Terminally fail retrying deliveries with a non-retry target type (closes #82) (#104)

A delivery left in `retrying` whose target type was edited to a fire-and-forget
or unknown type was skipped forever by both restart recovery and the retry
sweep. Both paths now record a result row and mark it `failed`.

TODO.md

@@ -29,6 +29,10 @@ databases currently grow without bound.
 
 # Completed Steps
 
+- 2026-08-09 Restart recovery and the 60s retry sweep terminally fail an
+  orphaned `retrying` delivery whose target type no longer supports
+  retries, recording a `DeliveryResult` with the reason instead of
+  leaving the delivery stuck forever (#82)
 - 2026-08-09 Root the delivery engine's worker pool and the retention
   reaper's sweep loop at `context.Background()` rather than the fx
   `OnStart` hook context (#97), which carries fx's 15s start timeout and