Now that os.alloc/free ship (db2b05b), the heap-shape printf wrapper
that bb10ee7 deferred is implementable.
`asprintf(fmt: str, args: field...) str` — Hare wrappers.ha:29 shape.
Body wires memio.dynamic, runs fprintf into it, takes a stringview,
and shrink-to-fit-copies into a fresh os.alloc(view.len) before
io.closing the dynamic stream (which frees the cap-sized internal
buffer). The shrink-to-fit copy is forced by os.free's (p, n) shape:
n must match the mmap length, so the caller can't free a
cap-allocated body if cap > len.
Caller contract documented inline: free with `os.free(r.ptr, r.len)`
when r.len > 0; skip when r.len == 0 (no allocation happens).
Mirrors strings.dup's shape; not a workaround.
The fprintf io.closed arm is matched-and-ignored — memio.dynamicwrite
only returns size, never io.closed (verified at memio.ww:163-175).
Same shape as Hare's `case size => void;` in print.ha.
Hare's nomem variant intentionally dropped; ww's os.alloc returns a
poisonous pointer on OOM (per #14 contract) which faults on deref —
no in-band error to model.
Tests (signalled 27-30): basic (str + i64), growth (34B output
through 8→16→32→64 grow), empty (no-alloc / skip-free), indexed_mods
({1:_05} through heap sink).
errorf / error / errorln family deferred — drew's call to ship the
whole error story in one commit when the error type lands.
Hojun-Cho
f906081c8c