refactor(streaming): share approval and stream message builders

src/agents/stream-message-shared.ts

@@ -0,0 +1,53 @@
+import type { AssistantMessage, StopReason, Usage } from "@mariozechner/pi-ai";
+
+export type StreamModelDescriptor = {
+  api: string;
+  provider: string;
+  id: string;
+};
+
+export function buildZeroUsage(): Usage {
+  return {
+    input: 0,
+    output: 0,
+    cacheRead: 0,
+    cacheWrite: 0,
+    totalTokens: 0,
+    cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+  };
+}
+
+export function buildAssistantMessageWithZeroUsage(params: {
+  model: StreamModelDescriptor;
+  content: AssistantMessage["content"];
+  stopReason: StopReason;
+  timestamp?: number;
+}): AssistantMessage {
+  return {
+    role: "assistant",
+    content: params.content,
+    stopReason: params.stopReason,
+    api: params.model.api,
+    provider: params.model.provider,
+    model: params.model.id,
+    usage: buildZeroUsage(),
+    timestamp: params.timestamp ?? Date.now(),
+  };
+}
+
+export function buildStreamErrorAssistantMessage(params: {
+  model: StreamModelDescriptor;
+  errorMessage: string;
+  timestamp?: number;
+}): AssistantMessage & { stopReason: "error"; errorMessage: string } {
+  return {
+    ...buildAssistantMessageWithZeroUsage({
+      model: params.model,
+      content: [],
+      stopReason: "error",
+      timestamp: params.timestamp,
+    }),
+    stopReason: "error",
+    errorMessage: params.errorMessage,
+  };
+}