Thanks, here is the output. Note I noticed the event loop hadn't started before the call to watchDirectory failed. So I added a sleep for 10 seconds before the failing call to watchDirectory. It still failed but now with a full stack trace.
[09ED2E01:00000000 dbg] Create FreeListAlloc 8
[09ED2E01:00000000 dbg] Create FreeListAlloc 16
[09ED2E01:00000000 dbg] Create FreeListAlloc 32
[09ED2E01:00000000 dbg] Create FreeListAlloc 64
[09ED2E01:00000000 dbg] Create FreeListAlloc 128
[09ED2E01:00000000 dbg] Create FreeListAlloc 256
[09ED2E01:00000000 dbg] Create FreeListAlloc 512
[09ED2E01:00000000 dbg] Create FreeListAlloc 1024
[09ED2E01:00000000 dbg] Create FreeListAlloc 2048
[09ED2E01:00000000 dbg] Create FreeListAlloc 65540
[09ED2E01:00000000 dia] libevent version: 2.0.21-stable
[09ED2E01:00000000 dia] libevent is using kqueue for events.
[09ED2E01:00000000 dbg] Initializing OpenSSL...
[09ED2E01:00000000 dbg] ... done.
[09ED2E01:00000000 dbg] Creating new fiber...
sleeping for 10 seconds
[09ED2E01:00000000 dia] Running event loop...
starting watch
[09ED2E01:09ED5F01 CRITICAL] CoreTaskFiber was terminated unexpectedly: Assertion failure
[09ED2E01:09ED5F01 dia] Full error: core.exception.AssertError@vibe.core.drivers.libevent2(176): Assertion failure
[09ED2E01:09ED5F01 dia] ----------------
[09ED2E01:09ED5F01 dia] 5 my_vibe_project 0x000000010979b136 _d_assertm + 38
[09ED2E01:09ED5F01 dia] 6 my_vibe_project 0x0000000109657c5a void vibe.core.drivers.libevent2.__assert(int) + 26
[09ED2E01:09ED5F01 dia] 7 my_vibe_project 0x00000001096d7967 vibe.core.file.DirectoryWatcher vibe.core.drivers.libevent2.Libevent2Driver.watchDirectory(vibe.inet.path.Path, bool) + 99
[09ED2E01:09ED5F01 dia] 8 my_vibe_project 0x00000001096e357d vibe.core.file.DirectoryWatcher vibe.core.file.watchDirectory(vibe.inet.path.Path, bool) + 57
[09ED2E01:09ED5F01 dia] 9 my_vibe_project 0x00000001096e35e2 vibe.core.file.DirectoryWatcher vibe.core.file.watchDirectory(immutable(char)[], bool) + 94
[09ED2E01:09ED5F01 dia] 10 my_vibe_project 0x0000000109659009 void app._sharedStaticCtor1().__lambda1() + 125
[09ED2E01:09ED5F01 dia] 11 my_vibe_project 0x00000001096d0cbf void vibe.core.core.CoreTask.run() + 251
[09ED2E01:09ED5F01 dia] 12 my_vibe_project 0x000000010979e191 void core.thread.Fiber.run() + 49
[09ED2E01:09ED5F01 dia] 13 my_vibe_project 0x000000010979dd3a fiber_entryPoint + 98
[09ED2E01:09ED5F01 dia] 14 ??? 0x0000000000000000 0x0 + 0