Locate an output within the current shared computation
Value
An absolute path in a private staging directory. After success,
shared_run() returns the corresponding permanent cache path.
Details
Call this only inside a format = "file" shared computation. Write all output
files and required sidecars under this directory, then return their paths.
Avoid embedding these temporary physical paths inside the output contents.
The cache preserves relative paths; it does not rewrite file contents.