diff --git a/zephcore/boards/common/esp32_common.conf b/zephcore/boards/common/esp32_common.conf
index 61a6e91..79dbc29 100644
--- a/zephcore/boards/common/esp32_common.conf
+++ b/zephcore/boards/common/esp32_common.conf
@@ -75,10 +75,10 @@ CONFIG_BT_PRIVACY=y
 # (CONFIG_ZEPHCORE_MEM_STATS, devdocs/tools/mem_load.py: fresh pairing, bonded
 # reconnects, protocol golden over BLE and TCP, bulk contact dump), peak 724 B,
 # so 2048 (2.8x). Was 4096.
-# The controller task is not trimmable here: on S3/C3 the HAL hardcodes its
-# stack to 4096 (components/bt/controller/esp32c3/bt.c) and
-# ESP32_BT_CONTROLLER_STACK_SIZE is only a lower-bound check; on classic ESP32
-# it is the real size but that controller (BTDM) was not measured.
+# The controller task (ESP32_BT_CONTROLLER_STACK_SIZE, default 4096) is not set
+# here: classic ESP32 (BTDM) and the C6 controller were not measured and keep
+# the default. S3 and C3 trim it in esp32c3s3_common.conf, where the symbol
+# became the real stack size with hal_espressif b16851b3c2 (2026-10-06).
 CONFIG_BT_TX_PROCESSOR_STACK_SIZE=2048
 CONFIG_BT_RX_STACK_SIZE=4096
 
diff --git a/zephcore/boards/common/esp32c3s3_common.conf b/zephcore/boards/common/esp32c3s3_common.conf
index 5f93e9b..a685656 100644
--- a/zephcore/boards/common/esp32c3s3_common.conf
+++ b/zephcore/boards/common/esp32c3s3_common.conf
@@ -27,3 +27,21 @@
 # Repeater builds do not use this value: wifi_ota.conf, appended later, sets
 # the heap back to 64 KB for the WiFi driver.
 CONFIG_HEAP_MEM_POOL_SIZE=45056
+
+# ========== BLE controller task stack ==========
+# Default 4096 (drivers/bluetooth/hci/Kconfig.esp32).  Since hal_espressif
+# b16851b3c2 (Zephyr pin 74b7173e9c9, 2026-10-06) this symbol is the real size
+# of the controller task's stack on these chips; before that
+# components/bt/controller/esp32c3/bt.c hardcoded 4096 and the symbol was only
+# a lower-bound check.  The same symbol is the size the controller is
+# configured with (esp_bt.h, .controller_task_stack_size), and the HAL refuses
+# to start BT if the controller asks for more than the buffer.
+#
+# Measured on a XIAO ESP32-S3 companion (2026-10-06, CONFIG_ZEPHCORE_MEM_STATS,
+# devdocs/tools/mem_load.py: fresh pairing, bonded reconnects, protocol golden
+# over BLE, 8 KB sign, 121-contact dump over BLE): peak 980 B at 4096, and
+# 964 B in the same run with the stack at 2048.  2048 is 2.1x the peak and
+# returns 2 KB of dram0, which the no-PSRAM Wi-Fi + BLE companions (Heltec V3,
+# Wireless Tracker) need.  Not measured with a Wi-Fi station link up
+# (coexistence), and not measured on C3 hardware.
+CONFIG_ESP32_BT_CONTROLLER_STACK_SIZE=2048