refactor: simplify tool server to asyncio tasks with per-agent isolation

- Replace multiprocessing/threading with single asyncio task per agent
- Add task cancellation: new request cancels previous for same agent
- Add per-agent state isolation via ContextVar for Terminal, Browser, Python managers
- Add posthog telemetry for tool execution errors (timeout, http, sandbox)
- Fix proxy manager singleton pattern
- Increase client timeout buffer over server timeout
- Add context.py to Dockerfile

strix/tools/executor.py

@@ -5,6 +5,7 @@ from typing import Any
 import httpx
 
 from strix.config import Config
+from strix.telemetry import posthog
 
 
 if os.getenv("STRIX_SANDBOX_MODE", "false").lower() == "false":
@@ -20,7 +21,8 @@ from .registry import (
 )
 
 
-SANDBOX_EXECUTION_TIMEOUT = float(Config.get("strix_sandbox_execution_timeout") or "120")
+_SERVER_TIMEOUT = float(Config.get("strix_sandbox_execution_timeout") or "120")
+SANDBOX_EXECUTION_TIMEOUT = _SERVER_TIMEOUT + 30
 SANDBOX_CONNECT_TIMEOUT = float(Config.get("strix_sandbox_connect_timeout") or "10")
 
 
@@ -82,14 +84,17 @@ async def _execute_tool_in_sandbox(tool_name: str, agent_state: Any, **kwargs: A
             response.raise_for_status()
             response_data = response.json()
             if response_data.get("error"):
+                posthog.error("tool_execution_error", f"{tool_name}: {response_data['error']}")
                 raise RuntimeError(f"Sandbox execution error: {response_data['error']}")
             return response_data.get("result")
         except httpx.HTTPStatusError as e:
+            posthog.error("tool_http_error", f"{tool_name}: HTTP {e.response.status_code}")
             if e.response.status_code == 401:
                 raise RuntimeError("Authentication failed: Invalid or missing sandbox token") from e
             raise RuntimeError(f"HTTP error calling tool server: {e.response.status_code}") from e
         except httpx.RequestError as e:
             error_type = type(e).__name__
+            posthog.error("tool_request_error", f"{tool_name}: {error_type}")
             raise RuntimeError(f"Request error calling tool server: {error_type}") from e