From 1fa7a587d6332572e5811bd93027ef81dc2bde45 Mon Sep 17 00:00:00 2001
From: Peter Steinberger <steipete@gmail.com>
Date: Mon, 12 Jan 2026 02:54:57 +0000
Subject: [PATCH] fix: flush block reply buffers on tool boundaries (#750)
 (thanks @sebslight)

---
 CHANGELOG.md                             |  1 +
 src/agents/pi-embedded-subscribe.test.ts | 54 ++++++++++++++++++++++++
 src/agents/pi-embedded-subscribe.ts      | 16 ++++++-
 3 files changed, 70 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5930eac9c..f1a6b23ef 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -34,6 +34,7 @@
 - Plugins: treat `plugins.load.paths` directory entries as package roots when they contain `package.json` + `clawdbot.extensions`.
 - Config: expand `~` in `CLAWDBOT_CONFIG_PATH` and common path-like config fields (including `plugins.load.paths`).
 - Auto-reply: align `/think` default display with model reasoning defaults. (#751) — thanks @gabriel-trigo.
+- Auto-reply: flush block reply buffers on tool boundaries. (#750) — thanks @sebslight.
 - Docker: tolerate unset optional env vars in docker-setup.sh under strict mode. (#725) — thanks @petradonka.
 - CLI/Update: preserve base environment when passing overrides to update subprocesses. (#713) — thanks @danielz1z.
 - Agents: treat message tool errors as failures so fallback replies still send; require `to` + `message` for `action=send`. (#717) — thanks @theglove44.
diff --git a/src/agents/pi-embedded-subscribe.test.ts b/src/agents/pi-embedded-subscribe.test.ts
index 974faea4d..2b8afa6fb 100644
--- a/src/agents/pi-embedded-subscribe.test.ts
+++ b/src/agents/pi-embedded-subscribe.test.ts
@@ -1815,6 +1815,60 @@ describe("subscribeEmbeddedPiSession", () => {
     expect(onBlockReplyFlush).toHaveBeenCalledTimes(2);
   });
 
+  it("flushes buffered block chunks before tool execution", () => {
+    let handler: SessionEventHandler | undefined;
+    const session: StubSession = {
+      subscribe: (fn) => {
+        handler = fn;
+        return () => {};
+      },
+    };
+
+    const onBlockReply = vi.fn();
+    const onBlockReplyFlush = vi.fn();
+
+    subscribeEmbeddedPiSession({
+      session: session as unknown as Parameters<
+        typeof subscribeEmbeddedPiSession
+      >[0]["session"],
+      runId: "run-flush-buffer",
+      onBlockReply,
+      onBlockReplyFlush,
+      blockReplyBreak: "text_end",
+      blockReplyChunking: { minChars: 50, maxChars: 200 },
+    });
+
+    handler?.({
+      type: "message_start",
+      message: { role: "assistant" },
+    });
+
+    handler?.({
+      type: "message_update",
+      message: { role: "assistant" },
+      assistantMessageEvent: {
+        type: "text_delta",
+        delta: "Short chunk.",
+      },
+    });
+
+    expect(onBlockReply).not.toHaveBeenCalled();
+
+    handler?.({
+      type: "tool_execution_start",
+      toolName: "bash",
+      toolCallId: "tool-flush-buffer-1",
+      args: { command: "echo flush" },
+    });
+
+    expect(onBlockReply).toHaveBeenCalledTimes(1);
+    expect(onBlockReply.mock.calls[0]?.[0]?.text).toBe("Short chunk.");
+    expect(onBlockReplyFlush).toHaveBeenCalledTimes(1);
+    expect(onBlockReply.mock.invocationCallOrder[0]).toBeLessThan(
+      onBlockReplyFlush.mock.invocationCallOrder[0],
+    );
+  });
+
   it("does not call onBlockReplyFlush when callback is not provided", () => {
     let handler: SessionEventHandler | undefined;
     const session: StubSession = {
diff --git a/src/agents/pi-embedded-subscribe.ts b/src/agents/pi-embedded-subscribe.ts
index f69209dd0..9b9b04f68 100644
--- a/src/agents/pi-embedded-subscribe.ts
+++ b/src/agents/pi-embedded-subscribe.ts
@@ -446,6 +446,19 @@ export function subscribeEmbeddedPiSession(params: {
     });
   };
 
+  const flushBlockReplyBuffer = () => {
+    if (!params.onBlockReply) return;
+    if (blockChunker?.hasBuffered()) {
+      blockChunker.drain({ force: true, emit: emitBlockChunk });
+      blockChunker.reset();
+      return;
+    }
+    if (blockBuffer.length > 0) {
+      emitBlockChunk(blockBuffer);
+      blockBuffer = "";
+    }
+  };
+
   const emitReasoningStream = (text: string) => {
     if (!streamReasoning || !params.onReasoningStream) return;
     const formatted = formatReasoningMessage(text);
@@ -485,7 +498,8 @@ export function subscribeEmbeddedPiSession(params: {
       }
 
       if (evt.type === "tool_execution_start") {
-        // Flush pending block replies to preserve message boundaries before tool execution
+        // Flush pending block replies to preserve message boundaries before tool execution.
+        flushBlockReplyBuffer();
         if (params.onBlockReplyFlush) {
           void params.onBlockReplyFlush();
         }