Say what actually went wrong

Every failure produced the same reply: read the directions, and check your
context size. For a card Janitor truncated that was fair. For a request
shape the user never chose, or for a bug in sucker, it blamed them for
something they could not have done anything about — and sent them back to
directions they had already followed.

Failures that can be explained now explain themselves: no card in the
request, no greeting in the chat, a card that arrived truncated (which
keeps the context-size advice, since that is where it belongs), and a
request with nothing in it. Anything else is a bug nobody anticipated, so
the reply says as much, says it is not the user's fault, and asks them to
DM @lyseverian on Discord — an unexplained failure nobody reports never
gets fixed. Internals are never echoed back.

SuckerError is recognised by name as well as by identity, because Next can
bundle a module into more than one chunk and a mismatched class would
quietly send every explained error down the unknown-bug path.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NX2SsmUqQftWTZAY4BDuFa

tests/errors.test.ts

@@ -0,0 +1,44 @@
+/**
+ * Which failures explain themselves, and which ask to be reported.
+ */
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import {
+  CONTACT,
+  NO_CARD,
+  NO_GREETING,
+  SuckerError,
+  TOO_FEW_MESSAGES,
+  TRUNCATED_CARD,
+  isSuckerError,
+  userFacingMessage,
+} from "../src/lib/errors.ts";
+
+test("an explained failure is shown to the user as written", () => {
+  for (const e of [NO_CARD, NO_GREETING, TOO_FEW_MESSAGES, TRUNCATED_CARD]) {
+    assert.equal(userFacingMessage(e), e.message);
+    assert.ok(!/dingus/i.test(e.message), "nobody is called a dingus for these");
+  }
+});
+
+test("an unexplained failure owns it and asks to be reported", () => {
+  const msg = userFacingMessage(new TypeError("Cannot read properties of undefined"));
+  assert.match(msg, /not your fault/i);
+  assert.ok(msg.includes(CONTACT), "must say where to report it");
+  // The internals must not leak into a user-facing reply.
+  assert.ok(!msg.includes("Cannot read properties"));
+});
+
+test("the truncated-card case keeps the context-size advice", () => {
+  assert.match(TRUNCATED_CARD.message, /Context Size/);
+  assert.ok(TRUNCATED_CARD.message.includes(CONTACT));
+});
+
+test("recognised across module boundaries, not just by identity", () => {
+  assert.ok(isSuckerError(new SuckerError("x")));
+  // What a second copy of the class in another bundle would look like.
+  assert.ok(isSuckerError({ name: "SuckerError", message: "x" }));
+  assert.ok(!isSuckerError(new Error("x")));
+  assert.ok(!isSuckerError(null));
+  assert.ok(!isSuckerError("SuckerError"));
+});