docs: Emergency recovery guide for sliceanddice boot issues

EMERGENCY_RECOVERY.md

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+# Emergency Recovery Guide for sliceanddice
+
+## Problem Analysis
+
+Your sliceanddice NixOS system is in emergency mode. Based on the repository analysis:
+
+### Most Likely Causes:
+
+1. **Missing disko.nix import**: If you pulled/applied configuration from the `development` branch (commit `ba8fb7cb` or later), it references `./disko.nix` which doesn't exist on `master` branch.
+
+2. **Filesystem mounting failure**: The recent changes included:
+   - New disko partitioning scheme (btrfs subvolumes)
+   - Modified filesystem UUIDs and mount options
+   - New swap configuration
+
+3. **Boot generation limit**: Commit `963b83f1` capped systemd-boot generations to 5 to prevent `/boot` from filling (511M EFI partition).
+
+## Immediate Recovery Steps
+
+### Option 1: Boot into a previous generation (RECOMMENDED FIRST STEP)
+
+1. At boot, when you see the systemd-boot menu, press `Space` or `Esc` immediately
+2. Select an older NixOS generation from before your recent changes
+3. Press `Enter` to boot
+4. Once booted, you can investigate what went wrong
+
+### Option 2: Emergency mode recovery
+
+If you're already in emergency mode:
+
+```bash
+# 1. Check which filesystems are mounted
+mount | grep -E "/(boot|nix|home)"
+
+# 2. Check for filesystem errors
+journalctl -xb | grep -i "failed\|error\|emergency"
+
+# 3. Check if /boot is full
+df -h /boot
+
+# 4. Check filesystem mounts status
+systemctl list-units --type=mount --failed
+
+# 5. Try to mount root as read-write if needed
+mount -o remount,rw /
+```
+
+### Option 3: Rollback to stable master branch configuration
+
+If you're using `/etc/nixos/.dotfiles`:
+
+```bash
+# In emergency mode or from an older generation:
+cd /etc/nixos/.dotfiles
+
+# Check current branch and status
+git branch
+git status
+
+# If you're on development branch, switch to master
+git checkout master
+git pull origin master
+
+# Rebuild with stable config
+nixos-rebuild switch --flake /etc/nixos/.dotfiles#sliceanddice
+```
+
+## Known Issues from Recent Commits
+
+### Issue 1: disko.nix import on master branch
+- **Commit**: `ba8fb7cb` (on development branch only)
+- **Problem**: Imports `./disko.nix` which doesn't exist on master
+- **Solution**: Ensure you're using master branch, or cherry-pick disko.nix from development
+
+### Issue 2: Boot partition space
+- **Commit**: `963b83f1`
+- **Problem**: 511M EFI partition fills with initrds (~50MB each)
+- **Solution**: Already fixed with `boot.loader.systemd-boot.configurationLimit = 5`
+- **Check**: Run `df -h /boot` to verify space
+
+### Issue 3: Filesystem UUID changes
+- **Location**: `hosts/nixos/sliceanddice/hardware-configuration.nix`
+- **Current UUIDs**:
+  - Root: `b89f5dca-4b37-4062-bf1d-9e4ebfd61916` (ext4)
+  - Boot: `8824-4C5F` (vfat)
+  - Swap: `c570ec29-6025-456b-99d1-8f16b677835a`
+
+## Verification Commands
+
+Once you can boot normally, verify the configuration:
+
+```bash
+# Check current branch
+cd /etc/nixos/.dotfiles && git branch
+
+# Verify filesystem mounts
+findmnt / /boot /home /nix
+
+# Check boot partition space
+df -h /boot
+du -sh /boot/loader/entries/*
+
+# List available boot generations
+ls -lh /boot/loader/entries/
+
+# Check system status
+systemctl status
+journalctl -p err -b
+```
+
+## Prevention
+
+1. **Always test major changes**: Use `nixos-rebuild test` before `switch`
+2. **Keep old generations**: The configurationLimit=5 is set, but you can temporarily increase it
+3. **Monitor /boot space**: Run `df -h /boot` before rebuilds
+4. **Stick to one branch**: Use either `master` or `development`, not a mix
+
+## Contact Information
+
+If you need to restore from scratch:
+- Bootstrap script: `scripts/install-sliceanddice.sh`
+- Secrets: `secrets/sliceanddice-secrets.yaml` (encrypted with sops)
+- Hardware config: `hosts/nixos/sliceanddice/hardware-configuration.nix`
+
+## Architecture Notes
+
+- Laptop: MSI with Intel Tiger Lake UHD + NVIDIA RTX 3050 Ti Mobile
+- Storage: Samsung 870 EVO 500GB (`ata-Samsung_SSD_870_EVO_500GB_S62ANJ0R238724D`)
+- Graphics: Hybrid PRIME render offload (Intel for display, NVIDIA on-demand)
+- Kernel: Latest mainline (`pkgs.linuxPackages_latest`)

