fix: recover from mid-run sandbox death (#1274)

* fix: recover from mid-run sandbox death

Recreate dead sandboxes during tool execution and stop repeated unrecoverable timeout loops with a user-facing notification.

* fix: count repeated sandbox recreations

Treat consecutive sandbox recreations as an unrecovered failure streak so outages cannot loop until the model-call limit.

agent/middleware/__init__.py

@@ -3,6 +3,7 @@ from .ensure_no_empty_msg import ensure_no_empty_msg
 from .exclude_tools import ExcludeToolsMiddleware
 from .notify_step_limit import notify_step_limit_reached
 from .refresh_slack_status import SlackAssistantStatusMiddleware
+from .sandbox_circuit_breaker import SandboxCircuitBreakerMiddleware
 from .sanitize_tool_inputs import SanitizeToolInputsMiddleware
 from .tool_error_handler import ToolErrorMiddleware
 
@@ -10,6 +11,7 @@ __all__ = [
     "ExcludeToolsMiddleware",
     "SanitizeToolInputsMiddleware",
     "ToolErrorMiddleware",
+    "SandboxCircuitBreakerMiddleware",
     "SlackAssistantStatusMiddleware",
     "check_message_queue_before_model",
     "ensure_no_empty_msg",

agent/middleware/sandbox_circuit_breaker.py

@@ -0,0 +1,261 @@
+"""Circuit breaker for repeated unrecoverable sandbox failures."""
+
+from __future__ import annotations
+
+import logging
+import re
+from collections.abc import Mapping, Sequence
+from dataclasses import dataclass
+from typing import Any, Literal
+
+from langchain.agents.middleware import AgentMiddleware, AgentState, hook_config
+from langchain_core.messages import AIMessage, BaseMessage, ToolMessage
+from langgraph.config import get_config
+from langgraph.runtime import Runtime
+
+from ..utils.github_app import get_github_app_installation_token
+from ..utils.github_comments import post_github_comment
+from ..utils.github_token import get_github_token
+from ..utils.linear import comment_on_linear_issue
+from ..utils.slack import post_slack_thread_reply
+
+logger = logging.getLogger(__name__)
+
+SANDBOX_CIRCUIT_BREAKER_THRESHOLD = 2
+SANDBOX_UNRECOVERABLE_MESSAGE = "Sandbox became unrecoverable mid-task. Please retrigger."
+
+_CIRCUIT_BREAKER_MARKER = "Sandbox circuit breaker triggered"
+_SANDBOX_RECREATED_AFTER_CLIENT_ERROR = "sandbox_recreated_after_client_error"
+_SANDBOX_ID_RE = re.compile(r"\bsb-[A-Za-z0-9-]+\b")
+
+
+@dataclass(frozen=True)
+class SandboxErrorStreak:
+    reason: Literal["client_error", "recreated"]
+    sandbox_id: str | None
+    count: int
+
+
+def _content_to_text(content: object) -> str:
+    if isinstance(content, str):
+        return content
+    if not isinstance(content, list):
+        return str(content)
+
+    parts: list[str] = []
+    for block in content:
+        if isinstance(block, Mapping):
+            text = block.get("text", "")
+            parts.append(text if isinstance(text, str) else str(text))
+        else:
+            parts.append(str(block))
+    return " ".join(parts)
+
+
+def _extract_sandbox_id(text: str) -> str | None:
+    match = _SANDBOX_ID_RE.search(text)
+    return match.group(0) if match else None
+
+
+def _last_message_has_circuit_breaker_marker(messages: Sequence[BaseMessage]) -> bool:
+    if not messages:
+        return False
+    content = _content_to_text(getattr(messages[-1], "content", "") or "")
+    return _CIRCUIT_BREAKER_MARKER in content
+
+
+def _sandbox_error_streak(messages: Sequence[BaseMessage]) -> SandboxErrorStreak | None:
+    sandbox_id: str | None = None
+    reason: Literal["client_error", "recreated"] | None = None
+    count = 0
+
+    for message in reversed(messages):
+        if isinstance(message, ToolMessage):
