Position overwritten by lower-precision data in _onPositionReceive() #910

Bug Description

_onPositionReceive() in meshtastic/__init__.py (line 183) blindly overwrites a node's position in the node database whenever a POSITION_APP packet is received, regardless of precision:

iface._getOrCreateByNum(asDict["from"])["position"] = p

This specifically affects the local node's position. When other nodes relay our position via map reports at low precision (e.g., precisionBits: 13), it overwrites the locally-stored high-precision GPS position (precisionBits: 32). Since the local device has the GPS internally, any lower-precision update is always an echo from the mesh, never fresh data.

Remote nodes are not affected in practice — any position they broadcast is their own current state at whatever precision their GPS provides.

Steps to Reproduce

1. Connect to a Meshtastic device with GPS via the Python library
2. Read iface.nodes[my_node]["position"] immediately after connection — correct high-precision position
3. Wait 10-15 seconds for mesh traffic
4. Read position again — it has been overwritten with a lower-precision value from a relayed map report

Observed Behavior

• Local node position changes from correct value (e.g., 32.9315311) to incorrect truncated value (e.g., 32.9515008)
• Multiple unrelated nodes may show the exact same latitude because they all received the same low-precision map report
• Both latitudeI and latitude fields are overwritten
• The corruption happens every time, typically within 10-15 seconds of connecting

Expected Behavior

_onPositionReceive() should not overwrite the local node's position with a lower-precision echo from the mesh. The local GPS is authoritative.

Proposed Fix

Check if the position update is for the local node, and if so, only accept updates with equal or better precisionBits:

node = iface._getOrCreateByNum(asDict["from"])
is_local_node = (
    iface.myInfo is not None
    and asDict["from"] == iface.myInfo.my_node_num
)
if is_local_node:
    existing = node.get("position", {})
    existing_precision = existing.get("precisionBits", 0) or 0
    new_precision = p.get("precisionBits", 0) or 0
    if existing_precision == 0 or new_precision >= existing_precision:
        node["position"] = p
else:
    node["position"] = p

See PR #911 for the implementation.

Environment

• Meshtastic Python library: 2.7.8
• Device: LILYGO T-BeamSUPREME (ESP32-S3, SX1262, U-blox M10S GPS)
• Firmware: 2.7.15
• Connected via USB serial
• ~200 nodes in mesh