diff --git a/strix/core/execution.py b/strix/core/execution.py
index 06dc3ddf5..f252e3008 100644
--- a/strix/core/execution.py
+++ b/strix/core/execution.py
@@ -349,6 +349,15 @@ async def _run_cycle(  # noqa: PLR0912, PLR0915
     while True:
         try:
             await coordinator.mark_running(agent_id)
+
+            # --- PRODUCTION FIX FOR AWS BEDROCK TOOL_CHOICE COMPLIANCE ---
+            if hasattr(run_config, "extra_body") and isinstance(run_config.extra_body, dict):
+                if "tool_choice" in run_config.extra_body:
+                    run_config.extra_body["tool_choice"] = {"type": "auto"}
+            elif hasattr(run_config, "tool_choice") and (run_config.tool_choice == "auto" or isinstance(run_config.tool_choice, str)):
+                run_config.tool_choice = {"type": "auto"}
+            # -------------------------------------------------------------
+
             stream = Runner.run_streamed(
                 agent,
                 input=input_data,
diff --git a/strix/runtime/backends.py b/strix/runtime/backends.py
index d7eba3357..7d8a464ea 100644
--- a/strix/runtime/backends.py
+++ b/strix/runtime/backends.py
@@ -3,6 +3,8 @@
 from __future__ import annotations
 
 import logging
+import os
+import sys
 from collections.abc import Awaitable, Callable
 from typing import TYPE_CHECKING, Any
 
@@ -47,11 +49,46 @@ async def _docker_backend(
 
     from strix.runtime.docker_client import StrixDockerSandboxClient
 
+    # Handle Issue #671 Edge Cases
+    concurrency_limits = None
+    default_limit = 1 if sys.platform == "win32" else None
+    limit_val = os.environ.get("STRIX_DOCKER_CONCURRENCY", default_limit)
+
+    if limit_val is not None:
+        try:
+            # Prevents <= 0 limits breaking the SDK validation
+            limit = max(1, int(limit_val)) 
+            
+            # Try primary import path, fallback if SDK changes
+            try:
+                from agents.sandbox.artifacts import SandboxConcurrencyLimits
+            except ImportError:
+                from agents.sandbox import SandboxConcurrencyLimits
+
+            concurrency_limits = SandboxConcurrencyLimits(
+                manifest_entries=limit,
+                local_dir_files=limit
+            )
+            logger.debug(f"Applied SandboxConcurrencyLimits: {limit}")
+        except (ImportError, ValueError) as e:
+            if sys.platform == "win32" and limit_val == 1:
+                # Fail loudly on Windows to avoid silent race condition
+                raise RuntimeError("Failed to import SandboxConcurrencyLimits required for Windows execution.") from e
+            logger.warning("Invalid STRIX_DOCKER_CONCURRENCY or import failed. Proceeding with defaults.")
+
     client = StrixDockerSandboxClient(docker.from_env())
     client.strix_bind_mounts = bind_mounts or []
     options = DockerSandboxClientOptions(image=image, exposed_ports=exposed_ports)
+    
+    # Create the session (without concurrency_limits keyword)
     session = await client.create(options=options, manifest=manifest)
-    await session.start()
+    
+    # Pass concurrency_limits where the session is actually started/materialized
+    start_kwargs = {}
+    if concurrency_limits is not None:
+        start_kwargs["concurrency_limits"] = concurrency_limits
+        
+    await session.start(**start_kwargs)
     return client, session
 
 
@@ -90,4 +127,4 @@ def register_backend(name: str, backend: SandboxBackend) -> None:
 
 
 def supported_backends() -> list[str]:
-    return sorted(_BACKENDS)
+    return sorted(_BACKENDS)
\ No newline at end of file