Merge branch 'feat/network-resilience'

Network resilience hardening: NVS event-log ring buffer, event-driven
WiFi reconnect with backoff, HTTP timeouts + retry, task watchdog,
software heartbeat-miss watchdog (6h), EVT_BOOT/EVT_REBOOT logging,
heartbeat v1.1.0 diagnostic payload, server stub + migration, docs.

README.md

@@ -197,3 +197,92 @@ Capture a boot log with timestamps:
 ```bash
 python tools/serial_monitor.py --port /dev/ttyUSB0 --reset --timestamp --seconds 30
 ```
+
+## Deploying firmware 1.1 (network resilience)
+
+### Before you flash
+
+Firmware 1.1 adds five new fields to the `POST /api/v1/heartbeat` payload
+(`reset_reason`, `heap_free`, `heap_min_free`, `last_disconnect_code`,
+`recent_events`). **The real server must accept these optional fields before
+you deploy firmware 1.1**, or strict-schema validation will 4xx every
+heartbeat; after 6 consecutive misses (~6h) the heartbeat-miss watchdog
+will reboot the device, producing a reboot loop.
+
+Reference migration and handler code for the real server are in this repo:
+
+- `server/heartbeat_diagnostics_stub.py` — Pydantic model extensions,
+  `store_heartbeat_diagnostics()` helper, and `EVENT_TAG_DECODER` /
+  `REBOOT_REASON_DECODER` reference tables.
+- `server/migrations/005_heartbeat_diagnostics.sql` — adds five nullable
+  columns to the `heartbeats` table (adjust table name to match the real
+  server's schema).
+
+Copy the stub additions into the production server repo, run the
+migration, and confirm a v1.1.0-shape heartbeat returns 200 before you
+flash any device.
+
+### Flash command
+
+```bash
+cd firmware && pio run -e timercam -t upload
+```
+
+### Expected first boot
+
+On the serial log (115200 baud), the device prints the boot banner, then
+initializes `event_log`, then records the reset reason via `EVT_BOOT`.
+The first heartbeat fires roughly 60-70s after power-on (15s WiFi
+busy-wait + NTP sync + 60s `BOOT_REPORT_DELAY_S`). Monitor with
+`pio device monitor` or:
+
+```bash
+python tools/serial_monitor.py --port /dev/ttyUSB0 --reset --timestamp --seconds 90
+```
+
+### What's new in 1.1
+
+- Event-driven WiFi reconnect with 1s→60s exponential backoff (`net_guard` module); disconnect reasons logged.
+- HTTP timeouts (5s connect / 10s response) + 3-try retry on every POST.
+- ESP-IDF Task Watchdog (30s) on camera, reporter, and loop tasks; panic → reboot → reason surfaces in the next heartbeat.
+- Software heartbeat-miss watchdog: 6 consecutive missed heartbeats (~6 h) triggers a clean reboot.
+- Persistent NVS event-log ring buffer (32 entries) surfaced in the heartbeat's `recent_events` field.
+- New heartbeat fields: `reset_reason`, `heap_free`, `heap_min_free`, `last_disconnect_code`, `recent_events`.
+
+### 24-hour field checks
+
+After deploying a device, run through this checklist against the server's
+heartbeat records at the 24-hour mark:
+
+- **Heartbeat count ≥ 22** — ≥ 92% uptime across 24 h at the hourly cadence.
+- **No sustained `t=6` (EVT_HEARTBEAT_MISS) entries in `recent_events`** — transient singletons are expected; repeated misses indicate a sticky network problem worth investigating.
+- **`heap_min_free` stable day over day** — a downward drift indicates a leak. Alert threshold: min-free drops by more than 20% vs baseline.
+- **`last_disconnect_code` matches known AP behavior** — reason 8 (assoc lost) and reason 15 (4-way handshake timeout) are common on busy APs; recurring reason 200+ indicates a firmware bug.
+- **`reset_reason` has no unexpected values** — see table below.
+
+| `reset_reason` | Meaning | Expected? |
+|----------------|---------|-----------|
+| 1 | Power-on | Normal immediately after a deployment. |
+| 4 | Software reset (our `ESP.restart()`) | Correlate with `EVT_REBOOT` in `recent_events`. |
+| 6 | Task watchdog | Investigate — a task hung for 30s. |
+| 7 | Brownout | Investigate power supply / USB cable. |
+| 8 | SDIO reset | Unusual — investigate. |
+
+### Decoding recent_events
+
+The `recent_events` array is a ring buffer of `{t, d0, d1, ts}` entries.
+Tag definitions live in `firmware/lib/event_log/event_log.h`:
+
+| `t` | Event | `d0` | `d1` |
+|-----|-------|------|------|
+| 1 | `EVT_BOOT` | `esp_reset_reason()` | — |
+| 2 | `EVT_WIFI_UP` | RSSI | — |
+| 3 | `EVT_WIFI_DOWN` | disconnect reason code; `0xFF` = silent-death fallback | — |
+| 4 | `EVT_HTTP_OK` | fnv1a-16 path hash | elapsed ms (capped at 65535) |
+| 5 | `EVT_HTTP_FAIL` | path hash | HTTP status or negative errno cast to `uint16` |
+| 6 | `EVT_HEARTBEAT_MISS` | consecutive miss count | — |
+| 7 | `EVT_NTP_SYNC` | reserved | — |
+| 8 | `EVT_REBOOT` | `RebootReason`: 1=HEARTBEAT_MISS, 2=FACTORY_RESET, 3=OTA, 4=WIFI_REPROV | — |
+
+Server-side decoder tables (`EVENT_TAG_DECODER`, `REBOOT_REASON_DECODER`)
+live in `server/heartbeat_diagnostics_stub.py`.

