ci: fix three platform-specific build failures

- Linux: Qt6 metatype static_assert requires complete types; declare
  OakEngineBlock with Q_DECLARE_OPAQUE_POINTER in the public header
  (outside extern "C")
- Windows: gtest discovery runs the freshly linked test exe at build
  time and it cannot find the DLLs (0xc0000135); copy oakcore/oakengine/
  ffmpeg_bridge DLLs next to the test binaries on WIN32
- macOS: Imath header mixing between otio-install's stale bundled Imath
  and Homebrew's Imath broke ImathBox.h (V2h undeclared); bump the OTIO
  cache to v2 and drop bundled Imath headers so the system one is the
  only set in play

.github/workflows/ci.yml

@@ -62,11 +62,17 @@ jobs:
         uses: actions/cache@v4
         with:
           path: otio-install
-          key: otio-0.16.0-${{ runner.os }}-v1
+          key: otio-0.16.0-${{ runner.os }}-v2
 
       - name: Set OTIO location (Unix)
         if: runner.os != 'Windows'
-        run: echo "OTIO_LOCATION=${PWD}/otio-install" >> "$GITHUB_ENV"
+        run: |
+          echo "OTIO_LOCATION=${PWD}/otio-install" >> "$GITHUB_ENV"
+          # With OTIO_FIND_IMATH=ON the system (brew/apt) Imath must be the
+          # only Imath header set in play; drop any bundled headers a stale
+          # cache entry may have brought back (they collide with the system
+          # include guards and break ImathBox.h).
+          rm -rf "${PWD}/otio-install/include/Imath"
 
       - name: Build OpenTimelineIO (Unix)
         if: runner.os != 'Windows' && steps.otio-cache.outputs.cache-hit != 'true'
@@ -120,7 +126,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: otio-install
-          key: otio-0.16.0-${{ runner.os }}-v1
+          key: otio-0.16.0-${{ runner.os }}-v2
 
       - name: Set OTIO location (Windows)
         if: runner.os == 'Windows'

core/tests/CMakeLists.txt

@@ -32,3 +32,10 @@ target_include_directories(oakcore_gtest PRIVATE
 )
 
 gtest_discover_tests(oakcore_gtest)
+
+if (WIN32)
+  # gtest discovery executes the binary at build time; it needs the DLL next to it
+  add_custom_command(TARGET oakcore_gtest POST_BUILD
+    COMMAND ${CMAKE_COMMAND} -E copy_if_different
+            $<TARGET_FILE:olivecore> $<TARGET_FILE_DIR:oakcore_gtest>)
+endif ()

engine/CMakeLists.txt

@@ -292,6 +292,17 @@ if (BUILD_TESTS)
         # Freshly linked binaries can exceed the 5s default discovery
         # timeout on first run (dyld cold cache + Qt/OCIO init)
         gtest_discover_tests(${name} DISCOVERY_TIMEOUT 60)
+        if (WIN32)
+            # gtest discovery executes the binary at build time; it needs
+            # the engine DLLs next to it
+            add_custom_command(TARGET ${name} POST_BUILD
+                COMMAND ${CMAKE_COMMAND} -E copy_if_different
+                        $<TARGET_FILE:oakengine> $<TARGET_FILE_DIR:${name}>
+                COMMAND ${CMAKE_COMMAND} -E copy_if_different
+                        $<TARGET_FILE:olivecore> $<TARGET_FILE_DIR:${name}>
+                COMMAND ${CMAKE_COMMAND} -E copy_if_different
+                        $<TARGET_FILE:ffmpeg_bridge> $<TARGET_FILE_DIR:${name}>)
+        endif ()
     endfunction()
 
     make_oakengine_gtest(oakengine_ipc_test)

engine/include/oakengine/timeline.h

@@ -1308,6 +1308,11 @@ oakengine_clip_get_connected_viewer(const OakEngineBlock *clip);
 
 #ifdef __cplusplus
 }
+
+// Qt6 on some toolchains requires complete types in meta-type instantiations
+// (e.g. QList<OakEngineBlock*> in TimelinePanel signals); declare the handle
+// opaque instead of pulling the engine definition into the public header.
+Q_DECLARE_OPAQUE_POINTER(OakEngineBlock *)
 #endif
 
 #endif /* OAKENGINE_TIMELINE_H */