acw: airtime-scale jitter caps, companion surroundings awareness

- flood retransmit jitter now capped at min(2000ms, 6·airtime) instead of
  fixed 2000ms — spreads tighter at SF7, unchanged at SF8
- reactive per-dupe backoff cap now min(2000ms, 12·airtime), keeps
  semantic of "push past ~12 relay slots"
- contention ring 16 → 24 for 50-neighbor hilltops
- companions passively track heard floods (warms EMA without forwarding)
  and spread their own TX by up to min(1000ms, 3·airtime), hopefully
  fixing repeaters missing companion's first transmission

config cleanup:
- move BLE TX buffer bumps (ACL_TX=12 etc.) from zephcore_common.conf to
  esp32_common.conf — the Espressif blob needs them, nRF doesn't, and
  the bumps were overflowing nRF52840 RAM
- remove CONFIG_ZEPHCORE_MAX_CONTACTS=510 overrides from 5 nRF52840
  companion boards; Kconfig default of 350 fits with comfortable margin
  (wio prod: 91% → 79% RAM)

zephcore/boards/common/esp32_common.conf

@@ -15,6 +15,15 @@ CONFIG_BT_PRIVACY=y
 # BLE thread stacks — ESP32 software BLE controller needs larger stacks
 CONFIG_BT_TX_PROCESSOR_STACK_SIZE=2048
 
+# BLE TX buffers — the Espressif BLE controller blob bursts more aggressively
+# than the nRF softdevice and will deadlock the system workqueue if ACL TX
+# buffers run dry (bt_hci_cmd_alloc(K_FOREVER) blocks the cooperative syswq).
+# EVT_RX must strictly exceed ACL_TX (enforced by BUILD_ASSERT in buf.h).
+CONFIG_BT_BUF_ACL_TX_COUNT=12
+CONFIG_BT_L2CAP_TX_BUF_COUNT=12
+CONFIG_BT_CONN_TX_MAX=12
+CONFIG_BT_BUF_EVT_RX_COUNT=14
+
 # ========== Heap ==========
 # ESP32 BLE stack requires larger heap (override zephcore_common 2KB default)
 CONFIG_HEAP_MEM_POOL_SIZE=32768

zephcore/boards/common/prod.conf

@@ -1,22 +1,22 @@
-# Production Config - Common to ALL boards (Companion & Repeater)
-# Build: west build -b <board> zephcore --pristine -- \
-#   -DEXTRA_CONF_FILE="boards/common/prod.conf"
-#
-# Disables logging for smaller binary and lower power consumption.
-# USB CDC still works for CLI commands on repeaters.
-
-# Disable logging subsystem (saves ~62KB flash, ~2-5mA power)
-CONFIG_LOG=n
-
-# Disable asserts (saves flash, removes CMake warning)
-CONFIG_ASSERT=n
-
-# Disable SEGGER RTT (saves ~4KB RAM ring buffer + init code)
-CONFIG_USE_SEGGER_RTT=n
-
-# Disable thread name strings (saves flash — only useful for debug)
-CONFIG_THREAD_NAME=n
-
-# Max contacts: Kconfig default is 350 (safe for 100KB ExtraFS).
-# Do NOT set here — EXTRA_CONF_FILE overrides board.conf, which would
-# prevent boards with more storage (Wio QSPI=510) from raising the limit.
+# Production Config - Common to ALL boards (Companion & Repeater)
+# Build: west build -b <board> zephcore --pristine -- \
+#   -DEXTRA_CONF_FILE="boards/common/prod.conf"
+#
+# Disables logging for smaller binary and lower power consumption.
+# USB CDC still works for CLI commands on repeaters.
+
+# Disable logging subsystem (saves ~62KB flash, ~2-5mA power)
+CONFIG_LOG=n
+
+# Disable asserts (saves flash, removes CMake warning)
+CONFIG_ASSERT=n
+
+# Disable SEGGER RTT (saves ~4KB RAM ring buffer + init code)
+CONFIG_USE_SEGGER_RTT=n
+
+# Disable thread name strings (saves flash — only useful for debug)
+CONFIG_THREAD_NAME=n
+
+# Max contacts: Kconfig default is 350 — fits nRF52840 RAM with ~10% headroom
+# and is safe for 100KB ExtraFS.  RAM-limited boards (xiao_nrf54l15=450,
+# xiao_esp32c3=300) override in their own board.conf.  Do not set here.

zephcore/boards/common/zephcore_common.conf

@@ -93,12 +93,11 @@ CONFIG_BT_BUF_ACL_RX_SIZE=251
 CONFIG_BT_BUF_ACL_TX_SIZE=251
 CONFIG_BT_L2CAP_TX_MTU=247
 
-# BLE TX buffers — default 3 is too low, causes system workqueue deadlock
-# when BLE activity bursts (DLE + param update + ATT) exhaust all buffers
-# and bt_hci_cmd_alloc(K_FOREVER) blocks the cooperative syswq forever.
-CONFIG_BT_BUF_ACL_TX_COUNT=12
-CONFIG_BT_L2CAP_TX_BUF_COUNT=12
-CONFIG_BT_CONN_TX_MAX=12
+# BLE TX buffers — platform-specific.  ESP32 gets a large bump in
+# esp32_common.conf to prevent syswq deadlock during BLE bursts (DLE +
+# param update + ATT exhausting buffers and bt_hci_cmd_alloc(K_FOREVER)
+# blocking the cooperative syswq).  nRF52 uses Zephyr defaults — RAM is
+# tight on nRF52840 and the nRF controller rarely deadlocks.
 
 # BLE RX thread stack — default 1200 too small for ATT handlers + logging + asserts
 CONFIG_BT_RX_STACK_SIZE=2048