Name the modules that hold a cache key's device part and its record of written keys (#493)

src/cache/key.rs

@@ -111,12 +111,23 @@ impl<'a> ServerPart<'a> {
 /// The three parts of a key that do not change between two requests.
 ///
 /// The server, the account as the identifier the server gave back at sign-in
-/// rather than the username, and the device identity from #36. 0068 promises a
-/// caller that signing out removes every entry under one of these, and 0041
-/// makes that set well defined without making it reachable: 0040 gives the store
-/// no listing and a digest does not reverse, so the removal in #114 needs the
-/// core's own record of which keys it wrote, which is the bookkeeping 0040 hands
-/// to #42.
+/// rather than the username, and the device identity [`crate::session::device`]
+/// holds. 0068 promises a caller that signing out removes every entry under one
+/// of these, and 0041 makes that set well defined without making it reachable:
+/// 0040 gives the store no listing and a digest does not reverse, so the removal
+/// in #114 needs the core's own record of which keys it wrote. That record is
+/// the bookkeeping inside [`crate::cache::bound::TieredCache`], and it covers
+/// what THIS run wrote: the index does not survive a restart, which that module
+/// states of itself.
+///
+/// BOTH OF THOSE WERE ADDRESSES ON THE TRACKER UNTIL THIS EDIT, AND THE TWO WENT
+/// WRONG IN DIFFERENT WAYS. The record of written keys was handed to #42. That
+/// issue closed as completed sixteen hours before this file landed and
+/// [`crate::cache::bound`] was already in the tree, so that half landed refuted,
+/// which is the harder of the two states to defend. The device part read `from
+/// #36` while #36 was still open and [`crate::session::device`] did not exist, so
+/// that half was the best available address when it was written and went stale
+/// six hours later, which is the milder. #493 is where both were found.
 ///
 /// Thread safety, from 0009: a plain value, safe from any thread.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -125,7 +136,7 @@ pub struct KeySpace<'a> {
     pub server: ServerPart<'a>,
     /// The account, as the identifier the server gave back at sign-in.
     pub account: &'a str,
-    /// The device identity from #36.
+    /// The device identity, as [`crate::session::device`] holds it.
     pub device: &'a str,
 }