Move the TODO.md entry for the negative cache cleanup to the top

The rebase onto next left it below the entries next gained since.

Model: opus-5-5

TODO.md

@@ -30,6 +30,17 @@ P2: security: per-origin rate limiting
 
 # Completed Steps
 
+- 2026-10-15 expired negative cache rows are removed on a schedule (closes
+  #244): the row of a failed fetch, which makes pixa answer 502 for that source
+  URL for 5 minutes, was deleted only when the same URL was requested again
+  after that, so a client asking for a new missing path each time added rows
+  that stayed for good. The eviction goroutine now calls `CleanExpired` at
+  startup and on each periodic tick, every 5 minutes in pixad, so a row stays at
+  most about 10 minutes. `CleanExpired` deletes at most 1000 rows per statement,
+  so a request waits behind 1000 deletions at most, however many rows have
+  expired. The goroutine runs with the disk cache disabled
+  (`cache_max_bytes: 0`) too, where it does nothing else, as the negative cache
+  is used either way.
 - 2026-10-15 a cached variant is served while its source URL is in the negative
   cache (closes #245): `Get` checked the negative cache before the variant
   cache, so once a fetch of the source failed, as one does when another variant
@@ -59,17 +70,6 @@ P2: security: per-origin rate limiting
   and the query now have each `%` written as `%25` and each `:` as `%3A`; a path
   and query holding neither are signed and keyed as before. Signature
   Specification in `README.md` says so.
-- 2026-10-15 expired negative cache rows are removed on a schedule (closes
-  #244): the row of a failed fetch, which makes pixa answer 502 for that source
-  URL for 5 minutes, was deleted only when the same URL was requested again
-  after that, so a client asking for a new missing path each time added rows
-  that stayed for good. The eviction goroutine now calls `CleanExpired` at
-  startup and on each periodic tick, every 5 minutes in pixad, so a row stays at
-  most about 10 minutes. `CleanExpired` deletes at most 1000 rows per statement,
-  so a request waits behind 1000 deletions at most, however many rows have
-  expired. The goroutine runs with the disk cache disabled
-  (`cache_max_bytes: 0`) too, where it does nothing else, as the negative cache
-  is used either way.
 - 2026-10-15 the example config allowlists no host (closes #249): it allowlisted
   `github.com` and `user-images.githubusercontent.com`, where anyone can put an
   image, so a deployment set up as Getting Started says served those images to