Harness: expose botocore read_timeout for bedrock-runtime model calls

[tycenjmccann]

Problem

The AgentCore Harness runtime internally constructs a BedrockModel (Strands SDK) without exposing the boto_client_config parameter to customers. The default read_timeout of 120 seconds is insufficient for agents with complex tool chains where accumulated context causes time-to-first-token (TTFT) to exceed 120s.

Impact

• 100% failure rate on our security reviewer agent (Sonnet 4.5, 8 gateway tools)
• 56 timeout events across 7 invocations in 24 hours
• Any agent requiring >3-5 tool call cycles is at risk
• Model confirmed via OTel metrics: global.anthropic.claude-sonnet-4-5-20250929-v1:0
• Even Sonnet 4.5 (not just Opus) times out when context grows from accumulated tool results

Root Cause

From strands/models/bedrock.py:

DEFAULT_READ_TIMEOUT = 120

# If boto_client_config is NOT passed (harness default path):
client_config = BotocoreConfig(user_agent_extra="strands-agents", read_timeout=DEFAULT_READ_TIMEOUT)

The Harness constructs BedrockModel without customer-controlled boto_client_config, so there's no way to increase read_timeout.

Stack Trace (from CloudWatch)

strands/event_loop/event_loop.py:238 → event_loop_cycle
strands/event_loop/event_loop.py:646 → _handle_tool_execution
strands/event_loop/event_loop.py:318 → recurse_event_loop
strands/event_loop/event_loop.py:198 → event_loop_cycle (model invocation)
→ botocore eventstream → urllib3 ReadTimeoutError

urllib3.exceptions.ReadTimeoutError: AWSHTTPSConnectionPool(host='bedrock-runtime.us-east-1.amazonaws.com', port=443): Read timed out.

Proposed Solution

Expose a model_read_timeout (or full boto_client_config) parameter in one or more of:

1. harness.json configuration file
2. InvokeHarness API / agentcore invoke CLI
3. Environment variable (e.g., BEDROCK_READ_TIMEOUT_SECONDS)

Workaround (requires ditching Harness)

Deploy as a regular Strands agent on AgentCore Runtime and pass boto_client_config directly:

from botocore.config import Config as BotocoreConfig
from strands.models import BedrockModel

model = BedrockModel(
    model_id="us.anthropic.claude-sonnet-4-5-20250929-v1:0",
    boto_client_config=BotocoreConfig(read_timeout=300)
)

This defeats the purpose of the managed Harness experience.

Environment

• Account: 023392223961
• Region: us-east-1
• Runtime: harness_team_security_reviewer-Lpq9zN5Ve7
• Log Group: /aws/bedrock-agentcore/runtimes/harness_team_security_reviewer-Lpq9zN5Ve7-DEFAULT
• Trace ID: 6a0c0285679e59e00d1010a7ee2a910e
• Strands SDK version: bundled with Harness runtime (OTel SDK 1.40.0, auto-instrumentation 0.17.0-aws)