ci: install only libobs from the OBS sub-build

macOS got all the way through this time: the synthesised SDK path satisfied
OBS's version check, the sub-build configured, and libobs built and installed
-- libobs.framework with its headers, libobsConfig.cmake and
libobsTargets.cmake all landed. Then the install failed on the NEXT
subproject:

  file INSTALL cannot find ".../UI/obs-frontend-api/obs-frontend-api.dylib":
  No such file or directory

Installing from the top-level build directory walks every subproject's
cmake_install.cmake, and obs-frontend-api is a target this build deliberately
never builds -- that is the whole point of dropping Qt. Pointing --install at
the libobs subdirectory installs exactly what find_package(libobs) needs and
nothing else.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RL8abRmgFXkVASHkkqiJbE

cmake/common/buildspec_common.cmake

@@ -20,6 +20,10 @@
 #      branch: a runner with only the Command Line Tools has no xcodebuild.
 #   5. Generator flags are built as CMake lists so each becomes its own argv
 #      entry, rather than upstream's space-separated strings passed unquoted.
+#   6. The install step targets the libobs subdirectory rather than the whole
+#      build tree, so it does not trip over the install rules of targets that
+#      were deliberately never built.
+#   7. _resolve_versioned_macos_sdk exists at all -- see its own comment.
 #
 
 include_guard(GLOBAL)
@@ -207,10 +211,21 @@ function(_setup_obs_studio)
   )
   message(STATUS "Build ${label} (Release - ${arch}) - done")
 
+  # Install only libobs's own rules, not the whole build tree's. Installing
+  # from the top-level build directory walks every subproject's
+  # cmake_install.cmake, including UI/obs-frontend-api's, which then fails on
+  # a binary that was deliberately never built:
+  #
+  #   file INSTALL cannot find ".../obs-frontend-api.dylib": No such file
+  #
+  # Pointing --install at the libobs subdirectory installs the framework /
+  # import library, the headers, and libobsConfig.cmake + libobsTargets.cmake
+  # -- everything find_package(libobs) needs -- and nothing else.
   message(STATUS "Install ${label} (${arch})")
   execute_process(
     COMMAND
-      "${CMAKE_COMMAND}" --install build_${arch} --component Development --config Release --prefix "${dependencies_dir}"
+      "${CMAKE_COMMAND}" --install build_${arch}/libobs --component Development --config Release --prefix
+      "${dependencies_dir}"
     WORKING_DIRECTORY "${dependencies_dir}/${_obs_destination}"
     RESULT_VARIABLE _process_result
     COMMAND_ERROR_IS_FATAL ANY