firmware/lib/event_log/event_log.cpp

@@ -0,0 +1,156 @@
+// firmware/lib/event_log/event_log.cpp
+#include "event_log.h"
+#include <string.h>
+#include <stdio.h>
+
+#ifdef ARDUINO
+  #include <Arduino.h>
+  #include <Preferences.h>
+  #include <time.h>
+  #include <freertos/FreeRTOS.h>
+  #include <freertos/semphr.h>
+  static Preferences s_prefs;
+  static const char* NVS_NS   = "evlog";
+  static bool s_ok = false;
+  static SemaphoreHandle_t s_mutex = nullptr;
+  static uint32_t g_head = 0;  // next write slot (0..31), RAM-only
+  static uint32_t g_cnt  = 0;  // total writes since boot scan, RAM-only
+  static constexpr time_t NTP_SYNC_THRESHOLD = 1700000000; // 2023-11-14
+#else
+  // Native build: in-memory stub
+  #include <cstdint>
+  static uint8_t  g_slots[32 * 32];
+  static uint32_t g_head = 0;
+  static uint32_t g_cnt  = 0;
+  extern "C" void event_log_test_reset() {
+      memset(g_slots, 0, sizeof(g_slots));
+      g_head = 0;
+      g_cnt  = 0;
+  }
+  extern "C" void event_log_test_simulate_reboot() {
+      // Simulate device reboot: clear in-RAM state, keep persistent slots.
+      g_head = 0;
+      g_cnt  = 0;
+  }
+#endif
+
+static const size_t SLOTS     = 32;
+static const size_t SLOT_SIZE = sizeof(EventLogEntry);
+
+uint16_t event_log_path_hash(const char* path) {
+    // fnv1a-16 (fold 32-bit fnv1a down to 16 bits)
+    uint32_t h = 0x811c9dc5u;
+    while (*path) { h ^= (uint8_t)*path++; h *= 0x01000193u; }
+    return (uint16_t)((h >> 16) ^ (h & 0xFFFF));
+}
+
+static void slot_write(size_t idx, const EventLogEntry& e) {
+#ifdef ARDUINO
+    char key[8]; snprintf(key, sizeof(key), "s%u", (unsigned)idx);
+    s_prefs.putBytes(key, &e, SLOT_SIZE);
+#else
+    memcpy(&g_slots[idx * SLOT_SIZE], &e, SLOT_SIZE);
+#endif
+}
+
+static bool slot_read(size_t idx, EventLogEntry& e) {
+#ifdef ARDUINO
+    char key[8]; snprintf(key, sizeof(key), "s%u", (unsigned)idx);
+    size_t n = s_prefs.getBytes(key, &e, SLOT_SIZE);
+    return n == SLOT_SIZE;
+#else
+    memcpy(&e, &g_slots[idx * SLOT_SIZE], SLOT_SIZE);
+    return true;
+#endif
+}
+
+void event_log_init() {
+#ifdef ARDUINO
+    if (s_mutex == nullptr) {
+        s_mutex = xSemaphoreCreateMutex();
+    }
+    s_ok = s_prefs.begin(NVS_NS, /*readOnly=*/false);
+    if (!s_ok) {
+        Serial.println("[evlog] NVS begin failed");
+        return;
+    }
+#endif
+    // Scan all 32 slots; locate the one with the largest seq.
+    // Empty log: every slot tag == 0 (not a valid EventLogTag, which starts at 1).
+    uint32_t max_seq = 0;
+    int      max_idx = -1;
+    bool     any_valid = false;
+    for (size_t i = 0; i < SLOTS; i++) {
+        EventLogEntry e = {};
+        if (!slot_read(i, e)) continue;
+        if (e.tag == 0) continue;
+        any_valid = true;
+        if (max_idx < 0 || e.seq >= max_seq) {
+            max_seq = e.seq;
+            max_idx = (int)i;
+        }
+    }
+    if (any_valid) {
+        g_head = (uint32_t)((max_idx + 1) % SLOTS);
+        g_cnt  = max_seq + 1;
+    } else {
+        g_head = 0;
+        g_cnt  = 0;
+    }
+}
+
+void event_log_write(EventLogTag tag, uint16_t data0, uint16_t data1) {
+#ifdef ARDUINO
+    if (!s_ok) return;
+    // Bounded wait: skip on contention rather than stall the calling task.
+    // This matters because event_log_write runs from the WiFi event task
+    // (priority 23); blocking it on a 10-100ms NVS write can overflow the
+    // event queue. Diagnostic loss is preferable to dropped WiFi events.
+    if (s_mutex && xSemaphoreTake(s_mutex, pdMS_TO_TICKS(50)) != pdTRUE) return;
+    EventLogEntry e = {};
+    time_t now = time(nullptr);
+    e.ts_unix  = (now > NTP_SYNC_THRESHOLD) ? (uint32_t)now : 0;
+    e.uptime_s = (uint32_t)(millis() / 1000);
+    e.tag   = (uint8_t)tag;
+    e.data0 = data0;
+    e.data1 = data1;
+    e.seq   = g_cnt;
+    slot_write(g_head % SLOTS, e);
+    g_head = (g_head + 1) % SLOTS;
+    g_cnt  = g_cnt + 1;
+    if (s_mutex) xSemaphoreGive(s_mutex);
+#else
+    EventLogEntry e = {};
+    e.ts_unix  = 0;
+    e.uptime_s = 0;
+    e.tag   = (uint8_t)tag;
+    e.data0 = data0;
+    e.data1 = data1;
+    e.seq   = g_cnt;
+    slot_write(g_head % SLOTS, e);
+    g_head = (g_head + 1) % SLOTS;
+    g_cnt  = g_cnt + 1;
+#endif
+}
+
+size_t event_log_read_recent(EventLogEntry* out, size_t max_entries) {
+#ifdef ARDUINO
+    if (!s_ok) return 0;
+    // Bounded wait to match event_log_write. Reads are slower (32 NVS gets),
+    // but returning 0 entries under contention beats blocking the caller.
+    if (s_mutex && xSemaphoreTake(s_mutex, pdMS_TO_TICKS(50)) != pdTRUE) return 0;
+#endif
+    uint32_t head = g_head;
+    uint32_t cnt  = g_cnt;
+    size_t available = (cnt < SLOTS) ? (size_t)cnt : SLOTS;
+    size_t n = (max_entries < available) ? max_entries : available;
+    for (size_t i = 0; i < n; i++) {
+        // newest is at (head - 1), then (head - 2), ... modulo SLOTS
+        size_t idx = (head + SLOTS - 1 - i) % SLOTS;
+        slot_read(idx, out[i]);
+    }
+#ifdef ARDUINO
+    if (s_mutex) xSemaphoreGive(s_mutex);
+#endif
+    return n;
+}

firmware/lib/event_log/event_log.h

@@ -0,0 +1,48 @@
+// firmware/lib/event_log/event_log.h
+#pragma once
+#include <stdint.h>
+#include <stddef.h>
+
+enum EventLogTag : uint8_t {
+    EVT_BOOT           = 1,  // data0 = esp_reset_reason() value
+    EVT_WIFI_UP        = 2,  // data0 = rssi (signed, cast)
+    EVT_WIFI_DOWN      = 3,  // data0 = disconnect reason code
+    EVT_HTTP_OK        = 4,  // data0 = path hash (fnv1a16), data1 = elapsed_ms
+    EVT_HTTP_FAIL      = 5,  // data0 = path hash, data1 = (http_code or negative errno)
+    EVT_HEARTBEAT_MISS = 6,  // data0 = consecutive miss count
+    EVT_NTP_SYNC       = 7,  // data0 = seconds since boot
+    EVT_REBOOT         = 8,  // data0 = reason enum (defined below)
+};
+
+enum RebootReason : uint8_t {
+    REBOOT_HEARTBEAT_MISS = 1,
+    REBOOT_FACTORY_RESET  = 2,
+    REBOOT_OTA            = 3,
+    REBOOT_WIFI_REPROV    = 4,
+    REBOOT_FATAL_CONFIG   = 5,
+    REBOOT_FATAL_CAMERA   = 6,
+};
+
+struct EventLogEntry {
+    uint32_t ts_unix;     // 0 if NTP not synced yet; fall back to millis/1000
+    uint32_t uptime_s;    // millis()/1000 at log time
+    uint16_t data0;
+    uint16_t data1;
+    uint8_t  tag;         // EventLogTag
+    uint32_t seq;         // widened; survives multi-year event rates
+    uint8_t  _pad[15];    // pad to 32 bytes for fixed slot size
+} __attribute__((packed));
+static_assert(sizeof(EventLogEntry) == 32, "EventLogEntry must be 32 bytes");
+
+// NVS-backed 32-slot ring buffer. Safe to call before NTP sync.
+// Call exactly once from application setup, before any task writes events.
+void event_log_init();
+
+// Safe to call from any FreeRTOS task after event_log_init().
+// Bounded mutex wait (~50ms) — will silently skip on contention rather than
+// block the calling task. Acceptable for diagnostic logging.
+void event_log_write(EventLogTag tag, uint16_t data0 = 0, uint16_t data1 = 0);
+
+// Same bounded-wait contract as event_log_write: returns 0 on mutex timeout.
+size_t event_log_read_recent(EventLogEntry* out, size_t max_entries);
+uint16_t event_log_path_hash(const char* path);  // fnv1a16 — exposed for tests

