feat(brainstorm-companion): resilient reconnect, live status, paused overlay

The injected client reconnected on a fixed 1s timer with no feedback: if the
laptop slept or the server restarted, the page showed 'Connected' over a dead
socket and silently queued events. And when the server stopped, the user got a
bare connection-refused with no explanation.

helper.js now:
- reconnects with exponential backoff (500ms, doubling, capped at 30s; reset on
  open), with an onerror->close handler, nulls the socket on close, and clears a
  pending timer before scheduling another;
- drives the frame status pill Connected/Reconnecting/Disconnected via a
  --status-color custom property (frame-template.html);
- after ~15s disconnected, shows a self-styled 'Companion paused' overlay
  (tombstone) explaining the companion stopped and will reconnect automatically;
- on recovery from a tombstoned outage (e.g. server restarted on the same port)
  reloads to pick up the restarted server's current screen.

The reconnect-backoff is an exported pure function; helper.test.js unit-tests it
(doubling + cap progression) and asserts the status/tombstone/reconnect wiring.
DOM behaviour is verified live.

Refs #856, #1237

tests/brainstorm-server/helper.test.js

@@ -0,0 +1,84 @@
+/**
+ * Tests for the injected browser client (helper.js).
+ *
+ * helper.js runs in the browser, so its DOM behaviour is exercised live; here we
+ * unit-test the pure reconnect-backoff function it exports and assert that the
+ * reconnect / status / tombstone wiring is present.
+ */
+
+const assert = require('assert');
+const fs = require('fs');
+const path = require('path');
+
+const HELPER = path.join(__dirname, '../../skills/brainstorming/scripts/helper.js');
+
+const src = fs.readFileSync(HELPER, 'utf-8');
+
+// helper.js is browser code, and the repo is an ES module package, so a plain
+// require() won't surface its exports. Evaluate the source in a CommonJS sandbox
+// with no `window`, so only the exported pure helpers run (not the browser code).
+const moduleShim = { exports: {} };
+new Function('module', src)(moduleShim);
+const { nextReconnectDelay, MIN_RECONNECT_MS, MAX_RECONNECT_MS, TOMBSTONE_AFTER_MS } = moduleShim.exports;
+
+let passed = 0, failed = 0;
+function test(name, fn) {
+  try { fn(); console.log(`  PASS: ${name}`); passed++; }
+  catch (e) { console.log(`  FAIL: ${name}`); console.log(`    ${e.message}`); failed++; }
+}
+
+console.log('\n--- Backoff (pure) ---');
+
+test('doubles the delay each call', () => {
+  assert.strictEqual(nextReconnectDelay(500, 30000), 1000);
+  assert.strictEqual(nextReconnectDelay(1000, 30000), 2000);
+  assert.strictEqual(nextReconnectDelay(2000, 30000), 4000);
+});
+
+test('caps at the maximum', () => {
+  assert.strictEqual(nextReconnectDelay(20000, 30000), 30000);
+  assert.strictEqual(nextReconnectDelay(30000, 30000), 30000);
+});
+
+test('full progression from MIN caps at MAX and never exceeds it', () => {
+  const seq = [MIN_RECONNECT_MS];
+  let d = MIN_RECONNECT_MS;
+  for (let i = 0; i < 10; i++) { d = nextReconnectDelay(d, MAX_RECONNECT_MS); seq.push(d); }
+  assert.strictEqual(seq[0], 500);
+  assert.deepStrictEqual(seq.slice(0, 7), [500, 1000, 2000, 4000, 8000, 16000, 30000]);
+  assert(seq.every(v => v <= MAX_RECONNECT_MS), 'never exceeds max');
+  assert.strictEqual(seq[seq.length - 1], 30000, 'settles at the cap');
+});
+
+test('exposes sane constants', () => {
+  assert.strictEqual(MIN_RECONNECT_MS, 500);
+  assert.strictEqual(MAX_RECONNECT_MS, 30000);
+  assert(TOMBSTONE_AFTER_MS >= 5000, 'tombstone grace is at least a few seconds');
+});
+
+console.log('\n--- Wiring (source) ---');
+
+test('reflects all three connection states', () => {
+  assert(/Connected/.test(src) && /Reconnecting/.test(src) && /Disconnected/.test(src),
+    'should set Connected / Reconnecting / Disconnected status');
+  assert(src.includes("setProperty('--status-color'"), 'drives the status dot via --status-color');
+});
+
+test('renders a tombstone overlay when paused', () => {
+  assert(src.includes('bs-tombstone'), 'creates the tombstone element');
+  assert(/Companion paused/.test(src), 'tombstone explains the companion paused');
+});
+
+test('hardens reconnection (onerror, null socket, clears pending timer)', () => {
+  assert(src.includes('onerror'), 'handles onerror');
+  assert(/ws = null/.test(src), 'nulls the socket on close so sendEvent queues');
+  assert(src.includes('clearTimeout'), 'clears a pending reconnect before scheduling another');
+  assert(src.includes('nextReconnectDelay'), 'uses exponential backoff for reconnects');
+});
+
+test('reloads on recovery and on reload messages', () => {
+  assert(/location\.reload\(\)/.test(src), 'reloads to pick up restarted/updated content');
+});
+
+console.log(`\n--- Results: ${passed} passed, ${failed} failed ---`);
+if (failed > 0) process.exit(1);

tests/brainstorm-server/package.json

@@ -2,7 +2,7 @@
   "name": "brainstorm-server-tests",
   "version": "1.0.0",
   "scripts": {
-    "test": "node ws-protocol.test.js && node server.test.js && node lifecycle.test.js && bash stop-server.test.sh"
+    "test": "node ws-protocol.test.js && node helper.test.js && node server.test.js && node lifecycle.test.js && bash stop-server.test.sh"
   },
   "dependencies": {
     "ws": "^8.19.0"