fix(macos): stop stealing OS focus when opening/switching tabs

[daniel771277]

Problem

On macOS, driving a headful Chrome with browser-harness repeatedly yanks the user's focus (and Space) over to the browser window. It happens on essentially every task, because it fires on tab creation.

Two CDP calls are responsible:

1. Target.activateTarget — raises the browser window, which on macOS activates the app. switch_tab() called it on every switch, and new_tab() calls switch_tab(), so every tab creation stole focus.
2. Target.createTarget in the foreground (the default) — when the browser has zero windows, it has to open a new one, and macOS raises + activates that window.

Fix

• new_tab() creates targets with background=True.
• switch_tab(target, activate=False) no longer activates unless the caller explicitly asks. Activation is only needed when a human has to look at the tab (e.g. logging in), not for automation.

Screenshots, coordinate clicks and key input all work on a non-selected tab — they go through the CDP session, not the OS window — so nothing is lost.

Verification (macOS 15, Chrome 150)

Tracked the frontmost app (System Events) across each individual CDP call:

call	frontmost after
Target.createTarget (background=True)	unchanged
Target.attachToTarget	unchanged
Target.activateTarget	Google Chrome ← the thief

End-to-end in the worst case (browser with zero windows open): new_tab → wait_for_load → click_at_xy → type_text no longer brings Chrome forward, and the click registered, the typed text landed in the input, and Page.captureScreenshot returned the correct content of the non-selected tab in 0.2s.

🤖 Generated with Claude Code

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Summary by cubic

Stop macOS from stealing focus when creating or switching tabs in headful Chrome. switch_tab() no longer activates the window by default, and new_tab() creates background targets so Chrome stays in the background.

• Bug Fixes
  • new_tab() and daemon attach_first_page() call Target.createTarget with background=True to avoid activating Chrome when no windows exist.
  • switch_tab(target, activate=False) only calls Target.activateTarget when explicitly requested, keeping automation in the background while clicks, typing, and screenshots still work.

^{Written for commit e529bc1. Summary will update on new commits.}

[browser-harness-review]

✅ Skill review passed

Reviewed 1 file(s) — no findings.

[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}

[daniel771277]

Closing this — handling the fix downstream instead. Thanks!