Arrival time fix perhaps (#11274)

* Add explicit presence for MeshPacket.rx_time (arrival time)

rx_time is now proto3 optional with a has_rx_time presence bit, matching
the rx_rssi treatment. A node with no GPS and no phone connected yet has
no time source at all, so a bare 0 was indistinguishable from a genuine
1970-01-01 reading; downstream consumers (replay packets, JSON
serialization) now check has_rx_time instead of the value.

* Dedupe rx_time stamping into a shared helper; trim a debug log string

Extract the repeated haveTime/rx_time/has_rx_time stamp logic (5 call
sites across Router.cpp, MeshBeaconModule.cpp, MeshService.cpp) into
Router::computeRxTimeStamp()/stampRxTime(). Also shorten the new RTC.cpp
LOG_DEBUG string. Saves 48 bytes of flash on rak4631 (measured), no
behavior change.

* Fix has_rx_rssi presence carried unconditionally through StoreForward replay

preparePayload() set has_rx_rssi = true unconditionally on replay, regardless
of whether the packet's rx_rssi at store time was a genuine measurement (e.g.
MQTT-relayed packets carry no real RSSI). Store the presence bit alongside
rx_rssi in PacketHistoryStruct and restore it on replay instead.

Flagged by Copilot on #11271 (same root cause the has_rx_time explicit
presence work fixes) but never addressed before that PR merged.

* Trim comment blocks to the repo's 1-2 line guideline

.github/copilot-instructions.md:338 caps code comments at 1-2 lines; several
blocks added across the rx_time explicit-presence work ran well past that.
Also consolidates Time.cpp's file-level doc comment into Time.h, where the
rest of the Time:: API contract already lives.

No behavior change.

* Add rx_time explicit-presence test coverage

- test_meshpacket_serializer: has_rx_time=false fixture plus tests asserting
  JsonSerialize/JsonSerializeEncrypted emit 0 rather than leaking the
  millis() placeholder, alongside the has_rx_time=true baseline.
- test_stream_api: two tests driving a real PhoneAPI handshake (want_config_id
  through STATE_SEND_PACKETS) that simulate a phone time-giving transaction
  arriving before vs. after a queued packet is drained - covering both the
  reconciled and the ships-with-placeholder-absent paths of
  MeshService::reconcilePendingRxTimes().

* Fix three correctness issues flagged in review

- Time.h: drop the reserved-identifier include guard (_MT_TIME_H); pragma
  once already covers it, matching convention elsewhere (e.g. RTC.h).
- Time.cpp: rebase getMillis64()'s wrap accumulator when the test seam
  swaps clock sources, so a real<->injected clock jump isn't miscounted
  as a genuine 32-bit wrap.
- NodeInfoModule: the 12h reply-suppression window is a local dedup
  duration, not a wall-clock reading - switch it to Time::getMillis64()
  so RTC-quality jumps and replayed packets' stale rx_time can't perturb
  it.
- StoreForwardModule: has_rx_time was derived from *current* RTC quality
  at replay time rather than stored at capture time, so a history entry
  saved while time-blind could be misreported as a valid epoch once the
  clock later improved. Persist the presence bit in PacketHistoryStruct
  instead.

* tryfix CI

* post review fixes

* more test fixes

src/mesh/Router.cpp

@@ -5,6 +5,7 @@
 #include "MeshService.h"
 #include "NodeDB.h"
 #include "PositionPrecision.h"
+#include "UptimeClock.h"
 #include "gps/RTC.h"
 
 #include "configuration.h"
@@ -269,6 +270,19 @@ PacketId generatePacketId()
     return id;
 }
 
+RxTimeStamp computeRxTimeStamp()
+{
+    const bool haveTime = getRTCQuality() >= RTCQualityFromNet;
+    return {haveTime ? getValidTime(RTCQualityFromNet) : Time::getMillis(), haveTime};
+}
+
+void stampRxTime(meshtastic_MeshPacket *p)
+{
+    const RxTimeStamp ts = computeRxTimeStamp();
+    p->rx_time = ts.time;
+    p->has_rx_time = ts.valid;
+}
+
 meshtastic_MeshPacket *Router::allocForSending()
 {
     meshtastic_MeshPacket *p = packetPool.allocZeroed();
@@ -280,8 +294,8 @@ meshtastic_MeshPacket *Router::allocForSending()
     p->to = NODENUM_BROADCAST;
     p->hop_limit = Default::getConfiguredOrDefaultHopLimit(config.lora.hop_limit);
     p->id = generatePacketId();
-    p->rx_time =
-        getValidTime(RTCQualityFromNet); // Just in case we process the packet locally - make sure it has a valid timestamp
+    // Just in case we process the packet locally - make sure it has a timestamp.
+    stampRxTime(p);
 
     return p;
 }
@@ -1305,12 +1319,15 @@ void Router::dispatchReceived(meshtastic_MeshPacket *p, RxSource src)
     if (src == RX_SRC_RADIO)
         applyRoutingAuthCache(p);
 
-    // Also, we should set the time from the ISR and it should have msec level resolution.
     // Keep the decoded working packet and encrypted MQTT copy on the same local arrival timestamp.
-    const uint32_t rxTime = getValidTime(RTCQualityFromNet);
-    p->rx_time = rxTime;
-    if (p_encrypted)
-        p_encrypted->rx_time = rxTime;
+    // See computeRxTimeStamp() for the placeholder/has_rx_time semantics.
+    const RxTimeStamp rxStamp = computeRxTimeStamp();
+    p->rx_time = rxStamp.time;
+    p->has_rx_time = rxStamp.valid;
+    if (p_encrypted) {
+        p_encrypted->rx_time = rxStamp.time;
+        p_encrypted->has_rx_time = rxStamp.valid;
+    }
 
     // Take those raw bytes and convert them back into a well structured protobuf we can understand
     auto decodedState = perhapsDecode(p);
@@ -1443,7 +1460,8 @@ void Router::perhapsHandleReceived(meshtastic_MeshPacket *p)
 #if ARCH_PORTDUINO
     // Even ignored packets get logged in the trace
     if (portduino_config.traceFilename != "" || portduino_config.logoutputlevel == level_trace) {
-        p->rx_time = getValidTime(RTCQualityFromNet); // store the arrival timestamp for the phone
+        // Store the arrival timestamp for the phone before it's traced.
+        stampRxTime(p);
         LOG_TRACE("%s", MeshPacketSerializer::JsonSerializeEncrypted(p).c_str());
     }
 #endif