You don't seem to want a right to decompile/disassemble (which you could do in the same form for WASM than for most other languages) but a right to directly vie

You don't seem to want a right to decompile/disassemble (which you could do in the same form for WASM than for most other languages) but a right to directly view the original source code. Such a right does not exist in general. The owners of the source code (the intellectual property) may give you the possibility to view it, but they could also decide that they don't give it to you. The only exceptions I know of are if the creator incorporates other software parts which mandate releasing the source code, e.g. GPL libraries.