[djbclark]

--simulate=diff aborted an assert-enabled cf-agent when the same package was recorded as installed twice without a version: DiffPkgOperations() passed the two empty versions to PkgVersionIsGreater(), which asserts both non-empty. ManifestPkgOperations() already guards that comparison; the diff branch now uses the same guard and keeps the same record (versioned over unversioned, otherwise the higher version, otherwise the first). Release builds compile the assert out and already picked the same record, so nothing changes for them. Two unit tests; the first aborts on the unguarded code (library built with asserts on):

$ tests/unit/simulate_mode_test      # without the fix
test_diff_repeated_unversioned_install: Starting test
simulate_mode_test: simulate_mode.c:676: PkgVersionIsGreater: Assertion `!NULL_OR_EMPTY(ver1) && !NULL_OR_EMPTY(ver2)' failed.
Aborted
$ tests/unit/simulate_mode_test      # with the fix
test_diff_repeated_unversioned_install: Test completed successfully.
test_diff_unversioned_then_versioned_install: Test completed successfully.
All 7 tests passed

Ubuntu 24.04 (--enable-debug): make -C tests/unit check → All 76 tests passed; tests/acceptance/29_simulate_mode/ as root → 4 of 4 Pass. Fork CI: djbclark#45

AI-assisted. I can't vouch for the C syntax beyond a basic level, but I did look at the logic and it seemed sound.

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