Parity markup and tolerance configurable as % or flat £

- config: parity_markup_value/_unit + parity_tolerance_value/_unit
  (pct|gbp), legacy *_pct keys still read as fallback
- expected rate = newbook + £X or newbook × (1 + X%); breach test uses
  the tolerance in its own unit
- Settings parity tab: unit selects + live worked example line
- Parity Alerts tab: unit-aware description, badge now shows £ deviation
  alongside %

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

frontend/src/pages/MarketView.tsx

@@ -777,8 +777,12 @@ const ParityAlertsTab: React.FC = () => {
     },
   })
 
-  const markup = parityConfig?.['parity_expected_markup_pct'] ?? '0'
-  const tolerance = parityConfig?.['parity_tolerance_pct'] ?? '2'
+  const markupUnit = parityConfig?.['parity_markup_unit'] ?? 'pct'
+  const toleranceUnit = parityConfig?.['parity_tolerance_unit'] ?? 'pct'
+  const markupVal = parityConfig?.['parity_markup_value'] ?? parityConfig?.['parity_expected_markup_pct'] ?? '0'
+  const toleranceVal = parityConfig?.['parity_tolerance_value'] ?? parityConfig?.['parity_tolerance_pct'] ?? '2'
+  const markupLabel = markupUnit === 'gbp' ? `£${markupVal}` : `${markupVal}%`
+  const toleranceLabel = toleranceUnit === 'gbp' ? `£${toleranceVal}` : `${toleranceVal}%`
 
   const thStyle: React.CSSProperties = {
     textAlign: 'left', padding: '8px 12px', fontSize: 11, fontWeight: 600,
@@ -793,7 +797,7 @@ const ParityAlertsTab: React.FC = () => {
     <div>
       <div style={{ fontSize: 12, color: 'var(--text-mid)', marginBottom: 14, maxWidth: 720 }}>
         Dates where our Booking.com rate deviates from the expected level
-        (Newbook rate + {markup}% markup, ±{tolerance}% tolerance). Checked daily at 06:45 —
+        (Newbook rate + {markupLabel} markup, ±{toleranceLabel} tolerance). Checked daily at 06:45 —
         adjust the markup and tolerance in Settings → Rate Parity. Acknowledge a date once
         dealt with; alerts auto-resolve when the rates come back in line.
       </div>
@@ -850,11 +854,21 @@ const ParityAlertsTab: React.FC = () => {
                   <td style={tdStyle}>{a.newbook_rate != null ? `£${a.newbook_rate.toFixed(2)}` : '—'}</td>
                   <td style={tdStyle}>{a.booking_com_rate != null ? `£${a.booking_com_rate.toFixed(2)}` : '—'}</td>
                   <td style={tdStyle}>
-                    {a.difference_pct != null && (
-                      <span style={badgeStyle(a.alert_type === 'higher' ? 'warning' : 'error')}>
-                        {a.difference_pct > 0 ? '+' : ''}{a.difference_pct.toFixed(1)}% vs expected
-                      </span>
-                    )}
+                    {a.difference_pct != null && (() => {
+                      // expected = booking / (1 + dev%); £ deviation derived from that
+                      const expected = a.booking_com_rate != null
+                        ? a.booking_com_rate / (1 + a.difference_pct / 100)
+                        : null
+                      const devGbp = expected != null && a.booking_com_rate != null
+                        ? a.booking_com_rate - expected
+                        : null
+                      return (
+                        <span style={badgeStyle(a.alert_type === 'higher' ? 'warning' : 'error')}>
+                          {a.difference_pct > 0 ? '+' : ''}{a.difference_pct.toFixed(1)}%
+                          {devGbp != null ? ` (${devGbp > 0 ? '+' : '−'}£${Math.abs(devGbp).toFixed(2)})` : ''} vs expected
+                        </span>
+                      )
+                    })()}
                   </td>
                   <td style={mergeStyles(tdStyle, { color: 'var(--text-mid)', fontSize: 12 })}>{a.room_category || '—'}</td>
                   <td style={tdStyle}>

frontend/src/pages/Settings.tsx

@@ -115,14 +115,18 @@ function ParityTab({ config, isLoading, onSave, saving }: {
   saving: boolean
 }) {
   const [markup, setMarkup] = useState('')
+  const [markupUnit, setMarkupUnit] = useState('pct')
   const [tolerance, setTolerance] = useState('')
+  const [toleranceUnit, setToleranceUnit] = useState('pct')
   const [loaded, setLoaded] = useState(false)
   const [checkResult, setCheckResult] = useState<ParityCheckResult | null>(null)
 
