A generic free fn whose `$R` is inferred from a worker `Closure(..$args) -> $R` (+ trailing `..$args`) and which returns a type built from `$R` (`-> Wrap($R)`) monomorphizes correctly when called directly (`f(recv, worker, ..)`) but leaves `$R` UNRESOLVED when called via UFCS dot syntax (`recv.f(worker, ..)`) — the unresolved type reaches LLVM emission and trips the `.unresolved` tripwire (SIGTRAP). Distinct from RESOLVED issue 0119 (UFCS `$T` from receiver/slice). Blocks the B1.2 user-facing async idiom `context.io.async((a,b) -> R => ..., x, y)` (a UFCS call inferring $R from the worker closure's return type). The Io/async library + compiler plumbing are in place and correct (landed in the prior commit); only the UFCS call form hits this inference gap. Repro depends on no project symbols beyond modules/std.sx; unpinned (no expected/ marker) so it does not run in the corpus.
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