v1.12.3: defaut CO2 = sentinelle ISO_17 seule (retrait bit 7)

Decision avec le dev serveur Miotiq: l'absence/defaut du capteur CO2 est
signalee uniquement par ISO_17=0xFFFF (sentinelle, source de verite). Le bit 7
error_flags ajoute en v1.12.2 est retire (ambigu WIND/CO2 selon device_type).

- SARA_send_data_v2.py: suppression ERR_CO2 + s88_disconnected + |= ERR_CO2
- la logique sentinelle (set_co2 seulement si s88_status==0) reste inchangee
- error_flags.md: bit 7 = WIND_ERROR, note que le CO2 passe par la sentinelle

On garde v1.12.1 (s88_status + ecriture systematique) qui garantit la sentinelle.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

loop/SARA_send_data_v2.py

@@ -160,10 +160,6 @@ ERR_ENVEA            = 0x10
 ERR_NOISE            = 0x20
 ERR_MPPT             = 0x40
 ERR_WIND             = 0x80
-# Bit 7 is dual-purpose per product (server decodes by device_type):
-#   NebuleAir -> WIND_ERROR, ModuleAir / CO2-equipped units -> CO2_ERROR.
-# On these CO2 boxes the server reads bit 7 as CO2_ERROR (confirmed).
-ERR_CO2              = 0x80
 
 # database connection
 conn = sqlite3.connect("/var/www/nebuleair_pro_4g/sqlite/sensors.db")
@@ -1091,9 +1087,10 @@ try:
     # Only transmit when the LAST reading is valid (s88_status == 0). If the
     # sensor is down (s88_status == 0xFF), leave bytes 81-82 at 0xFFFF (= "CO2
     # sensor absent" in the Miotiq spec) instead of sending a stale value.
-    # Absence is signalled two ways: the 0xFFFF sentinel in the CO2 field, and
-    # the CO2_ERROR bit (0x80) in error_flags (byte 66) — see build below.
-    s88_disconnected = False
+    # Absence/fault is signalled solely by the 0xFFFF sentinel in the CO2 field
+    # (ISO_17, source of truth per the Miotiq spec): only transmit when the LAST
+    # reading is valid (s88_status == 0). No error_flags bit — bit 7 is ambiguous
+    # (WIND on NebuleAir / CO2 on ModuleAir), the sentinel is unambiguous.
     if s88_sensor:
         print("➡️Getting S88 CO2 value")
         cursor.execute("SELECT * FROM data_S88 ORDER BY rowid DESC LIMIT 1")
@@ -1105,11 +1102,9 @@ try:
                 print(f"CO2 (S88): {co2_ppm} ppm")
                 payload.set_co2(co2_ppm)
             else:
-                s88_disconnected = True
-                print(f"S88 last reading invalid (s88_status=0x{s88_status_value:02X}) -> CO2 marked absent (0xFFFF), set CO2_ERROR")
+                print(f"S88 last reading invalid (s88_status=0x{s88_status_value:02X}) -> CO2 marked absent (0xFFFF)")
         else:
-            s88_disconnected = True
-            print("No S88 data available in the database. -> set CO2_ERROR")
+            print("No S88 data available in the database. -> CO2 marked absent (0xFFFF)")
 
     #print("Verify SARA connection (AT)")
     
@@ -1243,8 +1238,6 @@ try:
         error_flags |= ERR_NPM
     if noise_disconnected:
         error_flags |= ERR_NOISE
-    if s88_disconnected:
-        error_flags |= ERR_CO2  # bit 7, read as CO2_ERROR by the server on these units
     payload.set_error_flags(error_flags)
 
     # ---- Firmware version (bytes 69-71) ----