Add skills system with Claude Code compatibility (#171)

* Add skills system with Claude Code compatibility

* consolidate skills into single module, merge loaders, add <available_skills> XML tags

* add Codex CLI skills compatibility, skip hidden/symlinks

packages/coding-agent/src/core/system-prompt.ts

@@ -6,6 +6,7 @@ import chalk from "chalk";
 import { existsSync, readFileSync } from "fs";
 import { join, resolve } from "path";
 import { getAgentDir, getDocsPath, getReadmePath } from "../config.js";
+import { loadSkills, type Skill } from "./skills.js";
 import type { ToolName } from "./tools/index.js";
 
 /** Tool descriptions for system prompt */
@@ -101,12 +102,39 @@ export function loadProjectContextFiles(): Array<{ path: string; content: string
 	return contextFiles;
 }
 
+function buildSkillsSection(skills: Skill[]): string {
+	if (skills.length === 0) {
+		return "";
+	}
+
+	const lines = [
+		"\n\n<available_skills>",
+		"The following skills provide specialized instructions for specific tasks.",
+		"Use the read tool to load a skill's file when the task matches its description.",
+		"Skills may contain {baseDir} placeholders - replace them with the skill's base directory path.\n",
+	];
+
+	for (const skill of skills) {
+		lines.push(`- ${skill.name}: ${skill.description}`);
+		lines.push(`  File: ${skill.filePath}`);
+		lines.push(`  Base directory: ${skill.baseDir}`);
+	}
+
+	lines.push("</available_skills>");
+
+	return lines.join("\n");
+}
+
+export interface BuildSystemPromptOptions {
+	customPrompt?: string;
+	selectedTools?: ToolName[];
+	appendSystemPrompt?: string;
+	skillsEnabled?: boolean;
+}
+
 /** Build the system prompt with tools, guidelines, and context */
-export function buildSystemPrompt(
-	customPrompt?: string,
-	selectedTools?: ToolName[],
-	appendSystemPrompt?: string,
-): string {
+export function buildSystemPrompt(options: BuildSystemPromptOptions = {}): string {
+	const { customPrompt, selectedTools, appendSystemPrompt, skillsEnabled = true } = options;
 	const resolvedCustomPrompt = resolvePromptInput(customPrompt, "system prompt");
 	const resolvedAppendPrompt = resolvePromptInput(appendSystemPrompt, "append system prompt");
 
@@ -141,6 +169,13 @@ export function buildSystemPrompt(
 			}
 		}
 
+		// Append skills section (only if read tool is available)
+		const customPromptHasRead = !selectedTools || selectedTools.includes("read");
+		if (skillsEnabled && customPromptHasRead) {
+			const skills = loadSkills();
+			prompt += buildSkillsSection(skills);
+		}
+
 		// Add date/time and working directory last
 		prompt += `\nCurrent date and time: ${dateTime}`;
 		prompt += `\nCurrent working directory: ${process.cwd()}`;
@@ -241,6 +276,12 @@ Documentation:
 		}
 	}
 
+	// Append skills section (only if read tool is available)
+	if (skillsEnabled && hasRead) {
+		const skills = loadSkills();
+		prompt += buildSkillsSection(skills);
+	}
+
 	// Add date/time and working directory last
 	prompt += `\nCurrent date and time: ${dateTime}`;
 	prompt += `\nCurrent working directory: ${process.cwd()}`;