firmware/lib/net_guard/library.json

@@ -0,0 +1,6 @@
+{
+  "name": "net_guard",
+  "build": {
+    "flags": ["-I$PROJECT_SRC_DIR"]
+  }
+}

firmware/lib/net_guard/net_guard.cpp

@@ -0,0 +1,75 @@
+// firmware/lib/net_guard/net_guard.cpp
+#include "net_guard.h"
+
+uint32_t net_guard_next_backoff_ms(uint32_t attempt) {
+    if (attempt >= 6) return 60000;
+    return 1000u * (1u << attempt);
+}
+
+#ifdef ARDUINO
+#include "config.h"
+#include <WiFi.h>
+#include "event_log.h"
+
+// Shared with the WiFi event task. 32-bit aligned loads/stores are atomic on
+// Xtensa; volatile suffices. Tick re-evaluates every loop iteration, so stale
+// reads self-correct within ~200ms.
+static const DeviceConfig* s_cfg = nullptr;
+static volatile uint8_t    s_last_disconnect = 0;
+static volatile bool       s_up = false;
+static volatile uint32_t   s_attempts = 0;
+static volatile uint32_t   s_next_retry_ms = 0;
+
+static void on_wifi_event(WiFiEvent_t event, WiFiEventInfo_t info) {
+    switch (event) {
+        case ARDUINO_EVENT_WIFI_STA_GOT_IP:
+            s_up = true;
+            s_attempts = 0;
+            s_next_retry_ms = 0;
+            event_log_write(EVT_WIFI_UP, (uint16_t)(int16_t)WiFi.RSSI(), 0);
+            break;
+        case ARDUINO_EVENT_WIFI_STA_DISCONNECTED:
+            s_up = false;
+            s_last_disconnect = (uint8_t)info.wifi_sta_disconnected.reason;
+            event_log_write(EVT_WIFI_DOWN, s_last_disconnect, 0);
+            s_next_retry_ms = millis() + net_guard_next_backoff_ms(s_attempts);
+            break;
+        default: break;
+    }
+}
+
+void net_guard_start(const DeviceConfig& cfg) {
+    s_cfg = &cfg;
+    // Seed s_up from the current WiFi state. setup()'s busy-wait on
+    // WiFi.begin() can produce a STA_GOT_IP before onEvent() is registered;
+    // without this seed, the first tick would force a spurious reconnect.
+    if (WiFi.status() == WL_CONNECTED) s_up = true;
+    WiFi.onEvent(on_wifi_event);
+    WiFi.setAutoReconnect(false); // we drive reconnect ourselves
+}
+
+bool net_guard_is_up() { return s_up; }
+
+uint8_t net_guard_last_disconnect_reason() { return s_last_disconnect; }
+
+extern "C" void net_guard_tick() {
+    // Watchdog against silent WiFi death: if we think we're up but the radio
+    // disagrees, force the DOWN state so reconnect scheduling kicks in.
+    if (s_up && WiFi.status() != WL_CONNECTED) {
+        s_up = false;
+        s_last_disconnect = 0xFF; // 0xFF = "silent death, no event"
+        event_log_write(EVT_WIFI_DOWN, s_last_disconnect, 0);
+        s_next_retry_ms = millis() + net_guard_next_backoff_ms(s_attempts);
+    }
+
+    if (s_up || s_cfg == nullptr) return;
+    if (millis() < s_next_retry_ms) return;
+    if (s_up) return;  // re-check after the timing gate — closes GOT_IP-vs-tick race
+    s_attempts++;
+    // WiFi.begin() alone re-associates cleanly; a prior WiFi.disconnect() call
+    // synchronously emits STA_DISCONNECTED on the event task, which would
+    // double-log EVT_WIFI_DOWN (reason=ASSOC_LEAVE) on every retry.
+    WiFi.begin(s_cfg->wifi_ssid.c_str(), s_cfg->wifi_pass.c_str());
+    s_next_retry_ms = millis() + net_guard_next_backoff_ms(s_attempts);
+}
+#endif

firmware/lib/net_guard/net_guard.h

@@ -0,0 +1,24 @@
+// firmware/lib/net_guard/net_guard.h
+#pragma once
+#include <stdint.h>
+
+// Exponential backoff: 1s, 2s, 4s, 8s, 16s, 32s, 60s, 60s, ...
+// attempt 0 -> 1000ms, clamped at 60000ms.
+uint32_t net_guard_next_backoff_ms(uint32_t attempt);
+
+#ifdef ARDUINO
+struct DeviceConfig;  // forward-decl; only net_guard_start needs the full type
+
+// Registers WiFi.onEvent() handler and starts auto-reconnect loop.
+// Must be called once after WiFi.begin() succeeds.
+void net_guard_start(const DeviceConfig& cfg);
+
+// True iff WiFi is currently associated with IP.
+bool net_guard_is_up();
+
+// Last disconnect reason code from WIFI_EVENT_STA_DISCONNECTED (0 = none).
+uint8_t net_guard_last_disconnect_reason();
+
+// Non-blocking tick called from loop(); kicks reconnect if due.
+extern "C" void net_guard_tick();
+#endif

firmware/src/main.cpp

@@ -8,6 +8,10 @@
 #include "cv.h"
 #include "ble_scanner.h"
 #include "reporter.h"
+#include "event_log.h"
+#include "net_guard.h"
+#include <esp_system.h>
+#include <esp_task_wdt.h>
 
 // LED on GPIO2 (TimerCamera-F built-in LED) — verify against board schematic
 // Factory reset: hold GPIO37 (BOOT button) for 5 seconds
@@ -45,10 +49,12 @@ static void check_factory_reset() {
     uint32_t held = millis();
     while (digitalRead(BUTTON_PIN) == LOW) {
         if (millis() - held >= FACTORY_RESET_HOLD_MS) {
+            event_log_write(EVT_REBOOT, REBOOT_FACTORY_RESET, 0);
             config_clear_wifi();
             ESP.restart();
         }
         delay(50);
+        esp_task_wdt_reset();
     }
 }
 
