Derive the notation names from one table and refuse an smsIdFormat that is not the pair

test/session-extras.test.ts

@@ -872,6 +872,8 @@ describe('message id notation', () => {
 
 		assert.ok(checked.err instanceof Error);
 		assert.match(checked.err.message, /smsIdFormat\.receipt/);
+		// The shape todo.md sketched, which a caller without types would otherwise pass unnoticed.
+		assert.ok(checkSessionOptions({ smsIdFormat: 'hex' }).err instanceof Error);
 		assert.equal(checkSessionOptions({ smsIdFormat: { submitResp: 'hex' } }).err, undefined);
 	});
 });

test/sms-id.test.ts

@@ -0,0 +1,23 @@
+import assert from 'node:assert/strict';
+import test, { describe } from 'node:test';
+import { normaliseSmsId } from '../src/sms-id.ts';
+
+describe('normaliseSmsId()', () => {
+	test('reads an id the length a message_id may be, and leaves a longer one alone', () => {
+		const padded = `0${'1'.repeat(63)}`;
+		const tooLong = `0${'1'.repeat(64)}`;
+
+		assert.equal(normaliseSmsId(padded, 'decimal'), '1'.repeat(63));
+		assert.equal(normaliseSmsId(tooLong, 'decimal'), tooLong);
+	});
+
+	test('leaves an id the notation cannot read as it arrived', () => {
+		assert.equal(normaliseSmsId('', 'hex'), '');
+		assert.equal(normaliseSmsId('0x1f', 'hex'), '0x1f');
+		assert.equal(normaliseSmsId('beef-1', 'hex'), 'beef-1', 'the segment convention stays whole');
+	});
+
+	test('reads either case of a hexadecimal id', () => {
+		assert.equal(normaliseSmsId('1a2B', 'hex'), normaliseSmsId('1A2b', 'hex'));
+	});
+});