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extensions/system-select.ts

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+/**
+ * System Select — Switch the system prompt via /system
+ *
+ * Scans .pi/agents/, .claude/agents/, .gemini/agents/, .codex/agents/
+ * (project-local and global) for agent definition .md files.
+ *
+ * /system opens a select dialog to pick a system prompt. The selected
+ * agent's body is prepended to Pi's default instructions so tool usage
+ * still works. Tools are restricted to the agent's declared tool set
+ * if specified.
+ *
+ * Usage: pi -e extensions/system-select.ts -e extensions/minimal.ts
+ */
+
+import type { ExtensionAPI } from "@mariozechner/pi-coding-agent";
+import { readdirSync, readFileSync, existsSync } from "node:fs";
+import { join, basename } from "node:path";
+import { homedir } from "node:os";
+import { applyExtensionDefaults } from "./themeMap.ts";
+
+interface AgentDef {
+	name: string;
+	description: string;
+	tools: string[];
+	body: string;
+	source: string;
+}
+
+function parseFrontmatter(raw: string): { fields: Record<string, string>; body: string } {
+	const match = raw.match(/^---\s*\n([\s\S]*?)\n---\s*\n([\s\S]*)$/);
+	if (!match) return { fields: {}, body: raw };
+	const fields: Record<string, string> = {};
+	for (const line of match[1].split("\n")) {
+		const idx = line.indexOf(":");
+		if (idx > 0) fields[line.slice(0, idx).trim()] = line.slice(idx + 1).trim();
+	}
+	return { fields, body: match[2] };
+}
+
+function scanAgents(dir: string, source: string): AgentDef[] {
+	if (!existsSync(dir)) return [];
+	const agents: AgentDef[] = [];
+	try {
+		for (const file of readdirSync(dir)) {
+			if (!file.endsWith(".md")) continue;
+			const raw = readFileSync(join(dir, file), "utf-8");
+			const { fields, body } = parseFrontmatter(raw);
+			agents.push({
+				name: fields.name || basename(file, ".md"),
+				description: fields.description || "",
+				tools: fields.tools ? fields.tools.split(",").map((t) => t.trim()) : [],
+				body: body.trim(),
+				source,
+			});
+		}
+	} catch {}
+	return agents;
+}
+
+function displayName(name: string): string {
+	return name.split("-").map(w => w.charAt(0).toUpperCase() + w.slice(1)).join(" ");
+}
+
+export default function (pi: ExtensionAPI) {
+	let activeAgent: AgentDef | null = null;
+	let allAgents: AgentDef[] = [];
+	let defaultTools: string[] = [];
+
+	pi.on("session_start", async (_event, ctx) => {
+		applyExtensionDefaults(import.meta.url, ctx);
+		activeAgent = null;
+		allAgents = [];
+
+		const home = homedir();
+		const cwd = ctx.cwd;
+
+		const dirs: [string, string][] = [
+			[join(cwd, ".pi", "agents"), ".pi"],
+			[join(cwd, ".claude", "agents"), ".claude"],
+			[join(cwd, ".gemini", "agents"), ".gemini"],
+			[join(cwd, ".codex", "agents"), ".codex"],
+			[join(home, ".pi", "agent", "agents"), "~/.pi"],
+			[join(home, ".claude", "agents"), "~/.claude"],
+			[join(home, ".gemini", "agents"), "~/.gemini"],
+			[join(home, ".codex", "agents"), "~/.codex"],
+		];
+
+		const seen = new Set<string>();
+		const sourceCounts: Record<string, number> = {};
+
+		for (const [dir, source] of dirs) {
+			const agents = scanAgents(dir, source);
+			for (const agent of agents) {
+				const key = agent.name.toLowerCase();
+				if (seen.has(key)) continue;
+				seen.add(key);
+				allAgents.push(agent);
+				sourceCounts[source] = (sourceCounts[source] || 0) + 1;
+			}
+		}
+
+		defaultTools = pi.getActiveTools();
+		ctx.ui.setStatus("system-prompt", "System Prompt: Default");
+
+		const defaultPrompt = ctx.getSystemPrompt();
+		const lines = defaultPrompt.split("\n").length;
+		const chars = defaultPrompt.length;
+		
+		const loadedSources = Object.entries(sourceCounts)
+			.map(([src, count]) => `${count} from ${src}`)
+			.join(", ");
+		
+		const notifyLines = [];
+		if (allAgents.length > 0) {
+			notifyLines.push(`Loaded ${allAgents.length} agents (${loadedSources})`);
+		}
+		notifyLines.push(`System Prompt: Default (${lines} lines, ${chars} chars)`);
+		
+		ctx.ui.notify(notifyLines.join("\n"), "info");
+	});
+
+	pi.registerCommand("system", {
+		description: "Select a system prompt from discovered agents",
+		handler: async (_args, ctx) => {
+			if (allAgents.length === 0) {
+				ctx.ui.notify("No agents found in .*/agents/*.md", "warning");
+				return;
+			}
+
+			const options = [
+				"Reset to Default",
+				...allAgents.map((a) => `${a.name} — ${a.description} [${a.source}]`),
+			];
+
+			const choice = await ctx.ui.select("Select System Prompt", options);
+			if (choice === undefined) return;
+
+			if (choice === options[0]) {
+				activeAgent = null;
+				pi.setActiveTools(defaultTools);
+				ctx.ui.setStatus("system-prompt", "System Prompt: Default");
+				ctx.ui.notify("System Prompt reset to Default", "success");
+				return;
+			}
+
+			const idx = options.indexOf(choice) - 1;
+			const agent = allAgents[idx];
+			activeAgent = agent;
+
+			if (agent.tools.length > 0) {
+				pi.setActiveTools(agent.tools);
+			} else {
+				pi.setActiveTools(defaultTools);
+			}
+
+			ctx.ui.setStatus("system-prompt", `System Prompt: ${displayName(agent.name)}`);
+			ctx.ui.notify(`System Prompt switched to: ${displayName(agent.name)}`, "success");
+		},
+	});
+
+	pi.on("before_agent_start", async (event, _ctx) => {
+		if (!activeAgent) return;
+		return {
+			systemPrompt: activeAgent.body + "\n\n" + event.systemPrompt,
+		};
+	});
+}