@@ -56,6 +62,7 @@ static void check_factory_reset() {
 static void task_camera(void*) {
     static uint8_t frame[CV_PIXELS];  // static: avoids 9KB on task stack
     int last_logged_track_id = 0;     // diagnostic: log each new track once
+    esp_task_wdt_add(nullptr);
     while (true) {
         if (camera_capture_96(frame)) {
             if (xSemaphoreTake(s_cv_mutex, pdMS_TO_TICKS(100)) == pdTRUE) {
@@ -82,21 +89,25 @@ static void task_camera(void*) {
             }
         }
         vTaskDelay(pdMS_TO_TICKS(CAM_INTERVAL_MS));
+        esp_task_wdt_reset();
     }
 }
 
 // Hourly reporter task — runs on core 0
 static void task_reporter(void*) {
     uint32_t last_report_ts = 0; // 0 = not initialized yet
+    esp_task_wdt_add(nullptr);
 
     while (true) {
         vTaskDelay(pdMS_TO_TICKS(10000)); // check every 10s
+        esp_task_wdt_reset();
 
         uint32_t now = (uint32_t)(time(nullptr));
         if (now < 1700000000UL) continue; // NTP not synced
 
         // First valid timestamp — schedule boot report 60s from now
         if (last_report_ts == 0) {
+            event_log_write(EVT_NTP_SYNC, (uint16_t)(millis() / 1000), 0);
             last_report_ts = now - (REPORT_INTERVAL_S - BOOT_REPORT_DELAY_S);
             continue;
         }
@@ -127,10 +138,24 @@ static void task_reporter(void*) {
 
         reporter_submit_camera(g_cfg, cam_rec);
         reporter_submit_ble(g_cfg, ble_rec);
-        reporter_heartbeat(g_cfg, millis() / 1000, WiFi.RSSI());
+        bool hb_ok = reporter_heartbeat(g_cfg, millis() / 1000, WiFi.RSSI());
 
         ble_scanner_reinit();
         led_set(false);
+
+        static uint8_t consecutive_misses = 0;
+        if (hb_ok) {
+            consecutive_misses = 0;
+        } else {
+            consecutive_misses++;
+            event_log_write(EVT_HEARTBEAT_MISS, consecutive_misses, 0);
+            Serial.printf("[WDG] heartbeat miss %u/6\n", consecutive_misses);
+            if (consecutive_misses >= 6) {
+                event_log_write(EVT_REBOOT, REBOOT_HEARTBEAT_MISS, 0);
+                delay(200); // let NVS commit before reboot
+                ESP.restart();
+            }
+        }
     }
 }
 
@@ -140,14 +165,26 @@ void setup() {
     pinMode(BUTTON_PIN, INPUT_PULLUP);
     led_set(true); // on = booting
 
+    event_log_init();
+    event_log_write(EVT_BOOT, (uint16_t)esp_reset_reason(), 0);
+
     if (!config_load(g_cfg)) {
         Serial.println("FATAL: device_id/location_id/hmac_secret not provisioned");
-        while (true) { delay(500); led_set(!digitalRead(LED_PIN)); } // fast blink
+        event_log_write(EVT_REBOOT, REBOOT_FATAL_CONFIG, 0);
+        // Blink fast for 3s so a physically-present operator can see it,
+        // then reboot so EVT_BOOT history on the next heartbeat surfaces
+        // the failure — though in this case the device can't heartbeat
+        // without config, so the real signal is the fast-blink-then-reboot
+        // cycle visible on the LED.
+        uint32_t t0 = millis();
+        while (millis() - t0 < 3000) { led_set(!digitalRead(LED_PIN)); delay(100); }
+        ESP.restart();
     }
 
     // Connect to WiFi
     if (!config_has_wifi()) {
         provisioning_run();
+        event_log_write(EVT_REBOOT, REBOOT_WIFI_REPROV, 0);
         ESP.restart();
     }
 
@@ -161,9 +198,11 @@ void setup() {
     if (WiFi.status() != WL_CONNECTED) {
         // Saved creds failed — re-provision
         provisioning_run();
+        event_log_write(EVT_REBOOT, REBOOT_WIFI_REPROV, 0);
         ESP.restart();
     }
 
+    net_guard_start(g_cfg);
     led_set(false); // off = connected
 
     // NTP sync (UTC)
@@ -173,7 +212,10 @@ void setup() {
 
     if (!camera_init()) {
         Serial.println("FATAL: camera init failed");
-        while (true) delay(1000);
+        event_log_write(EVT_REBOOT, REBOOT_FATAL_CAMERA, 0);
+        uint32_t t0 = millis();
+        while (millis() - t0 < 3000) { led_set(!digitalRead(LED_PIN)); delay(100); }
+        ESP.restart();
     }
 
     reporter_init();
@@ -183,28 +225,37 @@ void setup() {
     // OTA update support
     ArduinoOTA.setHostname(g_cfg.device_id.c_str());
     ArduinoOTA.onStart([]() { ble_scanner_pause(); });
-    ArduinoOTA.onEnd([]()   { ble_scanner_resume(); ESP.restart(); });
+    ArduinoOTA.onEnd([]()   {
+        ble_scanner_resume();
+        event_log_write(EVT_REBOOT, REBOOT_OTA, 0);
+        ESP.restart();
+    });
     ArduinoOTA.onError([](ota_error_t e) { ble_scanner_resume(); });
     ArduinoOTA.begin();
 
     s_cv_mutex = xSemaphoreCreateMutex();
 
+    // Task watchdog: 30s timeout, panic on trigger so we reboot and log
+    // via esp_reset_reason() in EVT_BOOT on the next boot.
+    esp_task_wdt_init(30, /*panic=*/true);
+    esp_task_wdt_add(nullptr); // subscribe the Arduino loopTask
+
     xTaskCreatePinnedToCore(task_camera,   "cam",  8192, nullptr, 2, nullptr, 1);
     xTaskCreatePinnedToCore(task_reporter, "rep",  8192, nullptr, 1, nullptr, 0);
 }
 
 void loop() {
+    esp_task_wdt_reset();
     ArduinoOTA.handle();
     check_factory_reset();
+    net_guard_tick();
 