+            text = _content_to_text(message.content)
+            if _SANDBOX_RECREATED_AFTER_CLIENT_ERROR in text:
+                if reason is None:
+                    reason = "recreated"
+                elif reason != "recreated":
+                    break
+                count += 1
+                continue
+
+            message_sandbox_id = _extract_sandbox_id(text)
+            if "SandboxClientError" not in text or message_sandbox_id is None:
+                break
+            if reason is None:
+                reason = "client_error"
+                sandbox_id = message_sandbox_id
+            elif reason != "client_error" or message_sandbox_id != sandbox_id:
+                break
+            count += 1
+            continue
+
+        text = _content_to_text(getattr(message, "content", "") or "")
+        if _CIRCUIT_BREAKER_MARKER in text:
+            return None
+        if getattr(message, "type", "") in {"human", "system"}:
+            break
+
+    if reason is None:
+        return None
+    return SandboxErrorStreak(reason=reason, sandbox_id=sandbox_id, count=count)
+
+
+def _get_slack_target(configurable: Mapping[str, Any]) -> tuple[str, str] | None:
+    slack_thread = configurable.get("slack_thread")
+    if not isinstance(slack_thread, Mapping):
+        return None
+    channel_id = slack_thread.get("channel_id")
+    thread_ts = slack_thread.get("thread_ts")
+    if not isinstance(channel_id, str) or not isinstance(thread_ts, str):
+        return None
+    if not channel_id or not thread_ts:
+        return None
+    return channel_id, thread_ts
+
+
+def _get_linear_issue_id(configurable: Mapping[str, Any]) -> str | None:
+    linear_issue = configurable.get("linear_issue")
+    if not isinstance(linear_issue, Mapping):
+        return None
+    issue_id = linear_issue.get("id")
+    return issue_id if isinstance(issue_id, str) and issue_id else None
+
+
+def _coerce_issue_number(value: object) -> int | None:
+    if isinstance(value, int):
+        return value
+    if isinstance(value, str) and value.isdigit():
+        return int(value)
+    return None
+
+
+def _get_github_target(configurable: Mapping[str, Any]) -> tuple[dict[str, str], int] | None:
+    repo_config = configurable.get("repo")
+    if not isinstance(repo_config, Mapping):
+        return None
+    owner = repo_config.get("owner")
+    name = repo_config.get("name")
+    if not isinstance(owner, str) or not isinstance(name, str) or not owner or not name:
+        return None
+    repo = {"owner": owner, "name": name}
+
+    github_pr_or_issue = configurable.get("github_pr_or_issue")
+    if isinstance(github_pr_or_issue, Mapping):
+        number = _coerce_issue_number(github_pr_or_issue.get("number"))
+        target_repo = github_pr_or_issue.get("repo")
+        if isinstance(target_repo, Mapping):
+            target_owner = target_repo.get("owner")
+            target_name = target_repo.get("name")
+            if isinstance(target_owner, str) and isinstance(target_name, str):
+                repo = {"owner": target_owner, "name": target_name}
+        if number is not None:
+            return repo, number
+
+    github_issue = configurable.get("github_issue")
+    if isinstance(github_issue, Mapping):
+        number = _coerce_issue_number(github_issue.get("number"))
+        if number is not None:
+            return repo, number
+
+    pr_number = _coerce_issue_number(configurable.get("pr_number"))
+    if pr_number is not None:
+        return repo, pr_number
+    return None
+
+
+async def _post_unrecoverable_notification(config: Mapping[str, Any]) -> None:
