Changing recipe in assembler should reuse what's in it

[kubaxius]

Changing recipe in assembler should reuse what's in it.

Factorio 2.0 added the ability to change an assembler’s recipe via signals. However, when the recipe is switched, the new recipe does not start until all items currently inside the assembler are removed. This can be particularly frustrating when switching between recipes that share the same ingredients, such as the different logistic network chests. In those cases the assembler first has to empty the ingredients, only for inserters to put the exact same items back a moment later.

Proposed solution?

When a recipe is changed, any items already inside the assembler should remain there if they are valid inputs for the new recipe. These items would simply be reassigned to the input slots of the new recipe.

If some items do not belong to the new recipe, they should instead be treated as output items and removed by inserters as usual.

Here's how it should look like when switching from Assembling machine 1 to Assembling machine 2:

03-13-2026, 00-11-01.png (365.6 KiB) Viewed 188 times

Why?

Currently, inserters often pull items out of an assembler only to insert them again seconds later. This looks odd in practice and makes factory logic harder to reason about. Reusing compatible ingredients already inside the assembler would make recipe switching cleaner and more intuitive.