test: expand unit test coverage (+437 tests, 17 new files)

Add comprehensive unit tests for previously uncovered API lib modules,
web stores, and plugin functions. Fix 2 pre-existing editor-store test
failures (invertSelection mask values).

Coverage: 30.3% -> 36.85% stmts (unit), 57.71% stmts (integration).

tests/unit/api/heic-converter.test.ts

@@ -0,0 +1,113 @@
+import { readFile } from "node:fs/promises";
+import { join } from "node:path";
+import sharp from "sharp";
+import { describe, expect, it } from "vitest";
+import { decodeHeic, ensureSharpCompat } from "../../../apps/api/src/lib/heic-converter.js";
+
+const FIXTURES = join(__dirname, "../../fixtures");
+
+function isPng(buf: Buffer): boolean {
+  return buf[0] === 0x89 && buf[1] === 0x50 && buf[2] === 0x4e && buf[3] === 0x47;
+}
+
+function makeHeicHeader(brand: string): Buffer {
+  const buf = Buffer.alloc(12);
+  buf.writeUInt32BE(12, 0);
+  buf.write("ftyp", 4, 4, "ascii");
+  buf.write(brand, 8, 4, "ascii");
+  return buf;
+}
+
+describe("decodeHeic", () => {
+  it("decodes sample.heic to a valid PNG buffer", async () => {
+    const heicBuf = await readFile(join(FIXTURES, "formats/sample.heic"));
+    const result = await decodeHeic(heicBuf);
+    expect(isPng(result)).toBe(true);
+    const meta = await sharp(result).metadata();
+    expect(meta.width).toBeGreaterThan(0);
+    expect(meta.height).toBeGreaterThan(0);
+  });
+
+  it("decodes sample.heif to a valid PNG buffer", async () => {
+    const heifBuf = await readFile(join(FIXTURES, "formats/sample.heif"));
+    const result = await decodeHeic(heifBuf);
+    expect(isPng(result)).toBe(true);
+    const meta = await sharp(result).metadata();
+    expect(meta.width).toBeGreaterThan(0);
+    expect(meta.height).toBeGreaterThan(0);
+  });
+
+  it("preserves image dimensions after decoding", async () => {
+    const heicBuf = await readFile(join(FIXTURES, "formats/sample.heic"));
+    const result = await decodeHeic(heicBuf);
+    const meta = await sharp(result).metadata();
+    expect(meta.width).toBeGreaterThan(0);
+    expect(meta.height).toBeGreaterThan(0);
+    expect(meta.format).toBe("png");
+  });
+
+  it("rejects invalid/corrupt data", async () => {
+    const garbage = Buffer.from("this is not a heic file at all");
+    await expect(decodeHeic(garbage)).rejects.toThrow();
+  });
+
+  it("rejects an empty buffer", async () => {
+    await expect(decodeHeic(Buffer.alloc(0))).rejects.toThrow();
+  });
+
+  it("cleans up temp files after success", async () => {
+    const heicBuf = await readFile(join(FIXTURES, "formats/sample.heic"));
+    const { tmpdir } = await import("node:os");
+    const { readdirSync } = await import("node:fs");
+    const before = readdirSync(tmpdir()).filter(
+      (f) => f.startsWith("heic-in-") || f.startsWith("heic-out-"),
+    );
+    await decodeHeic(heicBuf);
+    const after = readdirSync(tmpdir()).filter(
+      (f) => f.startsWith("heic-in-") || f.startsWith("heic-out-"),
+    );
+    expect(after.length).toBeLessThanOrEqual(before.length);
+  });
+});
+
+describe("ensureSharpCompat", () => {
+  it("decodes a HEIC buffer to PNG", async () => {
+    const heicBuf = await readFile(join(FIXTURES, "formats/sample.heic"));
+    const result = await ensureSharpCompat(heicBuf);
+    expect(isPng(result)).toBe(true);
+  });
+
+  it("passes through a PNG buffer unchanged", async () => {
+    const pngBuf = await readFile(join(FIXTURES, "formats/sample.png"));
+    const result = await ensureSharpCompat(pngBuf);
+    expect(result).toBe(pngBuf);
+  });
+
+  it("passes through a JPEG buffer unchanged", async () => {
+    const jpgBuf = await readFile(join(FIXTURES, "formats/sample.jpg"));
+    const result = await ensureSharpCompat(jpgBuf);
+    expect(result).toBe(jpgBuf);
+  });
+
+  it("passes through a WebP buffer unchanged", async () => {
+    const webpBuf = await readFile(join(FIXTURES, "formats/sample.webp"));
+    const result = await ensureSharpCompat(webpBuf);
+    expect(result).toBe(webpBuf);
+  });
+
+  it("detects heic brand in ftyp box", async () => {
+    const fakeBuf = makeHeicHeader("heic");
+    await expect(ensureSharpCompat(fakeBuf)).rejects.toThrow();
+  });
+
+  it("detects mif1 brand in ftyp box", async () => {
+    const fakeBuf = makeHeicHeader("mif1");
+    await expect(ensureSharpCompat(fakeBuf)).rejects.toThrow();
+  });
+
+  it("does not treat a short buffer as HEIF", async () => {
+    const shortBuf = Buffer.from("tiny");
+    const result = await ensureSharpCompat(shortBuf);
+    expect(result).toBe(shortBuf);
+  });
+});