Agent: add get_daily_spending for day-scoped questions

Prod showed the failure mode after the date fix: get_current_date
returned the right day, but the model answered "¿cuánto he gastado
hoy?" from cycle-level aggregates (the only spend tools it had) and
concluded ₡0. Give it a day-grained tool — per-day CRC totals mirroring
/analytics/daily-spending (COMPRA only, no installment anchors, no
future cuotas) — and a prompt rule to match tool to time grain.
Verified: fresh thread now calls get_current_date →
get_daily_spending(2026-07-04, 2026-07-05) and answers correctly.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/app/agent/agent.py

@@ -30,6 +30,10 @@ Context you can rely on:
 
 How to answer:
 - ALWAYS call a tool to get data. Do not invent balances, dates or merchants.
+- Match the tool to the question's time grain: day-scoped questions ("hoy",
+  "ayer", "el martes", a specific date) need get_daily_spending with that
+  day's bounds — cycle or category summaries have NO per-day data, so never
+  answer a day question from them.
 - Call multiple tools in parallel when the question spans domains
   (e.g. net worth + recent transactions).
 - Format currency with the appropriate symbol: ₡ for CRC (no decimals), $ for

backend/app/agent/tools.py

@@ -35,6 +35,7 @@ from app.models.models import (
 from app.services.budget_projection import (
     MAX_YEAR,
     MIN_YEAR,
+    NOT_INSTALLMENT_ANCHOR,
     compute_monthly_projection,
     compute_yearly_projection_with_cumulative,
     get_cycle_range,
@@ -496,6 +497,39 @@ def list_categories() -> list[dict]:
 
 
 # Registered with the agent in agent.py
+def get_daily_spending(
+    start_date: Annotated[str, Field(description="ISO date lower bound, inclusive")],
+    end_date: Annotated[str, Field(description="ISO date upper bound, exclusive")],
+) -> list[dict]:
+    """Spending per day in CRC (converted), COMPRA only, excluding future
+    Tasa Cero cuotas and installment anchors. THE tool for day-scoped
+    questions: 'cuánto gasté hoy / ayer / el martes'. Days with no spending
+    are simply absent from the result."""
+    session = _s()
+    amount_crc = get_converted_amount_expr(session)
+    rows = session.exec(
+        select(
+            func.date(Transaction.date).label("day"),
+            func.coalesce(func.sum(amount_crc), 0),
+            func.count(),
+        )
+        .where(
+            Transaction.transaction_type == TransactionType.COMPRA,
+            NOT_INSTALLMENT_ANCHOR,
+            Transaction.date >= datetime.fromisoformat(start_date),
+            Transaction.date < datetime.fromisoformat(end_date),
+            # Future-dated Tasa Cero cuotas are not money already spent.
+            Transaction.date < datetime.combine(today_cr() + timedelta(days=1), time.min),
+        )
+        .group_by(func.date(Transaction.date))
+        .order_by(func.date(Transaction.date))
+    ).all()
+    return [
+        {"date": str(day), "total_crc": float(total), "count": count}
+        for day, total, count in rows
+    ]
+
+
 def get_current_date() -> dict:
     """Today's date in the user's timezone (Costa Rica, UTC-6) and the
     active credit-card billing cycle. ALWAYS call this before resolving any
@@ -523,6 +557,7 @@ def get_current_date() -> dict:
 
 TOOLS = [
     get_current_date,
+    get_daily_spending,
     get_accounts,
     get_net_worth,
     get_recent_transactions,

backend/tests/test_agent_tools.py

@@ -183,3 +183,34 @@ def test_get_current_date_is_costa_rica_and_cycle_consistent():
     start, end = out["cycle_range"]
     assert start <= out["date"] < end
     assert start.endswith("-18") and end.endswith("-18")
+
+
+def test_daily_spending_day_scoped(bound_session):
+    from datetime import timedelta
+
+    from app.timeutil import today_cr
+
+    today = datetime.combine(today_cr(), datetime.min.time())
+    bound_session.add(
+        Transaction(amount=Decimal("100"), merchant="TODAY-A", date=today.replace(hour=9))
+    )
+    bound_session.add(
+        Transaction(amount=Decimal("50"), merchant="TODAY-B", date=today.replace(hour=15))
+    )
+    bound_session.add(
+        Transaction(
+            amount=Decimal("999"),
+            merchant="FUTURE CUOTA",
+            date=today + timedelta(days=40),
+        )
+    )
+    bound_session.commit()
+
+    out = tools.get_daily_spending(
+        start_date=today.date().isoformat(),
+        end_date=(today.date() + timedelta(days=60)).isoformat(),
+    )
+    assert len(out) == 1
+    assert out[0]["date"] == today.date().isoformat()
+    assert out[0]["total_crc"] == 150.0
+    assert out[0]["count"] == 2