Adds assistants.

AGENTS.md

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+# AGENTS.md — Castle
+
+You are working in the **Castle** repository — Paul's personal software platform,
+a monorepo of independent programs (services, tools, libraries, frontends) managed
+by the `castle` CLI.
+
+## What Castle does
+
+Castle turns a source repo into something running on this node. The two halves:
+
+- **programs/** — the software catalog: what software exists (`source`, `stack`,
+  `build`, `system_dependencies`).
+- **deployments/** — how a program is realized here, discriminated on its
+  **`manager`**: `systemd` (a service, or a job with a `schedule`), `caddy` (a
+  static frontend), `path` (a CLI on your PATH), or `none` (an external
+  reference). The human-facing **kind** (service/job/tool/static/reference) is
+  *derived* from the manager, never stored.
+
+## Using the `castle` CLI
+
+It's resource-first — operations live under the resource they act on:
+
+```bash
+castle program create <name> --stack <python-cli|python-fastapi|react-vite>
+castle program add <path|git-url>              # adopt an existing repo
+castle service create <name> --program <p> --port <n>
+castle service deploy <name> && castle service enable <name>
+castle gateway reload                          # update reverse-proxy routes
+castle deploy && castle start                  # apply config, then start everything
+castle status                                  # unified status
+castle list --json                             # all deployments, machine-readable
+```
+
+Expose a service on the network by setting `proxy: true` (→
+`<name>.<gateway.domain>`); add `public: true` for the Cloudflare tunnel.
+
+## Read this first
+
+- **@CLAUDE.md** — full architecture, the complete `castle` verb list, registry
+  model, DNS/TLS, and code-style conventions. This is the authoritative guide.
+- `docs/registry.md`, `docs/dns-and-tls.md`, and `docs/stacks/*.md` — deep dives.
+
+**Key principle:** regular programs must never depend on castle. They take
+standard config (data dir, port, URLs) via env vars; only castle's own programs
+(CLI, gateway, api) know castle internals.
+
+Broader context about this machine and Paul's other projects lives at
+`/data/.lakehouse/AGENTS.md`.