+    configurable = config.get("configurable", {})
+    if not isinstance(configurable, Mapping):
+        logger.info("No runtime configurable found for sandbox circuit breaker notification")
+        return
+
+    slack_target = _get_slack_target(configurable)
+    if slack_target is not None:
+        channel_id, thread_ts = slack_target
+        await post_slack_thread_reply(channel_id, thread_ts, SANDBOX_UNRECOVERABLE_MESSAGE)
+        logger.info("Sent sandbox circuit breaker notification to Slack thread %s", thread_ts)
+        return
+
+    linear_issue_id = _get_linear_issue_id(configurable)
+    if linear_issue_id is not None:
+        await comment_on_linear_issue(linear_issue_id, SANDBOX_UNRECOVERABLE_MESSAGE)
+        logger.info("Sent sandbox circuit breaker notification to Linear issue %s", linear_issue_id)
+        return
+
+    github_target = _get_github_target(configurable)
+    if github_target is not None:
+        token = get_github_token(config) or await get_github_app_installation_token()
+        if not token:
+            logger.info("No GitHub token available for sandbox circuit breaker notification")
+            return
+        repo, issue_number = github_target
+        await post_github_comment(
+            repo,
+            issue_number,
+            SANDBOX_UNRECOVERABLE_MESSAGE,
+            token=token,
+        )
+        logger.info("Sent sandbox circuit breaker notification to GitHub item #%s", issue_number)
+        return
+
+    logger.info("No user-facing target found for sandbox circuit breaker notification")
+
+
+class SandboxCircuitBreakerMiddleware(AgentMiddleware[AgentState, Any]):
+    """Stop runs that repeatedly hit the same dead sandbox."""
+
+    state_schema = AgentState
+
+    def __init__(self, *, threshold: int = SANDBOX_CIRCUIT_BREAKER_THRESHOLD) -> None:
+        self.threshold = threshold
+
+    @hook_config(can_jump_to=["end"])
+    def before_model(self, state: AgentState, runtime: Runtime) -> dict[str, Any] | None:  # noqa: ARG002
+        messages = state.get("messages", [])
+        if _last_message_has_circuit_breaker_marker(messages):
+            return None
+
+        streak = _sandbox_error_streak(messages)
+        if streak is None or streak.count <= self.threshold:
+            return None
+
+        if streak.reason == "recreated":
+            detail = (
+                f"{streak.count} consecutive sandbox recreations did not recover tool execution"
+            )
+        else:
+            detail = f"{streak.count} consecutive sandbox tool failures against {streak.sandbox_id}"
+        content = f"{_CIRCUIT_BREAKER_MARKER}: {detail}. {SANDBOX_UNRECOVERABLE_MESSAGE}"
+        return {"jump_to": "end", "messages": [AIMessage(content=content)]}
+
+    @hook_config(can_jump_to=["end"])
+    async def abefore_model(
+        self,
+        state: AgentState,
+        runtime: Runtime,
+    ) -> dict[str, Any] | None:
+        return self.before_model(state, runtime)
+
+    async def aafter_agent(
+        self,
+        state: AgentState,
+        runtime: Runtime,  # noqa: ARG002
+    ) -> dict[str, Any] | None:
+        messages = state.get("messages", [])
+        if not messages:
+            return None
+
+        last_msg = messages[-1]
+        content = _content_to_text(getattr(last_msg, "content", "") or "")
+        if _CIRCUIT_BREAKER_MARKER not in content:
+            return None
+
+        try:
+            config = get_config()
+            await _post_unrecoverable_notification(config)
+        except Exception:
+            logger.exception("Failed to send sandbox circuit breaker notification")
+
+        return None

