Require system focus for gamepad user gesture

[nondebug]

Closes #206

The following tasks have been completed:

• Modified Web platform tests (link to pull request)

Implementation commitment:

• WebKit
• Chromium (https://bugs.chromium.org/p/chromium/issues/detail?id=)
• Gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=)

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Preview | Diff

[marcoscaceres]

This seems reasonable. I need to check if WebKit already does this or not.

[nondebug]

This seems reasonable. I need to check if WebKit already does this or not.

I think WebKit on macOS already requires focus even for normal gamepad inputs because it uses Game Controller API which requires focus.

[marcoscaceres]

We might actually want this:
https://html.spec.whatwg.org/multipage/interaction.html#fully-active-descendant-of-a-top-level-traversable-with-user-attention

• Fully active
• visibly requirement
• and system system focus!

[marcoscaceres]

This looks ok to me.

[Copilot]

Pull request overview

Updates the Gamepad spec’s “gamepad user gesture” handling to require the relevant document to have user attention (i.e., be focused/active) before the initial gesture unlocks exposure of gamepad data, addressing issue #206’s cross-tab gesture concerns.

Changes:

• Gate setting Navigator/[[hasGamepadGesture]] on the associated document being a fully active descendant of a top-level traversable with user attention.
• Hoist the associated Document lookup earlier in the “update gamepad state” algorithm (so it can be used for the new focus/user-attention check).

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[Copilot]

The condition uses “|document| is a Document/fully active descendant …” but |document| is defined as Document? and can be null. Add an explicit |document| is not null (or change the condition to handle null) before applying the HTML definition, to avoid a type-mismatched check and make the focus requirement unambiguous.

Suggested change

	|document| is a [=Document/fully active descendant of a top-level
	traversable with user attention=] and |gamepad| [=contains a gamepad
	user gesture=]:
	|document| is not `null` and is a [=Document/fully active descendant
	of a top-level traversable with user attention=] and |gamepad|
	[=contains a gamepad user gesture=]:

[marcoscaceres]

Ok, yeah... maybe this check should also happen earlier. If you don't have a document anyway, then none of the above really matters, right?

[Copilot]

This algorithm step is duplicated: Let |gamepads:sequence<Gamepad?>| be an empty list appears twice in a row. Remove the extra step to avoid confusion about variable re-declaration and keep the algorithm consistent.

Suggested change

	<li>Let |gamepads:sequence&lt;Gamepad?&gt;| be an empty [=list=].
	</li>