feat(data): avatar file store helper

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/data/avatars.test.ts

@@ -0,0 +1,61 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { mkdtempSync, rmSync, existsSync, readFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { createAvatarStore } from "./avatars.js";
+
+let dir: string;
+
+beforeEach(() => {
+  dir = mkdtempSync(join(tmpdir(), "avatar-test-"));
+});
+
+describe("createAvatarStore", () => {
+  it("write returns a relative path under the store dir", () => {
+    const store = createAvatarStore(dir);
+    const buf = Buffer.from("fake-png");
+    const rel = store.write("bot-1", "image/png", buf);
+    expect(rel).toBe("bot-1.png");
+    expect(readFileSync(join(dir, "bot-1.png")).equals(buf)).toBe(true);
+  });
+
+  it("write picks correct extension for jpeg / webp", () => {
+    const store = createAvatarStore(dir);
+    expect(store.write("a", "image/jpeg", Buffer.from(""))).toBe("a.jpg");
+    expect(store.write("b", "image/webp", Buffer.from(""))).toBe("b.webp");
+  });
+
+  it("write rejects unsupported MIME types", () => {
+    const store = createAvatarStore(dir);
+    expect(() => store.write("c", "image/gif", Buffer.from(""))).toThrow(/unsupported/i);
+  });
+
+  it("read returns the bytes for an existing file", () => {
+    const store = createAvatarStore(dir);
+    store.write("bot-1", "image/png", Buffer.from("hello"));
+    const buf = store.read("bot-1.png");
+    expect(buf?.equals(Buffer.from("hello"))).toBe(true);
+  });
+
+  it("read returns null when path is missing", () => {
+    const store = createAvatarStore(dir);
+    expect(store.read("missing.png")).toBeNull();
+  });
+
+  it("remove deletes the file (idempotent)", () => {
+    const store = createAvatarStore(dir);
+    store.write("bot-1", "image/png", Buffer.from("x"));
+    store.remove("bot-1.png");
+    expect(existsSync(join(dir, "bot-1.png"))).toBe(false);
+    expect(() => store.remove("bot-1.png")).not.toThrow();
+  });
+
+  it("write replaces any existing file for the same botId regardless of old extension", () => {
+    const store = createAvatarStore(dir);
+    store.write("bot-1", "image/png", Buffer.from("old"));
+    const rel = store.write("bot-1", "image/jpeg", Buffer.from("new"));
+    expect(rel).toBe("bot-1.jpg");
+    expect(existsSync(join(dir, "bot-1.png"))).toBe(false);
+    expect(existsSync(join(dir, "bot-1.jpg"))).toBe(true);
+  });
+});