Enable the on-demand mOTA context for every classic ESP32 build

Move OTA_HEAP_CONTEXT from two hand-edited envs to a pre-script gated on
build.mcu == "esp32", so every classic ESP32 image gets it and none can drift.
S2/S3/C-series and nRF52 keep the .bss singleton: they have no equivalent
static-DRAM ceiling, so there a guaranteed-present workspace is the better
trade for what is ultimately a recovery path. It has to be a build flag rather
than a header default, because OTA_HEAP_CONTEXT must hold the same value in
every translation unit that sees OtaContext.h - OtaContext.cpp included - and a
header test on CONFIG_IDF_TARGET_ESP32 would depend on include order relative
to sdkconfig.h. The script defers to OTA_SHARED_COMPANION_QUEUE where a Full
Companion recipe already owns the storage.

Fix a gap this exposes in the roles that now use it. Only CLI entry points
acquire the context, so once it was released, a repeater with the temporary
radio profile up would no longer serve or announce its own firmware - LoRa OTA
would look enabled and silently do nothing. ota_service_temp_radio_context()
holds the workspace for exactly the temp-radio window and hands it back
outside it, which is where the saving was coming from anyway. Wired into the
repeater, room server and sensor loops; the Companion keeps its own
acquire-on-host-demand policy, since its context is borrowed from the offline
message queue and must not be taken speculatively.

Static DRAM, classic ESP32 (bytes occupied of a 124,580 region):
  Heltec_v2_repeater                   108,332 -> 70,732
  Heltec_v2_room_server                 83,716 -> 68,300
  Heltec_v2_companion_radio_ble        123,236 -> 107,772  (was failing on main)
  Tbeam_SX1262_repeater                 86,932 -> 71,468
  Tbeam_SX1262_repeater_observer_mqtt  121,132 -> 83,532   (was failing)

examples/simple_repeater/MyMesh.cpp

@@ -12036,10 +12036,7 @@ void MyMesh::loop() {
   processDeferredCliCommand();
   servicePostMeshLoop();
 #if defined(ENABLE_OTA) && OTA_DYNAMIC_CONTEXT
-  // Hand the OTA workspace back once no transfer, apply or folder link needs
-  // it. A repeater is idle almost all of its life, so this is where the bulk
-  // of the saving actually lands.
-  mesh::ota::ota_release_context_if_idle(isTempRadioActive());
+  mesh::ota::ota_service_temp_radio_context(isTempRadioActive());
 #endif
 }
 

examples/simple_room_server/MyMesh.cpp

@@ -1,5 +1,8 @@
 #include "MyMesh.h"
 #include <helpers/UsbLogging.h>
+#if defined(ENABLE_OTA)
+#include <helpers/ota/OtaContext.h>
+#endif
 #include <helpers/FileRead.h>
 #include <helpers/radiolib/RxBoostedGainDefaults.h>
 #include <helpers/CLICommandUtils.h>
@@ -2774,6 +2777,9 @@ void MyMesh::loop() {
     }
   }
 #endif
+#if defined(ENABLE_OTA) && OTA_DYNAMIC_CONTEXT
+  mesh::ota::ota_service_temp_radio_context(isTempRadioActive());
+#endif
 }
 
 bool MyMesh::isMillisTimerDue(unsigned long timestamp) const {

examples/simple_sensor/SensorMesh.cpp

@@ -5,6 +5,9 @@
 #include <helpers/LazyPersistence.h>
 #include <helpers/radiolib/RXPowerSaving.h>
 #include <helpers/UsbLogging.h>
+#if defined(ENABLE_OTA)
+#include <helpers/ota/OtaContext.h>
+#endif
 
 static uint32_t nextRadioApplyRetryDelay(uint8_t& failure_count) {
   uint8_t shift = failure_count < 5 ? failure_count : 5;
@@ -1343,6 +1346,9 @@ void SensorMesh::loop() {
           (unsigned long)retry_delay);
     }
   }
+#if defined(ENABLE_OTA) && OTA_DYNAMIC_CONTEXT
+  mesh::ota::ota_service_temp_radio_context(isTempRadioActive());
+#endif
 }
 
 bool SensorMesh::isMillisTimerDue(unsigned long timestamp) const {

platformio.ini

@@ -74,6 +74,7 @@ extra_scripts =
   pre:scripts/generate_webconfig_html.py
   pre:scripts/meshcore_image_identity.py
   pre:scripts/portable_esp32_link.py
+  pre:scripts/esp32_ota_heap_context.py
   merge-bin.py
   post:tools/mota/pio_endf.py
   post:scripts/check_esp32_dram.py

