What format did you have in mind?
Instead of plain list, would it be acceptable for the isolated tool to accept a 'file manifest' that maps absolute src path of a file to relative dest path when pulled down from the cache?

cc'ing folks who may have an opinion. I prefer a flat list. I want to remove everything out of the isolated file, including the command and the relative directory.

There is a lot of value in having the command and cwd be part of the isolate; it means that in order to reproduce a task locally (assuming you didn't have extra args) is to download and re-run the isolate.

M-A, how would you replicate (or improve upon) that experience if we were to remove this from the isolate?

That's a larger question, but I really want to get rid of the 'isolate' tool eventually; RBE is also not compatible with this concept; the relative_cwd and commands are passed as part of the task, not as part of the content.

The reason the command was in the isolate was that back in the GYP days, I needed to switch the used command based on the OS. This is not needed anymore.

That doesn't really answer the question, though, right? We can't get rid of functionality we use until we have a replacement?

Unless you were just saying that you wanted to support an alternate, file-only format as well? If so, that's fine ...

The file based alternative must be supported first, which can then be built upon to create "swarming tasks prototypes" from these which would include the command line.

"isolate" implements the isolate parsing, "isolated" doesn't and is much simpler, there's no concept of variables.

>>Instead of plain list, would it be acceptable for the isolated tool to accept a 'file manifest' that maps absolute src path of a file to relative dest path when pulled down from the cache?

@Marc-Antoine: I take back what I said about a 'file manifest'! I too would now prefer a flat list of files (relative to a fixed directory).

There is now an isolated recipe module in recipes-py (https://chromium-review.googlesource.com/c/infra/luci/recipes-py/+/1281366), which features an `Isolated` object for incrementally building up an archive, relative to a fixed directory:
https://chromium.googlesource.com/infra/luci/recipes-py/+/001848147e74b8f8e63e32dc8bed9ff16e11820f/recipe_modules/isolated/api.py#60
The idea of a flat file list seems to lend itself well to a simple add_file_list() wrapper method on this class.

True.