Technical Documentation for the overview of routing and FS Router

[taefi]

This technical documentation should be part of the repository as a markdown document, available for the contributors as well as the maintainers, describing the overall overview of how the feature is working:

• What are the inputs and outputs of FS Router?
• What is the basis for selecting @ and _ as special characters as well as files that are considered as special files?
• How the output of FS Router ends up configuring the React router?
• The role and responsibilities of file-router vite-plugin?
• What's the role of the RouteUnifyingServiceInitListener and RouteUnifyingIndexHtmlRequestListener?
• What are the behavioural differences in DEV mode vs. PROD mode
• What parts of this feature in Hilla depends on routing logic in Flow
• What parts of routing behaviours of a hybrid application depends on Hilla FS Router

When writing about the above bullet points, we strive to answer the following questions:

• Why any element of this feature is implemented this way?
• What were the motivations and limitations that led us to the current design/implementation?

This calls for a design document to describe the overall Hows and Whys, and should only mention Classes, Files, APIs to the extent that it gives enough clue to the maintainers/contributors where to look in the code when something is not working, or when we want to evaluate the possibilities for an enhancement or a behavioural change. It should avoid going further, unless there's specific logic worth explaining and only if it is not possible to do that as Javadoc/JsDoc - very rare cases.

The designated file for this documentation is a Design.md file at the root of related TS package(s) / Java module(s):

• TS: file-router
• Java: endpint