diff --git a/src/matrix_harness.zig b/src/matrix_harness.zig
index 3cb7eca..782b1e4 100644
--- a/src/matrix_harness.zig
+++ b/src/matrix_harness.zig
@@ -360,7 +360,9 @@ fn onProgressEvent(ctx: ?*anyopaque, ev: letta.Event) void {
             p.ret(out);
         },
         .chunk => |c| {
-            defer p.alloc.free(c);
+            // NOTE: chunk/step payloads are BORROWED — handleLine frees them
+            // via defer (same contract as the overlay UI). Freeing here too
+            // is a double free (heap corruption, silently lost reply tails).
             _ = p.replyChunk(c, false);
         },
         .step => {}, // legacy pre-formatted lines: superseded by structured