agent/middleware/tool_error_handler.py

@@ -6,20 +6,26 @@ returned as error ToolMessages instead of crashing the agent run.
 
 from __future__ import annotations
 
+import asyncio
 import json
 import logging
-from collections.abc import Awaitable, Callable
+from collections.abc import Awaitable, Callable, Mapping
+from typing import Any
 
 from langchain.agents.middleware.types import (
     AgentMiddleware,
     AgentState,
 )
 from langchain_core.messages import ToolMessage
+from langgraph.config import get_config
 from langgraph.prebuilt.tool_node import ToolCallRequest
 from langgraph.types import Command
+from langsmith.sandbox import SandboxClientError
 
 logger = logging.getLogger(__name__)
 
+SANDBOX_RECREATED_AFTER_CLIENT_ERROR = "sandbox_recreated_after_client_error"
+
 
 def _get_name(candidate: object) -> str | None:
     if not candidate:
@@ -55,12 +61,101 @@ def _to_error_payload(e: Exception, request: ToolCallRequest | None = None) -> d
     return data
 
 
+def _to_sandbox_recreated_payload(
+    e: SandboxClientError,
+    sandbox_id: str,
+    request: ToolCallRequest | None = None,
+) -> dict[str, str]:
+    data: dict[str, str] = {
+        "status": "error",
+        "error_type": e.__class__.__name__,
+        "previous_error": str(e),
+        "recovery": SANDBOX_RECREATED_AFTER_CLIENT_ERROR,
+        "sandbox_id": sandbox_id,
+        "error": (
+            "The previous sandbox became unreachable mid-run. A fresh sandbox "
+            f"({sandbox_id}) has been created and cached for this thread. "
+            "Retry the last tool call; if repository files are missing, re-clone or "
+            "reinitialize the workspace first."
+        ),
+    }
+    tool_name = _extract_tool_name(request)
+    if tool_name:
+        data["name"] = tool_name
+    return data
+
+
 def _get_tool_call_id(request: ToolCallRequest) -> str | None:
     if isinstance(request.tool_call, dict):
         return request.tool_call.get("id")
     return None
 
 
+def _get_thread_id(request: ToolCallRequest) -> str | None:
+    runtime_config = getattr(getattr(request, "runtime", None), "config", None)
+    config: Mapping[str, Any] | None = (
+        runtime_config if isinstance(runtime_config, Mapping) else None
+    )
+    if config is None:
+        try:
+            maybe_config = get_config()
+        except Exception:
+            logger.exception("Failed to read runnable config while handling sandbox error")
+            return None
+        config = maybe_config if isinstance(maybe_config, Mapping) else None
+    if config is None:
+        return None
+
+    configurable = config.get("configurable", {})
+    if not isinstance(configurable, Mapping):
+        return None
+    thread_id = configurable.get("thread_id")
+    return thread_id if isinstance(thread_id, str) and thread_id else None
+
+
+async def _recreate_sandbox_for_thread(thread_id: str) -> str:
+    from agent.server import _configure_git_identity, _recreate_sandbox, client
+    from agent.utils.sandbox_state import SANDBOX_BACKENDS
+
+    sandbox_backend = await _recreate_sandbox(thread_id)
+    SANDBOX_BACKENDS[thread_id] = sandbox_backend
+    await client.threads.update(thread_id=thread_id, metadata={"sandbox_id": sandbox_backend.id})
+    await _configure_git_identity(sandbox_backend)
+    return sandbox_backend.id
+
+
+def _recreate_sandbox_for_thread_sync(thread_id: str) -> str:
+    try:
+        asyncio.get_running_loop()
+    except RuntimeError:
+        return asyncio.run(_recreate_sandbox_for_thread(thread_id))
+    raise RuntimeError(
+        "Cannot recreate sandbox from a sync tool call while an event loop is running"
+    )
+
+
+def _sandbox_recreated_tool_message(
+    e: SandboxClientError,
+    sandbox_id: str,
+    request: ToolCallRequest,
+) -> ToolMessage:
+    data = _to_sandbox_recreated_payload(e, sandbox_id, request)
+    return ToolMessage(
+        content=json.dumps(data),
+        tool_call_id=_get_tool_call_id(request),
+        status="error",
+    )
+
+
+def _generic_error_tool_message(e: Exception, request: ToolCallRequest) -> ToolMessage:
+    data = _to_error_payload(e, request)
+    return ToolMessage(
+        content=json.dumps(data),
+        tool_call_id=_get_tool_call_id(request),
+        status="error",
+    )
+
+
 class ToolErrorMiddleware(AgentMiddleware):
     """Normalize tool execution errors into predictable payloads.
 
@@ -78,14 +173,19 @@ class ToolErrorMiddleware(AgentMiddleware):
     ) -> ToolMessage | Command:
         try:
             return handler(request)
+        except SandboxClientError as e:
+            logger.exception("Sandbox error during tool call handling; request=%r", request)
+            thread_id = _get_thread_id(request)
+            if thread_id:
+                try:
+                    sandbox_id = _recreate_sandbox_for_thread_sync(thread_id)
+                    return _sandbox_recreated_tool_message(e, sandbox_id, request)
+                except Exception:
+                    logger.exception("Failed to recreate sandbox for thread %s", thread_id)
+            return _generic_error_tool_message(e, request)
         except Exception as e:
             logger.exception("Error during tool call handling; request=%r", request)
-            data = _to_error_payload(e, request)
-            return ToolMessage(
-                content=json.dumps(data),
-                tool_call_id=_get_tool_call_id(request),
-                status="error",
-            )
+            return _generic_error_tool_message(e, request)
 
