fix: parse HAL two-anchor ranging format (8-byte int32×2)

The app's old parser expected a multi-anchor protocol:
  [count][anchorID+rangeMM+RSSI+age]×N (min 10 bytes)
HAL's firmware sends a fixed 8-byte packet:
  [int32 front_mm LE][int32 back_mm LE]

With the old parser data[0] was interpreted as anchor count
(e.g. 0xF8 = 248 for a 4.6m reading), the loop guard failed
immediately, and every notify returned [] — hence "waiting for
ranging data" despite the tag showing live ranges on OLED.

Changes:
- BLEPackets: detect 8-byte HAL format by length; decode as
  anchor id=0 (Front) and id=1 (Back); legacy multi-anchor path
  retained for forward compatibility
- AnchorInfo: rssiDBm is now Optional (nil when not reported);
  label maps id 0→"F", 1→"B" for the two-anchor HAL format
- BLEStatusView: guard on optional rssiString before rendering

Auto-reconnect confirmed correct (2s delay, bluetooth-central
background mode declared in Info.plist).

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

SulTee/SulTee/AnchorInfo.swift

@@ -4,15 +4,22 @@ import Foundation
 struct AnchorInfo: Identifiable {
     let id:           UInt8
     let rangeMetres:  Double
-    let rssiDBm:      Double
-    let ageMs:        UInt16    // age reported by tag firmware
+    let rssiDBm:      Double?   // nil when not reported (HAL two-anchor format)
+    let ageMs:        UInt16    // age reported by tag firmware; 0 when not reported
     let receivedAt:   Date
 
     /// True when the measurement is more than 3 seconds old (local wall-clock).
     var isStale: Bool { Date().timeIntervalSince(receivedAt) > 3.0 }
 
     /// Display string for the anchor identifier.
-    var label: String { "A\(id)" }
+    /// IDs 0/1 map to Front/Back (HAL two-anchor format); others show "A<n>".
+    var label: String {
+        switch id {
+        case 0: return "F"
+        case 1: return "B"
+        default: return "A\(id)"
+        }
+    }
 
     /// Formatted range string matching the Flutter app style.
     var rangeString: String {
@@ -21,6 +28,9 @@ struct AnchorInfo: Identifiable {
             : String(format: "%.1f m", rangeMetres)
     }
 
-    /// Formatted RSSI string.
-    var rssiString: String { "\(Int(rssiDBm.rounded())) dBm" }
+    /// Formatted RSSI string, or nil when RSSI was not reported.
+    var rssiString: String? {
+        guard let r = rssiDBm else { return nil }
+        return "\(Int(r.rounded())) dBm"
+    }
 }

SulTee/SulTee/BLEPackets.swift

@@ -87,27 +87,46 @@ enum BLEPackets {
 
     // MARK: - Ranging notification parser
     //
-    // [0]      Uint8    anchor count  N
-    // Per anchor (9 bytes, offset = 1 + i×9):
-    //   [+0]   Uint8    anchor index
-    //   [+1-4] Int32 LE range mm
-    //   [+5-6] Int16 LE RSSI × 10 (dBm × 10)
-    //   [+7-8] Uint16LE age ms
+    // HAL firmware format (8 bytes, 2 fixed anchors):
+    //   [0-3]  Int32 LE  front anchor range mm  (id=0)
+    //   [4-7]  Int32 LE  back  anchor range mm  (id=1)
+    //
+    // Legacy multi-anchor format (future):
+    //   [0]      Uint8    anchor count  N
+    //   Per anchor (9 bytes):
+    //     [+0]   Uint8    anchor index
+    //     [+1-4] Int32 LE range mm
+    //     [+5-6] Int16 LE RSSI × 10 (dBm × 10)
+    //     [+7-8] Uint16LE age ms
 
     static func parseRanging(_ data: Data) -> [AnchorInfo] {
+        let now = Date()
+
+        // HAL two-anchor format: exactly 8 bytes, two Int32 LE range values
+        if data.count == 8 {
+            let frontMM = data.readInt32LE(at: 0)
+            let backMM  = data.readInt32LE(at: 4)
+            return [
+                AnchorInfo(id: 0, rangeMetres: Double(frontMM) / 1000.0,
+                           rssiDBm: nil, ageMs: 0, receivedAt: now),
+                AnchorInfo(id: 1, rangeMetres: Double(backMM)  / 1000.0,
+                           rssiDBm: nil, ageMs: 0, receivedAt: now)
+            ]
+        }
+
+        // Legacy multi-anchor format: [count][anchorID+rangeMM+RSSI+age] × N
         guard data.count >= 1 else { return [] }
         let count = Int(data[0])
-        let now   = Date()
         var result: [AnchorInfo] = []
 
         for i in 0..<count {
             let base = 1 + i * 9
             guard base + 9 <= data.count else { break }
 
-            let anchorID   = data[base]
-            let rangeMM    = data.readInt32LE(at: base + 1)
+            let anchorID    = data[base]
+            let rangeMM     = data.readInt32LE(at: base + 1)
             let rssiTimes10 = data.readInt16LE(at: base + 5)
-            let ageMs      = data.readUInt16LE(at: base + 7)
+            let ageMs       = data.readUInt16LE(at: base + 7)
 
             result.append(AnchorInfo(
                 id:          anchorID,
@@ -116,6 +135,7 @@ enum BLEPackets {
                 ageMs:       ageMs,
                 receivedAt:  now
             ))
+
         }
         return result
     }

SulTee/SulTee/BLEStatusView.swift

@@ -144,9 +144,11 @@ struct BLEStatusView: View {
             Spacer()
 
             VStack(alignment: .trailing, spacing: 2) {
-                Text(anchor.rssiString)
-                    .font(.system(size: 11))
-                    .foregroundStyle(.secondary)
+                if let rssi = anchor.rssiString {
+                    Text(rssi)
+                        .font(.system(size: 11))
+                        .foregroundStyle(.secondary)
+                }
                 if anchor.isStale {
                     Text("STALE")
                         .font(.system(size: 10, weight: .bold))