examples: to_gbp currency normalisation helper

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