[Elektr0Vodka]

What

Adds battery voltage and the other device health data the firmware already keeps to the SNMP agent, so a poller can see why a node rebooted, whether it is hot or congested, and what the packet filter and region gating are doing.

All under .1.3.6.1.4.1.99999:

Group	OIDs	Type
System	.1.4.0 battery mV (0 when the board cannot measure it), .1.5.0 MCU temperature °C (-127 when there is no sensor), .1.6.0 reset reason code, .1.7.0 reset reason text	INTEGER / STRING
Radio	.2.12.0 TX queue length, .2.16.0 TX duty cycle %, .2.17.0 error flags bitmask	INTEGER
Radio	.2.13.0 flood dups, .2.14.0 direct dups, .2.15.0 RX airtime s	Counter32
MQTT	.3.4.0 clock set by NTP (1/0)	INTEGER
Memory	.4.5.0 lowest free heap since boot	INTEGER
Duty gate (repeater only)	.6.1.0-.6.5.0 enabled, gated layers, max layer, threshold, hysteresis	INTEGER
Filter (repeater only)	.7.1.0 enabled, .7.2.0 dry-run	INTEGER
Filter (repeater only)	.7.3.0-.7.13.0 drop totals (hops, rate, channel, hash, malformed, advert, path, sender, text, age) and airtime saved (ms)	Counter32
Neighbours	.8.1.0 neighbour count	INTEGER

• src/helpers/SNMPAgent.{h,cpp}: new fields, setters and handlers. The duty gate and filter groups are only registered after enableRepeaterGroups(), so room servers return noSuchObject for them instead of a misleading 0.
• examples/simple_repeater/MyMesh.cpp, examples/simple_room_server/MyMesh.cpp: the push code moves into MyMesh::pushSNMPStats(). The reset reason is set once at startup.
• src/helpers/bridges/MQTTBridge.cpp: passes _ntp_synced to updateMQTTStats().
• MQTT_SNMP.md: OID tables, a note on types and counter resets, updated architecture notes, and the out-of-date board list replaced with a pointer to WITH_SNMP=1.

Why

The agent exposed radio, MQTT, memory and Wi-Fi stats, but no battery, temperature or reboot cause, and nothing about filter or region gating. A solar node with a dying pack, a node that keeps resetting on brownouts, or a repeater shedding traffic could not be seen from LibreNMS, Zabbix or RTFM-EV.

Design notes

• Battery and temperature are read every 30 s, not every 2 s. HeltecV4Board::getBattMilliVolts() calls delay(10), which held up the mesh task every 2 s in the first version of this PR. Both values are read on the mesh task (Core 1), so the ADC is never touched from the SNMP loop on Core 0. The first reading is pushed straight away.
• New running totals are Counter32 so pollers graph them as rates. The existing INTEGER totals (.2.1-.2.11, .3.3) are unchanged, to avoid breaking RTFM-EV's app/snmp/mib.py. Changing those types would be a separate PR.
• Filter hop and rate totals are summed across payload types with a saturating add, matching the filter's own counters, which saturate instead of wrapping.
• Counters start again from 0 after a reboot or clear stats.
• The meshcomod companion SNMP agent (Feat/companion-snmp) is being aligned to the same numbers so one poller reads both. RTFM-EV's mib.py needs the new scalars to show them.

Testing

• pio run -e Heltec_v3_repeater_observer_mqtt -e Heltec_v3_room_server_observer_mqtt: both build, no new warnings.
• Not yet tested on hardware (no snmpwalk against a running node).

Known issue, not fixed here

ESP32Board::getMCUTemperature() adds the float readings into a uint32_t, so below 0 °C die temperature .1.5.0 will read wrong. The die usually runs well above ambient, so this is rare. It is upstream code, so I left it alone.

Firmware impact

Observer builds with WITH_SNMP=1 only. About 160 bytes of static RAM, plus heap for 31 more OID handlers on repeaters (13 on room servers, which skip the 18 duty gate and filter OIDs). No prefs or wire format change. SNMPAgent.* comes from agessaman's observer firmware, so expect it on the next catch-up merge.

🤖 Generated with Claude Code

[Elektr0Vodka]

Pushed 7a4928e: the room server's neighbour table only exists with WITH_MQTT_NEIGHBORS, so pushSNMPStats() broke Heltec_v2_room_server_observer_mqtt (no PSRAM). It now reports .8.1.0 = 0 there (documented in MQTT_SNMP.md).

Verified merged onto dmc-observer-dev 9895e83: Heltec_v2 repeater + room and heltec_v4 repeater + room observer builds SUCCESS; pio test -e native 709/709. Not hardware-tested.

🤖 Generated with Claude Code