Comment made by: timgilbert
Ok, so {{0001-Adding-cp-jar-argument.patch}} adds a command-line flag {{--cp-jar}} to the {{make-classpath}} bit of tools.deps. When this file is present, tools.deps will produce a pathing jar as described above, by converting the classpath to be a space-separated list of {{file://}} URLs, bunging that into a jar manifest, and then creating a jar file containing only the manifest. This code wound up being simpler than I expected it to be.
This will also need another bit of code to get it to work correctly - the scripts in {{brew-install}} or the Windows equivalent will need to pass this flag to the make-classpath script when they build the path, and then call {{java -cp .cpcache/1864468523.jar clojure.main}} to actually launch clojure.
I've tested this code from Windows in powershell and from WSL (ie, Linux) by calling {{(write-pathing-jar "path.jar" (slurp cached-cp-filename))}} from the repl. After that I was able to execute Clojure via {{java -cp path.jar clojure.main}} to launch a REPL, and then {{(require 'clojure.tools.deps.alpha.script.make-classpath)}} from inside that REPL to validate that I can require local namespaces.