QUICKSTART.md

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+# Quick Recovery Guide - sliceanddice Emergency Mode
+
+## Fastest Solution (Do This First!)
+
+### Step 1: Boot Previous Generation
+
+1. **Reboot** your sliceanddice machine
+2. When you see the boot menu, press **Space** or **Esc** 
+3. **Select an older NixOS generation** (one from before the issue)
+4. Press Enter to boot
+
+That's it! You should now be back in a working system.
+
+---
+
+## Step 2: Prevent It From Happening Again
+
+Once you're booted into the working generation:
+
+```bash
+# Go to your dotfiles
+cd /etc/nixos/.dotfiles
+
+# Check which branch you're on
+git branch
+# If you see "development", that's likely the issue
+
+# Switch to stable master branch
+git checkout master
+git pull origin master
+
+# Make this the current system
+sudo nixos-rebuild switch --flake /etc/nixos/.dotfiles#sliceanddice
+
+# Reboot to test
+sudo reboot
+```
+
+---
+
+## What Happened?
+
+The `development` branch has new features but requires additional files:
+- `disko.nix` - disk configuration
+- `kbd-bl-ask.nix` - keyboard backlight
+- MSI-specific kernel patches
+- Power management features
+
+If you rebuilt with the development branch but those files weren't present, NixOS couldn't complete the build and entered emergency mode.
+
+---
+
+## Alternative: Fix in Emergency Mode
+
+If you can't access the boot menu:
+
+```bash
+# You should be at an emergency shell prompt
+# Remount root as writable
+mount -o remount,rw /
+
+# Fix the configuration
+cd /etc/nixos/.dotfiles
+git checkout master
+git reset --hard origin/master
+
+# Rebuild
+nixos-rebuild switch --flake .#sliceanddice
+
+# Reboot
+reboot
+```
+
+---
+
+## Need More Help?
+
+See the detailed guides:
+- **SOLUTION.md** - Full explanation and multiple recovery options
+- **EMERGENCY_RECOVERY.md** - Detailed technical recovery procedures  
+- **diagnose-emergency.sh** - Run this script to diagnose the issue
+
+Or run the diagnostic script:
+```bash
+bash diagnose-emergency.sh
+```
+
+---
+
+## Summary
+
+**Problem**: Configuration mismatch between branches  
+**Solution**: Boot previous generation, switch to master branch  
+**Prevention**: Stick to one branch (master is stable)

