fix(web): agent clicks in background browsers no longer steal prompt focus

[RealDoc06]

What Changed

HostedBrowserWebview now checks whether a guest is on screen when it gains focus. If the guest is hidden, focus goes back to the element that just lost it (or the webview blurs when nothing had focus). A visible guest behaves as before and still replays the outside press that dismisses host popovers.

Why

On desktop, I kept losing the prompt box while typing: partway through a sentence it lost focus and my keystrokes went nowhere. It happened in a thread with no browser panel open while agents were working in other threads.

Desktop keeps every thread's browser tab mounted. Inactive tabs sit offscreen on macOS, and while an agent drives one it renders behind the app on every platform. When an agent clicks inside one of those hidden tabs, Input.dispatchMouseEvent makes Chromium focus that guest. The host document's focus moves to the invisible <webview> and the composer loses it.

A person can't click a hidden guest (it's offscreen or pointer-events: none), so focus on one always comes from automation, and handing it back is safe. Agent typing and key presses are already built to work without guest focus (execCommand in the page, focus emulation for keys), so automation keeps working. This also stops agent clicks in hidden tabs from closing the user's open menus.

UI Changes

Reproduced in the real dev desktop app (Linux, Xvfb) against a copy of real data. Thread A had a browser tab on a test page. Thread B was open with no panel. The test typed before- into the prompt, fired an agent click at thread A's hidden tab through the same activity lease and desktopBridge.preview.automation.click call that PreviewAutomationHosts uses, then typed after.

Before: after is lost. Focus is on the hidden <webview>.

After: the prompt reads before-after, and the agent click still reached the page. Same result across 4 runs. A real click on a visible browser panel still focuses the guest.

Not covered: an agent click in a browser panel the user can see still moves focus. The host can't tell that click apart from a person's click on the panel, so fixing it needs the desktop side to mark agent input. I left that out to keep this PR to one concern.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes (not applicable)

Made by Claude Opus 5.5 (1M context) in the Claude Code harness, running inside T3 Code.

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Summary by CodeRabbit

• Bug Fixes
  • Improved focus handling for hidden webviews and webviews without a visible surface, including returning focus to the related host element when possible.
  • Prevented popup-dismissal pointer replay when the webview is hidden or has no visible surface.

[macroscopeapp]

Approvability

Verdict: Approved at 0790ffa

Macroscope's review found this PR approvable — This is a narrowly scoped one-file fix for background browser webviews stealing focus from the prompt. Visible browser behavior remains unchanged, while hidden guests now restore or release focus without altering schemas, defaults, infrastructure, or sensitive code.

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📝 Walkthrough

Walkthrough

The webview focus handler now checks guest visibility and surface placement. For hidden or unplaced guests, it restores focus to a related host element when possible, or blurs the webview. Visible guests retain the pointerdown replay.

Changes

Webview focus handling

Layer / File(s)	Summary
Visibility-aware focus handling apps/web/src/browser/HostedBrowserWebview.tsx	The focus handler restores focus to a related host element or blurs the webview when the guest is hidden or unplaced. Visible guests retain pointerdown replay. The focus listener and its cleanup use the updated handler.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: juliusmarminge

Merge Risk: 🔵 Low · up to 0790f

A hidden browser click can still leave the prompt unfocused when the focus event has no usable relatedTarget, causing subsequent typing to miss the composer. Refocusing the composer is a workaround, but the focus-restoration gap should be addressed.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 0790f

The change is narrowly scoped to restoring application focus after hidden-browser activity and does not appear to grant additional access or privileges. Unusual focus targets and overlapping tab-lifecycle transitions remain unverified.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The directly affected resource is input focus and popup state in the hosting application document. The changed handler introduces no service, credential, persistent-data, or privileged automation operation.

Trust Boundaries and Controls

• observed — Guest focus enters an existing host-side event listener. The recovery destination comes from FocusEvent.relatedTarget and is checked for HTMLElement membership, not resolved from a guest-supplied selector or command. Presentation metadata is maintained through host-owned surface leases.

Resilience and Maintainability Implications

• observed — The recovery branch does not verify connectivity, focusability, guest identity, or successful terminal focus transfer after calling focus. Runtime behavior for these cases remains unverified; this is a coverage limitation, not an established security regression.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the primary change: preventing agent clicks in background browsers from stealing prompt focus.
Description check	✅ Passed	The description includes complete What Changed and Why sections, explains the hidden guest focus behavior, documents the reproduction and validation results, includes UI screenshots, and provides a co…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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🧪 Generate unit tests (beta)

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Actionable comments posted: 1

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🤖 Prompt to fix review comments

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only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @apps/web/src/browser/HostedBrowserWebview.tsx:
- Around line 162-179: Update the hidden-webview focus handling in
onWebviewFocus to restore the last focused non-webview host element when
event.relatedTarget is unavailable. Track that element from document focus
events, initialize it from the current active element when appropriate, and
focus it only if it remains connected; otherwise preserve the existing
webview.blur fallback.

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ℹ️ Review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 8792f95 and 0790ffa.

📒 Files selected for processing (1)

• apps/web/src/browser/HostedBrowserWebview.tsx

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[RealDoc06]

Closing in favor of #13914, which fixes the same bug (#10980) at the automation call site and also covers agent clicks in a visible browser panel. I verified #13914 against the same real-app repro used here and left the results on that PR.