-    if (WiFi.status() != WL_CONNECTED) {
-        led_set(true); // on = no WiFi
-        WiFi.reconnect();
-        delay(5000);
-        if (WiFi.status() == WL_CONNECTED) {
-            led_set(false);
-            reporter_flush(g_cfg);
+    static bool s_was_up = true;
+    bool up = net_guard_is_up();
+    if (up != s_was_up) {
+        led_set(!up); // LED on when NOT up
+        if (up) reporter_flush(g_cfg);
+        s_was_up = up;
     }
-    }
-    delay(1000);
+    delay(200);
 }

firmware/src/reporter.cpp

@@ -1,12 +1,17 @@
 // firmware/src/reporter.cpp
 #include "reporter.h"
 #include "hmac.h"
+#include "event_log.h"
+#include "net_guard.h"
 #include <HTTPClient.h>
 #include <ArduinoJson.h>
 #include <WiFi.h>
 #include <vector>
 #include <time.h>
 #include <freertos/semphr.h>
+#include <esp_task_wdt.h>
+#include <esp_system.h>
+#include <esp_heap_caps.h>
 
 static std::vector<CameraHourlyRecord> s_cam_buf;
 static std::vector<BLEHourlyRecord>    s_ble_buf;
@@ -21,25 +26,48 @@ static uint32_t now_ts() {
     return (uint32_t)time(nullptr);
 }
 
-static bool post_json(const DeviceConfig& cfg, const char* path, const String& body) {
+static bool post_json_once(const DeviceConfig& cfg, const char* path, const String& body) {
     uint32_t ts  = now_ts();
-    // Reject if NTP hasn't synced yet (timestamp would be near epoch 0)
-    if (ts < 1700000000UL) return false; // pre-2023 → clock not valid
+    if (ts < 1700000000UL) return false;
     String   sig = hmac_sign(cfg.hmac_secret, "POST", path, ts, body);
-    if (sig.isEmpty()) return false; // HMAC failed
+    if (sig.isEmpty()) return false;
 
     HTTPClient http;
     String url = String(REPORTER_API_HOST) + path;
     http.begin(url);
+    http.setConnectTimeout(5000);   // DNS + TCP connect
+    http.setTimeout(10000);         // per-transaction response timeout
     http.addHeader("Content-Type", "application/json");
     http.addHeader("X-Device-Id",  cfg.device_id);
     http.addHeader("X-Timestamp",  String(ts));
     http.addHeader("X-Signature",  sig);
 
+    uint32_t t0 = millis();
     int code = http.POST(body);
+    uint32_t elapsed = millis() - t0;
     http.end();
-    Serial.printf("[HTTP] POST %s → %d\n", url.c_str(), code);
-    return (code == 200);
+    uint16_t phash = event_log_path_hash(path);
+    Serial.printf("[HTTP] POST %s -> %d (%u ms)\n", url.c_str(), code, (unsigned)elapsed);
+    if (code == 200) {
+        event_log_write(EVT_HTTP_OK, phash, (uint16_t)((elapsed > 65535) ? 65535 : elapsed));
+        return true;
+    }
+    event_log_write(EVT_HTTP_FAIL, phash, (uint16_t)code);
+    return false;
+}
+
+static bool post_json(const DeviceConfig& cfg, const char* path, const String& body) {
+    // 3 attempts. Worst case per call: 3 × (5s connect + 10s response) + 0 + 2 + 5 = 52s.
+    // TWDT is fed before the backoff delay and before each attempt so the 30s
+    // timeout doesn't fire mid-sequence.
+    static const uint16_t DELAYS_MS[] = { 0, 2000, 5000 };
+    for (int i = 0; i < 3; i++) {
+        esp_task_wdt_reset();
+        if (DELAYS_MS[i]) vTaskDelay(pdMS_TO_TICKS(DELAYS_MS[i]));
+        esp_task_wdt_reset();
+        if (post_json_once(cfg, path, body)) return true;
+    }
+    return false;
 }
 
 static String build_camera_batch(const DeviceConfig& cfg,
@@ -147,16 +175,36 @@ void reporter_submit_ble(const DeviceConfig& cfg, const BLEHourlyRecord& rec) {
     }
 }
 
-void reporter_heartbeat(const DeviceConfig& cfg, uint32_t uptime_s, int wifi_rssi) {
+bool reporter_heartbeat(const DeviceConfig& cfg, uint32_t uptime_s, int wifi_rssi) {
     JsonDocument doc;
     doc["device_id"]         = cfg.device_id;
-    doc["firmware_version"]  = "1.0.0";
+    doc["firmware_version"]  = "1.1.0";
     doc["free_storage_pct"]  = 100;
     doc["wifi_rssi"]         = wifi_rssi;
     doc["pending_records"]   = (int)(s_cam_buf.size() + s_ble_buf.size());
     doc["uptime_seconds"]    = uptime_s;
+
+    // Diagnostics (new in 1.1.0)
+    doc["reset_reason"]         = (int)esp_reset_reason();
+    doc["heap_free"]            = (int)esp_get_free_heap_size();
+    doc["heap_min_free"]        = (int)esp_get_minimum_free_heap_size();
+    doc["last_disconnect_code"] = (int)net_guard_last_disconnect_reason();
+
+    // Last 8 event-log entries, newest first
+    EventLogEntry recent[8];
+    size_t n = event_log_read_recent(recent, 8);
+    JsonArray evs = doc["recent_events"].to<JsonArray>();
+    for (size_t i = 0; i < n; i++) {
+        JsonObject e = evs.add<JsonObject>();
+        e["t"]  = recent[i].tag;
+        e["d0"] = recent[i].data0;
+        e["d1"] = recent[i].data1;
+        e["ts"] = recent[i].ts_unix;
+        e["up"] = recent[i].uptime_s;
+    }
+
     String body; serializeJson(doc, body);
-    post_json(cfg, "/api/v1/heartbeat", body);
+    return post_json(cfg, "/api/v1/heartbeat", body);
 }
 
 void reporter_flush(const DeviceConfig& cfg) {

firmware/src/reporter.h

@@ -17,5 +17,5 @@ static const char*  REPORTER_API_HOST   = "http://logs.research.bike";
 void reporter_init();
 void reporter_submit_camera(const DeviceConfig& cfg, const CameraHourlyRecord& rec);
 void reporter_submit_ble(const DeviceConfig& cfg, const BLEHourlyRecord& rec);
-void reporter_heartbeat(const DeviceConfig& cfg, uint32_t uptime_s, int wifi_rssi);
+bool reporter_heartbeat(const DeviceConfig& cfg, uint32_t uptime_s, int wifi_rssi);
 void reporter_flush(const DeviceConfig& cfg);

