feat: add create-skill — AI-powered skill generator

dex create-skill <name> -d "description" [--install]
Aliases: dex new-skill

Uses agentic tool loop to generate manifest.json + handler.ts
from natural language description. Optionally auto-installs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 2 people

src/skills/built-in/create-skill/handler.ts

@@ -0,0 +1,94 @@
+import type { SkillHandler } from "../../types.js";
+import { streamQuery } from "../../handler-utils.js";
+
+const SYSTEM_PROMPT = `You are an expert at creating dex CLI skills. Your job is to generate a complete, working skill based on the user's description.
+
+A dex skill consists of two files in a directory:
+
+## 1. manifest.json
+
+\`\`\`json
+{
+  "name": "skill-name",
+  "version": "1.0.0",
+  "description": "What this skill does",
+  "inputs": {
+    "args": [
+      { "name": "file", "description": "Target file", "required": true }
+    ],
+    "flags": [
+      { "name": "verbose", "short": "v", "type": "boolean", "default": false }
+    ],
+    "context": ["current-file", "git-diff", "git-diff-staged", "git-log", "file-tree", "package-json", "stdin"]
+  },
+  "agent": {
+    "maxTurns": 5,
+    "allowedTools": ["bash", "read_file", "write_file", "list_files", "search_files", "apply_diff"]
+  },
+  "aliases": ["short-name"]
+}
+\`\`\`
+
+Rules:
+- "name" must be lowercase with hyphens
+- Only include "args", "flags", "context" that the skill actually needs
+- Only include "agent.allowedTools" if the skill needs to read/write files or run commands
+- Omit "agent" entirely for simple single-turn skills (review, explain, etc.)
+
+## 2. handler.ts
+
+\`\`\`typescript
+import type { SkillHandler } from "../../types.js";
+import { streamQuery } from "../../handler-utils.js";
+
+const SYSTEM_PROMPT = \\\`Your system prompt here\\\`;
+
+const handler: SkillHandler = async (ctx) => {
+  // Access inputs:
+  // ctx.args.file — positional arg
+  // ctx.flags.verbose — flag value
+  // ctx.context.gitDiff — context data
+  // ctx.context.currentFile?.content — file content
+  // ctx.context.stdin — piped input
+  // ctx.context.cwd — working directory
+
+  const prompt = \\\`Your prompt with \${ctx.context.currentFile?.content}\\\`;
+  await streamQuery(ctx.agent, prompt, { systemPrompt: SYSTEM_PROMPT });
+};
+
+export default handler;
+\`\`\`
+
+## Your workflow:
+
+1. Understand what the user wants
+2. Design the manifest (what inputs, context, and tools are needed)
+3. Write the handler with a good system prompt
+4. Create the skill directory with write_file
+5. If the user wants it installed, run: \`dex skill add ./<name>\`
+
+Keep skills simple and focused. One skill = one job.`;
+
+const handler: SkillHandler = async (ctx) => {
+  const name = ctx.args.name;
+  const description = ctx.flags.description as string | undefined;
+  const install = ctx.flags.install as boolean;
+
+  if (!name) {
+    throw new Error("Skill name is required. Usage: dex create-skill <name> -d 'what it does'");
+  }
+
+  const prompt = `Create a new dex skill called "${name}" in the directory "./${name}/".
+
+${description ? `Description: ${description}` : "Ask me what this skill should do, then create it."}
+
+${install ? "After creating the files, install it by running: dex skill add ./" + name : ""}
+
+${ctx.context.fileTree ? `Current project structure for reference:\n\`\`\`\n${ctx.context.fileTree}\n\`\`\`` : ""}
+
+Create the manifest.json and handler.ts files now.`;
+
+  await streamQuery(ctx.agent, prompt, { systemPrompt: SYSTEM_PROMPT });
+};
+
+export default handler;

src/skills/built-in/create-skill/manifest.json

@@ -0,0 +1,30 @@
+{
+  "name": "create-skill",
+  "version": "1.0.0",
+  "description": "Generate a new dex skill from a natural language description",
+  "inputs": {
+    "args": [
+      { "name": "name", "description": "Skill name (lowercase-with-hyphens)", "required": true }
+    ],
+    "flags": [
+      {
+        "name": "description",
+        "short": "d",
+        "type": "string",
+        "description": "What the skill should do"
+      },
+      {
+        "name": "install",
+        "type": "boolean",
+        "description": "Automatically install after creation",
+        "default": false
+      }
+    ],
+    "context": ["file-tree"]
+  },
+  "agent": {
+    "maxTurns": 10,
+    "allowedTools": ["read_file", "write_file", "list_files", "bash"]
+  },
+  "aliases": ["new-skill"]
+}