refactor: split src into domain / application / infrastructure layers

Replace the history-driven lib/ + utils/ split with DDD layers:
- domain/: aggregate, repositories, value objects, pure parsers/format
- application/: feed-service, email-processor, feed-fetcher, stats
- infrastructure/: logging, auth, KV/R2 adapters, HTTP, framework glue

Pure file relocation; imports updated mechanically. Behaviour unchanged.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/infrastructure/favicon-fetcher.test.ts

@@ -0,0 +1,149 @@
+import { describe, it, expect } from "vitest";
+import { http, HttpResponse } from "msw";
+import { server, createMockEnv } from "../test/setup";
+import {
+  cacheFaviconForDomain,
+  extractEmailDomain,
+  getCachedIcon,
+} from "./favicon-fetcher";
+import { MAX_ICON_BYTES } from "../config/constants";
+
+const iconKey = (domain: string) => `icon:${domain}`;
+import type { Env } from "../types";
+
+const PNG = new Uint8Array([0x89, 0x50, 0x4e, 0x47, 1, 2, 3, 4]);
+
+function imageResponse(bytes: Uint8Array, contentType = "image/png") {
+  return new HttpResponse(bytes, { headers: { "Content-Type": contentType } });
+}
+
+describe("extractEmailDomain", () => {
+  it("parses a bare address", () => {
+    expect(extractEmailDomain("news@github.com")).toBe("github.com");
+  });
+
+  it("parses a display-form address", () => {
+    expect(extractEmailDomain("GitHub <news@GitHub.com>")).toBe("github.com");
+  });
+
+  it("strips a trailing dot and lowercases", () => {
+    expect(extractEmailDomain("a@Example.COM.")).toBe("example.com");
+  });
+
+  it("returns null when there is no address", () => {
+    expect(extractEmailDomain("not an email")).toBeNull();
+  });
+});
+
+describe("cacheFaviconForDomain", () => {
+  it("caches the direct /favicon.ico when available", async () => {
+    const env = createMockEnv() as unknown as Env;
+    server.use(
+      http.get("https://github.com/favicon.ico", () => imageResponse(PNG)),
+    );
+
+    await cacheFaviconForDomain("github.com", env);
+
+    const record = await env.EMAIL_STORAGE.get(iconKey("github.com"), "json");
+    expect(record).toMatchObject({ contentType: "image/png" });
+    expect((record as { data: string }).data).toBeTruthy();
+    expect(record).not.toHaveProperty("fetchedAt");
+
+    const icon = await getCachedIcon("github.com", env);
+    expect(icon?.contentType).toBe("image/png");
+    expect(new Uint8Array(icon!.bytes)).toEqual(PNG);
+  });
+
+  it("falls back to DuckDuckGo when the direct icon 404s", async () => {
+    const env = createMockEnv() as unknown as Env;
+    server.use(
+      http.get("https://acme.test/favicon.ico", () =>
+        HttpResponse.text("nope", { status: 404 }),
+      ),
+      http.get("https://icons.duckduckgo.com/ip3/acme.test.ico", () =>
+        imageResponse(PNG, "image/x-icon"),
+      ),
+    );
+
+    await cacheFaviconForDomain("acme.test", env);
+
+    const icon = await getCachedIcon("acme.test", env);
+    expect(icon?.contentType).toBe("image/x-icon");
+  });
+
+  it("writes a negative entry when no icon is found", async () => {
+    const env = createMockEnv() as unknown as Env;
+    server.use(
+      http.get("https://nope.test/favicon.ico", () =>
+        HttpResponse.text("", { status: 404 }),
+      ),
+      http.get("https://icons.duckduckgo.com/ip3/nope.test.ico", () =>
+        HttpResponse.text("", { status: 404 }),
+      ),
+    );
+
+    await cacheFaviconForDomain("nope.test", env);
+
+    const record = await env.EMAIL_STORAGE.get(iconKey("nope.test"), "json");
+    expect(record).toEqual({ data: null, contentType: "" });
+    expect(await getCachedIcon("nope.test", env)).toBeNull();
+  });
+
+  it("rejects oversized responses as negative", async () => {
+    const env = createMockEnv() as unknown as Env;
+    const big = new Uint8Array(MAX_ICON_BYTES + 1);
+    server.use(
+      http.get("https://big.test/favicon.ico", () => imageResponse(big)),
+      http.get("https://icons.duckduckgo.com/ip3/big.test.ico", () =>
+        HttpResponse.text("", { status: 404 }),
+      ),
+    );
+
+    await cacheFaviconForDomain("big.test", env);
+    expect(await getCachedIcon("big.test", env)).toBeNull();
+  });
+
+  it("rejects non-image content types as negative", async () => {
+    const env = createMockEnv() as unknown as Env;
+    server.use(
+      http.get("https://html.test/favicon.ico", () =>
+        HttpResponse.text("<html>", {
+          headers: { "Content-Type": "text/html" },
+        }),
+      ),
+      http.get("https://icons.duckduckgo.com/ip3/html.test.ico", () =>
+        HttpResponse.text("", { status: 404 }),
+      ),
+    );
+
+    await cacheFaviconForDomain("html.test", env);
+    expect(await getCachedIcon("html.test", env)).toBeNull();
+  });
+
+  it("short-circuits when an entry already exists (no outbound fetch)", async () => {
+    const env = createMockEnv() as unknown as Env;
+    // Pre-seed a record; with MSW onUnhandledRequest:"error", any fetch fails.
+    await env.EMAIL_STORAGE.put(
+      iconKey("cached.test"),
+      JSON.stringify({ data: null, contentType: "" }),
+    );
+
+    await expect(
+      cacheFaviconForDomain("cached.test", env),
+    ).resolves.toBeUndefined();
+  });
+
+  it("never throws on network errors", async () => {
+    const env = createMockEnv() as unknown as Env;
+    server.use(
+      http.get("https://err.test/favicon.ico", () => HttpResponse.error()),
+      http.get("https://icons.duckduckgo.com/ip3/err.test.ico", () =>
+        HttpResponse.error(),
+      ),
+    );
+
+    await expect(
+      cacheFaviconForDomain("err.test", env),
+    ).resolves.toBeUndefined();
+  });
+});