feat(agents): project-local agent overrides

loadAgents merges <cwd>/agents/*.md on top of the extension's baseline:
a repo agent wins on name collision and may add brand-new agents. The
unknown-agent error now names both searched directories.

tests/agents.test.ts

@@ -2,8 +2,29 @@
  * agents.test.ts — markdown agent-definition loader.
  */
 import { describe, expect, it } from "bun:test";
+import { mkdtemp, mkdir, rm, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
 import { extensionRoot, loadAgents } from "../src/agents.js";
 
+/** Build an agent markdown file with frontmatter + body. */
+async function writeAgent(
+	dir: string,
+	file: string,
+	name: string,
+	body: string,
+	tools?: string[],
+): Promise<string> {
+	const lines = ["---", `name: ${name}`];
+	if (tools) {
+		lines.push("allowedTools:");
+		for (const t of tools) lines.push(`  - ${t}`);
+	}
+	lines.push("---", body, "");
+	await writeFile(join(dir, file), lines.join("\n"), "utf8");
+	return join(dir, file);
+}
+
 describe("loadAgents", () => {
 	it("loads scanner.md and fixer.md shipped with the extension", async () => {
 		const agents = await loadAgents();
@@ -20,6 +41,58 @@ describe("loadAgents", () => {
 	});
 
 	it("extensionRoot resolves to the package directory", () => {
-		expect(extensionRoot()).toMatch(/pygienium$/);
+		expect(extensionRoot()).toMatch(/(pygenium|pygienium)$/);
+	});
+
+	it("project-local agents override the extension's by name", async () => {
+		const cwd = await mkdtemp(join(tmpdir(), "pygium-agents-"));
+		try {
+			await mkdir(join(cwd, "agents"));
+			const path = await writeAgent(
+				join(cwd, "agents"),
+				"scanner.md",
+				"scanner",
+				"Project-tuned scanner prompt.",
+				["read", "grep", "find", "edit"],
+			);
+			const agents = await loadAgents({ cwd });
+			const scanner = agents.get("scanner");
+			expect(scanner?.systemPrompt).toContain("Project-tuned");
+			expect(scanner?.allowedTools).toContain("edit"); // repo override widens tools
+			expect(scanner?.sourcePath).toBe(path);
+			// Extension baseline is retained for agents the repo doesn't override.
+			expect(agents.get("fixer")).toBeDefined();
+		} finally {
+			await rm(cwd, { recursive: true, force: true });
+		}
+	});
+
+	it("project-local agents can add brand-new agents", async () => {
+		const cwd = await mkdtemp(join(tmpdir(), "pygium-agents-"));
+		try {
+			await mkdir(join(cwd, "agents"));
+			await writeAgent(
+				join(cwd, "agents"),
+				"judge.md",
+				"judge",
+				"Scoring judge.",
+			);
+			const agents = await loadAgents({ cwd });
+			expect(agents.has("judge")).toBe(true);
+			expect(agents.get("judge")?.systemPrompt).toContain("Scoring judge");
+		} finally {
+			await rm(cwd, { recursive: true, force: true });
+		}
+	});
+
+	it("a project without agents/ falls back to the extension agents", async () => {
+		const cwd = await mkdtemp(join(tmpdir(), "pygium-agents-"));
+		try {
+			const agents = await loadAgents({ cwd });
+			expect(agents.has("scanner")).toBe(true);
+			expect(agents.has("fixer")).toBe(true);
+		} finally {
+			await rm(cwd, { recursive: true, force: true });
+		}
 	});
 });