Eigen triggers "fatal error: Eigen: No such file or directory #include <Eigen>"

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fatal error: Eigen: No such file or directory #include <Eigen>

The problem seems to be with the linking, somehow. When I call catkin_make_isolated there is no problem finding FindEigen3.config, but the source files themselves don't see #include <Eigen>

CMakeLists.txt has the following references to Eigen3:

 find_package(Eigen3 REQUIRED)

 include_directories(
    ${catkin_INCLUDE_DIRS}
    ${Eigen3_INCLUDE_DIRS}
  )

  catkin_package(CATKIN_DEPENDS message_runtime
    DEPENDS Eigen3
  )

and package.xml has

  <build_depend>roscpp</build_depend>
  <run_depend>roscpp</run_depend>
  <build_depend>cmake_modules</build_depend>
  <run_depend>cmake_modules</run_depend>

I've gone back and forth with this problem for hours, but I'm at my wits end. I'd be really grateful if you could shed a light on this.

Tell me if you need to see other file contents. I really appreciate it!