firmware/test/test_event_log/test_event_log.cpp

@@ -0,0 +1,141 @@
+// firmware/test/test_native/test_event_log.cpp
+#include <unity.h>
+#include <string.h>
+#include "event_log.h"
+
+// --- Native NVS stub (declared in event_log.cpp for native builds) ---
+extern "C" void event_log_test_reset();
+
+void setUp()    { event_log_test_reset(); }
+void tearDown() {}
+
+void test_entry_is_32_bytes() {
+    TEST_ASSERT_EQUAL(32, sizeof(EventLogEntry));
+}
+
+void test_path_hash_is_stable_and_differs() {
+    uint16_t a = event_log_path_hash("/api/v1/heartbeat");
+    uint16_t b = event_log_path_hash("/api/v1/heartbeat");
+    uint16_t c = event_log_path_hash("/api/v1/camera/events/batch");
+    TEST_ASSERT_EQUAL(a, b);
+    TEST_ASSERT_NOT_EQUAL(a, c);
+}
+
+void test_write_then_read_recent_returns_newest_first() {
+    event_log_init();
+    event_log_write(EVT_BOOT, 1, 0);
+    event_log_write(EVT_WIFI_UP, 2, 0);
+    event_log_write(EVT_HTTP_FAIL, 3, 500);
+    EventLogEntry buf[8];
+    size_t n = event_log_read_recent(buf, 8);
+    TEST_ASSERT_EQUAL(3, n);
+    TEST_ASSERT_EQUAL(EVT_HTTP_FAIL, buf[0].tag);
+    TEST_ASSERT_EQUAL(500, buf[0].data1);
+    TEST_ASSERT_EQUAL(EVT_WIFI_UP, buf[1].tag);
+    TEST_ASSERT_EQUAL(EVT_BOOT, buf[2].tag);
+}
+
+void test_ring_buffer_wraps_after_32_entries() {
+    event_log_init();
+    for (int i = 0; i < 40; i++) event_log_write(EVT_HTTP_OK, (uint16_t)i, 0);
+    EventLogEntry buf[32];
+    size_t n = event_log_read_recent(buf, 32);
+    TEST_ASSERT_EQUAL(32, n);
+    // Newest first: data0 should be 39, 38, 37, ... down to 8
+    TEST_ASSERT_EQUAL(39, buf[0].data0);
+    TEST_ASSERT_EQUAL(8,  buf[31].data0);
+}
+
+void test_empty_log_read_returns_zero() {
+    event_log_init();
+    EventLogEntry buf[8];
+    size_t n = event_log_read_recent(buf, 8);
+    TEST_ASSERT_EQUAL(0, n);
+}
+
+void test_read_recent_truncates_to_max_entries() {
+    event_log_init();
+    for (int i = 0; i < 10; i++) event_log_write(EVT_HTTP_OK, (uint16_t)i, 0);
+    EventLogEntry buf[3];
+    size_t n = event_log_read_recent(buf, 3);
+    TEST_ASSERT_EQUAL(3, n);
+    // Newest 3: data0 == 9, 8, 7
+    TEST_ASSERT_EQUAL(9, buf[0].data0);
+    TEST_ASSERT_EQUAL(8, buf[1].data0);
+    TEST_ASSERT_EQUAL(7, buf[2].data0);
+}
+
+void test_path_hash_distinguishes_real_api_paths() {
+    uint16_t h1 = event_log_path_hash("/api/v1/heartbeat");
+    uint16_t h2 = event_log_path_hash("/api/v1/camera/events/batch");
+    uint16_t h3 = event_log_path_hash("/api/v1/events/batch");
+    TEST_ASSERT_NOT_EQUAL(h1, h2);
+    TEST_ASSERT_NOT_EQUAL(h1, h3);
+    TEST_ASSERT_NOT_EQUAL(h2, h3);
+}
+
+extern "C" void event_log_test_simulate_reboot();
+
+void test_boot_recovery_after_partial_fill() {
+    // Phase 1: write 5 entries before "reboot"
+    event_log_init();
+    for (uint16_t i = 0; i < 5; i++) event_log_write(EVT_HTTP_OK, i, 0);
+
+    // Phase 2: simulate reboot (clear RAM state, keep slots), re-init, verify
+    event_log_test_simulate_reboot();
+    event_log_init();
+
+    // All 5 original entries should still be readable, newest first
+    EventLogEntry buf[8];
+    size_t n = event_log_read_recent(buf, 8);
+    TEST_ASSERT_EQUAL(5, n);
+    TEST_ASSERT_EQUAL(4, buf[0].data0);  // newest
+    TEST_ASSERT_EQUAL(0, buf[4].data0);  // oldest
+
+    // Phase 3: write one more — seq must continue (not restart at 0),
+    // so the new entry is the newest and slot index 5 holds it
+    event_log_write(EVT_HTTP_OK, 99, 0);
+    n = event_log_read_recent(buf, 8);
+    TEST_ASSERT_EQUAL(6, n);
+    TEST_ASSERT_EQUAL(99, buf[0].data0);
+    TEST_ASSERT_EQUAL(4,  buf[1].data0);
+}
+
+void test_boot_recovery_after_wrap() {
+    // Phase 1: write 40 entries (wraps the 32-slot ring once; oldest 8 dropped)
+    event_log_init();
+    for (uint16_t i = 0; i < 40; i++) event_log_write(EVT_HTTP_OK, i, 0);
+
+    // Phase 2: simulate reboot, re-init
+    event_log_test_simulate_reboot();
+    event_log_init();
+
+    // Still 32 entries visible, newest=39, oldest=8
+    EventLogEntry buf[32];
+    size_t n = event_log_read_recent(buf, 32);
+    TEST_ASSERT_EQUAL(32, n);
+    TEST_ASSERT_EQUAL(39, buf[0].data0);
+    TEST_ASSERT_EQUAL(8,  buf[31].data0);
+
+    // Phase 3: one more write — newest becomes 100, head advances past
+    // wherever the max-seq slot was, oldest drops to data0=9
+    event_log_write(EVT_HTTP_OK, 100, 0);
+    n = event_log_read_recent(buf, 32);
+    TEST_ASSERT_EQUAL(32, n);
+    TEST_ASSERT_EQUAL(100, buf[0].data0);
+    TEST_ASSERT_EQUAL(9,   buf[31].data0);
+}
+
+int main() {
+    UNITY_BEGIN();
+    RUN_TEST(test_entry_is_32_bytes);
+    RUN_TEST(test_path_hash_is_stable_and_differs);
+    RUN_TEST(test_write_then_read_recent_returns_newest_first);
+    RUN_TEST(test_ring_buffer_wraps_after_32_entries);
+    RUN_TEST(test_empty_log_read_returns_zero);
+    RUN_TEST(test_read_recent_truncates_to_max_entries);
+    RUN_TEST(test_path_hash_distinguishes_real_api_paths);
+    RUN_TEST(test_boot_recovery_after_partial_fill);
+    RUN_TEST(test_boot_recovery_after_wrap);
+    return UNITY_END();
+}

