Add a README to the client library

packages/libs/client/README.md

@@ -0,0 +1,79 @@
+# @restate-agents/client
+
+A typed HTTP client for one agent, through the Restate ingress. It runs in
+Node and in the browser. Each method calls one public handler of `Agent` or
+`AgentSession`.
+
+```ts
+import {createAgentClient} from "@restate-agents/client";
+
+const agent = createAgentClient({
+  ingressUrl: "http://localhost:8080",
+  agentId: "demo",
+});
+
+await agent.ask("What is the weather in Berlin?");
+
+for await (const {sequence, entry} of agent.follow()) {
+  if (entry.role === "assistant") {
+    console.log(sequence, entry.text);
+  }
+}
+```
+
+## Options
+
+| Option | Meaning |
+| --- | --- |
+| `ingressUrl` | Restate ingress base URL, such as `http://localhost:8080` |
+| `agentId` | The agent's key. A new ID creates an agent |
+| `headers` | Sent with every request, such as `Authorization: Bearer <token>` |
+| `retry` | Retry policy for idempotent calls. On by default |
+
+## Methods
+
+| Area | Methods |
+| --- | --- |
+| Conversation | `ask`, `steer`, `interrupt`, `deliver` |
+| Reading | `history`, `notifications`, `watch`, `follow` |
+| Profile and memory | `profile`, `updateProfile`, `searchMemories`, `readMemories`, `deleteMemory`, `toolCatalog` |
+| Lifecycle | `metadata`, `children`, `retire` |
+| Schedules | `schedules`, `createSchedule`, `cancelSchedule` |
+| Approvals | `approvals`, `resolveApproval` |
+
+`follow` is the one method that is not a single handler. It reads the history
+from a cursor, and when it has caught up it waits for new entries with
+`watch`. It keeps going until its `signal` aborts:
+
+```ts
+const stop = new AbortController();
+
+for await (const {entry} of agent.follow({fromSequence: 1, signal: stop.signal})) {
+  // ...
+}
+```
+
+A network failure does not end the stream: `follow` waits and tries again.
+A failed wait retries under the same idempotency key, so it joins the wait
+already parked in Restate instead of starting another.
+
+## Errors
+
+A call that Restate rejects throws `AgentClientError`, with the HTTP
+`status` and the handler's error message.
+
+```ts
+import {AgentClientError} from "@restate-agents/client";
+
+try {
+  await agent.retire();
+} catch (error) {
+  if (error instanceof AgentClientError) {
+    console.error(error.status, error.message);
+  }
+}
+```
+
+The payloads and what each handler does are in
+[`docs/protocol.md`](../../../docs/protocol.md). The web app uses this client
+in `packages/apps/web/src/server/restate.ts`.