Keep the process alive while a send waits for a link

todo.md

@@ -137,8 +137,9 @@ session message is a change to every call site.
       bind already need, with `Session` calling it when a link comes up or goes down instead of
       spreading `linkDown()` and `retrying()` across both sides. It would also close two smaller
       things — `LinkGate.deadline()` and `wait(deadline)` are a two-call protocol whose only failure
-      mode is calling `deadline()` inside the loop, which nothing catches; and `Session.linkDown()`
-      is read from both sides of the seam. Every one of these is unpublished, so it is a two-way
+      mode is calling `deadline()` inside the loop, which nothing catches; `Session.linkDown()` is
+      read from both sides of the seam; and `UnansweredError` sits in `pending-requests.ts`, which
+      never uses it, for the sole edge that makes `send-sms` import that module at all. Every one of these is unpublished, so it is a two-way
       door and belongs after 1.0.0. Raised by review, 2026-09-01.
 - [ ] **Does an intermediate delivery notification deserve to be a `dlr`?** `esm_class` message type
       `INTERMEDIATE_DELIVERY` (0x20) is classified as a message today, so a peer that reports