refactor(web): unify form controls, one notification rule, dedupe i18n copy (#54)

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

packages/core/test/describe-error.test.ts

@@ -0,0 +1,45 @@
+import { describe, expect, it } from "vitest";
+import { describeError } from "../src/llm/generative-model.js";
+
+describe("describeError", () => {
+  it("walks the cause chain, surfacing the real reason behind a wrapper like 'terminated'", () => {
+    // Node's fetch throws TypeError("terminated") with the actual transport failure on cause.
+    const cause = Object.assign(new Error("other side closed"), { code: "UND_ERR_SOCKET" });
+    const err = new TypeError("terminated", { cause });
+    expect(describeError(err)).toBe("terminated: other side closed (UND_ERR_SOCKET)");
+  });
+
+  it("appends a top-level error code when not already in the message", () => {
+    const err = Object.assign(new Error("connect failed"), { code: "ECONNREFUSED" });
+    expect(describeError(err)).toBe("connect failed (ECONNREFUSED)");
+  });
+
+  it("does not duplicate a code already present in the message", () => {
+    const err = Object.assign(new Error("connect ECONNREFUSED 1.2.3.4:443"), {
+      code: "ECONNREFUSED",
+    });
+    expect(describeError(err)).toBe("connect ECONNREFUSED 1.2.3.4:443");
+  });
+
+  it("returns a plain message unchanged and stringifies non-Errors", () => {
+    expect(describeError(new Error("boom"))).toBe("boom");
+    expect(describeError("nope")).toBe("nope");
+  });
+
+  it("keeps a non-Error cause tail and de-duplicates repeated segments", () => {
+    expect(describeError(new Error("outer", { cause: "inner reason" }))).toBe(
+      "outer: inner reason",
+    );
+    const a = new Error("same");
+    (a as { cause?: unknown }).cause = new Error("same"); // duplicate message, dropped
+    expect(describeError(a)).toBe("same");
+  });
+
+  it("guards against a cyclic cause chain", () => {
+    const a = new Error("a");
+    const b = new Error("b");
+    (a as { cause?: unknown }).cause = b;
+    (b as { cause?: unknown }).cause = a; // cycle
+    expect(describeError(a)).toBe("a: b");
+  });
+});