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ad493d6f9d
The native (zero-serialization) path previously handed `{.ffi.}` struct
params to the FFI thread using the Nim object layout (GC'd `string` fields),
which does not match the C-POD layout the generated header declares — an ABI
mismatch that left struct-param procs uncallable from C and skipped by the Go
codegen.
Wire the generated POD machinery into both the `{.ffi.}` and `{.ffiCtor.}`
native paths: a registered `{.ffi.}` struct now travels as its `<T>Pod`
mirror — `clonePod` deep-copies it off the caller's buffers into shared
(`c_malloc`) memory on the caller thread, `podToNim` rebuilds the Nim value on
the FFI thread, and `freePod` releases it from the CArgs free proc. `string`
collapses to `cstring` (alloc/ffiCFree); scalars copy direct. New classifiers
(`nativeWireType` / `nativeArgCopyStmt` / `nativeArgUnpackStmt`) keep both
paths and the CArgs alloc/free in lockstep so ownership can't drift.
The load-bearing invariant: the `<T>Pod` `{.bycopy.}` layout is identical to
the C struct emitted by `codegen/c.emitCStructs`, so the `exportc` symbol's
ABI matches the header even though Nim's own struct name differs. Keep the two
emitters in sync.
Validated end-to-end from C (TimerConfig, EchoRequest, and a nested
ComplexRequest with seq-of-structs, seq-of-strings and two Options) and clean
under ASAN. Struct *returns* still travel as CBOR on the native path; that is
left for a follow-up.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>