diff --git a/current/CHECKPOINT-FFI.md b/current/CHECKPOINT-FFI.md
index d2774d8..97540a1 100644
--- a/current/CHECKPOINT-FFI.md
+++ b/current/CHECKPOINT-FFI.md
@@ -6,6 +6,39 @@ add a test and make it pass — that's two commits).
 
 ## Last completed step
 
+**M5.A.next.1a — variadic heterogeneous type packs: parse lockin**
+(this commit).
+
+First slice of the `..$args` (variadic heterogeneous type pack)
+feature per the plan saved at
+`~/.claude/plans/lets-see-options-for-merry-dijkstra.md` (see the
+"Variadic heterogeneous type packs" section). Locks in the
+current parser-rejection behavior so the next commit's parser
+extension shows up as a behavior shift.
+
+New: `examples/150-pack-parse.sx` declares
+`foo :: (..$args) -> s64`. Today's parser hits `..` where it
+expects a parameter name (after parsing the leading `dollar`
+sigil that doesn't appear) and emits "expected parameter name"
+at column 9 of line 15. Expected output captures this rejection.
+
+Per FFI cadence rule, this is a "test that fails today, passes
+after the next commit's parser change" pair. The next commit
+extends `parseParams()` (src/parser.zig:1558) to accept `..` at
+the start of a parameter — currently the parser only handles `..`
+inside the type position (after the colon).
+
+191 example tests + `zig build test` green.
+
+The pack feature itself lives in the FFI stream because its
+primary motivation is replacing the hand-rolled per-signature
+`Into(Block)` impls in `library/modules/std/objc_block.sx` with
+one generic `impl Into(Block) for Closure(..$args) -> $R`. Payoff
+extends beyond blocks — `print`/`format` get compile-time arity
+and type-mismatch errors instead of `..Any` runtime tag dispatch.
+
+---
+
 **M1.2 A.0 — `objc_defined_class_cache` + scan-pass registration**
 (`61a2593`).
 
diff --git a/examples/150-pack-parse.sx b/examples/150-pack-parse.sx
new file mode 100644
index 0000000..23ef749
--- /dev/null
+++ b/examples/150-pack-parse.sx
@@ -0,0 +1,22 @@
+// Variadic heterogeneous type packs — `..$args` — parse lockin.
+//
+// First slice of the pack feature: the parser does not yet accept
+// `..$args` (variadic-marker + comptime sigil + name, no type
+// annotation). This test pins the current parse-rejection so the
+// next commit's parser change is visible as a behavior shift.
+//
+// Expected next commit: parser accepts `..$args` and this test
+// either flips to a successful parse (compile error from later
+// passes that haven't been wired up yet) or is replaced by a
+// positive test.
+
+#import "modules/std.sx";
+
+foo :: (..$args) -> s64 {
+    return 0;
+}
+
+main :: () -> s32 {
+    print("never reached\n");
+    return 0;
+}
diff --git a/tests/expected/150-pack-parse.exit b/tests/expected/150-pack-parse.exit
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/tests/expected/150-pack-parse.exit
@@ -0,0 +1 @@
+1
diff --git a/tests/expected/150-pack-parse.txt b/tests/expected/150-pack-parse.txt
new file mode 100644
index 0000000..58d8286
--- /dev/null
+++ b/tests/expected/150-pack-parse.txt
@@ -0,0 +1 @@
+/Users/agra/projects/sx/examples/150-pack-parse.sx:15:9: error: expected parameter name