     async def awrap_tool_call(
         self,
@@ -94,11 +194,16 @@ class ToolErrorMiddleware(AgentMiddleware):
     ) -> ToolMessage | Command:
         try:
             return await handler(request)
+        except SandboxClientError as e:
+            logger.exception("Sandbox error during tool call handling; request=%r", request)
+            thread_id = _get_thread_id(request)
+            if thread_id:
+                try:
+                    sandbox_id = await _recreate_sandbox_for_thread(thread_id)
+                    return _sandbox_recreated_tool_message(e, sandbox_id, request)
+                except Exception:
+                    logger.exception("Failed to recreate sandbox for thread %s", thread_id)
+            return _generic_error_tool_message(e, request)
         except Exception as e:
             logger.exception("Error during tool call handling; request=%r", request)
-            data = _to_error_payload(e, request)
-            return ToolMessage(
-                content=json.dumps(data),
-                tool_call_id=_get_tool_call_id(request),
-                status="error",
-            )
+            return _generic_error_tool_message(e, request)

agent/server.py

@@ -29,6 +29,7 @@ from langsmith.sandbox import SandboxClientError
 
 from .integrations.langsmith import _configure_github_proxy
 from .middleware import (
+    SandboxCircuitBreakerMiddleware,
     SanitizeToolInputsMiddleware,
     SlackAssistantStatusMiddleware,
     ToolErrorMiddleware,
@@ -149,6 +150,14 @@ async def _refresh_github_proxy_or_recreate(
     return sandbox_backend
 
 
+async def _configure_git_identity(sandbox_backend: SandboxBackendProtocol) -> None:
+    await asyncio.to_thread(
+        sandbox_backend.execute,
+        "git config --global user.name 'open-swe[bot]' && "
+        "git config --global user.email 'open-swe@users.noreply.github.com'",
+    )
+
+
 async def _recreate_sandbox(thread_id: str) -> SandboxBackendProtocol:
     """Recreate a sandbox after a connection failure.
 
@@ -298,11 +307,7 @@ async def ensure_sandbox_for_thread(thread_id: str) -> SandboxBackendProtocol:
     # lost their `--global` config (or had it overwritten), and Vercel preview
     # deploys reject commits whose author email can't be resolved to a GitHub
     # account.
-    await asyncio.to_thread(
-        sandbox_backend.execute,
-        "git config --global user.name 'open-swe[bot]' && "
-        "git config --global user.email 'open-swe@users.noreply.github.com'",
-    )
+    await _configure_git_identity(sandbox_backend)
 
     return sandbox_backend
 
@@ -314,6 +319,13 @@ DEFAULT_RECURSION_LIMIT = 9_999
 MODEL_CALL_RECURSION_LIMIT = 5_000  # ~half the recursion limit to account for tool calls
 
 
+def _get_cached_sandbox_backend(thread_id: str) -> SandboxBackendProtocol:
+    sandbox_backend = SANDBOX_BACKENDS.get(thread_id)
+    if sandbox_backend is None:
+        raise RuntimeError(f"No sandbox backend cached for thread {thread_id}")
+    return sandbox_backend
+
+
 async def get_agent(config: RunnableConfig) -> Pregel:
     """Get or create an agent with a sandbox for the given thread."""
     thread_id = config["configurable"].get("thread_id", None)
@@ -342,6 +354,9 @@ async def get_agent(config: RunnableConfig) -> Pregel:
 
     work_dir = await aresolve_sandbox_work_dir(sandbox_backend)
 
+    def backend_factory(_runtime: object, _thread_id: str = thread_id) -> SandboxBackendProtocol:
+        return _get_cached_sandbox_backend(_thread_id)
+
     model_id = os.environ.get("LLM_MODEL_ID", DEFAULT_LLM_MODEL_ID)
     model_kwargs: ModelKwargs = {"max_tokens": DEFAULT_LLM_MAX_TOKENS}
     if model_id == DEFAULT_LLM_MODEL_ID:
@@ -371,7 +386,7 @@ async def get_agent(config: RunnableConfig) -> Pregel:
             slack_read_thread_messages,
             slack_thread_reply,
         ],
-        backend=sandbox_backend,
+        backend=backend_factory,
         middleware=[
             SanitizeToolInputsMiddleware(),
             ModelCallLimitMiddleware(run_limit=MODEL_CALL_RECURSION_LIMIT, exit_behavior="end"),
@@ -380,5 +395,6 @@ async def get_agent(config: RunnableConfig) -> Pregel:
             SlackAssistantStatusMiddleware(),
             ensure_no_empty_msg,
             notify_step_limit_reached,
+            SandboxCircuitBreakerMiddleware(),
         ],
     ).with_config(config)

