chore(quest): plan a crate's own double-ended, exact-size, and fused iterators

quest/m2/ts-model/README.md

@@ -47,3 +47,4 @@ Public API: the translator's output for moq-net's model.
 ## Required
 
 - [A crate's own hasher](/quest/m2/ts-model/own-hasher.md) - hashlink's default hasher, a crate's own `Hasher`, hashes keys as native's does
+- [A crate's own iterator traits](/quest/m2/ts-model/iter-traits.md) - hashlink's double-ended, exact-size, and fused iterators, and their `size_hint`

quest/m2/ts-model/iter-traits.md

@@ -0,0 +1,23 @@
+# [M] A crate's own double-ended, exact-size, and fused iterators
+
+## Goal
+
+[rust2-ts](/ts/README.md) translates a crate's own iterator that implements
+`DoubleEndedIterator`, `ExactSizeIterator`, or `FusedIterator`, or overrides `size_hint`, as
+hashlink's do, so std's adaptors and collectors call them where native's does, proven by
+differential tests against native Rust.
+
+## Plan
+
+Found by [#398](https://github.com/moq-dev/rust2/pull/398): once hashbrown translated, 39 of
+the model's census refusals were in these impls on hashlink's iterators, such as
+`LinkedHashMap`'s `Iter`, `Keys`, and `Drain`. They predate #398.
+
+- Read the refusals from `just ts census` on `ts/moq/model.toml` first, and close each kind.
+- `next_back`, `len`, and an overridden `size_hint` are the crate's methods, called wherever
+  std's adaptors and collectors call them, `rev`, `last`, a `collect`'s reserve, and the rest,
+  and nowhere they don't.
+- `FusedIterator` is only a marker, but `fuse` skips its guard for one, which a differential
+  test with an iterator that yields again after `None` shows.
+
+Public API: the translator's output.