examples: to_gbp currency normalisation helper

fire_planner/examples/llm_extract.py

@@ -179,3 +179,22 @@ async def extract_with_fallback(
         client=client,
     )
     return secondary or primary
+
+
+def to_gbp(
+    amount: Decimal | None,
+    currency: str | None,
+    rates: dict[str, Decimal],
+) -> Decimal | None:
+    """Convert `amount` in `currency` to GBP using `fx.fetch_rates` output.
+
+    `rates[X]` = "how much GBP one unit of X is worth" — the convention
+    used by `fire_planner/fx.py`. Returns None when amount/currency is
+    missing or the currency isn't in `rates`.
+    """
+    if amount is None or currency is None:
+        return None
+    rate = rates.get(currency.upper())
+    if rate is None:
+        return None
+    return (amount * rate).quantize(Decimal("0.01"))

tests/test_examples_llm_extract.py

@@ -12,6 +12,7 @@ import respx
 from fire_planner.examples.llm_extract import (
     extract_with_fallback,
     extract_with_qwen,
+    to_gbp,
 )
 from fire_planner.examples.models import RawPost
 
@@ -171,3 +172,20 @@ async def test_fallback_keeps_high_confidence_qwen_result() -> None:
     assert out is not None
     assert out.llm_model == "qwen3-8b"
     assert claude_route.called is False  # high-confidence qwen → claude not hit
+
+
+def test_to_gbp_converts_usd() -> None:
+    rates = {"GBP": Decimal("1"), "USD": Decimal("0.80")}
+    assert to_gbp(Decimal("100"), "USD", rates) == Decimal("80.00")
+
+
+def test_to_gbp_passes_through_gbp() -> None:
+    assert to_gbp(Decimal("100"), "GBP", {"GBP": Decimal("1")}) == Decimal("100.00")
+
+
+def test_to_gbp_returns_none_for_unknown_currency() -> None:
+    assert to_gbp(Decimal("100"), "XYZ", {"GBP": Decimal("1"), "USD": Decimal("0.8")}) is None
+
+
+def test_to_gbp_returns_none_for_none_amount() -> None:
+    assert to_gbp(None, "USD", {"USD": Decimal("0.8")}) is None