[codex] Slim ARM kernel arch with bluekernel_arch

[xuchang-vivo]

Summary

This PR slims down the ARM kernel architecture layer by moving Cortex-M-only building blocks into bluekernel_arch.

The kernel side now keeps the OS-specific exception and scheduler glue, while architecture-owned pieces such as NVIC/SCB/SysTick/MPU wrappers, xPSR and exception-frame helpers, HardFault decoding, IRQ registry logic, saved Context, local IRQ helpers, and the fixed Cortex-M exception vector layout live under kernel/arch.

Why

The main goal is to make kernel/src/arch/arm smaller and more focused. Cortex-M register layouts, exception frames, vector-table slots, and raw architectural helpers do not depend on kernel policy, so keeping them in the kernel makes the kernel layer heavier than necessary and mixes two different responsibilities.

Putting those pieces into bluekernel_arch gives BlueOS a local, controllable architecture crate. That is useful for maintenance because BlueOS uses GN: rustflags are not transparently forwarded into external Rust dependencies. For example, using the upstream cortex-m crate's FPU register support may require passing feature/cfg such as has_fpu; with the current GN integration that can force changes around an external dependency boundary. Maintaining a small in-tree low-level architecture crate avoids that friction, and with current AI-assisted development the cost of writing and maintaining these thin register/assembly wrappers is manageable.

Changes

• Re-export safe Cortex-M policy APIs from bluekernel_arch and remove duplicate kernel-side implementations.
• Move Cortex-M HardFault handling and IRQ registry code into bluekernel_arch.
• Move the saved Cortex-M Context type into bluekernel_arch, including hard-float ABI support.
• Define the Cortex-M exception vector slots in bluekernel_arch with global_asm!; the kernel now only provides the OS-specific handlers.
• Add linker defaults so NMI, MemManage, BusFault, and UsageFault can fall back to the HardFault handler when the kernel does not override them.
• Keep GOT sections inside the copied data range so optimized Rust code that emits GOT references still gets initialized correctly.
• Replace the old IsrContext alias usage with ExceptionStackFrame.
• Remove the CMSIS validation target's external cortex-m crate dependency and route its NVIC test shims through bluekernel_arch.

Validation

• Formatted touched Rust files with the fixed BlueOS toolchain rustfmt:
  /Users/xuchang/workspace/bluekernel_toolchain/usr/local/bin/rustfmt ...
• Checked touched GN formatting:
  gn format --dry-run adapter/cmsis/BUILD.gn
• Checked CMSIS validation Rust formatting:
  /Users/xuchang/workspace/bluekernel_toolchain/usr/local/bin/rustfmt --check adapter/cmsis/src/validation.rs
• ninja -C out/qemu_mps2_an385.release kernel/arch:bluekernel_arch kernel/kernel:blueos
• ninja -C out/qemu_mps2_an385.release kernel/adapter/cmsis:adapter_validation
• ninja -C out/qemu_mps2_an385.release kernel/adapter/cmsis:run_adapter_validation
• ninja -C out/qemu_mps2_an385.release check_all

Note: run_adapter_validation still prints the existing TC_osEventFlagsNew_1 FAILED CMSIS validation case, but the ninja target exits successfully as before.

[xuchang-vivo]

build_prs

[github-actions]

Job is started, see https://github.com/vivoblueos/kernel/actions/runs/25621202208.

[github-actions]

✅ All jobs completed successfully, see https://github.com/vivoblueos/kernel/actions/runs/25621202208.

[xuchang-vivo]

build_prs

[github-actions]

Job is started, see https://github.com/vivoblueos/kernel/actions/runs/25632972890.

[github-actions]

❌ Job failed. Failed jobs: build_and_check_boards (failure), see https://github.com/vivoblueos/kernel/actions/runs/25632972890.

[xuchang-vivo]

build_prs

[github-actions]

Job is started, see https://github.com/vivoblueos/kernel/actions/runs/25633396644.

[github-actions]

✅ All jobs completed successfully, see https://github.com/vivoblueos/kernel/actions/runs/25633396644.