feat: add Pi conversation worker pool

tests/fixtures/fake-pi-pool-child.mjs

@@ -0,0 +1,66 @@
+let input = '';
+let activeTimer = null;
+let activeMarker = null;
+
+function write(record) {
+  process.stdout.write(`${JSON.stringify(record)}\n`);
+}
+
+function respond(command, data = {}) {
+  write({
+    type: 'response',
+    id: command.id,
+    command: command.type,
+    success: true,
+    data,
+  });
+}
+
+function settle(reason) {
+  if (!activeMarker) return;
+  write({ type: 'agent_end', marker: activeMarker, reason });
+  write({ type: 'agent_settled', marker: activeMarker, reason });
+  activeMarker = null;
+  activeTimer = null;
+}
+
+function handle(command) {
+  if (command.type === 'prompt') {
+    activeMarker = command.message;
+    respond(command, { accepted: true });
+    write({ type: 'agent_start', marker: activeMarker });
+    activeTimer = setTimeout(() => settle('completed'), Number(command.delayMs ?? 100));
+    return;
+  }
+  if (command.type === 'abort') {
+    if (activeTimer) clearTimeout(activeTimer);
+    respond(command, { aborted: Boolean(activeMarker) });
+    settle('aborted');
+    return;
+  }
+  if (command.type === 'get_state') {
+    respond(command, { sessionId: `session-${process.pid}` });
+    return;
+  }
+  if (command.type === 'get_entries') {
+    respond(command, { entries: [] });
+    return;
+  }
+  respond(command);
+}
+
+process.stdin.setEncoding('utf8');
+process.stdin.on('data', (chunk) => {
+  input += chunk;
+  while (true) {
+    const newline = input.indexOf('\n');
+    if (newline === -1) break;
+    const line = input.slice(0, newline).replace(/\r$/, '');
+    input = input.slice(newline + 1);
+    if (line) handle(JSON.parse(line));
+  }
+});
+process.stdin.on('end', () => {
+  if (activeTimer) clearTimeout(activeTimer);
+  process.exit(0);
+});