feat: implement PI core chat timeline

src/lib/host-api.ts

@@ -66,6 +66,8 @@ type HostApiProxyResponse = {
     ok?: boolean;
     json?: unknown;
     text?: string;
+    bytes?: Uint8Array;
+    contentType?: string;
   };
   error?: { message?: string } | string;
   // backward compatibility fields
@@ -80,6 +82,8 @@ type HostApiProxyData = {
   ok?: boolean;
   json?: unknown;
   text?: string;
+  bytes?: Uint8Array;
+  contentType?: string;
   transport?: 'dispatcher' | 'loopback';
 };
 
@@ -297,6 +301,65 @@ export async function hostApiFetch<T>(path: string, init?: RequestInit): Promise
   }
 }
 
+export interface HostApiBinaryData {
+  bytes: Uint8Array;
+  contentType: string;
+}
+
+export async function hostApiFetchBytes(path: string): Promise<HostApiBinaryData> {
+  const startedAt = Date.now();
+  try {
+    const response = await invokeIpc<HostApiProxyResponse>('hostapi:fetch', {
+      path,
+      method: 'GET',
+      headers: { Accept: 'application/octet-stream' },
+      body: null,
+    });
+    if (!response.ok) throw new Error(resolveProxyErrorMessage(response.error));
+    const data = response.data;
+    if (!data || data.ok === false || (typeof data.status === 'number' && data.status >= 400)) {
+      throw createProxyHttpError(data ?? {});
+    }
+    if (!(data.bytes instanceof Uint8Array) || !data.contentType) {
+      throw new Error('Host API binary response is unavailable');
+    }
+    trackUiEvent('hostapi.fetch', {
+      route: telemetryRoute(path),
+      method: 'GET',
+      source: 'ipc-proxy',
+      durationMs: Date.now() - startedAt,
+      status: data.status ?? 200,
+    });
+    return { bytes: data.bytes, contentType: data.contentType };
+  } catch (error) {
+    const normalized = normalizeAppError(error, { source: 'ipc-proxy', path, method: 'GET' });
+    if (!shouldFallbackToBrowser(normalized.message) || !allowLocalhostFallback()) {
+      throw normalized;
+    }
+  }
+
+  const [token, hostApiBase] = await Promise.all([getHostApiToken(), getHostApiBaseUrl()]);
+  const response = await fetch(`${hostApiBase}${path}`, {
+    headers: {
+      Accept: 'application/octet-stream',
+      Authorization: `Bearer ${token}`,
+    },
+  });
+  if (!response.ok) {
+    throw normalizeAppError(new Error(`HTTP ${response.status}`), {
+      source: 'browser-fallback',
+      path,
+      method: 'GET',
+      status: response.status,
+    });
+  }
+  return {
+    bytes: new Uint8Array(await response.arrayBuffer()),
+    contentType: response.headers.get('content-type')?.split(';', 1)[0]?.trim()
+      || 'application/octet-stream',
+  };
+}
+
 export function createHostEventSource(path = '/api/events'): EventSource {
   // EventSource does not support custom headers, so pass the auth token
   // as a query parameter. The server accepts both mechanisms.