feat: soften block streaming chunking

src/agents/pi-embedded-subscribe.test.ts

@@ -231,6 +231,58 @@ describe("subscribeEmbeddedPiSession", () => {
     expect(subscription.assistantTexts).toEqual(["Hello block"]);
   });
 
+  it("streams soft chunks with paragraph preference", () => {
+    let handler: ((evt: unknown) => void) | undefined;
+    const session: StubSession = {
+      subscribe: (fn) => {
+        handler = fn;
+        return () => {};
+      },
+    };
+
+    const onBlockReply = vi.fn();
+
+    const subscription = subscribeEmbeddedPiSession({
+      session: session as unknown as Parameters<
+        typeof subscribeEmbeddedPiSession
+      >[0]["session"],
+      runId: "run",
+      onBlockReply,
+      blockReplyBreak: "message_end",
+      blockReplyChunking: {
+        minChars: 5,
+        maxChars: 40,
+        breakPreference: "paragraph",
+      },
+    });
+
+    const text = "First block line\n\nSecond block line";
+
+    handler?.({
+      type: "message_update",
+      message: { role: "assistant" },
+      assistantMessageEvent: {
+        type: "text_delta",
+        delta: text,
+      },
+    });
+
+    const assistantMessage = {
+      role: "assistant",
+      content: [{ type: "text", text }],
+    } as AssistantMessage;
+
+    handler?.({ type: "message_end", message: assistantMessage });
+
+    expect(onBlockReply).toHaveBeenCalledTimes(2);
+    expect(onBlockReply.mock.calls[0][0].text).toBe("First block line");
+    expect(onBlockReply.mock.calls[1][0].text).toBe("Second block line");
+    expect(subscription.assistantTexts).toEqual([
+      "First block line",
+      "Second block line",
+    ]);
+  });
+
   it("waits for auto-compaction retry and clears buffered text", async () => {
     const listeners: SessionEventHandler[] = [];
     const session = {