It seems wrong that you can't target weapon manufacturers, can you cite a source? Weapon manufacturers contribute to the military action, and destroying weapon manufacturers contributes to military advantage.
For a source, you can check out the Red Cross document I linked. Specifically, Ctrl+F for "continuous combat function" and read the commentary on recommendation V. The Guidance is considered authoritative in legal circles.
https://www.nationalreview.com/corner/hamas-is-using-unexplo...
This is an explicit ideal in the 'Resistance Axis', to develop the ability to produce military equipment locally and not be dependent on brittle trade routes or smuggling.
The West Bank seems to get rifles from several sources, both american style that probably comes from PA or IDF and russian style, probably smuggled through Jordan from Iraq, Iran, Russia. They produce IED:s locally, quite crude ones, not the directed type with concave copper plates favoured by iraqi militias. Eventually they'll learn to make those too, I'm sure.
And that should be emphasized: the Geneva Conventions allow the targeting of military objectives, combatants (i.e. members of armed forces) and "civilians directly participating in hostilities". The Guidance just interprets the latter and arguably widens the scope, because - without the invention of "continuous combatant function" - you could attack e.g. members of Hamas' armed wing during an attack and in preparation of one. Now you can attack them at any time.
> First, the interpretive Guidance is an expression solely of the ICRC's views. While international humanitarian law relating to the notion of direct participation in hostilities was examined over several years with a group of eminent legal experts, to whom the ICRC owes a huge debt of gratitude, the positions enunciated are the ICRC's alone. Second, while reflecting the ICRC's views, the interpretive Guidance is not and cannot be a text of a legally binding nature.
The purpose and of the Interpretive Guidance is to provide recommendations, as the document itself states, in an attempt to persuade states. It does not claim to be authoritative.
Of course, the document itself would not make a statement on its authoritative nature since, despite the broad consultation with experts, they cannot predict the wider reaction.
The ICRC stated that they couldn't reach consensus and that the Interpretive Guidance provided their own recommendations and does not necessarily reflect the majority opinion of participating experts.
The DPH meeting reports show there was considerable contention beyond the requirement of a continuous combat function or IX. Dissension was significant enough that over a third of the experts involved asked for their names to be removed from the Interpretive Guidance prior to publication which led the ICRC to remove all the experts' names.
Then there are all the papers published criticizing the document for reasons that go beyond just the two most contentious issues, several by experts were among those consulted by the ICRC (e.g. Schmitt, Parks).
Given the dissension, I find it strange that such a document could possibly be widely accepted as the authoritative interpretation of what constitutes DPH by States as you claim.