Fix reader rotation bug: replace-nav instead of a swipe-queue snapshot

The reader used to snapshot the article-id order of its list ONCE at
entry and page a HorizontalPager across that fixed queue. Two real
bugs traced back to one root cause: the snapshot lived in plain
remember state that did NOT survive an orientation change, while the
pager's own page index did -- rotating mid-session left the index
pointing into a freshly re-fetched (and by then shorter, since paging
past an article marks it read and drops it from the Unread query)
list, landing on a different article than the one actually being
read. Back was confusing for the same reason: it always returned to
wherever the ORIGINAL initialArticleId pointed, not wherever the pager
had since scrolled to.

Fixed by not having a separate queue/index at all: each Next/Previous
now replaces this screen's own back-stack entry with a fresh
navigation to the neighboring article's id (MainActivity wires
onNavigateToArticle with the same popUpTo-replace pattern
LinkReaderScreen already uses for its own link chain). "Which article
is showing" is now the nav route argument itself -- Android's own
Saved State mechanism, not custom state that can drift out of sync
with it -- and the back stack is always exactly [list, one reader
entry] no matter how many articles were paged through.

1 files changed, 13 insertions, 3 deletions

diff --git a/app/src/main/java/org/terst/feedreader/ui/MainActivity.kt b/app/src/main/java/org/terst/feedreader/ui/MainActivity.kt
index f7ca043..9add10a 100644
--- a/app/src/main/java/org/terst/feedreader/ui/MainActivity.kt
+++ b/app/src/main/java/org/terst/feedreader/ui/MainActivity.kt
@@ -89,13 +89,23 @@ fun FeedReaderApp() {
             val feedId = decodeNavArg(backStackEntry.arguments?.getString("feedId") ?: UNREAD_FEED_ID)
             val articleId = decodeNavArg(backStackEntry.arguments?.getString("articleId") ?: "")
             // feedId here is the list the article was opened from (Unread/Saved/a specific
-            // feed) -- ReaderScreen uses it to build the swipe queue of sibling articles.
+            // feed) -- ReaderScreen uses it to look up the current article's neighbors.
             ReaderScreen(
                 feedId = feedId,
-                initialArticleId = articleId,
+                articleId = articleId,
                 onBack = { navController.popBackStack() },
                 onOpenLink = { url -> navController.navigate("linkReader/${encodeNavArg(url)}") },
-                onOpenBrowser = { url -> navController.navigate("browser/${encodeNavArg(url)}") }
+                onOpenBrowser = { url -> navController.navigate("browser/${encodeNavArg(url)}") },
+                // Replaces this screen's own back-stack entry rather than stacking a new
+                // one per article (same popUpTo-replace pattern linkReader's own link-chain
+                // navigation already uses below) -- so the stack is always exactly
+                // [list, this one reader entry], and back always returns to the list in a
+                // single press no matter how many articles were paged through via Next/Previous.
+                onNavigateToArticle = { nextArticleId ->
+                    navController.navigate("reader/${encodeNavArg(feedId)}/${encodeNavArg(nextArticleId)}") {
+                        popUpTo("reader/{feedId}/{articleId}") { inclusive = true }
+                    }
+                }
             )
         }
         composable(