tests/middleware/test_sandbox_recovery.py

@@ -0,0 +1,208 @@
+import json
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+from langchain_core.messages import AIMessage, HumanMessage, ToolMessage
+from langgraph.prebuilt.tool_node import ToolCallRequest
+from langsmith.sandbox import SandboxClientError
+
+from agent.middleware.sandbox_circuit_breaker import (
+    SANDBOX_UNRECOVERABLE_MESSAGE,
+    SandboxCircuitBreakerMiddleware,
+)
+from agent.middleware.tool_error_handler import ToolErrorMiddleware
+from agent.utils.sandbox_state import SANDBOX_BACKENDS
+
+
+class FakeSandboxBackend:
+    id = "sb-new"
+
+    def execute(self, _command: str) -> None:
+        return None
+
+
+def _tool_request(thread_id: str = "thread-1") -> ToolCallRequest:
+    runtime = MagicMock(config={"configurable": {"thread_id": thread_id}})
+    return ToolCallRequest(
+        tool_call={"name": "ls", "args": {"path": "/"}, "id": "tc1"},
+        tool=MagicMock(),
+        state={},
+        runtime=runtime,
+    )
+
+
+def _sandbox_error_message(tool_call_id: str, sandbox_id: str = "sb-dead") -> ToolMessage:
+    return ToolMessage(
+        content=json.dumps(
+            {
+                "error": f"Sandbox request timed out: {sandbox_id}",
+                "error_type": "SandboxClientError",
+                "status": "error",
+            }
+        ),
+        tool_call_id=tool_call_id,
+        status="error",
+    )
+
+
+@pytest.mark.asyncio
+async def test_sandbox_client_error_recreates_sandbox() -> None:
+    middleware = ToolErrorMiddleware()
+    request = _tool_request()
+    backend = FakeSandboxBackend()
+
+    async def handler(_request: ToolCallRequest) -> ToolMessage:
+        raise SandboxClientError("Sandbox request timed out: sb-dead")
+
+    try:
+        with (
+            patch("agent.server._recreate_sandbox", new_callable=AsyncMock) as mock_recreate,
+            patch("agent.server.client") as mock_client,
+        ):
+            mock_recreate.return_value = backend
+            mock_client.threads.update = AsyncMock()
+
+            result = await middleware.awrap_tool_call(request, handler)
+
+        assert isinstance(result, ToolMessage)
+        mock_recreate.assert_awaited_once_with("thread-1")
+        mock_client.threads.update.assert_awaited_once_with(
+            thread_id="thread-1",
+            metadata={"sandbox_id": "sb-new"},
+        )
+        assert SANDBOX_BACKENDS["thread-1"] is backend
+
+        payload = json.loads(result.content)
+        assert payload["status"] == "error"
+        assert payload["error_type"] == "SandboxClientError"
+        assert payload["recovery"] == "sandbox_recreated_after_client_error"
+        assert payload["previous_error"] == "Sandbox request timed out: sb-dead"
+        assert "sb-new" in payload["error"]
+    finally:
+        SANDBOX_BACKENDS.pop("thread-1", None)
+
+
+def test_repeated_sandbox_errors_trigger_circuit_breaker_once() -> None:
+    middleware = SandboxCircuitBreakerMiddleware(threshold=2)
+    messages = [
+        HumanMessage(content="please fix this"),
+        AIMessage(content="", tool_calls=[{"name": "ls", "args": {}, "id": "tc1"}]),
+        _sandbox_error_message("tc1"),
+        AIMessage(content="", tool_calls=[{"name": "grep", "args": {}, "id": "tc2"}]),
+        _sandbox_error_message("tc2"),
+        AIMessage(content="", tool_calls=[{"name": "execute", "args": {}, "id": "tc3"}]),
+        _sandbox_error_message("tc3"),
+    ]
+
+    result = middleware.before_model({"messages": messages}, MagicMock())
+
+    assert result is not None
+    assert result["jump_to"] == "end"
+    assert len(result["messages"]) == 1
+    assert "Sandbox circuit breaker triggered" in result["messages"][0].content
+
+    repeated = middleware.before_model(
