First increment of typed host callbacks (roadmap #1): the data-structure
layer, independent of the FFI thread and the macro so it can be unit-tested
in isolation.
- FFIHostRegistry: wire-name -> (host fn ptr, userData). A missing entry is a
normal outcome (the imported proc errors), never a crash — never-crash
policy. nil fn unregisters.
- FFIPendingTable: monotonic token -> the chronos Future an awaiting
{.ffiHost.} proc is blocked on. completePending drops unknown/double
completions; failAllPending errors every outstanding future on teardown so
no awaiting handler is abandoned.
Both lock-guarded so a host thread and the FFI thread can touch them
concurrently; futures are only ever completed on the FFI thread. 6 unit tests
pass under orc and refc.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
