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

src/mesh/Default.h

@@ -66,9 +66,22 @@ class Default
         if (numOnlineNodes <= 40) {
             return 1.0;
         } else {
-            // Get bandwidth in kHz - convert from code if not using preset
-            float bwKHz =
-                config.lora.use_preset ? modemPresetToBwKHz(config.lora.modem_preset, false) : bwCodeToKHz(config.lora.bandwidth);
+            // Resolve SF and BW from preset or manual config
+            // When use_preset is true, config.lora.spread_factor and bandwidth may be 0
+            // because applyModemConfig() sets them on RadioInterface, not on config.lora
+            float bwKHz;
+            uint8_t sf;
+            uint8_t cr;
+            if (config.lora.use_preset) {
+                modemPresetToParams(config.lora.modem_preset, false, bwKHz, sf, cr);
+            } else {
+                sf = config.lora.spread_factor;
+                bwKHz = bwCodeToKHz(config.lora.bandwidth);
+            }
+
+            // Guard against invalid values
+            sf = clampSpreadFactor(sf);
+            bwKHz = clampBandwidthKHz(bwKHz);
 
             // throttlingFactor = 2^SF / (BW_in_kHz * scaling_divisor)
             // With scaling_divisor=100:
@@ -76,11 +89,11 @@ class Default
             // In SF10 and BW=250khz (mediumslow), this gives 0.04096 rather than the original 0.04
             // In SF9 and BW=250khz (mediumfast), this gives 0.02048 rather than the original 0.02
             // In SF7 and BW=250khz (shortfast), this gives 0.00512 rather than the original 0.01
-            float throttlingFactor = static_cast<float>(pow_of_2(config.lora.spread_factor)) / (bwKHz * 100.0f);
+            float throttlingFactor = static_cast<float>(pow_of_2(sf)) / (bwKHz * 100.0f);
 
 #if USERPREFS_EVENT_MODE
             // If we are in event mode, scale down the throttling factor by 4
-            throttlingFactor = static_cast<float>(pow_of_2(config.lora.spread_factor)) / (bwKHz * 25.0f);
+            throttlingFactor = static_cast<float>(pow_of_2(sf)) / (bwKHz * 25.0f);
 #endif
 
             // Scaling up traffic based on number of nodes over 40

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)