chrome Process

    Note over Test,Chrome: NEW: ignoreDefaultArgs flow for --site-per-process

    Test->>ULC: Call with user flags + ignoreDefaultArgs
    ULC->>GetArgs: NEW: Build args object
    GetArgs->>GetArgs: NEW: Separate default flags from user args
    GetArgs->>GetArgs: NEW: Check ignoreDefaultArgs for --site-per-process
    GetArgs->>GetArgs: NEW: Filter out --site-per-process from default set
    GetArgs-->>ULC: Return { chromeFlags, ignoreDefaultFlags: true }
    ULC->>Puppet: NEW: Launch with ignoreDefaultArgs: ["--site-per-process"]
    Puppet->>Chrome: Start process
    Note over Chrome: Process runs without --site-per-process

    alt User provides custom per-process flags
        Chrome->>Chrome: Respects --disable-features=site-per-process,IsolateOrigins
        Chrome->>Chrome: Respects --renderer-process-limit=6
        Chrome->>Chrome: Respects --remote-allow-origins=*
    end

    Puppet-->>ULC: Browser instance
    ULC-->>Test: Browser handle

    Note over Test,Chrome: VERIFICATION: Assertions on final args
    Test->>Test: Check ignoreDefaultFlags === true
    Test->>Test: Verify --site-per-process is absent
    Test->>Test: Verify user flags are preserved
    Test->>Test: Verify --remote-allow-origins=* still present

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_{Re-trigger cubic}