feat(exe): add skill

skills/using-exe-dev/SKILL.md 🔗

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+---
+name: using-exe-dev
+description: Guides working with exe.dev VMs. Use when the user mentions exe.dev, exe VMs, *.exe.xyz, or tasks involving exe.dev infrastructure.
+---
+
+# About
+
+exe.dev provides Linux VMs with persistent disks, instant HTTPS, and built-in auth. All management is via SSH.
+
+## Documentation
+
+- Docs index: https://exe.dev/docs.md
+- All docs in one page (big!): https://exe.dev/docs/all.md
+
+The index is organized for progressive discovery: start there and follow links as needed.
+
+## Quick reference
+
+```
+ssh exe.dev help             # show commands
+ssh exe.dev help <command>   # show command details
+ssh exe.dev new --json       # create VM
+ssh exe.dev ls --json        # list VMs
+ssh exe.dev rm <vm>          # delete VM
+ssh <vm>.exe.xyz             # connect to VM
+scp file.txt <vm>.exe.xyz:~/ # transfer file
+```
+
+Every VM gets `https://<vm>.exe.xyz/` with automatic TLS.
+
+## A tale of two SSH destinations
+
+- **`ssh exe.dev <command>`** — the exe.dev lobby. A REPL for VM lifecycle, sharing, and configuration. Does not support scp, sftp, or arbitrary shell commands.
+- **`ssh <vm>.exe.xyz`** — a direct connection to a VM. Full SSH: shell, scp, sftp, port forwarding, everything.
+
+## Working in non-interactive and sandboxed environments
+
+Coding agents often run SSH in non-interactive shells or sandboxes. Common issues and workarounds:
+
+**scp/sftp failures**: Ensure you're targeting `<vm>.exe.xyz` rather than `exe.dev`. Use ssh-based workarounds.
+
+**Hung connections**: Non-interactive SSH can block on host key prompts with no visible output. Use `-o StrictHostKeyChecking=accept-new` on first connection to a new VM.
+
+**SSH config**: Check whether both destinations are configured to use the right key:
+
+```
+Host exe.dev *.exe.xyz
+  IdentitiesOnly yes
+  IdentityFile ~/.ssh/id_ed25519
+```
Change summary

Detailed changes

skills/using-exe-dev/SKILL.md 🔗
