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Failure patterns

Divergent materialized-aggregate reducer implementation (1 task)

• Classification: Model limitation
• Confidence: Low
• What the model wrote:

  import { schema, table, t, SenderError, type InferSchema, type ReducerCtx } from 'spacetimedb/server';
  

  function applyDelta(ctx: Ctx, category: string, amountDelta: bigint, countDelta: bigint) {
    const existing = ctx.db.categoryTotal.category.find(category);
    if (existing) {
      const newCount = existing.saleCount + countDelta;
      const newTotal = existing.totalAmount + amountDelta;
      if (newCount <= 0n) {
        ctx.db.categoryTotal.category.delete(category);
      } else {
        ctx.db.categoryTotal.category.update({
          ...existing,
          totalAmount: newTotal,
          saleCount: newCount,
        });
      }
    } else {
      if (countDelta <= 0n) {
        throw new SenderError('aggregate underflow');
      }
      ctx.db.categoryTotal.insert({
        category,
        totalAmount: amountDelta,
        saleCount: countDelta,
      });
    }
  }
  

  function insertSale(ctx: Ctx, id: bigint, category: string, amount: bigint) {
    ctx.db.sale.insert({ id, category, amount });
    applyDelta(ctx, category, amount, 1n);
  }
  

• What was expected:

  function addToTotal(ctx: Ctx, category: string, amount: bigint) {
    const total = ctx.db.categoryTotal.category.find(category);
    if (total) ctx.db.categoryTotal.category.update({ ...total, totalAmount: total.totalAmount + amount, saleCount: total.saleCount + 1n });
    else ctx.db.categoryTotal.insert({ category, totalAmount: amount, saleCount: 1n });
  }
  

  function removeFromTotal(ctx: Ctx, category: string, amount: bigint) {
    const total = ctx.db.categoryTotal.category.find(category);
    if (!total) throw new Error('missing category total');
    if (total.saleCount === 1n) ctx.db.categoryTotal.category.delete(category);
    else ctx.db.categoryTotal.category.update({ ...total, totalAmount: total.totalAmount - amount, saleCount: total.saleCount - 1n });
  }
  

  function upsertSale(ctx: Ctx, row: { id: bigint; category: string; amount: bigint }) {
    const old = ctx.db.sale.id.find(row.id);
    if (old) { removeFromTotal(ctx, old.category, old.amount); ctx.db.s
  

• What the error says: schema_parity: failed
• Why this happened: The generated solution diverged from the golden materialized-aggregate pattern. The visible excerpt shows a different maintenance strategy (applyDelta plus insertSale) instead of the expected upsert-based recomputation flow, and the response is truncated, so the exact mismatch cannot be localized from the supplied evidence.
• Suggested action: None
• Suggested area: None
• Affected tasks: t_065_materialized_aggregate
• AI guidelines gap: Needs manual review