Latent bug from the stdlib-path resolution introduced in 4849cfb.
The earlier shape captured `const ci = decl.data.c_import_decl;`
BEFORE mutating `decl.data.c_import_decl.{sources,includes}` with
the resolved paths, then passed the stale `ci.includes` to
`c_import.processCImport`. Result: `#include "vendors/..."` paths
that resolved via the stdlib branch (i.e. only existed under
sx/library/vendors/) reached clang as the original unresolved
string and failed to parse — silently producing no synthesized
`#foreign` decls.
`#source` survived because the source list is re-read from
decl.data later (collectCImportSources walks the AST), so it
picked up the mutated value. Only `#include`'s synthesis path was
broken.
Fix: do the resolution first inside its own scope, then re-bind
`ci` from `decl.data.c_import_decl` so the include list passed to
processCImport sees the resolved paths.
Caught by ffi-07 baseline (next commit) — the test deliberately
puts its C helper only under library/vendors/ so the path is
findable solely via the stdlib chain.
43a30e727d