Provide connection previews when connecting a moving value block's input to an existing block (zelos)

[cpcallen]

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• I have searched for similar issues before opening a new one.

Problem

When dragging a value block with external inputs, if the block's inputs are moved within radius of an unconnected value output on the workspace a connection preview will appear if using geras or thrasos:

Screen.Recording.2025-08-31.at.10.30.25.mov

For some reason, that is not not if using zelos, even though all the same connections are possible:

Screen.Recording.2025-08-31.at.10.32.48.mov

Request

Given that blocks will still connect even absent a connection preview, it would seem to be preferable to be consistent and alway showing a connection preview if there is a connection candidate.

Alternatives considered

I note that Scratch and MakeCode both seem to forbid connecting a moving block via one of its value inputs, probably by not having any blocks with external inputs (since inline inputs do not connect in this way).

Additional context

I note that issue #3659 also concerns differences between zelos and the other renderers about how they handle inputs, though as it seems to relate to filled inputs (rather than unconnected ones) I am not sure it is directly relevant.

[maribethb]

Definitely a bug, pretty low priority because external inputs are not often used with zelos (because those blocks are ugly)