docs: Holesky on WSL2 (reth + Lighthouse) — docker.sock, DNS & --allow-insecure-genesis-sync

docs/guides/wsl2-holesky-lighthouse.md

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+# Holesky on WSL2: reth (Execution) + Lighthouse (Beacon)
+
+**Tested:** Windows 11 + WSL2 Ubuntu 24.04 (systemd enabled), Rust 1.90, Docker 28.2.2, Lighthouse v8.
+
+## 1) Docker on WSL2
+
+```bash
+sudo apt-get update
+sudo apt-get install -y docker.io
+sudo systemctl enable --now docker || sudo service docker start
+sudo usermod -aG docker $USER
+# close all terminals → in PowerShell: wsl --shutdown → reopen Ubuntu
+docker run --rm hello-world
+
+2) Run reth (Holesky)
+mkdir -p $HOME/reth-data/holesky
+./target/release/reth node \
+  --chain holesky \
+  --http --http.addr 0.0.0.0 --http.port 8545 \
+  --datadir $HOME/reth-data/holesky \
+  --authrpc.addr 127.0.0.1 --authrpc.port 8551 \
+  --authrpc.jwtsecret $HOME/.ethereum/jwt.hex
+
+3) Run Lighthouse
+A) Checkpoint sync (faster)
+sudo docker run --rm -it --network=host \
+  -v $HOME/.ethereum:/root/.ethereum \
+  -v $HOME/lighthouse:/root/.lighthouse \
+  sigp/lighthouse:latest lighthouse bn \
+  --network holesky \
+  --execution-endpoint http://127.0.0.1:8551 \
+  --execution-jwt /root/.ethereum/jwt.hex \
+  --checkpoint-sync-url https://holesky.checkpoint-sync.ethdevops.io
+# If DNS fails: add --dns 1.1.1.1 --dns 8.8.8.8 or try stakely/attestant.
+
+B) Genesis sync (works anywhere)
+sudo docker run --rm -it --network=host \
+  -v $HOME/.ethereum:/root/.ethereum \
+  -v $HOME/lighthouse:/root/.lighthouse \
+  sigp/lighthouse:latest lighthouse bn \
+  --network holesky \
+  --execution-endpoint http://127.0.0.1:8551 \
+  --execution-jwt /root/.ethereum/jwt.hex \
+  --allow-insecure-genesis-sync
+
+4) Common errors & fixes
+
+never seen beacon client (reth): start Lighthouse with Engine API as above.
+
+permission denied /var/run/docker.sock: add user to docker group → wsl --shutdown → reopen.
+
+DNS fails for checkpoint hosts: add --dns or use alternate checkpoint URLs.
+
+chainspec mismatch: use a fresh --datadir when switching networks.
+
+5) Verify
+curl -s -X POST http://127.0.0.1:8545 \
+ -H "Content-Type: application/json" \
+ -d '{"jsonrpc":"2.0","id":1,"method":"eth_blockNumber","params":[]}'