test(FN-4787): regression tests for heartbeat identity snapshot

Fusion-Task-Id: FN-4787
Fusion-Task-Lineage: 9f174f4f-d305-4779-ba0d-562f2eab064c

packages/engine/src/__tests__/identity-snapshot.test.ts

@@ -0,0 +1,79 @@
+import { createHash } from "node:crypto";
+import type { Agent } from "@fusion/core";
+import { describe, expect, it } from "vitest";
+import { buildIdentitySnapshot } from "../agent-heartbeat.js";
+
+function makeAgent(overrides: Partial<Agent> = {}): Agent {
+  const now = new Date().toISOString();
+  return {
+    id: "agent-1",
+    name: "Snapshot Agent",
+    role: "engineer",
+    state: "idle",
+    createdAt: now,
+    updatedAt: now,
+    metadata: {},
+    ...overrides,
+  };
+}
+
+function shortHash(value: string): string {
+  return createHash("sha256").update(value).digest("hex").slice(0, 8);
+}
+
+describe("buildIdentitySnapshot", () => {
+  it("renders loaded soul and instructions hashes", () => {
+    const soul = "I deeply care about reliability.";
+    const instructions = "Always run tests before done.";
+    const snapshot = buildIdentitySnapshot({
+      agent: makeAgent({ soul }),
+      resolvedInstructions: { status: "loaded", value: instructions },
+      workspaceMemory: { status: "unset" },
+    });
+
+    expect(snapshot).toContain(`- soul: loaded (${soul.length} chars, sha256:${shortHash(soul)})`);
+    expect(snapshot).toContain(`- instructions: loaded (${instructions.length} chars, sha256:${shortHash(instructions)})`);
+  });
+
+  it("renders empty soul when configured as whitespace", () => {
+    const snapshot = buildIdentitySnapshot({
+      agent: makeAgent({ soul: "   " }),
+      resolvedInstructions: { status: "unset" },
+      workspaceMemory: { status: "unset" },
+    });
+
+    expect(snapshot).toContain("- soul: empty");
+  });
+
+  it("renders unset soul when undefined", () => {
+    const snapshot = buildIdentitySnapshot({
+      agent: makeAgent(),
+      resolvedInstructions: { status: "unset" },
+      workspaceMemory: { status: "unset" },
+    });
+
+    expect(snapshot).toContain("- soul: unset");
+  });
+
+  it("renders instructions load-error distinctly", () => {
+    const snapshot = buildIdentitySnapshot({
+      agent: makeAgent(),
+      resolvedInstructions: { status: "load-error" },
+      workspaceMemory: { status: "unset" },
+    });
+
+    expect(snapshot).toContain("- instructions: load-error");
+    expect(snapshot).not.toContain("- instructions: unset");
+  });
+
+  it("prefers workspace memory with source label when inline memory is absent", () => {
+    const workspaceMemory = "Persist durable architecture constraints.";
+    const snapshot = buildIdentitySnapshot({
+      agent: makeAgent({ memory: undefined }),
+      resolvedInstructions: { status: "unset" },
+      workspaceMemory: { status: "loaded", value: workspaceMemory },
+    });
+
+    expect(snapshot).toContain(`- memory: loaded (${workspaceMemory.length} chars, sha256:${shortHash(workspaceMemory)}, source: workspace)`);
+  });
+});