review: clear stale attribution, gate numberless PUTs, cite the ADR

A Poll finding a higher number now clears series.latest_raised_by: the value
it stores is its own, so the next Poll must not credit that Reader with an
agreement they did not earn, nor charge them for a retraction of a number
they never reported.

A PUT carrying no chapter is no Sighting and defers nothing. The ceiling now
counts the Site's own rest rather than defaultRest. The userscripts PUT an
unchanged read too - the case the whole mechanism exists for was the one they
never sent.

ADR-0011 carries its citations and states honestly when a Reader's marks take
effect.

backend/AGENTS.md

@@ -79,7 +79,9 @@ Guidance for OpenCode (and Claude Code) working under `backend/`. See root `AGEN
   each re-checking that Site's bookmarked series' newest published chapter from
   backend's own network access, so `latest_chapter` stays fresh when the user
   isn't browsing. Second, parallel signal — the userscript keeps its own
-  `maybeCaptureLatestOnSeriesPage`/`backgroundRefreshLatest` logic unchanged.
+  `maybeCaptureLatestOnSeriesPage`/`backgroundRefreshLatest` schedule, and its
+  `reportLatestChapter` PUTs every read, unchanged numbers included, because an
+  unchanged read is exactly the Sighting worth deferring a Poll on (#103).
   Two independent clocks: per-series rest (`series.latest_checked_at`,
   enforced by `Store.DueForLatestCheck`'s WHERE clause — `now - Rest`) and
   per-Lane gap (the Lane sleeping between fetches, `effectiveGap`). Both live
@@ -98,17 +100,23 @@ Guidance for OpenCode (and Claude Code) working under `backend/`. See root `AGEN
   `series.latest_sighted_at` and, when the report raises the stored number,
   names its Reader in `series.latest_raised_by`. The due query's HAVING clause
   is where deferral lives: a Series is skipped only while it has exactly one
-  Bookmark, was sighted within one Rest, and is under the `sightingCeiling`
-  (six rests) since its last Poll. So a shared Series is never deferred, and no
-  Series goes six hours unpolled whatever arrives. `checkOne` judges the named
-  Reader off the comparison it already makes: a lower number is a
-  contradiction (logged with the Reader and both numbers), the same number an
-  agreement, a higher number the Site publishing and neither. Three
-  contradictions (`store.SightingDisagreementLimit`) stop that Reader deferring
-  — their reports still write the Latest Chapter — and twenty consecutive
-  agreements (`store.SightingAgreementsToClear`) forgive them, as does the
-  owner's clear-marks control. Deferral is recomputed from live facts every
-  round, so nothing needs invalidating when a Series gains a second Bookmark.
+  Bookmark, was sighted within one Rest, and is under the ceiling
+  (`sightingCeilingRests`, six of that Site's rests) since its last Poll. So a
+  shared Series is never deferred, and no Series goes six hours unpolled
+  whatever arrives. `checkOne` judges the named Reader off the comparison it
+  already makes: a lower number is a contradiction (logged with the Reader and
+  both numbers), the same number an agreement, a higher number the Site
+  publishing and neither — that last one clears the attribution instead, since
+  the value the Poll then stores is its own and a later retraction is not the
+  Reader's fault. Three contradictions
+  (`store.SightingDisagreementLimit`) stop that Reader deferring — their
+  reports still write the Latest Chapter — and twenty consecutive agreements
+  (`store.SightingAgreementsToClear`) forgive them, as does the owner's
+  clear-marks control. Deferral is recomputed from live facts every round, so
+  nothing needs invalidating when a Series gains a second Bookmark; the one
+  input read earlier is the Reader's marks, checked when the Sighting is
+  recorded, so crossing the threshold or being cleared takes effect from that
+  Reader's next Sighting and the standing already bought lasts out its rest.
   Refusals and browser loss are Lane-local: two `errChallengeHeld` in one pass
   stop that Site for `refuseBackoff` (15m) while other Lanes continue; an
   `errBrowserInterrupted` (remote Chrome restart) sets a shared Poller flag