fix(pfs): FR citations never read as codes; case-insensitive code matching (refs P48)

A Federal Register page number is five digits, so "91 FR 43842" used to
detect 43842 as a CPT code and price it. Strip citations before scanning,
and match/normalise codes case-insensitively so "g0556" is found.

src/pfs/families.py

@@ -13,12 +13,22 @@ from dataclasses import dataclass
 
 # HCPCS level II (letter + 4 digits) or CPT (5 digits). Validation against
 # the fee schedule happens at lookup time (pfs.valuation), not here.
-CODE_RE = re.compile(r"\b(?:[A-Z]\d{4}|\d{5})\b")
+CODE_RE = re.compile(r"\b(?:[A-Z]\d{4}|\d{5})\b", re.IGNORECASE)
+
+# "91 FR 43842" — an FR page number is five digits and so reads as a CPT
+# code; citations are removed before scanning so they never become one.
+_FR_CITE_RE = re.compile(r"\b\d{1,3}\s+FR\s+\d{3,6}\b", re.IGNORECASE)
 
 
 def find_codes(text: str) -> tuple[str, ...]:
-    """Sorted unique codes literally present in *text* (case-normalised)."""
+    """Sorted unique codes literally present in *text*, upper-cased.
-    return tuple(sorted({m.group(0) for m in CODE_RE.finditer(text)}))
+
+    Federal Register citations are stripped first: their page numbers are
+    not codes, and a chat answer that priced "43842" out of "91 FR 43842"
+    would be inventing money.
+    """
+    text = _FR_CITE_RE.sub(" ", text)
+    return tuple(sorted({m.group(0).upper() for m in CODE_RE.finditer(text)}))
 
 
 @dataclass(frozen=True)

tests/pfs/test_families.py

@@ -10,12 +10,19 @@ class TestFindCodes:
         assert find_codes("Codes G0556 and 99490 apply; see g0557.") == (
             "99490",
             "G0556",
+            "G0557",
         )
 
+    def test_lower_case_codes_are_normalised(self):
+        assert find_codes("what is g0556?") == ("G0556",)
+
     def test_no_false_hits_on_years_and_fr_pages(self):
-        # 2026 (4 digits) and 43842 (5 digits) — the CPT regex will match 43842;
+        # A Federal Register citation is stripped before scanning, so its page
-        # validation against the fee schedule happens at lookup, not here.
+        # number (43842 — a well-formed CPT code) never reads as a code.
-        assert find_codes("91 FR 43842, CY2026") == ("43842",)
+        assert find_codes("91 FR 43842, CY2026") == ()
+
+    def test_fr_citation_alone_yields_nothing(self):
+        assert find_codes("What does 91 FR 43842 say?") == ()
 
     def test_dedupes_and_sorts(self):
         assert find_codes("G0558 G0556 G0558") == ("G0556", "G0558")