den

name	den
description	Work on the Rust-canonical den CLI and MCP server for provisioning, deployment, lifecycle, and custom-domain flows across Sprite, Railway, Cloudflare, and sesame/Porkbun. Use when changing `den` commands, `den-mcp` workflows, runtime or domain provider dispatch, the self-hosted runtime design, or tests and docs that describe the Rust CLI and MCP behavior.

Den

Use this skill when a task touches den's Rust CLI, Rust MCP server, runtime providers, or custom-domain automation.

Workflow

1. Inspect crates/den-cli/src/main.rs, crates/den-cli/src/lib.rs, crates/den-core/src/lib.rs, and crates/den-mcp/src/tools.rs before editing.
2. Keep reusable parsing, command-building, provider selection, and Dhall helpers in den-core where possible.
3. Keep CLI UX, prompts, output, and asset resolution in den-cli.
4. Keep MCP workflows in crates/den-mcp/src/tools.rs structured, step-oriented, and minimal-call.
5. Validate with:
   • cargo test -p den-cli
   • cargo check -p den-mcp
   • cargo check -p den-cli
   • uv run pytest tests/python when changing the legacy Python reference implementation or parity tests
   • bash tests/test-den.sh when shell-smoke coverage matters
6. Update docs after code and tests agree.

Interface Rules

• CLI and MCP should expose the same underlying capability set unless an interface difference is intentional.
• If a feature exists in both CLI and MCP, prefer one shared helper in den-core instead of duplicating provider logic.
• MCP errors should return explicit remediation instead of vague provider failures.
• Do not invent provider capabilities. If Sprite or Railway cannot do something, return an explicit unsupported path.

Provider Rules

• Runtime provider is either sprite or railway.
• Domain provider is selected by ownership, not by preference: Cloudflare-held zones use Cloudflare and Porkbun-held zones use sesame.
• Use resolve_custom_domain(...) from den-core to choose the owning provider.
• For Railway custom domains, use Railway's attach response as the source of truth for required DNS records.
• For Sprite URL forwarding, make the Sprite URL public before creating the Porkbun forward.
• Keep forwarding and native DNS semantics separate. A forward is a redirect, not canonical edge attachment.

MCP Rules

• Use the Rust den-mcp workflow tools for create, lifecycle, and diagnostics flows.
• Prefer the fewest MCP tool calls that satisfy the task.
• Keep MCP workflow behavior aligned with the Rust CLI surface, not the legacy Python CLI.

CLI Examples

den spawn myproject
den spawn myproject --runtime railway
den deploy . --runtime railway
den doctor --verify-auth
den domain myproject app.example.com --runtime railway --mode dns --port 3000
den domain myproject app.dev.example.com --mode forward
den list --runtime railway --json
den status myproject --runtime railway

Tests To Update

• crates/den-cli/tests/assets_and_cli.rs for Rust CLI flags and install-health coverage
• crates/den-core/tests/core_properties.rs for parsing, provider selection, and command builders
• tests/python/test_core_properties.py for parsing, provider selection, and command builders
• tests/python/test_cli_commands.py for CLI behavior and provider dispatch
• tests/python/test_mcp_server.py for MCP workflows and error payloads

Files To Check

• crates/den-cli/src/main.rs
• crates/den-cli/src/lib.rs
• crates/den-core/src/lib.rs
• crates/den-mcp/src/tools.rs
• crates/den-core/tests/core_properties.rs
• README.md
• docs/mcp-server.md
• docs/workflows.md
• docs/selfhosted-runtime.md