[debugger] Add native ratatui TUI debugger PoC for GSOC 2026

[alaotach]

What this PR does

This PR adds the initial Proof-of-Concept for a native TUI debugger for Miri.

The debugger is:

• Built directly inside the Miri repository (no external process)
• Uses ratatui + crossterm for a clean terminal interface
• Hooked straight into the interpreter loop in src/concurrency/thread.rs
• Zero overhead when --debugger is not passed (single Option check)
• Fully functional PoC already working on real Miri executions

Features implemented in this PoC

• Step forward (n / space) through every MIR statement
• Reverse stepping (b) using snapshot history (up to 1000 states)
• Run to main (m) with live fast-forward animation
• Run to end (e)
• Run to frame (p / P)
• Live stack search (/)
• Pretty-printed locals pane with semantic colors (initialized, uninit, dead, pointers)
• Control-flow graph visualization with current block highlight
• Output pane capturing stdout/stderr through Miri shims
• Memory pane showing live/deallocated allocations
• Mouse support + full status bar with keybinding reference

Demo

Full PoC demo video:
https://drive.google.com/file/d/1VofdVai_xadl83qbdcmp_NBFb5e0o74-/view?usp=sharing

How to test

./miri-run.bat run <file-name> --debugger

[rustbot]

Thank you for contributing to Miri! A reviewer will take a look at your PR, typically within a week or two.
Please remember to not force-push to the PR branch except when you need to rebase due to a conflict or when the reviewer asks you for it.

[rustbot]

☔ The latest upstream changes (possibly #4950) made this pull request unmergeable. Please resolve the merge conflicts.

[zjp-CN]

Thanks for the work. I'd like to share the debugger I backported to kmiri (a fork of miri for OS development) based on this PR, with some refactoring and improvements.