From 5fb4a4abae864955b63dc5c20136f3269338b4ef Mon Sep 17 00:00:00 2001
From: bandzalkin <natan.zalkin@band.ai>
Date: Wed, 21 Oct 2026 15:26:56 +0300
Subject: [PATCH 1/2] fix: measure redacted file content with lone surrogates

A lone surrogate in band_send_room_file's content made the redactor's
byte count raise UnicodeEncodeError, dropping the whole tool_call event.
Encode with surrogatepass so the placeholder is measured and emitted.
---
 src/band/runtime/tools/registry.py            |  4 ++-
 .../copilot_sdk/test_tool_bridging.py         | 26 +++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/band/runtime/tools/registry.py b/src/band/runtime/tools/registry.py
index 28dc3df16..dcae0f26a 100644
--- a/src/band/runtime/tools/registry.py
+++ b/src/band/runtime/tools/registry.py
@@ -906,7 +906,9 @@ def redact_tool_call_args(tool_name: str, args: dict[str, Any]) -> dict[str, Any
         return args
     return {
         **args,
-        "content": file_content_placeholder(len(content.encode("utf-8"))),
+        "content": file_content_placeholder(
+            len(content.encode("utf-8", "surrogatepass"))
+        ),
     }
 
 
diff --git a/tests/adapters/copilot_sdk/test_tool_bridging.py b/tests/adapters/copilot_sdk/test_tool_bridging.py
index 4646d24ec..f96f736b6 100644
--- a/tests/adapters/copilot_sdk/test_tool_bridging.py
+++ b/tests/adapters/copilot_sdk/test_tool_bridging.py
@@ -419,3 +419,29 @@ async def test_tool_call_event_redacts_file_content(self):
             == f"<{len(raw_content.encode('utf-8'))} byte file content>"
         )
         assert raw_content not in call_event["content"]
+
+    @pytest.mark.asyncio
+    async def test_lone_surrogate_file_content_is_redacted_without_losing_event(self):
+        client = FakeCopilotClient()
+        adapter = await make_started_adapter(client, emit=Emit.TOOL_CALLS)
+        tools = _SendRoomFileFakeTools()
+        await run_message(adapter, tools)
+        handler = client.sessions[0].find_tool("band_send_room_file").handler
+        await handler(
+            ToolInvocation(
+                tool_call_id="surrogate-file",
+                tool_name="band_send_room_file",
+                arguments={"content": "\ud800", "filename": "notes.txt"},
+            )
+        )
+        call = json.loads(
+            next(e for e in tools.events_sent if e["message_type"] == "tool_call")[
+                "content"
+            ]
+        )
+        assert call["tool_call_id"] == "surrogate-file"
+        assert call["name"] == "band_send_room_file"
+        assert call["args"] == {
+            "filename": "notes.txt",
+            "content": "<3 byte file content>",
+        }

From 90292db5453ebb43aa4f77497741f0d35be64406 Mon Sep 17 00:00:00 2001
From: Alexander Zaikman <alexander.zaikman@band.ai>
Date: Fri, 23 Oct 2026 05:35:47 +0300
Subject: [PATCH 2/2] test: clarify surrogate redaction event assertion

---
 tests/adapters/copilot_sdk/test_tool_bridging.py | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/tests/adapters/copilot_sdk/test_tool_bridging.py b/tests/adapters/copilot_sdk/test_tool_bridging.py
index f96f736b6..9f84d48b5 100644
--- a/tests/adapters/copilot_sdk/test_tool_bridging.py
+++ b/tests/adapters/copilot_sdk/test_tool_bridging.py
@@ -10,9 +10,10 @@
 from pydantic import BaseModel, model_validator
 
 from band.adapters.copilot_sdk import _COPILOT_SDK_AVAILABLE
-from band.core.types import Emit
+from band.core.types import Emit, MessageType
 from band.runtime.custom_tools import declares_turn_effect
 from band.runtime.tools import ToolCallOutcome, TurnEffect
+from band.testing.fake_tools import events_of_type
 from tests.adapters.copilot_sdk.fakes import (
     FakeCopilotClient,
     FakeCopilotSession,
@@ -421,7 +422,9 @@ async def test_tool_call_event_redacts_file_content(self):
         assert raw_content not in call_event["content"]
 
     @pytest.mark.asyncio
-    async def test_lone_surrogate_file_content_is_redacted_without_losing_event(self):
+    async def test_lone_surrogate_file_content_is_redacted_without_losing_event(
+        self,
+    ) -> None:
         client = FakeCopilotClient()
         adapter = await make_started_adapter(client, emit=Emit.TOOL_CALLS)
         tools = _SendRoomFileFakeTools()
@@ -434,11 +437,8 @@ async def test_lone_surrogate_file_content_is_redacted_without_losing_event(self
                 arguments={"content": "\ud800", "filename": "notes.txt"},
             )
         )
-        call = json.loads(
-            next(e for e in tools.events_sent if e["message_type"] == "tool_call")[
-                "content"
-            ]
-        )
+        (call_event,) = events_of_type(tools, MessageType.TOOL_CALL)
+        call = json.loads(call_event["content"])
         assert call["tool_call_id"] == "surrogate-file"
         assert call["name"] == "band_send_room_file"
         assert call["args"] == {