fix(errors): warn on raw stringify fallback

tests/unit/error-taxonomy.test.ts

@@ -0,0 +1,42 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+vi.mock("electron-log/main.js", () => ({
+  default: {
+    warn: vi.fn(),
+  },
+}));
+
+import log from "electron-log/main.js";
+import { classifyUnknownError } from "../../src/main/errors/taxonomy";
+
+const warn = vi.mocked(log.warn);
+
+describe("error taxonomy", () => {
+  beforeEach(() => {
+    warn.mockClear();
+  });
+
+  it("warns once when raw thrown values cannot be JSON stringified", () => {
+    const raw: { self?: unknown } = {};
+    raw.self = raw;
+
+    const first = classifyUnknownError(raw, {
+      kind: "recoverable",
+      code: "test.raw.cyclic",
+      message: "Cyclic raw value.",
+    });
+    const second = classifyUnknownError(raw, {
+      kind: "recoverable",
+      code: "test.raw.cyclic",
+      message: "Cyclic raw value.",
+    });
+
+    expect(first.context?.raw).toBe("[object Object]");
+    expect(second.context?.raw).toBe("[object Object]");
+    expect(warn).toHaveBeenCalledTimes(1);
+    expect(warn).toHaveBeenCalledWith(
+      "[errors] stringifyRaw failed; using String(value) for raw thrown value.",
+      expect.stringContaining("circular"),
+    );
+  });
+});