fix(copilot): address review comments — slot counting, heartbeat, error detection

- Move run_in_background check before task_spawn_count increment so
  denied background Tasks don't consume a subtask slot
- Replace asyncio.wait_for() with asyncio.timeout() for heartbeat loop
  to avoid leaving the async generator in a broken state
- Tighten _is_tool_error_or_denial: remove overly broad markers
  ("error", "failed", "not found") that cause false positives; add
  markers for actual denial messages ("not supported", "maximum")

autogpt_platform/backend/backend/copilot/sdk/security_hooks.py

@@ -188,6 +188,18 @@ def create_security_hooks(
 
             # Rate-limit Task (sub-agent) spawns per session
             if tool_name == "Task":
+                # Block background task execution first — denied calls
+                # should not consume a subtask slot.
+                if tool_input.get("run_in_background"):
+                    logger.info(f"[SDK] Blocked background Task, user={user_id}")
+                    return cast(
+                        SyncHookJSONOutput,
+                        _deny(
+                            "Background task execution is not supported. "
+                            "Run tasks in the foreground instead "
+                            "(remove the run_in_background parameter)."
+                        ),
+                    )
                 task_spawn_count += 1
                 if task_spawn_count > max_subtasks:
                     logger.warning(
@@ -200,19 +212,6 @@ def create_security_hooks(
                             "Please continue in the main conversation."
                         ),
                     )
-                # Block background task execution — background agents stall
-                # the SSE stream (no messages flow while they run) and get
-                # killed when the main agent's turn ends.
-                if tool_input.get("run_in_background"):
-                    logger.info(f"[SDK] Blocked background Task, user={user_id}")
-                    return cast(
-                        SyncHookJSONOutput,
-                        _deny(
-                            "Background task execution is not supported. "
-                            "Run tasks in the foreground instead "
-                            "(remove the run_in_background parameter)."
-                        ),
-                    )
 
             # Strip MCP prefix for consistent validation
             is_copilot_tool = tool_name.startswith(MCP_TOOL_PREFIX)

autogpt_platform/backend/backend/copilot/sdk/service.py

@@ -77,6 +77,9 @@ class CapturedTranscript:
 
 _SDK_CWD_PREFIX = WORKSPACE_PREFIX
 
+# Heartbeat interval — keep SSE alive through proxies/LBs during tool execution.
+_HEARTBEAT_INTERVAL = 15.0  # seconds
+
 # Appended to the system prompt to inform the agent about available tools.
 # The SDK built-in Bash is NOT available — use mcp__copilot__bash_exec instead,
 # which has kernel-level network isolation (unshare --net).
@@ -407,7 +410,7 @@ def _format_conversation_context(messages: list[ChatMessage]) -> str | None:
     return "<conversation_history>\n" + "\n".join(lines) + "\n</conversation_history>"
 
 
-def _is_tool_error_or_denial(content: str) -> bool:
+def _is_tool_error_or_denial(content: str | None) -> bool:
     """Check if a tool message content indicates an error or denial.
 
     We include these in conversation context so the agent doesn't
@@ -420,14 +423,13 @@ def _is_tool_error_or_denial(content: str) -> bool:
         marker in lower
         for marker in (
             "[security]",
-            "error",
-            "failed",
+            "cannot be bypassed",
+            "not allowed",
+            "not supported",  # background-task denial
+            "maximum",  # subtask-limit denial
             "denied",
             "blocked",
-            "not found",
-            "not allowed",
-            "permission",
-            "cannot be bypassed",
+            '"iserror": true',  # MCP protocol error flag
         )
     )
 
@@ -656,15 +658,15 @@ async def stream_chat_completion_sdk(
                 # Use an explicit async iterator with timeout to send
                 # heartbeats when the CLI is idle (e.g. executing tools).
                 # This prevents proxies/LBs from closing the SSE connection.
-                _HEARTBEAT_INTERVAL = 15.0  # seconds
+                # asyncio.timeout() is preferred over asyncio.wait_for()
+                # because wait_for wraps in a separate Task whose cancellation
+                # can leave the async generator in a broken state.
                 msg_iter = client.receive_messages().__aiter__()
                 while not stream_completed:
                     try:
-                        sdk_msg = await asyncio.wait_for(
-                            msg_iter.__anext__(),
-                            timeout=_HEARTBEAT_INTERVAL,
-                        )
-                    except asyncio.TimeoutError:
+                        async with asyncio.timeout(_HEARTBEAT_INTERVAL):
+                            sdk_msg = await msg_iter.__anext__()
+                    except TimeoutError:
                         yield StreamHeartbeat()
                         continue
                     except StopAsyncIteration: