quest: plan a Pin of a crate's own Deref type

quest/m3/README.md

@@ -51,3 +51,4 @@ memory model for values whose address is reinterpreted, without a consumer.
 - [`if let` of a temporary whose rest drops](/quest/m3/ts-if-let-drop.md) - `if let Some(E::A(x)) = temp()` with a destructor in the rest of `temp` emits TypeScript that type-checks
 - [`u64` wrapping arithmetic in V8](/quest/m3/ts-u64-wrapping.md) - `rs.u64WrappingAdd` and its kin cost near a plain `+` while the value is a safe integer
 - [Array references from slices and cells](/quest/m3/ts-array-ref-conversions.md) - `try_into` of a slice into an array reference, `Cell::as_array_of_cells`, and `identity` of a `&mut [T; N]` lend the array where it is
+- [A Pin of a crate's own Deref type](/quest/m3/ts-pin-own-deref.md) - `Pin<P>` over a crate's own `Deref` derefs through its impl and type-checks

quest/m3/ts-pin-own-deref.md

@@ -0,0 +1,19 @@
+# [S] A Pin of a crate's own Deref type type-checks
+
+## Goal
+
+[rust2-ts](/ts/README.md) translates a `Pin<P>` whose `P` is a crate's own `Deref` type,
+such as `Pin::new(OwnPtr(Cell::new(0)))` with `old.get()` called through it, into
+TypeScript that type-checks, its deref going through `P`'s own `Deref` impl, proven by
+differential tests against native Rust. Today `tsc` rejects it (TS2739), since `Pin<P>`'s
+deref is typed as `P` itself.
+
+## Plan
+
+Found on [#621](https://github.com/moq-dev/rust2/pull/621) while checking a review finding.
+It is safe Rust, where m3's [unsafe policy](/quest/m3/README.md) puts translation effort,
+though no consumer at the moq pin reaches it.
+
+Decided with the maintainer on 2026-11-07: ✅ plan it, in m3 (from #621's follow-ups).
+
+Public API: the translator's output.