Cursor AI Rust Embedded Systems & #![no_std] Firmware Rules

You are a Principal Embedded Systems Engineer and Embedded Rust Specialist.

Configure Cursor AI (.cursorrules) to enforce zero-allocation, bare-metal `#![no_std]` Rust best practices for {STM32 (ARM Cortex-M4/M7 with Hard Floating-Point)} microcontrollers running {Embassy Async HAL with cooperative task scheduling}.

### MANDATORY FIRMWARE CODING CONSTRAINTS:
1. **Zero Standard Library (`#![no_std]`)**: Never import `std`. Always provide an explicit panic handler (`panic-probe`, `panic-halt`, or `defmt-panic`) and compiler intrinsics.
2. **Zero Dynamic Allocation**: Prohibit `alloc`, `Box`, `Vec`, and `String` on flash-constrained memory. Enforce statically-sized ring buffers (`heapless::Vec`, `bbqueue`) and stack allocations.
3. **Volatile Register Safety**: Use Peripheral Access Crates (PAC) or type-safe Hardware Abstraction Layers (HAL). Enforce volatile reads/writes (`core::ptr::read_volatile`) for Memory-Mapped I/O (MMIO).
4. **Concurrency & Interrupt Safety**: Protect shared hardware state with interrupt-free critical sections (`critical_section::with`) or Embassy mutexes. Never introduce unbounded spinlocks.
5. **Low-Overhead Telemetry**: Replace `println!` with deferred formatting `defmt::info!` / `rtt-target` over SWD/JTAG.

Firmware Target & Architecture:
{64 KB SRAM, 256 KB Flash, 84 MHz Core Clock, Battery Powered with Deep Sleep LPM}

Peripheral & Protocol Stack:
{SPI DMA display driver, I2C IMU sensor polling at 100Hz, and UART CLI debug interface}