Add attach_tab() and new_tab(background=True) for focus-preserving automation

[icekinder]

Motivation

When the harness drives a user's live browser (the daemon attached to their real Chrome), new_tab() and switch_tab() activate the target — which visibly yanks the user out of whatever tab they're working in every time automation runs. For background/batch workflows (CSV imports, polling a web app's UI, scraping a logged-in dashboard) the automation has no reason to be visible at all.

Changes

• attach_tab(target) — attach a session to a tab without activating it. switch_tab() keeps its exact behavior and is now literally activate + attach_tab().
• new_tab(url, background=False) — with background=True, the tab is created via Target.createTarget's background flag and only attached, never activated. Default behavior unchanged.
• The reuse-a-blank-current-tab shortcut in new_tab() is skipped when background=True: the current tab may be the user's visible one, and background is an explicit request not to touch what they see.
• Documented both in interaction-skills/tabs.md (code block + a "rules that held up" line).

Notes

Running this against a live daily-driver Chrome for a few weeks now — background CSV-import/enrichment runs no longer steal focus while the user keeps browsing.

🤖 Generated with Claude Code

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Summary by cubic

Adds attach_tab() and new_tab(background=True) so automation can attach to tabs without activating them, preventing focus theft in a user’s live browser. Default behavior remains unchanged.

• New Features
  • attach_tab(target): attach session without activating; switch_tab = activate + attach.
  • new_tab(url, background=True): create target with CDP background flag and attach only.
  • Skip “reuse current blank tab” when background=True to avoid touching the visible tab.
  • Docs: updated interaction-skills/tabs.md with examples and guidance.

^{Written for commit 5702b58. 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 2 files

_{Re-trigger cubic}