   useEffect(() => {
     if (config && !loaded) {
-      setMarkup(config['parity_expected_markup_pct'] ?? '0')
-      setTolerance(config['parity_tolerance_pct'] ?? '2')
+      setMarkup(config['parity_markup_value'] ?? config['parity_expected_markup_pct'] ?? '0')
+      setMarkupUnit(config['parity_markup_unit'] ?? 'pct')
+      setTolerance(config['parity_tolerance_value'] ?? config['parity_tolerance_pct'] ?? '2')
+      setToleranceUnit(config['parity_tolerance_unit'] ?? 'pct')
       setLoaded(true)
     }
   }, [config, loaded])
@@ -166,39 +170,67 @@ function ParityTab({ config, isLoading, onSave, saving }: {
           <div style={{ display: 'flex', gap: 16, flexWrap: 'wrap' }}>
             <div>
               <label style={{ fontSize: 12, fontWeight: 600, color: 'var(--text-mid)', display: 'block', marginBottom: 4 }}>
-                Expected Booking.com markup (%)
+                Expected Booking.com markup
               </label>
-              <input
-                type="number" step="0.5" style={{ width: 140 }}
-                value={markup} onChange={e => setMarkup(e.target.value)}
-                placeholder="e.g. 15"
-              />
+              <div style={{ display: 'flex', gap: 6 }}>
+                <input
+                  type="number" step="0.5" style={{ width: 110 }}
+                  value={markup} onChange={e => setMarkup(e.target.value)}
+                  placeholder={markupUnit === 'gbp' ? 'e.g. 20' : 'e.g. 15'}
+                />
+                <select style={{ width: 64 }} value={markupUnit} onChange={e => setMarkupUnit(e.target.value)}>
+                  <option value="pct">%</option>
+                  <option value="gbp">£</option>
+                </select>
+              </div>
               <div style={{ fontSize: 11, color: 'var(--text-mid)', marginTop: 4 }}>
-                How much higher Booking.com should be than Newbook.
+                How much higher Booking.com should be than Newbook
+                {markupUnit === 'gbp' ? ' (flat £ per night)' : ' (percentage)'}.
               </div>
             </div>
             <div>
               <label style={{ fontSize: 12, fontWeight: 600, color: 'var(--text-mid)', display: 'block', marginBottom: 4 }}>
-                Tolerance (± %)
+                Tolerance (±)
               </label>
-              <input
-                type="number" step="0.5" style={{ width: 140 }}
-                value={tolerance} onChange={e => setTolerance(e.target.value)}
-                placeholder="e.g. 2"
-              />
+              <div style={{ display: 'flex', gap: 6 }}>
+                <input
+                  type="number" step="0.5" style={{ width: 110 }}
+                  value={tolerance} onChange={e => setTolerance(e.target.value)}
+                  placeholder={toleranceUnit === 'gbp' ? 'e.g. 5' : 'e.g. 2'}
+                />
+                <select style={{ width: 64 }} value={toleranceUnit} onChange={e => setToleranceUnit(e.target.value)}>
+                  <option value="pct">%</option>
+                  <option value="gbp">£</option>
+                </select>
+              </div>
               <div style={{ fontSize: 11, color: 'var(--text-mid)', marginTop: 4 }}>
                 Allowed deviation from expected before alerting.
               </div>
             </div>
           </div>
 
+          <div style={{ padding: '8px 12px', background: '#f8fafc', borderRadius: 6, fontSize: 12, color: 'var(--text-mid)' }}>
+            Rule: alert when Booking.com ≠ Newbook {markupUnit === 'gbp' ? `+ £${markup || '0'}` : `+ ${markup || '0'}%`}
+            {' '}beyond ±{toleranceUnit === 'gbp' ? `£${tolerance || '0'}` : `${tolerance || '0'}%`}.
+            {' '}Example: Newbook £100 → expect £{(markupUnit === 'gbp'
+              ? 100 + (parseFloat(markup) || 0)
+              : 100 * (1 + (parseFloat(markup) || 0) / 100)).toFixed(0)},
+            {' '}alert outside £{(() => {
+              const exp = markupUnit === 'gbp' ? 100 + (parseFloat(markup) || 0) : 100 * (1 + (parseFloat(markup) || 0) / 100)
+              const tol = toleranceUnit === 'gbp' ? (parseFloat(tolerance) || 0) : exp * (parseFloat(tolerance) || 0) / 100
+              return `${(exp - tol).toFixed(0)}–£${(exp + tol).toFixed(0)}`
+            })()}.
+          </div>
+
           <div style={{ display: 'flex', gap: 8 }}>
             <button
               className="btn btn-primary"
               disabled={saving}
               onClick={() => {
-                onSave('parity_expected_markup_pct', markup || '0')
-                onSave('parity_tolerance_pct', tolerance || '2')
+                onSave('parity_markup_value', markup || '0')
+                onSave('parity_markup_unit', markupUnit)
+                onSave('parity_tolerance_value', tolerance || '2')
+                onSave('parity_tolerance_unit', toleranceUnit)
               }}
             >
               <Save size={13} strokeWidth={1.75} />