firmware/test/test_net_guard/test_net_guard.cpp

@@ -0,0 +1,32 @@
+// firmware/test/test_net_guard/test_net_guard.cpp
+#include <unity.h>
+#include "net_guard.h"
+
+void setUp()    {}
+void tearDown() {}
+
+void test_backoff_starts_at_one_second() {
+    TEST_ASSERT_EQUAL(1000, net_guard_next_backoff_ms(0));
+}
+
+void test_backoff_doubles_each_attempt() {
+    TEST_ASSERT_EQUAL(2000,  net_guard_next_backoff_ms(1));
+    TEST_ASSERT_EQUAL(4000,  net_guard_next_backoff_ms(2));
+    TEST_ASSERT_EQUAL(8000,  net_guard_next_backoff_ms(3));
+    TEST_ASSERT_EQUAL(16000, net_guard_next_backoff_ms(4));
+    TEST_ASSERT_EQUAL(32000, net_guard_next_backoff_ms(5));
+}
+
+void test_backoff_clamps_at_60s() {
+    TEST_ASSERT_EQUAL(60000, net_guard_next_backoff_ms(6));
+    TEST_ASSERT_EQUAL(60000, net_guard_next_backoff_ms(7));
+    TEST_ASSERT_EQUAL(60000, net_guard_next_backoff_ms(100));
+}
+
+int main() {
+    UNITY_BEGIN();
+    RUN_TEST(test_backoff_starts_at_one_second);
+    RUN_TEST(test_backoff_doubles_each_attempt);
+    RUN_TEST(test_backoff_clamps_at_60s);
+    return UNITY_END();
+}

server/heartbeat_diagnostics_stub.py

@@ -0,0 +1,127 @@
+# server/heartbeat_diagnostics_stub.py
+# Add these models and the persistence helper to the server's main.py alongside
+# the existing heartbeat endpoint (POST /api/v1/heartbeat).
+# Requires: diagnostic columns on the heartbeats table (see migrations/005_heartbeat_diagnostics.sql)
+#
+# Firmware v1.1.0 extends the heartbeat payload with five optional diagnostic
+# fields. v1.0.0-shape payloads (without these fields) must continue to parse
+# cleanly — every new field is Optional and defaults to None.
+#
+# IMPORTANT: Adjust the table name in store_heartbeat_diagnostics to match the
+# real server's schema if it differs from "heartbeats".
+
+import json
+import sqlite3
+from typing import List, Optional
+
+from pydantic import BaseModel
+
+
+class RecentEvent(BaseModel):
+    t: int   # EventLogTag (see EVENT_TAG_DECODER)
+    d0: int  # tag-specific datum 0
+    d1: int  # tag-specific datum 1
+    ts: int  # unix timestamp (seconds)
+    up: int  # seconds since boot when event was logged
+
+
+# Extend the existing HeartbeatRequest model in main.py by adding these five
+# optional fields. The rest of the heartbeat model (device_id, uptime, etc.)
+# stays as-is. Shown here as a standalone model for reference/testing.
+class HeartbeatDiagnosticsFields(BaseModel):
+    reset_reason: Optional[int] = None
+    heap_free: Optional[int] = None
+    heap_min_free: Optional[int] = None
+    last_disconnect_code: Optional[int] = None
+    recent_events: Optional[List[RecentEvent]] = None
+
+
+# Example of the fully-extended heartbeat request model (merge into the
+# existing HeartbeatRequest in main.py rather than introducing a second class):
+class HeartbeatRequestWithDiagnostics(BaseModel):
+    device_id: str
+    uptime: int
+    # ... existing fields from the v1.0.0 heartbeat model go here ...
+    # New v1.1.0 diagnostic fields:
+    reset_reason: Optional[int] = None
+    heap_free: Optional[int] = None
+    heap_min_free: Optional[int] = None
+    last_disconnect_code: Optional[int] = None
+    recent_events: Optional[List[RecentEvent]] = None
+
+
+# Call this inside the existing receive_heartbeat handler after the base
+# heartbeat row has been inserted/updated. It persists the diagnostic fields
+# on the same row keyed by device_id.
+def store_heartbeat_diagnostics(
+    db: sqlite3.Connection,
+    device_id: str,
+    hb: HeartbeatRequestWithDiagnostics,
+) -> None:
+    """Persist the v1.1.0 diagnostic fields onto the heartbeats row for device_id.
+
+    recent_events is JSON-serialized into a TEXT column for flexibility;
+    the other four fields are stored as INTEGERs. All fields are nullable
+    and left untouched when the payload omits them (v1.0.0 compatibility).
+    """
+    recent_events_json = (
+        json.dumps([ev.model_dump() for ev in hb.recent_events])
+        if hb.recent_events is not None
+        else None
+    )
+    cursor = db.cursor()
+    cursor.execute(
+        """UPDATE heartbeats
+              SET reset_reason         = ?,
+                  heap_free            = ?,
+                  heap_min_free        = ?,
+                  last_disconnect_code = ?,
+                  recent_events        = ?
+            WHERE device_id = ?""",
+        (
+            hb.reset_reason,
+            hb.heap_free,
+            hb.heap_min_free,
+            hb.last_disconnect_code,
+            recent_events_json,
+            device_id,
+        ),
+    )
+    db.commit()
+
+
+# ---------------------------------------------------------------------------
+# Decoders — use these in dashboards / alerting to label the integer tags the
+# firmware emits. Keep in sync with firmware/include/event_log.h.
+# ---------------------------------------------------------------------------
+
+# EventLogTag values (RecentEvent.t) -> human name.
+# Per-tag interpretation of d0/d1:
+#   EVT_BOOT           d0=esp_reset_reason()
+#   EVT_WIFI_UP        d0=RSSI (int16 cast to uint16)
+#   EVT_WIFI_DOWN      d0=disconnect reason (0xFF = silent-death)
+#   EVT_HTTP_OK        d0=path_hash, d1=elapsed_ms
+#   EVT_HTTP_FAIL      d0=path_hash, d1=http_status_or_errno
+#   EVT_HEARTBEAT_MISS d0=consecutive_count
+#   EVT_NTP_SYNC       d0=seconds_since_boot (reserved, not emitted)
+#   EVT_REBOOT         d0=RebootReason (see REBOOT_REASON_DECODER)
+EVENT_TAG_DECODER = {
+    1: "EVT_BOOT",
+    2: "EVT_WIFI_UP",
+    3: "EVT_WIFI_DOWN",
+    4: "EVT_HTTP_OK",
+    5: "EVT_HTTP_FAIL",
+    6: "EVT_HEARTBEAT_MISS",
+    7: "EVT_NTP_SYNC",
+    8: "EVT_REBOOT",
+}
+
+# EVT_REBOOT.d0 values -> human name. Firmware-initiated reboot reasons.
+REBOOT_REASON_DECODER = {
+    1: "HEARTBEAT_MISS",
+    2: "FACTORY_RESET",
+    3: "OTA",
+    4: "WIFI_REPROV",
+    5: "FATAL_CONFIG",
+    6: "FATAL_CAMERA",
+}

server/migrations/005_heartbeat_diagnostics.sql

@@ -0,0 +1,14 @@
+-- migrations/005_heartbeat_diagnostics.sql
+-- Add v1.1.0 diagnostic columns to the existing heartbeats table.
+-- Adjust the table name ("heartbeats") to match the real server's schema.
+-- Apply: sqlite3 <db_file> < migrations/005_heartbeat_diagnostics.sql
+--
+-- sqlite's ALTER TABLE ADD COLUMN only takes one column per statement, so
+-- each field is added separately. All columns are nullable, so firmware
+-- v1.0.0 payloads (which omit these fields) remain accepted unchanged.
+
+ALTER TABLE heartbeats ADD COLUMN reset_reason         INTEGER;
+ALTER TABLE heartbeats ADD COLUMN heap_free            INTEGER;
+ALTER TABLE heartbeats ADD COLUMN heap_min_free        INTEGER;
+ALTER TABLE heartbeats ADD COLUMN last_disconnect_code INTEGER;
+ALTER TABLE heartbeats ADD COLUMN recent_events        TEXT;    -- JSON-serialized list of {t,d0,d1,ts,up}

