[13] VKP80III / K80 serial thermal printer emulator and screen

[jvwaldrich0]

Task 13 of 16 — these are sequential, do them in order.

Previous: #15 · Next: #17

Port target: cloudpark-toolkit (Go) → this repo (Rust). Reference paths below are relative to that repo.

Goal

The VKP80III / K80 thermal-printer emulator on a serial line, plus its screen.

Scope

• Open the port: ttyS1, ttyS2, or pty (allocate a pty and print the slave path). Baud from --baud (ignored for pty). Crate: serialport or raw nix termios.
• Answer the host's probes so it believes a real printer is attached:
  • GS I FF = 1D 49 FF (model query) → 02 05 (VKP80)
  • DLE EOT 0x14 = 10 04 14 (status query) → 10 04 00 00 00 00 (paper present, ticket removed)
• Ticket framing: serial has no end-of-ticket marker — flush after 300 ms of line silence and treat the buffer as one ticket, rendered to PDF via task 10. Keep the window a named constant.
• Ticket counter exposed to the TUI.

Screen: menu Get info — port, baud, pty path, tickets saved, last ticket filename + log pane.

Reference

cloudpark-toolkit/internal/serialprinter/serialprinter.go, device_linux.go, serialprinter_test.go, internal/tui/printer.go

Done when

• Test: feeding a captured ESC/POS stream into the emulator writes exactly one PDF.
• Model and status queries get the exact byte replies above.
• A busy/absent serial port shows a readable error, not a panic.