docs(wiki): printer USB transport + open-question for the provisioning

New concepts/printer-usb-transport.md (the seam, usblp char device,
reachability-only status, threat model). open-questions #14: confirm the
on-site printer is USB and bake the usblp + udev write-access rule into the
appliance image (provisioning, not app code; unverified on hardware). Updated
rongta-printer.md (USB transport note), index.md, log.md.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

wiki/log.md

@@ -1588,3 +1588,21 @@ worker (one in-flight send/lamp, re-converges to the latest state → final stat
 in the UI works without a server restart. Workspace build+lint+test green (163 server tests). See
 [[dingtian-relay]] ("offline despite ping" + secret re-merge), [[button-light-indicator]] (serialized
 sends + hot-reload).
+
+## [2026-06-24] build | Printer USB transport behind the ESC/POS render layer
+The ESC/POS printer drivers were **TCP-only** (every path went through `sendRaw`/`probe` to a raw
+socket on port 9100); the original BOM intended one adapter to cover "USB **or** network". Added a
+**USB transport** behind the existing render layer without touching a single `render*()` function:
+a discriminated `Transport` (`transportFromConfig` → `{kind:"tcp",host,port}` | `{kind:"usb",
+devicePath}`) and `sendTo`/`probeTo` dispatchers in `printer-escpos.ts`; USB writes the same ESC/POS
+bytes to a kernel **`usblp`** char device (`/dev/usb/lp0`) via a plain `fs` write — **no libusb/CUPS/
+native dep** (keeps MIT-only + minimal-deps appliance). `cashino` + `rongta` resolve a Transport once;
+both are reachability-only over USB, and the Rongta's HTTP **status page degrades to the open-the-node
+probe** over USB (no guessed paper/cover — the standing honesty rule). Non-`usb` configs are unchanged
+(host-only = TCP), so no migration. Setup UI gains a **Connection** select + **USB device** field;
+host/port made not-required so a USB printer needs neither. Tests: `printer-escpos.test.ts` (USB writes
+the exact rendered bytes; probe present/absent; `transportFromConfig` TCP back-compat) +
+`printer-cashino.test.ts` (USB-configured driver prints to the node, ready/offline). Devices suite
+green (29). **Flagged open-questions #14**: confirm the on-site printer is USB and bake the
+**usblp + udev write-access** rule into the appliance image (provisioning, not app code; unverified on
+hardware). See [[printer-usb-transport]], [[rongta-printer]].