feat: add harness adapter registry for multi-harness support

Co-Authored-By: Codex (GPT-5.5) <noreply@openai.com>

Author: ithiria894

src/harness/registry.mjs

@@ -0,0 +1,95 @@
+import { readdir } from "node:fs/promises";
+import { join } from "node:path";
+import { pathToFileURL } from "node:url";
+import { validateAdapter } from "./interface.mjs";
+
+const adapters = new Map();
+let discoveryPromise = null;
+
+function adapterSummary(adapter) {
+  return {
+    id: adapter.id,
+    displayName: adapter.displayName,
+    shortName: adapter.shortName,
+    icon: adapter.icon,
+  };
+}
+
+async function importAdapterModule(filePath) {
+  const mod = await import(pathToFileURL(filePath).href);
+  const candidates = [];
+
+  if (mod.default) candidates.push(mod.default);
+  if (mod.adapter) candidates.push(mod.adapter);
+  if (Array.isArray(mod.adapters)) candidates.push(...mod.adapters);
+
+  for (const candidate of candidates) {
+    registerAdapter(candidate);
+  }
+}
+
+async function discoverAdapters() {
+  const adaptersDir = join(import.meta.dirname, "adapters");
+
+  let entries;
+  try {
+    entries = await readdir(adaptersDir, { withFileTypes: true });
+  } catch {
+    return;
+  }
+
+  await Promise.all(
+    entries
+      .filter(entry => entry.isFile() && entry.name.endsWith(".mjs"))
+      .map(entry => importAdapterModule(join(adaptersDir, entry.name)))
+  );
+}
+
+async function ensureDiscovered() {
+  if (!discoveryPromise) discoveryPromise = discoverAdapters();
+  await discoveryPromise;
+}
+
+/**
+ * Register one harness adapter.
+ *
+ * @param {import("./interface.mjs").HarnessAdapter} adapter
+ * @returns {import("./interface.mjs").HarnessAdapter}
+ */
+export function registerAdapter(adapter) {
+  const validated = validateAdapter(adapter);
+  adapters.set(validated.id, validated);
+  return validated;
+}
+
+/**
+ * Return a registered adapter by id.
+ *
+ * @param {string} id
+ * @returns {Promise<import("./interface.mjs").HarnessAdapter>}
+ */
+export async function getAdapter(id) {
+  await ensureDiscovered();
+  const adapter = adapters.get(id);
+  if (!adapter) throw new Error(`Unknown harness adapter: ${id}`);
+  return adapter;
+}
+
+/**
+ * List registered adapter descriptors.
+ *
+ * @returns {Promise<Array<{ id: string, displayName: string, shortName: string, icon: string }>>}
+ */
+export async function listAdapters() {
+  await ensureDiscovered();
+  return [...adapters.values()].map(adapterSummary);
+}
+
+/**
+ * Default harness adapter id.
+ *
+ * @returns {string}
+ */
+export function getDefaultAdapterId() {
+  return "claude";
+}