fix(drive-and-save): no negative savings when home metro is suppressed

When the home metro has insufficient hospital data (n_hospitals < min_hospitals),
its median price is unreliable. Guard the savings branch with `not home_suppressed`
so a suppressed home falls through to the else branch (savings=0.0) rather than
producing a nonsensical negative savings figure. Also moves `import h3` up to
sit with the other third-party imports at the top of core.py.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

core.py

@@ -9,6 +9,7 @@ import math
 from dataclasses import dataclass
 from pathlib import Path
 
+import h3
 import yaml
 
 CONFIG_PATH = Path(__file__).parent / "config.yaml"
@@ -24,8 +25,6 @@ def load_config(path: "Path | str" = CONFIG_PATH) -> dict:
 # H3 distance helpers
 # ---------------------------------------------------------------------------
 
-import h3
-
 
 def _haversine_km(lat1: float, lon1: float, lat2: float, lon2: float) -> float:
     R = 6371.0
@@ -141,6 +140,7 @@ def rank_metros(medians_df, metros_df, procedure_code: str, home_metro: str, cfg
     visible = [r for r in rows if not r.suppressed]
     home_row = next((r for r in rows if r.is_home), None)
     home_median = home_row.median_price if home_row else None
+    home_suppressed = home_row.suppressed if home_row else True
 
     candidates = [r for r in visible if not r.is_home]
     cheapest = candidates[0] if candidates else None  # rows already price-asc
@@ -148,7 +148,7 @@ def rank_metros(medians_df, metros_df, procedure_code: str, home_metro: str, cfg
         home_row and not home_row.suppressed and visible and visible[0].is_home
     )
 
-    if cheapest and home_median is not None and not home_is_cheapest:
+    if cheapest and home_median is not None and not home_suppressed and not home_is_cheapest:
         savings = home_median - cheapest.median_price
         savings_pct = (savings / home_median * 100.0) if home_median else 0.0
         drive_to = cheapest.drive_min

test_core.py

@@ -133,6 +133,16 @@ def test_build_cta_url_homepage_fallback_when_no_pattern():
     assert "utm_source=mile-hi-labs" in url
 
 
+def test_rank_metros_home_suppressed_no_negative_savings():
+    medians, metros = _fixtures()
+    # "Tiny Town" has n_hospitals=1 (suppressed) and the lowest price ($50)
+    r = core.rank_metros(medians, metros, "45378", "Tiny Town", CFG)
+    assert r.savings >= 0            # never negative
+    assert r.savings == 0            # home price unreliable -> no claimed savings
+    assert r.home_is_cheapest is False
+    assert r.cheapest_metro == "Boulder"   # cheapest non-suppressed shown informationally
+
+
 def test_build_cta_url_uses_deep_link_pattern():
     cfg = core.load_config()
     cfg["funnel"]["deep_link_pattern"] = "/procedure/{code}/?metro={metro_slug}"