F2 SLICE-1: artifact schema + CoauthorStore with round-trip tests (#4)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/model.test.ts

@@ -0,0 +1,58 @@
+import { describe, it, expect } from "vitest";
+import {
+  SCHEMA_VERSION,
+  emptyArtifact,
+  serializeArtifact,
+  type Artifact,
+} from "../src/model";
+
+function sampleArtifact(): Artifact {
+  return {
+    schemaVersion: SCHEMA_VERSION,
+    document: { path: "docs/spec.md" },
+    anchors: {
+      a2: { fingerprint: { text: "beta", before: "x", after: "y", lineHint: 5 } },
+      a1: { fingerprint: { text: "alpha", before: "", after: "", lineHint: 1 } },
+    },
+    threads: [
+      {
+        id: "t1",
+        anchorId: "a1",
+        status: "open",
+        messages: [
+          { id: "m1", author: { kind: "human", id: "ben" }, body: "hi", createdAt: "2026-06-10T00:00:00.000Z" },
+        ],
+      },
+    ],
+    attributions: [],
+    proposals: [],
+  };
+}
+
+describe("serializeArtifact", () => {
+  it("round-trips through JSON.parse", () => {
+    const a = sampleArtifact();
+    const parsed = JSON.parse(serializeArtifact(a)) as Artifact;
+    expect(parsed).toEqual(a);
+  });
+
+  it("emits stable, sorted anchor keys and a trailing newline regardless of insertion order", () => {
+    const a = sampleArtifact();
+    const out = serializeArtifact(a);
+    expect(out.endsWith("\n")).toBe(true);
+    // a1 must serialize before a2 even though a2 was inserted first
+    expect(out.indexOf('"a1"')).toBeLessThan(out.indexOf('"a2"'));
+    // byte-identical on re-serialize
+    expect(serializeArtifact(JSON.parse(out))).toBe(out);
+  });
+
+  it("emptyArtifact has the shared F3/F4 extension points present and empty", () => {
+    const e = emptyArtifact("docs/x.md");
+    expect(e.schemaVersion).toBe(SCHEMA_VERSION);
+    expect(e.document.path).toBe("docs/x.md");
+    expect(e.anchors).toEqual({});
+    expect(e.threads).toEqual([]);
+    expect(e.attributions).toEqual([]);
+    expect(e.proposals).toEqual([]);
+  });
+});

test/store.test.ts

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+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+import { CoauthorStore } from "../src/store";
+import { emptyArtifact, newId, serializeArtifact, type Artifact } from "../src/model";
+
+let root: string;
+
+beforeEach(() => {
+  root = fs.mkdtempSync(path.join(os.tmpdir(), "coauthor-store-"));
+});
+afterEach(() => {
+  fs.rmSync(root, { recursive: true, force: true });
+});
+
+function withThread(): Artifact {
+  const a = emptyArtifact("docs/spec.md");
+  a.anchors["a1"] = { fingerprint: { text: "hello", before: "", after: "", lineHint: 0 } };
+  a.threads.push({
+    id: "t1",
+    anchorId: "a1",
+    status: "open",
+    messages: [{ id: newId("m"), author: { kind: "human", id: "ben" }, body: "note", createdAt: "2026-06-10T00:00:00.000Z" }],
+  });
+  return a;
+}
+
+describe("CoauthorStore", () => {
+  it("returns null for a document with no sidecar", () => {
+    const store = new CoauthorStore(root);
+    expect(store.load("docs/spec.md")).toBeNull();
+  });
+
+  it("computes the sidecar path as .threads/<docPath>.json", () => {
+    const store = new CoauthorStore(root);
+    expect(store.sidecarPath("docs/spec.md")).toBe(path.join(root, ".threads", "docs", "spec.md.json"));
+  });
+
+  it("save then load round-trips the artifact", () => {
+    const store = new CoauthorStore(root);
+    const a = withThread();
+    store.save("docs/spec.md", a);
+    expect(store.load("docs/spec.md")).toEqual(a);
+  });
+
+  it("writes byte-stable, pretty JSON (re-save is identical)", () => {
+    const store = new CoauthorStore(root);
+    const a = withThread();
+    store.save("docs/spec.md", a);
+    const first = fs.readFileSync(store.sidecarPath("docs/spec.md"), "utf8");
+    store.save("docs/spec.md", store.load("docs/spec.md")!);
+    const second = fs.readFileSync(store.sidecarPath("docs/spec.md"), "utf8");
+    expect(second).toBe(first);
+    expect(first).toBe(serializeArtifact(a));
+  });
+});