Parity: best-available comparison as default, term-matching optional

parity_match_mode config ('best_available' default | 'match_terms').
Best available = cheapest bookable non-dinner direct tariff vs the BC
lead-in (already BC's best available) — simplest like-for-like. Term
matching kept as an option for days where BC's cheapest basis differs
from direct's. Settings gains a comparison-basis select.

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

backend/jobs/check_rate_parity.py

@@ -24,6 +24,10 @@ Dates back within tolerance auto-resolve; acknowledged dates stay quiet.
 
 Config (system_config):
   parity_check_enabled     true/false (default true)
+  parity_match_mode        'best_available' (default: cheapest bookable
+                           non-dinner tariff vs the BC lead-in, which is
+                           already BC's best available) or 'match_terms'
+                           (flex vs flex, prepaid vs prepaid)
   parity_markup_value      expected Booking.com premium over Newbook (default 0)
   parity_markup_unit       'pct' or 'gbp' (default pct)
   parity_tolerance_value   allowed deviation from expected before alerting (default 2)
@@ -74,6 +78,7 @@ def get_parity_config(db) -> dict:
     enabled_raw = (cfg.get('parity_check_enabled') or 'true').lower()
     return {
         "enabled": enabled_raw in ('true', '1', 'yes', 'enabled'),
+        "match_mode": 'match_terms' if (cfg.get('parity_match_mode') or '').lower() == 'match_terms' else 'best_available',
         "markup_value": num('parity_markup_value', 0.0, 'parity_expected_markup_pct'),
         "markup_unit": unit('parity_markup_unit'),
         "tolerance_value": num('parity_tolerance_value', 2.0, 'parity_tolerance_pct'),
@@ -133,19 +138,24 @@ def _candidate_tariffs(tariffs_data, days_ahead: int) -> list:
     return out
 
 
-def _pick_comparable(candidates: list, booking_flex: bool, booking_breakfast: bool):
+def _pick_comparable(candidates: list, booking_flex: bool, booking_breakfast: bool,
-    """Cheapest tariff matching the Booking.com rate's basis, tiered fallback.
+                     match_mode: str = 'best_available'):
-    All our tariffs include breakfast, so board matching reduces to excluding
+    """Newbook tariff to compare against the Booking.com lead-in.
-    dinner-inclusive tariffs unless nothing else exists.
+    best_available: cheapest bookable non-dinner tariff (the BC lead-in is
+    already BC's best available, so this is BAR vs BAR).
+    match_terms: cheapest tariff matching the BC rate's flex/prepaid basis,
+    falling back to best available. All our tariffs include breakfast, so
+    board matching reduces to excluding dinner-inclusive tariffs unless
+    nothing else exists.
     Returns (tariff, match_quality) or (None, None)."""
     if not candidates:
         return None, None
-    want_prepaid = not booking_flex
+    tiers = []
-    tiers = [
+    if match_mode == 'match_terms':
-        ([c for c in candidates if c["prepaid"] == want_prepaid and not c["dinner"]], 'matched'),
+        want_prepaid = not booking_flex
-        ([c for c in candidates if not c["dinner"]], 'any'),
+        tiers.append(([c for c in candidates if c["prepaid"] == want_prepaid and not c["dinner"]], 'matched'))
-        (candidates, 'any'),
+    tiers.append(([c for c in candidates if not c["dinner"]], 'best available'))
-    ]
+    tiers.append((candidates, 'best available'))
     for pool, quality in tiers:
         if pool:
             return min(pool, key=lambda c: c["rate"]), quality
@@ -197,7 +207,7 @@ def gather_comparisons(db, start: date, end: date, cfg: dict) -> list:
         for cat in cat_rows:
             candidates.extend(_candidate_tariffs(cat["tariffs_data"], days_ahead))
 
-        chosen, quality = _pick_comparable(candidates, booking_flex, booking_breakfast)
+        chosen, quality = _pick_comparable(candidates, booking_flex, booking_breakfast, cfg["match_mode"])
         if chosen:
             newbook_rate = chosen["rate"]
             tariff_name = chosen["name"]
@@ -305,6 +315,7 @@ def run_parity_check() -> dict:
         db.commit()
         summary = {
             "status": "ok",
+            "match_mode": cfg["match_mode"],
             "dates_compared": len(comparisons),
             "created": created,
             "updated": updated,

frontend/src/pages/Settings.tsx

@@ -167,6 +167,26 @@ function ParityTab({ config, isLoading, onSave, saving }: {
             Run daily parity check
           </label>
 
+          <div>
+            <label style={{ fontSize: 12, fontWeight: 600, color: 'var(--text-mid)', display: 'block', marginBottom: 4 }}>
+              Comparison basis
+            </label>
+            <select
+              style={{ width: 330 }}
+              value={(config?.['parity_match_mode'] ?? 'best_available')}
+              onChange={e => onSave('parity_match_mode', e.target.value)}
+            >
+              <option value="best_available">Best available (cheapest bookable tariff on both sides)</option>
+              <option value="match_terms">Match terms (flex vs flex, prepaid vs prepaid)</option>
+            </select>
+            <div style={{ fontSize: 11, color: 'var(--text-mid)', marginTop: 4, maxWidth: 480 }}>
+              Best available compares our cheapest bookable direct tariff against the Booking.com
+              lead-in rate (Booking.com's best available). Match terms instead picks the direct tariff
+              with the same conditions as the scraped Booking.com rate — only differs on days where
+              Booking.com's cheapest is flexible while a cheaper prepaid exists direct.
+            </div>
+          </div>
+
           <div style={{ display: 'flex', gap: 16, flexWrap: 'wrap' }}>
             <div>
               <label style={{ fontSize: 12, fontWeight: 600, color: 'var(--text-mid)', display: 'block', marginBottom: 4 }}>