+        {"messages": [*messages, *result["messages"]]},
+        MagicMock(),
+    )
+    assert repeated is None
+
+
+def test_repeated_sandbox_recreations_trigger_circuit_breaker() -> None:
+    middleware = SandboxCircuitBreakerMiddleware(threshold=2)
+    messages = [
+        HumanMessage(content="please fix this"),
+        AIMessage(content="", tool_calls=[{"name": "ls", "args": {}, "id": "tc1"}]),
+        ToolMessage(
+            content=json.dumps(
+                {
+                    "error_type": "SandboxClientError",
+                    "previous_error": "Sandbox request timed out: sb-old-1",
+                    "recovery": "sandbox_recreated_after_client_error",
+                    "sandbox_id": "sb-new-1",
+                    "status": "error",
+                }
+            ),
+            tool_call_id="tc1",
+            status="error",
+        ),
+        AIMessage(content="", tool_calls=[{"name": "grep", "args": {}, "id": "tc2"}]),
+        ToolMessage(
+            content=json.dumps(
+                {
+                    "error_type": "SandboxClientError",
+                    "previous_error": "Sandbox request timed out: sb-new-1",
+                    "recovery": "sandbox_recreated_after_client_error",
+                    "sandbox_id": "sb-new-2",
+                    "status": "error",
+                }
+            ),
+            tool_call_id="tc2",
+            status="error",
+        ),
+        AIMessage(content="", tool_calls=[{"name": "execute", "args": {}, "id": "tc3"}]),
+        ToolMessage(
+            content=json.dumps(
+                {
+                    "error_type": "SandboxClientError",
+                    "previous_error": "Sandbox request timed out: sb-new-2",
+                    "recovery": "sandbox_recreated_after_client_error",
+                    "sandbox_id": "sb-new-3",
+                    "status": "error",
+                }
+            ),
+            tool_call_id="tc3",
+            status="error",
+        ),
+    ]
+
+    result = middleware.before_model({"messages": messages}, MagicMock())
+
+    assert result is not None
+    assert result["jump_to"] == "end"
+    assert "consecutive sandbox recreations" in result["messages"][0].content
+
+
+@pytest.mark.asyncio
+async def test_circuit_breaker_posts_one_user_notification() -> None:
+    middleware = SandboxCircuitBreakerMiddleware(threshold=2)
+    state = {
+        "messages": [
+            AIMessage(
+                content=(
+                    "Sandbox circuit breaker triggered: 3 consecutive sandbox tool failures "
+                    "against sb-dead."
+                )
+            )
+        ]
+    }
+    config = {
+        "configurable": {
+            "slack_thread": {"channel_id": "C123", "thread_ts": "171.123"},
+            "linear_issue": {"id": "lin-1"},
+            "repo": {"owner": "langchain-ai", "name": "open-swe"},
+            "pr_number": 7,
+        }
+    }
+
+    with (
+        patch("agent.middleware.sandbox_circuit_breaker.get_config", return_value=config),
+        patch(
+            "agent.middleware.sandbox_circuit_breaker.post_slack_thread_reply",
+            new_callable=AsyncMock,
+        ) as mock_slack,
+        patch(
+            "agent.middleware.sandbox_circuit_breaker.comment_on_linear_issue",
+            new_callable=AsyncMock,
+        ) as mock_linear,
+        patch(
+            "agent.middleware.sandbox_circuit_breaker.post_github_comment",
+            new_callable=AsyncMock,
+        ) as mock_github,
+    ):
+        result = await middleware.aafter_agent(state, MagicMock())
+
+    assert result is None
+    mock_slack.assert_awaited_once_with("C123", "171.123", SANDBOX_UNRECOVERABLE_MESSAGE)
+    mock_linear.assert_not_called()
+    mock_github.assert_not_called()