fix(desktop): route mouse thumb buttons to the in-app browser

[akosbalogh]

What changed

Mouse thumb (side) buttons — back = button 3, forward = button 4 — now navigate the in-app browser's history when the pointer is over the preview <webview>, instead of navigating the host T3 Code app (threads/agents view).

Why

The preview is an Electron <webview> whose WebContents is driven by PreviewManager. When the pointer merely hovers the guest page (the guest isn't focused), Chromium routes thumb-button history navigation to the focused WebContents — the host app renderer — so pressing back/forward over the browser sent the app router back instead of the browser. This was intermittent ("sometimes") because it depended on which surface held focus.

How

• PickPreload.ts (runs inside every preview guest): capture-phase listeners for the thumb buttons preventDefault() + stopImmediatePropagation() on mousedown/mouseup/auxclick to suppress Chromium's default navigation, and forward an explicit { direction } over a new MOUSE_NAVIGATE_CHANNEL IPC. Guarded by event.isTrusted so automation-injected events are unaffected.
• Manager.ts: attachListeners registers a mouseNavigate handler that drives that tab's history via the existing wc.navigationHistory.goBack()/goForward() (guarded by canGoBack()/canGoForward()), mirroring the existing UI back/forward path. Registered/torn down alongside the existing HUMAN_INPUT_CHANNEL listener.
• GuestProtocol.ts: new MOUSE_NAVIGATE_CHANNEL constant.

Suppression in the guest is unconditional, so the host app never navigates while the cursor is over the browser — even when the browser has no back history.

Testing

• New unit test in Manager.test.ts asserting the IPC handler drives goBack/goForward, ignores unknown payloads, and does nothing when history is exhausted.
• apps/desktop typecheck, lint, format, and full Manager.test.ts suite (20 tests) pass locally.
• Manual (desktop): open the right-sidebar in-app browser, hover the site, press the mouse back/forward thumb buttons → the browser navigates its own history; the host app view no longer navigates.

🤖 Generated with Claude Code

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Note

Low Risk
Scoped to desktop preview input handling with guards on payload and history; no auth or data changes.

Overview
Mouse back/forward thumb buttons over the preview webview now move that tab’s browser history instead of the host app router when the guest isn’t focused.

In PickPreload.ts, capture-phase listeners on thumb buttons (button 3/4) call preventDefault / stopImmediatePropagation and send { direction: "back" | "forward" } on new preview:mouse-navigate IPC (trusted events only). PreviewManager registers a mouseNavigate handler alongside human-input listeners that calls navigationHistory.goBack() / goForward() when history allows. Manager.test.ts covers valid directions, bad payloads, and exhausted back history.

^{Reviewed by Cursor Bugbot for commit d04de2b. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Route mouse thumb buttons to the in-app browser for back/forward navigation

• The guest preload (PickPreload.ts) intercepts mousedown, auxclick, and mouseup events for mouse buttons 3 (back) and 4 (forward), suppresses Chromium's default focus-dependent navigation, and emits a preview:mouse-navigate IPC message with a direction payload.
• PreviewManager.ts handles the IPC message by calling wc.navigationHistory.goBack() or goForward() only when canGoBack()/canGoForward() returns true; invalid payloads are ignored.
• Behavioral Change: thumb-button navigation is now always handled via IPC rather than Chromium's built-in behavior, which previously depended on the webview having focus.

^{Macroscope summarized d04de2b.}

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[macroscopeapp]

Approvability

Verdict: Approved

This is a targeted bug fix for mouse thumb button navigation in the in-app browser. The changes follow existing patterns in the codebase, include comprehensive tests, and are self-contained within the preview system without touching sensitive areas.

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