feat(firmware): add the 16MB flash profile the C6 fleet runs on (#1877)

The 4MB and display layouts have 1.875MB and 2MB OTA slots, sized for 4MB
and 8MB parts. A 16MB C6 (DevKitC-1 N16) has no layout in the tree at all,
so building for one meant hand-editing sdkconfig -- and a smaller table
written over a deployed 16MB node relocates NVS and destroys its
provisioning, which is why this belongs in the repo rather than in a
workstation's untracked sdkconfig.

Two 4MB OTA slots, plus a 64K coredump partition and an 8000K FAT volume
for on-node storage. Rollback is enabled so an OTA'd image that cannot
confirm itself is reverted by the bootloader.

Layered, not inherited: sdkconfig.defaults.esp32c6 keeps its 4MB layout so
the common 4MB devkit is never silently repartitioned.


Claude-Session: https://claude.ai/code/session_01PVWMiHQifoYXL7uL3bphrZ

Co-authored-by: Joe <joe@GitDev.hedgehog>
Co-authored-by: claude-flow <ruv@ruv.net>

firmware/esp32-csi-node/partitions_16mb.csv

@@ -0,0 +1,25 @@
+# ESP32-C6 CSI Node - 16MB flash partition table
+# For boards with 16MB flash (e.g. ESP32-C6 DevKitC-1 N16).
+#
+# Two 4MB OTA slots. The app is ~1.04MB, so the slots are far larger than
+# needed for the binary alone -- the size is chosen so an OTA never has to
+# care how much the image has grown, and it leaves room for a coredump
+# partition and an 8MB FAT volume for on-node storage.
+#
+# The 4MB and display layouts do not fit this: their slots are 1.875MB and
+# 2MB, sized for 4MB and 8MB parts respectively.
+#
+# Usage: set in sdkconfig, or use the matching defaults file:
+#   CONFIG_PARTITION_TABLE_CUSTOM_FILENAME="partitions_16mb.csv"
+#   idf.py -DSDKCONFIG_DEFAULTS="sdkconfig.defaults;sdkconfig.defaults.esp32c6;sdkconfig.defaults.16mb" build
+#
+# Verify before flashing an already-deployed node: a smaller table written
+# over a 16MB node relocates NVS and destroys its provisioning.
+# Name, Type, SubType, Offset, Size, Flags
+nvs,data,nvs,0x9000,24K,
+otadata,data,ota,0xf000,8K,
+phy_init,data,phy,0x11000,4K,
+ota_0,app,ota_0,0x20000,4M,
+ota_1,app,ota_1,0x420000,4M,
+coredump,data,coredump,0x820000,64K,
+storage,data,fat,0x830000,8000K,

firmware/esp32-csi-node/sdkconfig.defaults.16mb

@@ -0,0 +1,23 @@
+# ESP32-C6 CSI Node - 16MB Flash SDK Configuration
+# For boards with 16MB flash (e.g. ESP32-C6 DevKitC-1 N16).
+#
+# Layered on top of sdkconfig.defaults.esp32c6, which keeps a 4MB layout
+# because 4MB C6 devkits are the common case and must not be silently
+# repartitioned by inheriting this.
+#
+# Build:
+#   idf.py -DSDKCONFIG_DEFAULTS="sdkconfig.defaults;sdkconfig.defaults.esp32c6;sdkconfig.defaults.16mb" build
+#
+# Confirm before flashing a deployed node: /ota/status must report
+# max_size 4194304. Writing a smaller table over a 16MB node relocates NVS
+# and destroys its provisioning.
+
+CONFIG_ESPTOOLPY_FLASHSIZE_16MB=y
+CONFIG_ESPTOOLPY_FLASHSIZE="16MB"
+CONFIG_PARTITION_TABLE_CUSTOM=y
+CONFIG_PARTITION_TABLE_CUSTOM_FILENAME="partitions_16mb.csv"
+
+# Firmware rollback: an OTA'd image boots PENDING_VERIFY and must confirm
+# itself, or the bootloader reverts on the next boot. See ota_rollback_* in
+# ota_update.c for when confirmation happens and why.
+CONFIG_BOOTLOADER_APP_ROLLBACK_ENABLE=y