docs(inventory): note blocking loop + raw-format diagnostic

code/inventory/README.md

@@ -31,8 +31,15 @@ result as an RS232 stream, so there is no special barcode driver call: the app
 opens the serial port and reads it. The scanner is on the top internal slot,
 which is port **D**, so the device is `TTY:D` (`bcode.c`).
 
-The scan loop is asynchronous: it waits on the scanner and the keyboard at the
-same time, so a scan is processed immediately and Esc quits at any point.
+The scan loop is blocking: it reads the scanner and prints each barcode; you
+exit via the System screen. (An asynchronous scan-or-Esc loop was tried but
+panicked the Window Server: on SIBO the keyboard is event-driven through the
+window server, not a raw `CON:` byte read, and a proper async loop needs the
+Window Server event API, whose reference manual is not in this repo's `docs/`.)
+
+This Phase 1 build also prints the byte length of each decoded barcode, so the
+exact format the scanner emits for a UPC can be confirmed before Phase 2 uses
+it as a database key.
 
 ## Things to confirm on the device
 
@@ -44,8 +51,7 @@ the SDK docs but may need adjusting once you build and test:
   `p_iow(chan, P_FSET, &config)` (E_CONFIG, `p_config.h`) after opening.
 - **Terminator.** `BCODE_TERM` in `bcode.h` is set to CR (`0x0D`), the common
   case. Change it if your scanner suffixes LF or something else.
-- **Esc key code.** `KEY_ESC` in `scan.c` is `27`; adjust if the console
-  delivers a different code.
-- **`CON:` async read.** Phase 1 reads single keystrokes asynchronously from
-  `CON:`; if that behaves differently on your unit, the keyboard handling in
-  `scan.c` is where to look.
+- **Raw scan format.** The build prints `len=NN [text]` per scan. Confirm
+  whether a UPC arrives as exactly 12 digits or with extra characters (a
+  leading zero / EAN-13, or a symbology prefix); Phase 2 normalises to the
+  database key based on this.