update doc

documentation/routing-paths.md

@@ -6,61 +6,70 @@ This page covers how MeshCore Open represents, selects, validates, and stores ro
 
 MeshCore supports variable-length multi-byte routing paths so the app can scale from small meshes to very large node sets.
 
-### Path Encoding Format
+### Hash Width and Multi-Byte Paths
 
-Each path byte packs both the hop count and the hash width:
+The device capability determines the hash width (number of bytes per hop):
 
-```
-Bit 7-6: Hash mode  (2 bits) → hash_bytes = 1 << mode
-Bit 5-0: Hop count   (6 bits) → max 63 hops
-```
-
-| Mode | Hash Bytes | Max Hops | Max Unique Nodes | Firmware |
-|------|-----------|----------|------------------|----------|
-| 0 | 1 | 63 | 256 | v1.13+ |
-| 1 | 2 | 63 | 65,536 | v1.14+ |
-| 2 | 3 | 63 | 16.7M | v1.14+ |
-| 3 | 4 | 63 | 4.3B | v1.14+ |
-
-### Path Byte Calculation
-
-```dart
-final pathLenRaw = frameData[index];
-final hopCount = pathLenRaw & 0x3F;
-final hashMode = (pathLenRaw >> 6) & 0x03;
-final hashBytes = 1 << hashMode;
-
-final pathByteLength = hopCount * hashBytes;
-final pathData = frameData.sublist(index + 1, index + 1 + pathByteLength);
-```
+| Width | Max Unique Nodes | Typical Use |
+|-------|-----------------|-------------|
+| 1 byte | 256 | Single-byte node IDs |
+| 2 bytes | 65,536 | Medium meshes |
+| 3 bytes | 16.7M | Large networks |
+| 4 bytes | 4.3B | Gigantic deployments |
 
 ### Device Capability Detection
 
-The app reads the device's reported capability byte to determine whether multi-byte paths are available:
+On device connection, the app reads the firmware capability to set `pathHashByteWidth`:
 
 ```dart
-if (firmwareBytes.length >= 82) {
-  final mode = (firmwareBytes[81] & 0xFF).clamp(0, 2);
-  pathHashByteWidth = mode + 1;
-} else {
-  pathHashByteWidth = 1;
-}
+// Read from device info response (offset 81)
+final modeRaw = firmwareBytes.length >= 82 
+    ? (firmwareBytes[81] & 0x3F) 
+    : 0;
+final mode = modeRaw.clamp(0, 3);
+_pathHashByteWidth = mode + 1; // 1, 2, 3, or 4 bytes per hop
 ```
 
+### Path Data Structure
+
+Paths in messages and storage consist of:
+
+- **`pathLength`**: Hop count reported in the radio header (may differ from decoded path)
+- **`pathBytes`**: Raw bytes of the path, grouped by `pathHashByteWidth`
+- **Example**: With `pathHashByteWidth=2`, a 3-hop path needs 6 bytes:
+  - `pathBytes = [0xA1, 0xA2, 0xB1, 0xB2, 0xC1, 0xC2]`
+  - Hops: `[0xA1A2]`, `[0xB1B2]`, `[0xC1C2]`
+
+### Hop Count Calculation
+
+Convert path byte length to hop count:
+
+```dart
+int hopCount = (byteCount + hashByteWidth - 1) ~/ hashByteWidth;
+```
+
+Use this consistently when displaying hop counts in UI to avoid mismatch between metadata (`pathLength`) and observed paths (`pathBytes`).
+
 ### Path Usage in Different Message Types
 
-- Direct messages extract the path from the decrypted payload to trace the sender route.
-- Channel messages decrypt a hop-by-hop routing chain from the payload.
-- Contact storage keeps the path length encoding in byte 32 and the raw path bytes in bytes 33-96.
+- **Direct messages**: Extract path from decrypted payload to trace sender route.
+- **Channel messages**: Decrypt hop-by-hop routing chain from payload; header includes `pathLength` metadata.
+- **Contact storage**: Path length in byte 32, raw path bytes in bytes 33-96, grouped by detected `pathHashByteWidth`.
 
-### Example Contact Path Parsing
+### UI Hop Count Display
+
+⚠️ **Important**: In screens like "Channel Message Path", prefer the actual decoded `pathBytes` hop count over `pathLength` metadata:
 
 ```dart
-// Mode 0 (1-byte): 3 hops = 3 bytes needed
-// [0x83, 0xA1, 0xB2, 0xC3] → hopCount=3, mode=0, path=[A1,B2,C3]
+// Preferred: use actual observed path length
+final effectiveHopCount = (pathBytes.length + width - 1) ~/ width;
 
-// Mode 1 (2-byte): 3 hops = 6 bytes needed
-// [0xC3, 0xA1, 0xA2, 0xB1, 0xB2, 0xC1, 0xC2]
-// → hopCount=3, mode=1, path=[A1A2, B1B2, C1C2]
+// Avoid: using radio metadata directly
+// pathLength can diverge from decoded bytes and cause UI mismatches
 ```
 
+Example scenario:
+- Radio header reports `pathLength: 32`
+- Decoded path bytes: `[0xAB, 0xCD]` (2 bytes = 1 hop with width=2)
+- **Display**: "1 hop" (from pathBytes), NOT "32 hops" (from pathLength)
+