diff --git a/build.sh b/build.sh
index 8ea83b40..8b65e0a6 100755
--- a/build.sh
+++ b/build.sh
@@ -162,10 +162,26 @@ build_firmware() {
   fi
   EMBEDDED_VERSION_STRING="${FIRMWARE_VERSION}${BUILD_NUMBER_SUFFIX}${VARIANT_TAG}-${COMMIT_HASH}"
 
+  # Release channel. The observer pull-OTA fetches its slim per-variant manifest
+  # from <OTA_MANIFEST_BASE>/<OTA_VARIANT>.json, so this URL IS the channel: a
+  # device only ever sees updates published under the base it was built with.
+  # Override OTA_MANIFEST_BASE_URL to publish a parallel channel (e.g. beta);
+  # unset gives the production channel.
+  #
+  # Deliberately injected here rather than declared in variants/*/platformio.ini
+  # (where it used to be duplicated 28 times), for symmetry with OTA_VARIANT and
+  # so a plain `pio run` leaves BOTH macros undefined — which is what makes
+  # ESP32Board.cpp's "ERR: OTA not configured (build via build.sh)" guard fire on
+  # dev builds. Do not add a default in a header: that would silently arm OTA on
+  # locally built firmware. Note that PLATFORMIO_BUILD_FLAGS cannot reliably
+  # override a -D coming from build_flags (SCons reorders -U/-D), which is why
+  # the .ini declarations were removed rather than overridden.
+  OTA_MANIFEST_BASE_URL="${OTA_MANIFEST_BASE_URL:-https://observer.gessaman.com/v}"
+
   # add firmware version info to end of existing platformio build flags in environment vars.
   # OTA_VARIANT is the env name ($1) — it selects this build's slim per-variant manifest
   # (<OTA_MANIFEST_BASE>/<OTA_VARIANT>.json) that the observer pull-OTA fetches.
-  export PLATFORMIO_BUILD_FLAGS="${PLATFORMIO_BUILD_FLAGS} -DFIRMWARE_BUILD_DATE='\"${FIRMWARE_BUILD_DATE}\"' -DFIRMWARE_VERSION='\"${EMBEDDED_VERSION_STRING}\"' -DOTA_VARIANT='\"$1\"'"
+  export PLATFORMIO_BUILD_FLAGS="${PLATFORMIO_BUILD_FLAGS} -DFIRMWARE_BUILD_DATE='\"${FIRMWARE_BUILD_DATE}\"' -DFIRMWARE_VERSION='\"${EMBEDDED_VERSION_STRING}\"' -DOTA_VARIANT='\"$1\"' -DOTA_MANIFEST_BASE='\"${OTA_MANIFEST_BASE_URL}\"'"
 
   # disable debug flags if requested
   disable_debug_flags
diff --git a/variants/heltec_t190/platformio.ini b/variants/heltec_t190/platformio.ini
index 96c1bb28..11bfaec6 100644
--- a/variants/heltec_t190/platformio.ini
+++ b/variants/heltec_t190/platformio.ini
@@ -112,7 +112,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
@@ -205,7 +204,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D ROOM_PASSWORD='"hello"'
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
diff --git a/variants/heltec_v3/platformio.ini b/variants/heltec_v3/platformio.ini
index 541a6c96..5c29fa2c 100644
--- a/variants/heltec_v3/platformio.ini
+++ b/variants/heltec_v3/platformio.ini
@@ -123,7 +123,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
@@ -204,7 +203,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D ROOM_PASSWORD='"hello"'
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
@@ -493,7 +491,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
@@ -543,7 +540,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D ROOM_PASSWORD='"hello"'
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
diff --git a/variants/heltec_v4/platformio.ini b/variants/heltec_v4/platformio.ini
index caffe9b4..3facd287 100644
--- a/variants/heltec_v4/platformio.ini
+++ b/variants/heltec_v4/platformio.ini
@@ -162,7 +162,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
@@ -214,7 +213,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
@@ -317,7 +315,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D ROOM_PASSWORD='"hello"'
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
@@ -357,7 +354,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D ROOM_PASSWORD='"hello"'
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
diff --git a/variants/lilygo_t3s3/platformio.ini b/variants/lilygo_t3s3/platformio.ini
index 8c93d6b3..446307e3 100644
--- a/variants/lilygo_t3s3/platformio.ini
+++ b/variants/lilygo_t3s3/platformio.ini
@@ -116,7 +116,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
