Fix millis() wraparound handling in timer comparisons

Fixes potential scheduler failures after ~49.7 days of continuous
uptime when millis() wraps around from 2^32-1 to 0.

Changed time comparisons from:
  if (millis() >= targetTime)
to:
  if ((int32_t)(millis() - targetTime) >= 0)

This uses signed subtraction to correctly handle wraparound,
matching the approach from MeshCore 1.14 commit 011edd3c.

Affected timers:
- pendingAdvertTime: scheduled ADVERT beacon after time sync
- tempRadioExpireTime: temporary radio parameter expiration
- rebootTime: delayed reboot from CLI command

Without this fix, scheduled events would get stuck and never
trigger after millis() wraparound, as the target time would
appear to be in the far future.

Author: atomozero

README.md

@@ -208,6 +208,10 @@ MIT License - See LICENSE file for details.
   - Default: 0 (no limit, backward compatible)
   - Reduces contact list pollution from distant nodes
   - Test script: `tools/test_autoadd_maxhops.py`
+- **Bug Fix: millis() Wraparound Handling** - Fixes scheduler issues after ~49.7 days uptime
+  - Fixed timer comparisons in pendingAdvertTime, tempRadioExpireTime, and rebootTime
+  - Uses signed subtraction to correctly handle millis() wraparound
+  - Prevents scheduled tasks from getting stuck when millis() wraps around
 
 ### v0.5.2 (2026-02-15)
 - **Extended MeshCore CLI** - 23 new commands for full MeshCore standard compatibility

src/main.cpp

@@ -2104,7 +2104,8 @@ void healthCheck() {
 
 void checkAdvertBeacon() {
     // Check for pending ADVERT after time sync
-    if (pendingAdvertTime > 0 && millis() >= pendingAdvertTime) {
+    // Use signed subtraction to handle millis() wraparound correctly
+    if (pendingAdvertTime > 0 && (int32_t)(millis() - pendingAdvertTime) >= 0) {
         pendingAdvertTime = 0;  // Clear pending
         LOG(TAG_ADVERT " Sched ADV post-sync\n\r");
         sendAdvert(true);
@@ -3241,7 +3242,8 @@ void loop() {
     feedWatchdog();
 
     // Auto-expire temporary radio settings
-    if (tempRadioActive && tempRadioExpireTime > 0 && millis() >= tempRadioExpireTime) {
+    // Use signed subtraction to handle millis() wraparound correctly
+    if (tempRadioActive && tempRadioExpireTime > 0 && (int32_t)(millis() - tempRadioExpireTime) >= 0) {
         tempRadioActive = false;
         tempRadioExpireTime = 0;
         setupRadio(); startReceive(); calculateTimings();
@@ -3258,7 +3260,8 @@ void loop() {
     }
 
     // Handle pending reboot from CLI command
-    if (pendingReboot && millis() >= rebootTime) {
+    // Use signed subtraction to handle millis() wraparound correctly
+    if (pendingReboot && (int32_t)(millis() - rebootTime) >= 0) {
         LOG(TAG_SYSTEM " Rebooting...\n\r");
         delay(100);  // Let serial flush
         HW_Reset(0);