GPT-5.3-Codex vs GPT-5.6 Sol for vibe coding

- Add labels for bill and tip fields to improve accessibility.
- Validate bill is a non-negative number; show helpful error when invalid.
- Use `document.getElementById` in `calc()` instead of implicit global element variables.

```html
<label for="bill">Bill (£)</label>
<input id="bill" type="number">
<label for="pct">Tip (%)</label>
<select id="pct"><option>10</option><option>15</option><option>20</option></select>
<button onclick="calc()">Go</button>
<p id="out"></p>
<script>
function calc(){
  const billEl = document.getElementById('bill');…

- Add accessible labels for bill amount and tip percentage.
- Reject empty, non-finite, or negative bill amounts with a clear message.
- Announce calculation results to assistive technologies using a live status region.

```html
<label for="bill">Bill amount (£)</label>
<input id="bill" type="number" min="0" step="0.01">

<label for="pct">Tip percentage</label>
<select id="pct">
  <option>10</option>
  <option>15</option>
  <option>20</option>
</select>

<button onclick="calc()">Go</button>
<p id="out" role="status" aria-live="polite"></p>

<sc…