feat: publish coauthoring-sidecar JSON Schema + rung-neutral validator (F5 SLICE-1, PUC-5, #14)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

test/helpers/validateSidecar.ts

@@ -0,0 +1,24 @@
+/**
+ * Schema-conformance helper (F5 SLICE-1, PUC-5): every serialized artifact in
+ * the unit suite must validate against the published cross-rung schema —
+ * contract drift fails CI (spec §7.4).
+ */
+import { readFileSync } from "node:fs";
+import Ajv from "ajv/dist/2020";
+import { serializeArtifact, type Artifact } from "../../src/model";
+
+const schemaUrl = new URL("../../schemas/coauthoring-sidecar.schema.json", import.meta.url);
+const schema = JSON.parse(readFileSync(schemaUrl, "utf8"));
+const ajv = new Ajv({ allErrors: true });
+const validate = ajv.compile(schema);
+
+export function validateSidecar(data: unknown): { valid: boolean; errors: string[] } {
+  const valid = validate(data) as boolean;
+  const errors = (validate.errors ?? []).map((e) => `${e.instancePath || "/"} ${e.message}`);
+  return { valid, errors };
+}
+
+export function expectValidSidecar(artifact: Artifact): void {
+  const { valid, errors } = validateSidecar(JSON.parse(serializeArtifact(artifact)));
+  if (!valid) throw new Error(`sidecar failed schema validation:\n${errors.join("\n")}`);
+}

test/schema.test.ts

@@ -0,0 +1,56 @@
+import { describe, it, expect } from "vitest";
+import { emptyArtifact, serializeArtifact, type Artifact } from "../src/model";
+import { expectValidSidecar, validateSidecar } from "./helpers/validateSidecar";
+
+function fullArtifact(): Artifact {
+  const a = emptyArtifact("docs/x.md");
+  a.anchors["a_1"] = { fingerprint: { text: "alpha", before: "", after: " beta", lineHint: 0 } };
+  a.threads.push({
+    id: "t_1",
+    anchorId: "a_1",
+    status: "open",
+    messages: [{ id: "m_1", author: { kind: "human", id: "ben" }, body: "hi", createdAt: "2026-06-10T00:00:00.000Z" }],
+  });
+  a.attributions.push({
+    id: "at_1",
+    anchorId: "a_1",
+    author: { kind: "agent", id: "claude", agent: { sdk: "@cline/sdk", model: "sonnet", sessionId: "run-1" } },
+    createdAt: "2026-06-10T00:00:00.000Z",
+    updatedAt: "2026-06-10T00:00:00.000Z",
+    turnId: "turn-1",
+  });
+  a.proposals.push({
+    id: "p_1",
+    anchorId: "a_1",
+    replacement: "ALPHA",
+    author: { kind: "agent", id: "claude", agent: { sdk: "@cline/sdk", model: "sonnet", sessionId: "run-1" } },
+    createdAt: "2026-06-10T00:00:00.000Z",
+    instruction: "shout",
+  });
+  return a;
+}
+
+describe("coauthoring-sidecar JSON Schema (F5 SLICE-1, PUC-5)", () => {
+  it("validates the empty artifact and a full artifact", () => {
+    expectValidSidecar(emptyArtifact("docs/x.md"));
+    expectValidSidecar(fullArtifact());
+  });
+
+  it("rejects a structurally broken sidecar with error paths", () => {
+    const broken = JSON.parse(serializeArtifact(fullArtifact()));
+    broken.threads[0].status = "closed"; // not in the enum
+    delete broken.schemaVersion;
+    const { valid, errors } = validateSidecar(broken);
+    expect(valid).toBe(false);
+    expect(errors.some((e) => e.includes("schemaVersion"))).toBe(true);
+  });
+
+  it("accepts unknown fields everywhere (forward compat, INV-16)", () => {
+    const data = JSON.parse(serializeArtifact(fullArtifact()));
+    data.futureSection = [{ id: "f_1" }];
+    data.threads[0].futureField = true;
+    data.threads[0].messages[0].reactions = ["+1"];
+    const { valid } = validateSidecar(data);
+    expect(valid).toBe(true);
+  });
+});