letter-shell-integration

# letter-shell Integration ## Overview Use this skill to integrate letter-shell as an embedded debug console safely. Prove the transport, shell task or polling loop, command registration, and authorization policy before exposing commands that modify flash, reset devices, or change production state. ## When To Use Use this skill when: - The user wants to add or debug letter-shell in MCU firmware. - Shell input/output is missing, commands are not found, history/completion behaves wrong, or shell blocks the system. - The task involves UART shell, RTT shell, RTOS shell task, command export macros, login/password, or runtime debug commands. Do not use this skill when the serial port itself is not trustworthy. Use `embedded-serial-log-debug` first. ## First Questions Ask for: - Target MCU/RTOS/compiler and letter-shell version or source. - Transport backend: UART, USB CDC, RTT, TCP, or custom. - Runtime model: polling loop, interrupt-driven RX, DMA RX, or RTOS task. - Existing shell config, command registration method, and linker section behavior. - Whether shell is allowed in production builds. - Commands that may be destructive, such as erase, reset, format, calibration, network write, or firmware update. ## Integration Checklist 1. Prove transport first. Confirm raw RX/TX works before debugging shell parsing. 1. Create one shell instance. Bind it to explicit read/write functions and initialize it once. 1. Decide scheduling model. Use a polling loop for simp...