fix(agents): unwrap read_agent_context DTO content (#140)

Le contexte projet d'un agent s'affichait "[object Object]" et se
vidait à la réouverture du panneau : read_agent_context renvoie déjà
{content} côté backend, mais les gateways front traitaient la réponse
comme une string brute. Les deux gateways (Tauri + HTTP) unwrap
maintenant .content ; type AgentContextDocument ajouté au domaine.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/adapters/http/agentGateway.test.ts

@@ -8,7 +8,7 @@
 import { describe, it, expect, vi } from "vitest";
 
 import { HttpAgentGateway } from "./streamGateways";
-import { HttpInvoker } from "./httpInvoker";
+import { HttpInvoker, type FetchLike } from "./httpInvoker";
 import { WsLiveClient, type WebSocketLike } from "./wsLiveClient";
 import { bytesToBase64 } from "./frames";
 
@@ -45,6 +45,27 @@ function gateway(): { gw: HttpAgentGateway; sockets: FakeSocket[] } {
   return { gw, sockets };
 }
 
+function httpAgentGateway(
+  fetchImpl: FetchLike,
+): { gw: HttpAgentGateway; calls: { url: string; init: unknown }[] } {
+  const calls: { url: string; init: unknown }[] = [];
+  const recordingFetch: FetchLike = async (url, init) => {
+    calls.push({ url, init });
+    return fetchImpl(url, init);
+  };
+  const ws = new WsLiveClient({
+    wsUrl: "wss://host",
+    socketFactory: () => new FakeSocket(),
+  });
+  return {
+    gw: new HttpAgentGateway(
+      new HttpInvoker({ baseUrl: "https://host", fetchImpl: recordingFetch }),
+      ws,
+    ),
+    calls,
+  };
+}
+
 async function replyToLast(
   socket: FakeSocket,
   index: number,
@@ -78,6 +99,26 @@ function attachedAck(
 const OPTS = { cwd: "/srv/app", rows: 24, cols: 80, nodeId: "node-1" };
 
 describe("HttpAgentGateway WS round-trip (B6 frames)", () => {
+  it("readContext unwraps the read_agent_context DTO content over HTTP", async () => {
+    const { gw, calls } = httpAgentGateway(async () => ({
+      ok: true,
+      status: 200,
+      json: async () => ({ content: "## Restored context" }),
+      text: async () => JSON.stringify({ content: "## Restored context" }),
+    }));
+
+    await expect(gw.readContext("proj-1", "agent-1")).resolves.toBe(
+      "## Restored context",
+    );
+
+    expect(calls).toHaveLength(1);
+    const init = calls[0].init as { body: string };
+    expect(JSON.parse(init.body)).toEqual({
+      command: "read_agent_context",
+      args: { projectId: "proj-1", agentId: "agent-1" },
+    });
+  });
+
   it("launch → attached: conforming agent.launch frame, assignedConversationId consumed", async () => {
     const { gw, sockets } = gateway();
     const chunks: Uint8Array[] = [];