fix(extension): activate tabs and focus window to fix background rendering failures

[ykswang]

Summary

When Chrome is not the focused OS window, elementFromPoint() returns null for background tabs. This causes isTopElement() to incorrectly mark all elements as non-visible. The LLM then sees an empty page and enters a loop of opening new tabs instead of operating on the current page.

Root cause: switchToTab() only updated internal state (currentTabId in storage) but never called chrome.tabs.update(tabId, { active: true }). Combined with new tabs being created via chrome.tabs.create({ active: false }), the target tab always remained a background tab with throttled rendering.

Three-layer fix:

• switchToTab() now activates the tab via chrome.tabs.update(tabId, { active: true }), ensuring the target tab gets full rendering priority from Chrome
• focusWindow() added and called at task start via chrome.windows.update(windowId, { focused: true }) to bring Chrome to the foreground when automation begins (especially important for MCP-driven workflows)
• isTopElement() graceful degradation — when all elementFromPoint() calls return null (indicating background window), optimistically assume elements are top-level instead of hiding them all

Files changed

• packages/extension/src/agent/TabsController.ts — switchToTab() activates tab, new focusWindow() method, updated TabAction type
• packages/extension/src/agent/TabsController.background.ts — new activate_tab and focus_window message handlers
• packages/extension/src/agent/MultiPageAgent.ts — call focusWindow() in onBeforeTask
• packages/page-controller/src/dom/dom_tree/index.js — isTopElement() fallback when elementFromPoint returns all nulls

Test plan

• Run agent via MCP with Chrome not the focused window — verify elements are detected and actions execute on the existing tab (no spurious new tabs)
• Run agent via MCP with Chrome focused — verify no regression
• Run agent from sidepanel — verify no regression
• Verify tab visually switches in Chrome when agent calls switchToTab()
• Verify Chrome window comes to foreground when task starts via MCP

🤖 Generated with Claude Code

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