feat(gamification): migration v13 — auto_completed column

Adds a flag on tasks to distinguish manual completions from the
cascade auto-completion performed by complete_subtask_and_check_parent.
Partial index on (done_at, auto_completed) supports the Phase 8
daily-count query without bloating the tasks index footprint.

Forward-only: pre-migration completed rows default to 0 (they count).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/storage/src/migrations.rs

@@ -430,6 +430,27 @@ const MIGRATIONS: &[(i64, &str, &str)] = &[
             ON implementation_rules(enabled, trigger_kind);
         "#,
     ),
+    (
+        13,
+        "gamification: auto_completed flag for cascade-completed parents",
+        r#"
+        -- Phase 8 of the feature-complete roadmap. Parents that close via
+        -- the complete_subtask_and_check_parent cascade must not count
+        -- towards daily completion totals. The user already got credit
+        -- for ticking the subtask. This column distinguishes manual
+        -- completions (0) from cascade completions (1). The daily-count
+        -- query then excludes auto_completed = 1.
+        --
+        -- Partial index keeps the index small: only completed rows occupy
+        -- it, since uncompleted rows have done_at IS NULL.
+        ALTER TABLE tasks ADD COLUMN auto_completed INTEGER NOT NULL DEFAULT 0
+            CHECK (auto_completed IN (0, 1));
+
+        CREATE INDEX idx_tasks_done_at_auto_completed
+            ON tasks(done_at, auto_completed)
+            WHERE done_at IS NOT NULL;
+        "#,
+    ),
 ];
 
 /// Split SQL into individual statements, respecting BEGIN...END trigger blocks.
@@ -579,7 +600,7 @@ mod tests {
             .fetch_one(&pool)
             .await
             .unwrap();
-        assert_eq!(count, 12);
+        assert_eq!(count, 13);
 
         sqlx::query("INSERT INTO settings (key, value) VALUES ('test', 'value')")
             .execute(&pool)
@@ -598,7 +619,7 @@ mod tests {
             .fetch_one(&pool)
             .await
             .unwrap();
-        assert_eq!(count, 12);
+        assert_eq!(count, 13);
     }
 
     #[tokio::test]
@@ -1054,4 +1075,41 @@ mod tests {
             "schema_version must not advance past the failed migration"
         );
     }
+
+    #[tokio::test]
+    async fn migration_v13_adds_auto_completed_column() {
+        let pool = SqlitePoolOptions::new()
+            .max_connections(1)
+            .connect("sqlite::memory:")
+            .await
+            .expect("pool");
+        run_migrations(&pool).await.expect("migrate");
+
+        // Column exists.
+        let info = sqlx::query("PRAGMA table_info(tasks)")
+            .fetch_all(&pool)
+            .await
+            .expect("pragma");
+        let names: Vec<String> = info.iter().map(|r| r.get::<String, _>("name")).collect();
+        assert!(
+            names.iter().any(|n| n == "auto_completed"),
+            "expected auto_completed column, got {names:?}"
+        );
+
+        // Existing completed rows default to 0. Insert a pre-existing-looking
+        // task via raw SQL to simulate a row from before the migration.
+        sqlx::query(
+            "INSERT INTO tasks (id, text, bucket, done, done_at) \
+             VALUES ('t1', 'pre-existing', 'inbox', 1, '2026-04-20 12:00:00')",
+        )
+        .execute(&pool)
+        .await
+        .expect("insert");
+
+        let auto: i64 = sqlx::query_scalar("SELECT auto_completed FROM tasks WHERE id = 't1'")
+            .fetch_one(&pool)
+            .await
+            .expect("query");
+        assert_eq!(auto, 0, "pre-existing completed rows must default to 0");
+    }
 }