swarm-ui try-out: stable live region, reasons for disabled buttons

The running line is a live region whose text changed every second, so a
screen reader announced the counter again each time. The sentence is now
stable and the elapsed seconds sit outside it.

The run and open-a-PR buttons point at the hint that says why they are
off, and add-a-classification says why it is off at the cap.

docs/swarm/review-classifier.md

@@ -483,7 +483,10 @@ rows as the review table.
 A page for writing classification prompts without touching the repo. Pick a
 repo and a PR, write or edit a classification, and run it against that PR;
 change the prompt and run it again until it answers the way you want.
-Nothing reaches the forge while you iterate.
+Nothing reaches the forge while you iterate. A button the page disables
+points at a line that says why, such as the 10-classification cap on **add a
+classification**, and a screen reader announces the run's progress once, with
+the elapsed seconds outside the announcement.
 
 The page posts the run to `swarm-controller` (`POST
 /api/review-classifier/try-out`), which reads the PR with its own forge token

frontend/packages/swarm-ui/src/pages/review-tryout/ReviewTryOut.tsx

@@ -33,6 +33,7 @@ import { TextField } from "../../ui/text-field/TextField.js";
 import { ClassificationEditor } from "./ClassificationEditor.js";
 import { TryOutResult } from "./TryOutResult.js";
 import {
+  addProblem,
   draftFromRule,
   hasTypedText,
   prNumber,
@@ -57,10 +58,9 @@ const PULLS = "/api/pulls";
 // does not ask for the PRs of each prefix of it.
 const PICK_DELAY_MS = 300;
 const POLL_MS = 2000;
-// More classifications than this are not offered a row. It is the try-out
-// endpoint's own cap, which answers a longer list with a 400 that the page
-// shows as it is.
-const MAX_CLASSIFICATIONS = 10;
+// Ids the buttons' `aria-describedby` points at.
+const HINT_ID = "tryout-hint";
+const CAP_ID = "tryout-cap";
 
 let nextKey = 0;
 function blankDraft(): ClassificationDraft {
@@ -221,6 +221,7 @@ export function ReviewTryOut() {
 
   const openPrProblem = rowsProblem(repo, drafts);
   const problem = runProblem(repo, pr, drafts);
+  const capProblem = addProblem(drafts.length);
 
   async function run(e: Event) {
     e.preventDefault();
@@ -398,7 +399,8 @@ export function ReviewTryOut() {
           <div class="ui-tryout-actions">
             <Button
               onClick={() => setDrafts((ds) => [...ds, blankDraft()])}
-              disabled={drafts.length >= MAX_CLASSIFICATIONS}
+              disabled={capProblem !== null}
+              describedBy={capProblem !== null ? CAP_ID : undefined}
             >
               add a classification
             </Button>
@@ -406,17 +408,28 @@ export function ReviewTryOut() {
               variant="primary"
               type="submit"
               disabled={running || problem !== null}
+              describedBy={problem !== null ? HINT_ID : undefined}
             >
               {running ? "running…" : "run"}
             </Button>
             <Button
               onClick={() => void openPr()}
               disabled={opening || openPrProblem !== null}
+              describedBy={openPrProblem !== null ? HINT_ID : undefined}
             >
               {opening ? "pushing…" : "open a PR"}
             </Button>
           </div>
-          {problem !== null ? <p class="ui-tryout-hint">{problem}</p> : null}
+          {capProblem !== null ? (
+            <p id={CAP_ID} class="ui-tryout-hint">
+              {capProblem}
+            </p>
+          ) : null}
+          {problem !== null ? (
+            <p id={HINT_ID} class="ui-tryout-hint">
+              {problem}
+            </p>
+          ) : null}
           {openError ? (
             <ApiErrorPanel
               context="the branch for the PR could not be pushed"
@@ -450,10 +463,13 @@ export function ReviewTryOut() {
       {running || result || error ? (
         <Panel title="result" icon="📋">
           {running ? (
+            <>
               <p class="ui-tryout-running" role="status">
-              Running — a run takes a minute or more, and up to half an hour for
-              a long list ({elapsed}s so far).
+                Running — a run takes a minute or more, and up to half an hour
+                for a long list.
               </p>
+              <p class="ui-tryout-running">{elapsed}s so far</p>
+            </>
           ) : null}
           {error ? (
             <ApiErrorPanel context="the try-out failed" problem={error} />

frontend/packages/swarm-ui/src/pages/review-tryout/TryOutTypes.ts

@@ -150,6 +150,17 @@ export function duplicateName(drafts: ClassificationDraft[]): string | null {
   return null;
 }
 
+/** More classifications than this are not offered a row. It is the try-out
+ * endpoint's own cap, which answers a longer list with a 400. */
+export const MAX_CLASSIFICATIONS = 10;
+
+/** Why another row cannot be added, or null while there is room. */
+export function addProblem(count: number): string | null {
+  return count >= MAX_CLASSIFICATIONS
+    ? `a run takes at most ${MAX_CLASSIFICATIONS} classifications`
+    : null;
+}
+
 /** What keeps the rows from going to the repo as a PR, or null: the repo, then
  * each row, then a shared name. Unlike a run, it needs no PR number. */
 export function rowsProblem(

frontend/packages/swarm-ui/src/ui/button/Button.tsx

@@ -14,12 +14,15 @@ export function Button({
   type = "button",
   disabled,
   onClick,
+  describedBy,
   children,
 }: {
   variant?: ButtonVariant;
   type?: "button" | "submit";
   disabled?: boolean;
   onClick?: (e: Event) => void;
+  /** Id of the element that says why the button is disabled. */
+  describedBy?: string;
   children: ComponentChildren;
 }) {
   return (
@@ -28,6 +31,7 @@ export function Button({
       type={type}
       disabled={disabled}
       onClick={onClick}
+      aria-describedby={describedBy}
     >
       {children}
     </button>

frontend/packages/swarm-ui/test/tryout-types.test.mjs

@@ -5,6 +5,8 @@
 import assert from "node:assert/strict";
 import { test } from "node:test";
 import {
+  MAX_CLASSIFICATIONS,
+  addProblem,
   draftFromRule,
   draftProblem,
   duplicateName,
@@ -17,6 +19,12 @@ import {
   toBody,
 } from "../src/pages/review-tryout/TryOutTypes.ts";
 
+test("a row is offered until the endpoint's cap is reached", () => {
+  assert.equal(addProblem(1), null);
+  assert.equal(addProblem(MAX_CLASSIFICATIONS - 1), null);
+  assert.match(addProblem(MAX_CLASSIFICATIONS), /at most 10 classifications/);
+});
+
 // A row ready to send, with `over` replacing any of its fields.
 function row(over = {}) {
   return {