Clarify OTA companion source setup

docs/ota_easy.md

@@ -47,6 +47,28 @@ Both paths require:
 LoRa OTA packets are generated, received, and relayed only while `tempradio` is active. If any required
 window closes, the transfer stops making progress and can resume during a later overlapping window.
 
+### Choose the source radio
+
+Use an ESP32 **MeshCore companion** as the source node. It receives the update folder from the computer,
+then advertises it over LoRa. Connect to that companion either by USB serial or by WiFi. For USB serial, the
+companion firmware must include `OTA_FOLDER_SERIAL`; before starting the transfer, its USB CLI must accept:
+
+```text
+ota folder on
+```
+
+If that command reports that `OTA_FOLDER_SERIAL` is not built in, use the WiFi method below. Do **not** use
+a KISS modem: KISS firmware is a TNC/KISS frame interface and does not provide the MeshCore CLI or the
+OTA-folder transport that `motatool serve` requires.
+
+For a companion connected by WiFi, use its dedicated OTA seeder connection instead:
+
+```bash
+motatool serve --dir ./motas --tcp <companion-host>:5001 -v
+```
+
+Port `5001` is the OTA seeder port; it is separate from the companion application port (`5000`).
+
 ## Install `motatool`
 
 Install Rust if necessary, then install the standalone packaging and serving tool:
@@ -183,8 +205,9 @@ Close any serial terminal using the source node's USB port, find its device name
 motatool serve --dir ./motas --serial /dev/ttyACM0 -v
 ```
 
-Replace `/dev/ttyACM0` with the source node's serial device. `motatool` attaches the folder to the source,
-which advertises the update over LoRa while its temporary-radio window is active.
+Replace `/dev/ttyACM0` with the USB serial device of the source companion selected above.
+`motatool` attaches the folder to the source, which advertises the update over LoRa while its temporary-radio
+window is active. KISS modem serial ports cannot be used here.
 
 Leave this command running until the destination finishes downloading.
 

docs/ota_protocol.md

@@ -104,6 +104,15 @@ EndF trailer (fixed 56 bytes):
 
 The "reconstructed image" referenced by the manifest is the full `BODY || EndF` (what gets flashed).
 
+### ESP32 portable app-slot profile
+
+ESP32 companion firmware is installed over USB and is exempt from the portable-slot limit. Every other
+ESP32 artifact, including room, sensor, and repeater roles, must fit the legacy slot from `0x10000` up to
+`0x150000` (`0x140000`, 1,310,720 bytes), including the 56-byte `EndF` trailer. The build checks both that
+limit and the target's actual app partition. For every ESP32 repeater, `build.sh` also exposes an explicit
+`*_lora_ota_no_external_sensors` artifact: the ordinary repeater remains sensor-enabled, while that sibling
+also disables optional external-sensor drivers for LoRa distribution.
+
 > **Implementer note:** the bootloader (and any non-Arduino consumer) MUST locate the body extent by
 > scanning for `EndF`, never by trusting a stored size — see the bootloader contract in §12.
 
@@ -538,6 +547,13 @@ MotaDesc wire (38 B): mid[4] target_id(4) fw_version(4) codec(1) flags(1)
 status: 0 = OK, non-zero = error (out of range / past EOF).
 ```
 
+**What to plug into `--serial`.** Use the USB serial console of an ESP32 MeshCore **companion** built with
+`OTA_FOLDER_SERIAL`. The companion is the required source node and must have a working LoRa radio plus an
+`ota folder on` command; that command confirms it can host and advertise the folder. A **KISS modem will not
+work**: KISS firmware exposes a TNC/KISS frame interface, not the MeshCore CLI and `mota-seeder`
+request/response transport. A companion connected over WiFi is the alternative source connection: use its
+dedicated seeder port with `motatool serve --tcp <host>:5001`.
+
 Device CLI: `ota folder on` (attach + announce), `ota folder` (list), `ota folder off`. Build flag
 `OTA_FOLDER_SERIAL` (default stream = console `Serial`; override `OTA_FOLDER_SERIAL_STREAM` + define
 `OTA_FOLDER_SERIAL_BEGIN` for a dedicated UART). On an ESP32 WiFi companion the node also runs a second