I tried looking at the build system and it indeed looks like it cannot find libcaesium. After applying the following patch
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -28,6 +28,7 @@ else ()
endif ()
find_library(LIBCAESIUM libcaesium)
+message(WARN, "***************** ${LIBCAESIUM}")
if (NOT LIBCAESIUM)
find_program(CARGO "cargo" REQUIRED)
endif ()
It prints
WARN,***************** LIBCAESIUM-NOTFOUND
And looking closer at the c-i-c patches I applied in caesium-image-compressor: init at 2.4.0 by jtojnar · Pull Request #232527 · NixOS/nixpkgs · GitHub, those appear to be an older version of my patches that got merged in build: Fix Linux builds by jtojnar · Pull Request #199 · Lymphatus/caesium-image-compressor · GitHub.
c-i-c 2.4.1 contains the final versions of the patches and those do not actually appear to work. I must have tested them incorrectly when I opened the pull request.
I have opened a new pull request fixing the build and rebased the Nixpkgs pull request.