README restructure + drills only from learned topics

api/src/srs.ts

@@ -166,9 +166,12 @@ export async function dueReviews(db: D1Database, date: string): Promise<ProblemR
 }
 
 /**
- * Blind drills: unsolved optional problems from topics taught in EARLIER
- * weeks (the current week's optional pool is reserved for Saturday's gate),
- * never repeated, seeded by date. Boosted topics contribute up to 2 extra.
+ * Blind drills: unsolved optional problems from topics ALREADY LEARNED —
+ * scheduled in an earlier week (the current week's optional pool is reserved
+ * for Saturday's gate) AND showing learning evidence: at least one of the
+ * topic's core problems has entered the ladder. A skipped learning day never
+ * feeds drills just because its calendar week lapsed. Never repeated,
+ * seeded by date. Boosted topics contribute up to 2 extra.
  */
 export async function pickDrills(
   db: D1Database,
@@ -184,6 +187,9 @@ export async function pickDrills(
        WHERE p.set_label = 'optional' AND p.stage = 'new'
          AND p.lc_number NOT IN (SELECT lc_number FROM drill_pool_used)
          AND NOT EXISTS (SELECT 1 FROM attempts a WHERE a.lc_number = p.lc_number)
+         AND EXISTS (SELECT 1 FROM problems c
+                     WHERE c.topic_issue = p.topic_issue
+                       AND c.set_label = 'core' AND c.stage != 'new')
        ORDER BY p.lc_number`,
     )
     .all<ProblemRow & { boost: number }>();