 ;  -D MQTT_DEBUG=1
@@ -162,7 +161,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D ROOM_PASSWORD='"hello"'
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
diff --git a/variants/lilygo_tbeam_1w/platformio.ini b/variants/lilygo_tbeam_1w/platformio.ini
index cdcf3126..6849018e 100644
--- a/variants/lilygo_tbeam_1w/platformio.ini
+++ b/variants/lilygo_tbeam_1w/platformio.ini
@@ -209,7 +209,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D PERSISTANT_GPS=1
@@ -256,7 +255,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D ROOM_PASSWORD='"hello"'
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D PERSISTANT_GPS=1
diff --git a/variants/lilygo_tbeam_SX1262/platformio.ini b/variants/lilygo_tbeam_SX1262/platformio.ini
index 0149e27b..6d381a9d 100644
--- a/variants/lilygo_tbeam_SX1262/platformio.ini
+++ b/variants/lilygo_tbeam_SX1262/platformio.ini
@@ -161,7 +161,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
 ;  -D MQTT_DEBUG=1
@@ -204,7 +203,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D ROOM_PASSWORD='"hello"'
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
diff --git a/variants/lilygo_tbeam_SX1276/platformio.ini b/variants/lilygo_tbeam_SX1276/platformio.ini
index 160d5ac9..04821471 100644
--- a/variants/lilygo_tbeam_SX1276/platformio.ini
+++ b/variants/lilygo_tbeam_SX1276/platformio.ini
@@ -160,7 +160,6 @@ build_flags =
   -D MAX_NEIGHBOURS=50
   -D PERSISTANT_GPS=1
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
 ;  -D MQTT_DEBUG=1
@@ -203,7 +202,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D ROOM_PASSWORD='"hello"'
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
diff --git a/variants/lilygo_tbeam_supreme_SX1262/platformio.ini b/variants/lilygo_tbeam_supreme_SX1262/platformio.ini
index 78c18198..53871835 100644
--- a/variants/lilygo_tbeam_supreme_SX1262/platformio.ini
+++ b/variants/lilygo_tbeam_supreme_SX1262/platformio.ini
@@ -120,7 +120,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
@@ -163,7 +162,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D ROOM_PASSWORD='"hello"'
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
diff --git a/variants/lilygo_tlora_v2_1/platformio.ini b/variants/lilygo_tlora_v2_1/platformio.ini
index 28d22605..8558cc57 100644
--- a/variants/lilygo_tlora_v2_1/platformio.ini
+++ b/variants/lilygo_tlora_v2_1/platformio.ini
@@ -157,7 +157,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_TASK_STACK_SIZE=16384
@@ -203,7 +202,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D ROOM_PASSWORD='"hello"'
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_TASK_STACK_SIZE=16384
diff --git a/variants/rak3112/platformio.ini b/variants/rak3112/platformio.ini
index e17550dd..b1b57525 100644
--- a/variants/rak3112/platformio.ini
+++ b/variants/rak3112/platformio.ini
@@ -113,7 +113,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
@@ -177,7 +176,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D ROOM_PASSWORD='"hello"'
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
diff --git a/variants/station_g2/platformio.ini b/variants/station_g2/platformio.ini
index 8a95e992..d64ce398 100644
--- a/variants/station_g2/platformio.ini
+++ b/variants/station_g2/platformio.ini
@@ -187,7 +187,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D ROOM_PASSWORD='"hello"'
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
@@ -306,7 +305,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
diff --git a/variants/xiao_s3_wio/platformio.ini b/variants/xiao_s3_wio/platformio.ini
index 5ed8a4bc..8e3ec15d 100644
--- a/variants/xiao_s3_wio/platformio.ini
+++ b/variants/xiao_s3_wio/platformio.ini
@@ -103,7 +103,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1
@@ -147,7 +146,6 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D ROOM_PASSWORD='"hello"'
   -D WITH_MQTT_BRIDGE=1
-  -D OTA_MANIFEST_BASE='"https://observer.gessaman.com/v"'
   -D MAX_MQTT_BROKERS=3
   -D MQTT_MAX_PACKET_SIZE=1024
   -D MQTT_DEBUG=1