Problem
I know that Inventree is more a storage management system and not MES (Manufacturing Execution System) however supporting build routing would add to it's trait I think in the build management aspects.

Foreword: the terminology I will use below comes from a company where I worked for. We can deviate from this terminology of course.

Most of the manufacturing processes can be broken down into separate individual steps (routing steps). The order of these steps for a single products make up the routing of the product.

Having this information added to the Inventree could help users to better understand the state of their build orders and could be used as a source of making statistic reports for the manufacturing process.

Suggested solution
Add an option to being able to assign routing for Assemblies which trackable.
This option would give the user ability for adding routing steps to the product routing.
Routing step would have an ID, a name and a description.
Two routing steps are special in the routing: the creation step and the completed step.

I know that manufacturing process flows can be more difficult than a simple a->b->c->d order of steps.
For e.g. your product goes for functional testing, if it fails it goes to rework, then goes back to test, if it passes it goes for packaging.

However for the shake of simplicity I would recommend to implementing a straight routing support only. The same approach were used in the factory I used to work for and the exceptions were handled with a simple To move/Reject result for each routing step.

The following information needed to be assigned to the Stock items (where routing is added):

• Current routing step of the Stock item
• History of past routing steps with their results (move to next step/reject) to see if the product was tested multiple times due to failure for e.g.

Manufacturing UI changes:
We need to implement a form to move/reject stock items identified by serial number from the current step.

Reports:
We could create an in depth build output completed report where each routing step would be listed with the amount of waiting/rejected products.
We could calculate a first pass yield for each step/the whole routing for a specific build order.

Describe alternatives you've considered
I have not really considered alternatives.

Examples of other systems
Oracle has a MES system which works the described way

Do you want to develop this?
Sure. Let's make a clear concept about what and how needs to be implemented and then I can work on this. I have some level of Python knowledge and used PHP MVC frameworks before (mainly CakePHP). I am looking forward to hear your opinion about this.