Modalizer: clicking back into a trap-focus popup after programmatic focus escape causes immediate blur

[petdud]

Summary

When focus is programmatically moved outside an active modalizer (e.g. via
element.focus() from application code), and the user then clicks on an
element inside that same modalizer, the element briefly receives focus and then
immediately loses it.

Tabster version

8.7.0

Steps to reproduce

1. Open a popover with trapFocus enabled (e.g. Fluent UI <Popover trapFocus>),
   focus is inside it.
2. Call element.focus() on an element outside the popover from application
   code (e.g. a keyboard shortcut handler moves focus to a sidebar element).
3. The popover remains visible. Tabster calls setActive(undefined) because the
   target is not inside any modalizer — the popup's modalizer is now deactivated.
4. Click on an input inside the still-visible popover.
5. Expected: input receives and retains focus.
6. Actual: input gets focus for ~100ms then immediately loses it.

Root cause

Step A — programmatic focus deactivates the modalizer.
isFocusedProgrammatically === true + target outside any modalizer → setActive(undefined)
→ this.activeId = undefined.

Step B — the user click is not recognized as targeting the active modal.
isFocusedProgrammatically === false, modalizer.userId !== activeId (undefined),
none of the allow-conditions pass → _restoreModalizerFocus is scheduled in 100ms.

Step C — _restoreModalizerFocus blurs the input.
The early-exit guard:

if (!modalizer && !activeId || modalizer && activeId === modalizer.userId) {
    return;
}

With modalizer truthy (input is inside the popup) and activeId === undefined:

• !modalizer && !activeId → false
• modalizer && activeId === modalizer.userId → false

Neither exits. findFirst({ useActiveModalizer: true }) returns undefined
(no active modalizer to search within) → falls through to:

outsideElement.blur();  // blurs the input the user just clicked

Workaround

Block the programmatic focus movement before it happens (e.g. prevent keyboard
shortcuts from firing while a trap-focus popup is open). Incomplete as a general
solution since any element.focus() call can trigger the same deactivation.