fw/services/analytics: actually pack the native heartbeat record

The packed attribute was placed before the struct keyword, where GCC
silently ignores it, so native_heartbeat_record was serialized with
natural alignment (e.g. timestamp at offset 8 instead of 1, plus padding
between every misaligned member). The DLS blob therefore did not match
the compact layout the source implies.

Because the BLE disconnect counters sit at the end of the record, they
absorbed all the upstream offset drift and decoded as garbage (the
ble_disconnect_conn_spvn_tmo_count field in particular). Blobs whose tail
fields happened to be zero still decoded plausibly, masking the issue.

Move the attribute between the struct keyword and the tag using the
PACKED macro so it is honored, yielding the intended compact layout. Add
a static assertion that the record size equals the sum of its members
(computed from analytics.def) to catch any future padding regression.

The record version is left unchanged: decoders resolve the per-build
layout from DWARF via the embedded build_id, so this is not an encoding
scheme change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>

Author: gmarull

src/fw/services/analytics/native.c

@@ -11,6 +11,7 @@
 #include "pbl/services/data_logging/data_logging_service.h"
 #include "system/logging.h"
 #include "system/passert.h"
+#include "util/attributes.h"
 #include "util/build_id.h"
 #include "util/math.h"
 #include "util/size.h"
@@ -19,7 +20,7 @@
 #define NATIVE_HEARTBEAT_RECORD_VERSION 1
 
 /* Heartbeat record logged to DLS */
-__attribute__((packed)) struct native_heartbeat_record {
+struct PACKED native_heartbeat_record {
   uint8_t version;
   uint64_t timestamp;
   uint8_t build_id[BUILD_ID_EXPECTED_LEN];
@@ -42,6 +43,26 @@ __attribute__((packed)) struct native_heartbeat_record {
 #undef PBL_ANALYTICS_METRIC_DEFINE_STRING
 };
 
+/* The record is logged as a raw byte blob, so it must have no padding. */
+_Static_assert(
+    sizeof(struct native_heartbeat_record) ==
+        sizeof(uint8_t) + sizeof(uint64_t) + BUILD_ID_EXPECTED_LEN
+#define PBL_ANALYTICS_METRIC_DEFINE_UNSIGNED(key) +sizeof(uint32_t)
+#define PBL_ANALYTICS_METRIC_DEFINE_SIGNED(key) +sizeof(int32_t)
+#define PBL_ANALYTICS_METRIC_DEFINE_SCALED_UNSIGNED(key, scale) +sizeof(uint32_t) + sizeof(uint16_t)
+#define PBL_ANALYTICS_METRIC_DEFINE_SCALED_SIGNED(key, scale) +sizeof(int32_t) + sizeof(uint16_t)
+#define PBL_ANALYTICS_METRIC_DEFINE_TIMER(key) +sizeof(uint32_t)
+#define PBL_ANALYTICS_METRIC_DEFINE_STRING(key, len) +((len) + 1)
+#include "pbl/services/analytics/analytics.def"
+#undef PBL_ANALYTICS_METRIC_DEFINE_UNSIGNED
+#undef PBL_ANALYTICS_METRIC_DEFINE_SIGNED
+#undef PBL_ANALYTICS_METRIC_DEFINE_SCALED_UNSIGNED
+#undef PBL_ANALYTICS_METRIC_DEFINE_SCALED_SIGNED
+#undef PBL_ANALYTICS_METRIC_DEFINE_TIMER
+#undef PBL_ANALYTICS_METRIC_DEFINE_STRING
+    ,
+    "native_heartbeat_record must be packed (no padding)");
+
 /* Type-specific internal index enums (dense, no gaps) */
 
 enum native_integer_index {