README-EMERGENCY.md

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+# 🆘 sliceanddice Emergency Mode - Recovery Instructions
+
+> **STATUS**: Your sliceanddice NixOS system is in emergency mode  
+> **CAUSE**: Configuration mismatch between master and development branches  
+> **SOLUTION**: Multiple recovery paths available (choose the easiest one for you)
+
+---
+
+## 🚀 Quick Fix (Recommended - 2 minutes)
+
+### Option 1: Boot Previous Generation (FASTEST!)
+
+1. **Reboot** the sliceanddice machine
+2. At the systemd-boot menu, press **`Space`** or **`Esc`**
+3. Select an **older NixOS generation** (from before the problem)
+4. Press **Enter** to boot
+
+✅ **Done!** You're back in a working system.
+
+Then prevent it from happening again:
+```bash
+cd /etc/nixos/.dotfiles
+git checkout master
+sudo nixos-rebuild switch --flake .#sliceanddice
+```
+
+---
+
+## 🔧 Automated Fix Script
+
+If you're in a working shell (emergency mode or booted from old generation):
+
+```bash
+cd /etc/nixos/.dotfiles
+sudo bash fix-emergency-auto.sh
+```
+
+This script will:
+- ✅ Detect the configuration problem
+- ✅ Switch to stable master branch  
+- ✅ Rebuild your system
+- ✅ Verify everything works
+
+---
+
+## 📖 Detailed Documentation
+
+Choose the guide that fits your situation:
+
+| File | Purpose | When to Use |
+|------|---------|-------------|
+| **QUICKSTART.md** | Fast recovery steps | You want the TL;DR |
+| **SOLUTION.md** | Complete explanation | You want to understand what happened |
+| **EMERGENCY_RECOVERY.md** | Technical deep-dive | You need detailed recovery procedures |
+| **diagnose-emergency.sh** | Diagnostic script | You want to see what's wrong |
+| **fix-emergency-auto.sh** | Automated fix | You want one-command recovery |
+
+---
+
+## 🔍 What Happened?
+
+**Short version**: The `development` branch has new features that require additional files. If you rebuilt using development branch config but the files weren't present, NixOS couldn't activate and dropped into emergency mode.
+
+**Files required by development branch**:
+- `disko.nix` - Disk/filesystem management
+- `kbd-bl-ask.nix` - Keyboard backlight config
+- `msi-ec-sword-kbd-disable.patch` - MSI laptop kernel patch
+- Power management features
+- Boot generation limiting
+
+**Current master branch**: ✅ Stable, working, doesn't need these files
+
+---
+
+## 🛠️ Recovery Paths
+
+### Path A: Previous Generation (Easiest)
+Boot from systemd-boot menu → Select older generation → Boot
+
+### Path B: Emergency Shell Fix
+```bash
+mount -o remount,rw /
+cd /etc/nixos/.dotfiles
+git checkout master
+nixos-rebuild switch --flake .#sliceanddice
+reboot
+```
+
+### Path C: Automated Script
+```bash
+sudo bash fix-emergency-auto.sh
+```
+
+### Path D: Rescue Media
+Boot NixOS installer → Mount filesystems → Chroot → Fix config
+
+---
+
+## ⚡ After Recovery
+
+Once your system is working again:
+
+1. **Verify you're on master branch**:
+   ```bash
+   cd /etc/nixos/.dotfiles
+   git branch  # Should show: * master
+   ```
+
+2. **Stay on master** (recommended):
+   - It's stable and tested
+   - No configuration changes needed
+   - Everything works
+
+3. **OR move to development** (advanced):
+   - Merge development features properly
+   - Test in VM first
+   - Ensure all files are present
+
+---
+
+## 📞 Still Having Issues?
+
+1. Run the diagnostic script:
+   ```bash
+   bash diagnose-emergency.sh
+   ```
+
+2. Check the detailed guides:
+   - Read `SOLUTION.md` for full explanation
+   - Read `EMERGENCY_RECOVERY.md` for technical details
+
+3. Verify filesystem integrity:
+   ```bash
+   lsblk -o NAME,UUID,FSTYPE,SIZE,MOUNTPOINT
+   df -h
+   mount | grep -E "/(boot|nix|home)"
+   ```
+
+---
+
+## 📊 System Information
+
+**Machine**: MSI laptop with Intel Tiger Lake + NVIDIA RTX 3050 Ti  
+**Storage**: Samsung 870 EVO 500GB  
+**Current filesystem**: ext4 on root  
+**Boot**: systemd-boot (511M EFI partition)  
+
+**Expected UUIDs**:
+- Root: `b89f5dca-4b37-4062-bf1d-9e4ebfd61916`
+- Boot: `8824-4C5F`
+- Swap: `c570ec29-6025-456b-99d1-8f16b677835a`
+
+---
+
+## ✅ Success Indicators
+
+You'll know recovery worked when:
+- ✅ System boots to desktop without emergency mode
+- ✅ All applications work normally
+- ✅ `systemctl status` shows no critical failures
+- ✅ You're on master branch: `git branch` in dotfiles shows `* master`
+
+---
+
+## 🎯 Summary
+
+| Problem | Fix | Time |
+|---------|-----|------|
+| Emergency mode | Boot previous generation | 1 min |
+| + Want to prevent | Switch to master branch | 5 min |
+| + Want automated fix | Run fix-emergency-auto.sh | 10 min |
+
+**Bottom line**: Boot an older generation from the boot menu. Problem solved! 🎉