You’re likely missing the manifest.v3 file. If you really want to go down this path, export a package using Developer/Designer or IS Admin and compare the resulting zip with what your script is doing. That should help determine why IS doesn’t like the zip you’re producing.
"The idea is that after unit testing, developers use the script to grab the package from subversion, compile it, zip it, and put it out on a build server for the operations staff. "
I would suggest this: after unit testing, developers export the package using Developer/Designer or IS and check that package in to svn. Use the package version numbers to help identify changes. Then use scripts to pull packages from svn to put into the inbound dir of IS for import. You should also be able to have the script activate the package as well, eliminating the manual step (if desired).
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