scripts/esp32_ota_heap_context.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python3
+"""Keep the idle mOTA workspace off classic ESP32's static DRAM.
+
+Classic ESP32 links into a dram0_0_seg of ~124 KiB: memory.ld reserves the BT
+controller's 0xdb5c bytes off the 0x2c200 window before the application gets
+any, and no runtime call gives those static bytes back. OtaContext is several
+kilobytes of that budget, held for the life of the device even though a
+repeater or room server is outside an OTA window essentially always.
+
+OTA_HEAP_CONTEXT switches OtaContext to the on-demand storage path, so it is
+allocated when an OTA operation needs it and freed once idle. Applied here
+rather than per-env so every classic ESP32 build gets it and none can drift.
+
+Scoped to build.mcu == "esp32" deliberately. S2/S3/C-series and nRF52 have no
+equivalent static-DRAM ceiling, so there the .bss singleton is the better
+trade: it guarantees the workspace is present, and OTA is a recovery path.
+
+This must be a build flag, not a header default. OTA_HEAP_CONTEXT has to hold
+the same value in every translation unit that sees OtaContext.h - including
+OtaContext.cpp, which defines the storage - and a header test on
+CONFIG_IDF_TARGET_ESP32 would depend on whether that unit had already reached
+sdkconfig.h.
+"""
+
+Import("env")  # noqa: F821 -- PlatformIO/SCons supplies Import
+
+# Both name the owner of the context storage, and OtaContext.h rejects the
+# pair. OTA_SHARED_COMPANION_QUEUE arrives via PLATFORMIO_BUILD_FLAGS from
+# build.sh's Full Companion recipes, which are nRF52/S3 today - but a future
+# classic ESP32 Full Companion must lose this default, not fail to compile.
+CONFLICTING = ("OTA_HEAP_CONTEXT", "OTA_SHARED_COMPANION_QUEUE")
+
+
+def _already_defined(env):
+    for define in env.get("CPPDEFINES", []):
+        name = define[0] if isinstance(define, (list, tuple)) else define
+        if str(name) in CONFLICTING:
+            return True
+    # PLATFORMIO_BUILD_FLAGS reaches BUILD_FLAGS as raw text, which may not be
+    # parsed into CPPDEFINES yet when this pre-script runs.
+    for flag in env.get("BUILD_FLAGS", []):
+        text = str(flag)
+        if any(("-D" + name) in text for name in CONFLICTING):
+            return True
+    return False
+
+
+def _apply(env):
+    if str(env.BoardConfig().get("build.mcu", "")).lower() != "esp32":
+        return
+    if _already_defined(env):
+        return
+    env.Append(CPPDEFINES=[("OTA_HEAP_CONTEXT", 1)])
+
+
+_apply(env)  # noqa: F821

src/helpers/ota/OtaContext.h

@@ -681,6 +681,22 @@ uint8_t ota_hop_limit();
 void ota_set_context_storage(void* owner, OtaContext* (*acquire)(void*),
                              void (*release)(void*));
 void ota_release_context_if_idle(bool temporary_radio_active);
+
+// Loop helper for roles whose LoRa OTA only runs under the temporary radio
+// profile (repeater, room server, sensor). Nothing else acquires the context
+// on their behalf: without this, serving and announcing would stop the moment
+// the context was released, because only CLI entry points acquire. Holding it
+// for the temp-radio window keeps behaviour identical to a permanent context,
+// and the node is outside that window nearly all the time, which is where the
+// saving comes from. Not for the Companion, whose context is borrowed from the
+// offline message queue and must only be taken on explicit host demand.
+inline void ota_service_temp_radio_context(bool temporary_radio_active) {
+  if (temporary_radio_active) {
+    ota_acquire_context(nullptr, 0);   // failure is reported at the CLI entry points
+  } else {
+    ota_release_context_if_idle(false);
+  }
+}
 #endif
 
 } // namespace ota

variants/heltec_v2/platformio.ini

@@ -38,7 +38,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
   -D FLOOD_CHANNEL_SCOPE_SLOTS=31 ; classic ESP32 DRAM cannot fit the default 255 with LoRa OTA
-  -D OTA_HEAP_CONTEXT=1           ; keep the idle mOTA workspace out of static DRAM
 ;  -D MESH_PACKET_LOGGING=1
 ;  -D MESH_DEBUG=1
 build_src_filter = ${Heltec_lora32_v2.build_src_filter}

variants/lilygo_tbeam_SX1262/platformio.ini

@@ -171,7 +171,6 @@ build_flags =
   -D MAX_NEIGHBOURS=50
   -D WITH_MQTT_BRIDGE=1
   -D FLOOD_CHANNEL_SCOPE_SLOTS=31 ; retain scope support within this observer's tight internal DRAM
-  -D OTA_HEAP_CONTEXT=1           ; keep the idle mOTA workspace out of static DRAM
   -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MQTT_MAX_PACKET_SIZE=1024
 ;  -D MQTT_DEBUG=1