Keep a just-read article visible (and Previous-reachable) until the next fetch

The Unread/Older views are live Room Flow queries filtered on
isRead = 0, so marking an article read (which only happens on
Next/Previous, not on open) makes it vanish from the list the instant
Room re-emits -- mid-scroll, or from underneath the reader's own
Previous button, which re-queries this same flow to find its
neighbors. Concretely: Next from C to D marks C read and prunes it
from the live list; Previous from D then can't find C anymore, and
jumps past it to whatever was unread before C. A misclick or the
in-flight prune could cost you the article you meant to keep reading.

Adds ArticleEntity.readAt (set whenever isRead flips true, cleared on
explicit "mark unread"); observeUnread/observeOlderUnread now match
"isRead = 0 OR readAt >= sinceFetch", where sinceFetch is
Settings.lastFetchAt -- the same durable signal the new-articles
snackbar already uses. A read article now lingers (shown dimmed via
the existing showReadState styling) until the next real fetch
actually completes, not the next DB write, and Previous/Next read from
the same still-inclusive query so stepping back to what you just read
finds it right where it was.

1 files changed, 12 insertions, 2 deletions

diff --git a/app/src/main/java/org/terst/feedreader/data/AppDatabase.kt b/app/src/main/java/org/terst/feedreader/data/AppDatabase.kt
index 7f33439..2fd5816 100644
--- a/app/src/main/java/org/terst/feedreader/data/AppDatabase.kt
+++ b/app/src/main/java/org/terst/feedreader/data/AppDatabase.kt
@@ -12,7 +12,7 @@ private const val TAG = "FeedMigration"
 
 @Database(
     entities = [FeedEntity::class, ArticleEntity::class, FilterRuleEntity::class],
-    version = 9,
+    version = 10,
     exportSchema = false
 )
 abstract class AppDatabase : RoomDatabase() {
@@ -258,6 +258,16 @@ abstract class AppDatabase : RoomDatabase() {
             }
         }
 
+        // v10: added ArticleEntity.readAt (epoch millis, null while unread). Plain nullable
+        // ADD COLUMN is safe here the way v2/v3's were -- no column is being removed or
+        // renamed, so there's nothing for Room's exact-match post-migration validation to
+        // trip on (see v4's comment above for what DOES require a full rebuild).
+        private val MIGRATION_9_10 = object : Migration(9, 10) {
+            override fun migrate(db: SupportSQLiteDatabase) {
+                db.execSQL("ALTER TABLE articles ADD COLUMN readAt INTEGER")
+            }
+        }
+
         fun get(context: Context): AppDatabase = instance ?: synchronized(this) {
             instance ?: Room.databaseBuilder(
                 context.applicationContext,
@@ -265,7 +275,7 @@ abstract class AppDatabase : RoomDatabase() {
                 "feedreader.db"
             ).addMigrations(
                 MIGRATION_1_2, MIGRATION_2_3, MIGRATION_3_4, MIGRATION_4_5,
-                MIGRATION_5_6, MIGRATION_6_7, MIGRATION_7_8, MIGRATION_8_9
+                MIGRATION_5_6, MIGRATION_6_7, MIGRATION_7_8, MIGRATION_8_9, MIGRATION_9_10
             ).build().also { instance = it }
         }
     }