Add some lora parameter clamping logic to coalesce to defaults and enforce some bounds (#9808)

src/mesh/MeshRadio.h

@@ -24,6 +24,45 @@ extern const RegionInfo *myRegion;
 
 extern void initRegion();
 
+// Valid LoRa spread factor range and defaults
+constexpr uint8_t LORA_SF_MIN = 7;
+constexpr uint8_t LORA_SF_MAX = 12;
+constexpr uint8_t LORA_SF_DEFAULT = 11; // LONG_FAST default
+
+// Valid LoRa coding rate range and default
+constexpr uint8_t LORA_CR_MIN = 4;
+constexpr uint8_t LORA_CR_MAX = 8;
+constexpr uint8_t LORA_CR_DEFAULT = 5; // LONG_FAST default
+
+// Default bandwidth in kHz (LONG_FAST)
+constexpr float LORA_BW_DEFAULT_KHZ = 250.0f;
+
+/// Clamp spread factor to the valid LoRa range [7, 12].
+/// Out-of-range values (including 0 from unset preset mode) return LORA_SF_DEFAULT.
+static inline uint8_t clampSpreadFactor(uint8_t sf)
+{
+    if (sf < LORA_SF_MIN || sf > LORA_SF_MAX)
+        return LORA_SF_DEFAULT;
+    return sf;
+}
+
+/// Clamp coding rate to the valid LoRa range [4, 8].
+/// Out-of-range values return LORA_CR_DEFAULT.
+static inline uint8_t clampCodingRate(uint8_t cr)
+{
+    if (cr < LORA_CR_MIN || cr > LORA_CR_MAX)
+        return LORA_CR_DEFAULT;
+    return cr;
+}
+
+/// Ensure bandwidth is positive. Non-positive values return LORA_BW_DEFAULT_KHZ.
+static inline float clampBandwidthKHz(float bwKHz)
+{
+    if (bwKHz <= 0.0f)
+        return LORA_BW_DEFAULT_KHZ;
+    return bwKHz;
+}
+
 static inline float bwCodeToKHz(uint16_t bwCode)
 {
     if (bwCode == 31)