Add readme with video demo

docs/DEBUGGING_SAFETY.md

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+# Debugging Panda Safety with Replay Drive + LLDB
+
+By default, `libsafety.so` is built with optimizations and stripped symbols, which makes C-level debugging impractical.
+This workflow fixes that by:
+
+1. Building `libsafety` with debug symbols and no optimizations.
+2. Running `replay_drive.py` with a user-provided route.
+3. Attaching LLDB automatically from VS Code.
+
+---
+
+## Building with Debug Symbols
+
+Rebuild `libsafety` with the `--unoptimized` flag:
+
+```bash
+scons -u -j$(nproc) --unoptimized
+```
+
+This enables the debug flags:
+
+* `-g` (include symbols)
+* `-O0` (disable optimizations)
+* `-fno-omit-frame-pointer` (keep stack traces usable)
+
+---
+
+## Debugging Workflow
+
+1. **Build with debug symbols**
+
+   ```bash
+   scons -u -j$(nproc) --unoptimized
+   ```
+
+2. **Start the debugger in VS Code**
+
+    * Select **Replay drive + Safety LLDB**.
+    * Enter the route or segment when prompted.
+
+3. **Attach LLDB**
+
+    * When prompted, pick the running **`replay_drive` process**.
+    * ⚠️ Attach quickly, or `replay_drive` will start consuming messages.
+
+   ✅ Tip: Add a Python breakpoint at the start of `replay_drive.py` to pause execution and give yourself time to attach LLDB.
+
+4. **Set breakpoints in VS Code**
+   Breakpoints can be set directly in `libsafety.c` (or any C file).
+   No extra LLDB commands are required — just place breakpoints in the editor.
+
+5. **Resume execution**
+   Once attached, you can step through both Python and C safety code as CAN logs are replayed.
+
+---
+
+## Notes
+
+* Always rebuild with `--unoptimized` before debugging.
+* Use short routes for quicker iteration.
+* Pause `replay_drive` early to avoid wasting log messages.
+
+### Video
+
+[demo safety debug.mp4](assets/demo%20safety%20debug.mp4)