feat: CallbackAction + SetSignalAction — trigger actions for server-side callbacks#24436
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…ide callbacks CallbackAction<T> forwards a value from a trigger's handler scope back to the server via a ReturnChannelRegistration, decodes it as T, and hands it to a SerializableConsumer<T> on the UI thread. Use it to bridge any client-side trigger into arbitrary server-side state — log a value, fire a custom event, push to a queue, etc. SetSignalAction is a thin named subclass for the common case of `signal::set`, with overloads for ValueSignal (local) and SharedValueSignal (shared). Signal parameters are typed as `? super T` so a wider signal can be paired with a narrower valueType.
Keep only the ValueSignal (local) constructor. Callers that want to write to a SharedValueSignal can still do so via CallbackAction with a method reference.
…ignal Wires an Input's "input" event to a SetSignalAction that pushes the field's value into a ValueSignal, with a Signal.effect mirroring the value into a status Div. The IT types into the field and asserts the status Div reflects each keystroke — exercising the full browser → trigger → return channel → signal → effect → DOM round-trip.
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tltv
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May 27, 2026
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LGTM. There could be tests for other types too than just String, but if it just repeats already existing tests (it's mainly testing that Jackson does its job anyway) then not needed here. Can be added in other PRs too, if there are none yet for the triggers/actions context.
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CallbackAction forwards a value from a trigger's handler scope back to the server via a ReturnChannelRegistration, decodes it as T, and hands it to a SerializableConsumer on the UI thread. Use it to bridge any client-side trigger into arbitrary server-side state — log a value, fire a custom event, push to a queue, etc.
SetSignalAction is a thin named subclass for the common case of
signal::set. Signal parameters are typed as? super Tso a wider signal can be paired with a narrower valueType.