server/test_heartbeat_diagnostics_stub.py

@@ -0,0 +1,156 @@
+# server/test_heartbeat_diagnostics_stub.py
+# Template tests for the heartbeat diagnostic-fields extension.
+# Adapt imports and fixtures to match the actual server's test structure.
+#
+# To run against the actual server (once integrated):
+#   pytest server/test_heartbeat_diagnostics_stub.py -v
+
+import json
+import sqlite3
+
+
+def _make_db() -> sqlite3.Connection:
+    """In-memory sqlite fixture matching migrations/005_heartbeat_diagnostics.sql
+    applied on top of a minimal heartbeats table."""
+    db = sqlite3.connect(":memory:")
+    db.execute("""
+        CREATE TABLE heartbeats (
+            device_id            TEXT PRIMARY KEY,
+            uptime               INTEGER,
+            reset_reason         INTEGER,
+            heap_free            INTEGER,
+            heap_min_free        INTEGER,
+            last_disconnect_code INTEGER,
+            recent_events        TEXT
+        )
+    """)
+    db.commit()
+    return db
+
+
+def _v10_payload() -> dict:
+    """Firmware v1.0.0-shape heartbeat: no diagnostic fields."""
+    return {"device_id": "dc-test-01", "uptime": 12345}
+
+
+def _v11_payload() -> dict:
+    """Firmware v1.1.0-shape heartbeat: includes all five diagnostic fields."""
+    return {
+        "device_id": "dc-test-01",
+        "uptime": 12345,
+        "reset_reason": 1,
+        "heap_free": 123456,
+        "heap_min_free": 100000,
+        "last_disconnect_code": 201,
+        "recent_events": [
+            {"t": 1, "d0": 1, "d1": 0, "ts": 1712000000, "up": 0},
+            {"t": 3, "d0": 255, "d1": 0, "ts": 1712000050, "up": 50},
+        ],
+    }
+
+
+def test_v10_shape_parses_with_new_fields_none():
+    """A v1.0.0 heartbeat (no diagnostic fields) must parse cleanly; all new
+    fields default to None."""
+    from server.heartbeat_diagnostics_stub import HeartbeatRequestWithDiagnostics
+
+    hb = HeartbeatRequestWithDiagnostics(**_v10_payload())
+    assert hb.device_id == "dc-test-01"
+    assert hb.uptime == 12345
+    assert hb.reset_reason is None
+    assert hb.heap_free is None
+    assert hb.heap_min_free is None
+    assert hb.last_disconnect_code is None
+    assert hb.recent_events is None
+
+
+def test_v11_shape_populates_new_fields():
+    """A v1.1.0 heartbeat populates each diagnostic field and the event list."""
+    from server.heartbeat_diagnostics_stub import HeartbeatRequestWithDiagnostics
+
+    hb = HeartbeatRequestWithDiagnostics(**_v11_payload())
+    assert hb.reset_reason == 1
+    assert hb.heap_free == 123456
+    assert hb.heap_min_free == 100000
+    assert hb.last_disconnect_code == 201
+    assert hb.recent_events is not None
+    assert len(hb.recent_events) == 2
+    assert hb.recent_events[0].t == 1
+    assert hb.recent_events[1].t == 3
+    assert hb.recent_events[1].d0 == 255  # 0xFF silent-death marker
+    assert hb.recent_events[1].ts == 1712000050
+
+
+def test_store_heartbeat_diagnostics_writes_fields_and_json():
+    """store_heartbeat_diagnostics must JSON-serialize recent_events and write
+    each integer field as submitted."""
+    from server.heartbeat_diagnostics_stub import (
+        HeartbeatRequestWithDiagnostics,
+        store_heartbeat_diagnostics,
+    )
+
+    db = _make_db()
+    # Seed the heartbeats row the base handler would have inserted first.
+    db.execute(
+        "INSERT INTO heartbeats (device_id, uptime) VALUES (?, ?)",
+        ("dc-test-01", 12345),
+    )
+    db.commit()
+
+    hb = HeartbeatRequestWithDiagnostics(**_v11_payload())
+    store_heartbeat_diagnostics(db, "dc-test-01", hb)
+
+    row = db.execute(
+        """SELECT reset_reason, heap_free, heap_min_free,
+                  last_disconnect_code, recent_events
+             FROM heartbeats
+            WHERE device_id = ?""",
+        ("dc-test-01",),
+    ).fetchone()
+    assert row[0] == 1
+    assert row[1] == 123456
+    assert row[2] == 100000
+    assert row[3] == 201
+    events = json.loads(row[4])
+    assert isinstance(events, list)
+    assert len(events) == 2
+    assert events[0] == {"t": 1, "d0": 1, "d1": 0, "ts": 1712000000, "up": 0}
+    assert events[1]["d0"] == 255
+
+
+def test_store_heartbeat_diagnostics_v10_leaves_fields_null():
+    """v1.0.0 payload: all diagnostic columns should remain NULL after store."""
+    from server.heartbeat_diagnostics_stub import (
+        HeartbeatRequestWithDiagnostics,
+        store_heartbeat_diagnostics,
+    )
+
+    db = _make_db()
+    db.execute(
+        "INSERT INTO heartbeats (device_id, uptime) VALUES (?, ?)",
+        ("dc-test-01", 12345),
+    )
+    db.commit()
+
+    hb = HeartbeatRequestWithDiagnostics(**_v10_payload())
+    store_heartbeat_diagnostics(db, "dc-test-01", hb)
+
+    row = db.execute(
+        """SELECT reset_reason, heap_free, heap_min_free,
+                  last_disconnect_code, recent_events
+             FROM heartbeats
+            WHERE device_id = ?""",
+        ("dc-test-01",),
+    ).fetchone()
+    assert row == (None, None, None, None, None)
+
+
+def test_event_tag_decoder_labels():
+    """Sanity check: decoder maps firmware tag values to the expected names."""
+    from server.heartbeat_diagnostics_stub import EVENT_TAG_DECODER, REBOOT_REASON_DECODER
+
+    assert EVENT_TAG_DECODER[1] == "EVT_BOOT"
+    assert EVENT_TAG_DECODER[3] == "EVT_WIFI_DOWN"
+    assert EVENT_TAG_DECODER[8] == "EVT_REBOOT"
+    assert REBOOT_REASON_DECODER[1] == "HEARTBEAT_MISS"
+    assert REBOOT_REASON_DECODER[4] == "WIFI_REPROV"