fix(gsd): discover project subagents in .gsd

Prefer the documented .gsd/agents location for project-local subagents while keeping a legacy fallback to .pi/agents so existing workarounds continue to function. Add a regression test covering both paths.

Closes #2864

src/resources/extensions/gsd/tests/subagent-agent-discovery.test.ts

@@ -0,0 +1,44 @@
+import assert from "node:assert/strict";
+import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import test from "node:test";
+
+import { discoverAgents } from "../../subagent/agents.ts";
+
+function makeProjectRoot(t: test.TestContext): string {
+	const root = mkdtempSync(join(tmpdir(), "gsd-subagent-agents-"));
+	t.after(() => rmSync(root, { recursive: true, force: true }));
+	return root;
+}
+
+function writeAgent(root: string, configDirName: ".gsd" | ".pi", name = "ping"): string {
+	const agentsDir = join(root, configDirName, "agents");
+	mkdirSync(agentsDir, { recursive: true });
+	writeFileSync(
+		join(agentsDir, `${name}.md`),
+		`---\nname: ${name}\ndescription: ${name} agent\n---\nSay hello\n`,
+	);
+	return agentsDir;
+}
+
+test("discoverAgents finds project agents in .gsd/agents", (t) => {
+	const root = makeProjectRoot(t);
+	const agentsDir = writeAgent(root, ".gsd");
+
+	const discovery = discoverAgents(root, "project");
+
+	assert.equal(discovery.projectAgentsDir, agentsDir);
+	assert.deepEqual(discovery.agents.map((agent) => agent.name), ["ping"]);
+	assert.equal(discovery.agents[0]?.source, "project");
+});
+
+test("discoverAgents falls back to legacy .pi/agents when needed", (t) => {
+	const root = makeProjectRoot(t);
+	const agentsDir = writeAgent(root, ".pi");
+
+	const discovery = discoverAgents(root, "project");
+
+	assert.equal(discovery.projectAgentsDir, agentsDir);
+	assert.deepEqual(discovery.agents.map((agent) => agent.name), ["ping"]);
+});

src/resources/extensions/subagent/agents.ts

@@ -6,6 +6,8 @@ import * as fs from "node:fs";
 import * as path from "node:path";
 import { getAgentDir, parseFrontmatter } from "@gsd/pi-coding-agent";
 
+const PROJECT_AGENT_DIR_CANDIDATES = [".gsd", ".pi"] as const;
+
 export type AgentScope = "user" | "project" | "both";
 
 export interface AgentConfig {
@@ -85,8 +87,12 @@ function isDirectory(p: string): boolean {
 function findNearestProjectAgentsDir(cwd: string): string | null {
 	let currentDir = cwd;
 	while (true) {
-		const candidate = path.join(currentDir, ".pi", "agents");
-		if (isDirectory(candidate)) return candidate;
+		// Prefer the documented project-local location while preserving support
+		// for older workarounds that placed agents under .pi/agents.
+		for (const configDir of PROJECT_AGENT_DIR_CANDIDATES) {
+			const candidate = path.join(currentDir, configDir, "agents");
+			if (isDirectory(candidate)) return candidate;
+		}
 
 		const parentDir = path.dirname(currentDir);
 		if (parentDir === currentDir) return null;