Recording chunked upload would fail with token length > 13

[nickvergessen]

But tokens can be up to 30 characters long, no? Or am I misunderstanding the entropy parameter? 🤔

Originally posted by @danxuliu in #18449 (comment)

[rajvveer]

I’d like to work on this. I’ll trace the chunk-upload token validation from the API route through storage naming, remove the incorrect 13-character assumption while retaining the manager’s actual token constraints, and add boundary tests for 13-, 14-, and 30-character tokens plus invalid input.

[rajvveer]

I found that #18491 already addresses this issue, so I’m stepping back and will not open a duplicate PR. Sorry for the noise.