ffi checkpoint: issue-0045 fix + step 1 wrap-up

Logs the issue-0045 fix (inline-return slot for comptime-call
bodies, commits 3d32ab0 + 9e78790) — the LLVM verifier crash
that surfaced when probing step 2 of the pack feature. Test
count now 194/194 with the new regression test.

current/CHECKPOINT-FFI.md

@@ -6,6 +6,45 @@ add a test and make it pass — that's two commits).
 
 ## Last completed step
 
+**issue-0045 fix — inline-return slot for comptime-call bodies**
+(commit `9e78790`, lock-in `3d32ab0`).
+
+Surfaced by probing step-2 territory of the pack feature: any
+comptime fn (`is_comptime` param, non-void return) with a block
+body containing `return X;` trips LLVM's "Terminator found in
+the middle of a basic block" verifier. `lowerComptimeCall`
+inlines the body's statements directly into the caller, and
+`lowerReturn` emits `ret` into the caller's basic block — but
+the caller still has trailing instructions.
+
+Root cause was broader than packs: `format`/`print` use arrow
+form (`=> expr`) or `#insert`-only bodies, so no stdlib comptime
+fn took the `return`-with-trailing-statements path. Step 1.b
+made `..$args` parseable; the natural smoke test
+`foo :: (..$args) -> s64 { return 42; }` was the first body to
+hit it.
+
+Fix in `src/ir/lower.zig`:
+- New `inline_return_target: ?InlineReturnInfo` on Lowering.
+  `InlineReturnInfo` carries a result slot Ref + the ret_ty.
+- `lowerComptimeCall` calls `fnBodyHasReturn` to scan the body;
+  when true, it allocates a slot, installs it as
+  `inline_return_target`, lowers the body, and either returns
+  the tail expression value OR loads the slot when
+  `block_terminated` is set. Pure tail-expression bodies skip
+  the slot entirely — keeps the common `#insert`-based path
+  unchanged.
+- `lowerReturn` checks `inline_return_target` first: when set,
+  stores the coerced value into the slot, drains pending
+  defers, sets `block_terminated = true`, and returns without
+  emitting `ret`. Otherwise the standard `ret` path runs.
+
+Regression test `examples/issue-0045.sx` flips from the LLVM
+verifier crash to `42`. 194/194 example tests + `zig build test`
+green.
+
+---
+
 **M5.A.next.1d.B — variadic heterogeneous type packs: pack-aware impl
 matching** (commit `08feb60`).
 
@@ -394,8 +433,10 @@ plus 2 codegen fixes surfaced along the way.**
 
 ## Current state
 
-- 185/185 example tests pass; `zig build test` green.
+- 194/194 example tests pass; `zig build test` green.
 - Phase 3.0/3.1/3.2 + M1.0–M1.3 + M2.1–M2.3 + M3 + M4.0 + M4.A all landed.
+- Pack feature step 1 done (1c.A → 1d.B; commits bb6eca6 → 08feb60).
+- issue-0045 (comptime-fn-with-return verifier crash) fixed (9e78790).
 - Chess on macOS / iOS-sim / Android all build and run.
 
 **M4.0 — context.allocator threading** (4 commits this session):