fix: remember ratings in 5-star space — odd server ratings no longer drift up

Change-detection compared a derived 10-scale value against a remembered
raw 10-scale value, but the summary can only hold whole stars: a pulled
server 9 (4.5 stars) applied as 5 stars, remembered 9, and the next
close-push derived 10 ≠ 9 and silently rounded the server rating up.
Every odd rating (9/7/5/3/1) drifted one half-star on the first close
after a pull.

The remembered state is now the star count actually written (5-space);
the POST fires only when the star count itself changed, converting at
the boundary. koreader's display is an array-index lookup (a fractional
rating would render nil), so whole stars are the only safe memory.
getMetaSyncState normalizes any 10-space value an older build wrote.

Verified: s → stars → 2s → stars is stable for all s in 1..10.

main.lua

@@ -1980,6 +1980,11 @@ function Bookhoard:getMetaSyncState(book_key)
     if type(state) ~= "table" then
         state = {}
         self.settings.meta_sync_state[book_key] = state
+    elseif type(state.rating) == "number" and state.rating > 5 then
+        -- Settings written by the first bridge build remembered ratings
+        -- in 10-space; normalize once. 10-space memory cannot survive
+        -- the round-trip (odd values would re-round at every push).
+        state.rating = rating10to5(state.rating)
     end
     return state
 end
@@ -2007,20 +2012,24 @@ function Bookhoard:pullBookMeta(interactive)
     if self.settings.sync_ratings then
         local ok, result = api:getRating(ref)
         if ok and result and not result.error then
-            local server10 = result.rating
+            -- Compare in 5-STAR SPACE. The summary cannot represent odd
-            local server5 = rating10to5(server10)
+            -- server values (9 = 4.5 stars), so remembering the raw
+            -- 10-scale would make every pulled odd rating look "changed"
+            -- at push time (9 remembered → 5★ local → push derives 10)
+            -- and silently round it up. Remember the star count we
+            -- actually wrote; conversion to 10 happens only at the POST.
+            local server5 = rating10to5(result.rating)
             local local5 = summary.rating or 0
-            local local10 = rating5to10(local5) or 0
+            local remembered5 = remembered.rating or 0
-            local remembered10 = remembered.rating or 0
+            if server5 ~= local5 and remembered5 == local5 then
-            if server10 ~= nil and server10 ~= local10 and remembered10 == local10 then
                 -- Server moved, koreader didn't → apply.
                 summary.rating = server5
                 self:writeSummary(summary)
-                remembered.rating = server10
+                remembered.rating = server5
                 table.insert(applied, T(_("rating %1/5"), server5))
-            elseif server10 ~= nil and server10 == local10 and remembered10 ~= local10 then
+            elseif server5 == local5 and remembered5 ~= local5 then
                 -- Values agree but our memory is stale; just re-sync memory.
-                remembered.rating = server10
+                remembered.rating = server5
             end
         end
     end
@@ -2068,12 +2077,15 @@ function Bookhoard:pushBookMeta(interactive)
     local api = self:getAPI()
 
     if self.settings.sync_ratings then
-        local local10 = rating5to10(summary.rating) or 0
+        -- 5-star space comparison (see the pull): the POST only fires
-        local remembered10 = remembered.rating or 0
+        -- when the star count itself changed; conversion happens at the
-        if local10 ~= remembered10 then
+        -- boundary (nil/0 → server clears).
-            local ok, result = api:setRating(ref, local10)
+        local local5 = summary.rating or 0
+        local remembered5 = remembered.rating or 0
+        if local5 ~= remembered5 then
+            local ok, result = api:setRating(ref, rating5to10(local5) or 0)
             if ok and result and not result.error then
-                remembered.rating = local10
+                remembered.rating = local5
                 table.insert(pushed, _("rating"))
             else
                 errors = errors + 1