feat(data): avatar file store helper

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

src/data/avatars.test.ts

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+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);
+  });
+});

src/data/avatars.ts

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+import { mkdirSync, writeFileSync, readFileSync, rmSync, readdirSync, existsSync } from "node:fs";
+import { join } from "node:path";
+
+const MIME_TO_EXT: Record<string, string> = {
+  "image/png": "png",
+  "image/jpeg": "jpg",
+  "image/webp": "webp",
+};
+
+export interface AvatarStore {
+  /** Returns the relative path written (e.g. "bot-1.png"). */
+  write(botId: string, mime: string, buffer: Buffer): string;
+  read(relPath: string): Buffer | null;
+  remove(relPath: string): void;
+  getDir(): string;
+}
+
+export function createAvatarStore(dir: string): AvatarStore {
+  if (!existsSync(dir)) mkdirSync(dir, { recursive: true });
+  return {
+    write(botId, mime, buffer) {
+      const ext = MIME_TO_EXT[mime];
+      if (!ext) throw new Error(`unsupported avatar MIME: ${mime}`);
+      for (const name of readdirSync(dir)) {
+        if (name.startsWith(`${botId}.`)) rmSync(join(dir, name), { force: true });
+      }
+      const rel = `${botId}.${ext}`;
+      writeFileSync(join(dir, rel), buffer);
+      return rel;
+    },
+    read(relPath) {
+      const full = join(dir, relPath);
+      if (!existsSync(full)) return null;
+      return readFileSync(full);
+    },
+    remove(relPath) {
+      rmSync(join(dir, relPath), { force: true });
+    },
+    getDir() {
+      return dir;
+    },
+  };
+}