bandit-runner/IMPLEMENTATION-SUMMARY.md

Agent Reliability, Terminal Fidelity, and Reasoning Visibility - Implementation Summary

Overview

This implementation addresses three critical issues identified in the agent's behavior:

1. Max-Retries User Decision Flow - Prevents dead-ends at max retries by giving users options to Stop, Intervene, or Continue
2. Terminal Fidelity Improvements - Enhanced command hygiene and pre-advance password validation for better agent behavior
3. Reasoning Visibility - Properly displays LLM thinking/reasoning in the chat panel
4. Error Recovery - Added retry logic with exponential backoff for all critical operations
5. Cost Tracking - Real-time token usage and cost display in the agent panel

Implementation Details

1. Max-Retries → User Decision Flow

Files Modified:

• bandit-runner-app/src/lib/durable-objects/BanditAgentDO.ts
• bandit-runner-app/src/lib/agents/bandit-state.ts
• bandit-runner-app/src/hooks/useAgentWebSocket.ts
• bandit-runner-app/src/components/terminal-chat-interface.tsx

Changes:

• BanditAgentDO now emits user_action_required events when max retries are hit instead of immediately failing
• Agent state transitions to paused rather than failed on max-retries errors
• The /retry endpoint now properly resets retry count AND resumes the agent run
• AgentEvent type extended with user_action_required event type and associated data fields
• WebSocket hook now supports callbacks for user_action_required events
• Terminal Interface displays a modal dialog (shadcn AlertDialog) with three options:
  • Stop: Ends the run completely
  • Intervene: Enables manual mode and pauses the agent
  • Continue: Resets retry counter and resumes the agent

Benefits:

• No more dead-ends at Level 1 or any level
• Users can provide manual assistance when the agent gets stuck
• Enables iterative debugging and agent improvement
• Maintains leaderboard integrity (manual intervention is tracked)

2. Terminal Fidelity & Command Hygiene

Files Modified:

• ssh-proxy/agent.ts

Changes:

• Updated SYSTEM_PROMPT to explicitly forbid nested SSH connections and dangerous commands
• Command Validation in executeCommand checks for forbidden patterns:
  • ssh commands (nested SSH)
  • scp, sudo, su commands
  • Dangerous patterns like rm -rf
• Forbidden commands return error messages and return to planning state instead of executing
• Pre-Advance Password Validation: After extracting a password, validateResult now:
  1. Tests the password with a non-interactive SSH connection (testOnly: true)
  2. Only advances if the password is valid
  3. Counts invalid passwords as retries (fail-fast approach)
  4. Falls back to proceeding on network errors (fail-open for robustness)
• Accurate completion events: run_complete now includes status information based on final state

Benefits:

• Prevents common agent errors (nested SSH causing timeouts)
• Reduces wasted retries on invalid passwords
• More reliable level advancement
• Better alignment with example terminal agent UX (like opencode)

3. Reasoning Visibility

Files Modified:

• bandit-runner-app/src/components/terminal-chat-interface.tsx

Changes:

• Updated chat message rendering to display thinking messages with their full content
• Thinking messages now show with distinct styling (blue border/text)
• Message type label shows "THINKING" for reasoning messages
• Already emitted by the agent, now properly rendered in the UI

Benefits:

• Full transparency into agent's decision-making process
• Critical for benchmarking and debugging
• Helps users understand what the agent is thinking before executing commands

4. Error Recovery with Exponential Backoff

Files Modified:

• ssh-proxy/agent.ts

Changes:

• Added retryWithBackoff helper function:
  • Generic retry logic with exponential backoff (1s → 2s → 4s)
  • Configurable max retries and base delay
  • Contextual error messages for debugging
• Applied to critical operations:
  • SSH connections (3 retries, 1s base delay)
  • LLM planning calls (3 retries, 2s base delay)
  • SSH command execution (2 retries, 1.5s base delay)
• Graceful error handling with informative error messages

Benefits:

• Resilient to transient network failures
• Reduces run failures due to temporary issues
• Better user experience (fewer unexplained failures)
• Production-ready reliability

5. Token Usage & Cost Tracking

Files Modified:

• ssh-proxy/agent.ts
• bandit-runner-app/src/lib/agents/bandit-state.ts
• bandit-runner-app/src/hooks/useAgentWebSocket.ts
• bandit-runner-app/src/components/terminal-chat-interface.tsx
• bandit-runner-app/src/components/agent-control-panel.tsx

Changes:

• Agent State now tracks totalTokens and totalCost (accumulated via reducers)
• Planning Node extracts token usage from LLM responses and estimates costs
• Agent emits usage_update events after each LLM call
• WebSocket Hook handles usage_update events with callbacks
• AgentControlPanel displays token count and cost in metadata section
• Terminal Interface updates agent state with usage data in real-time

Cost Estimation:

• Rough approximation: 70% prompt tokens ($1/M), 30% completion tokens ($5/M)
• Real-world costs may vary based on specific OpenRouter model pricing

Benefits:

• Real-time visibility into LLM costs
• Helps users make informed model selection decisions
• Essential for benchmarking tool economics
• Transparent cost tracking for production deployments

Testing Checklist

Max-Retries Flow

• Start a run with a model (e.g., openai/gpt-4o-mini)
• Wait for Level 1 to hit max retries (3 attempts)
• Verify modal appears with Stop/Intervene/Continue options
• Test "Continue" → verify retry count resets and agent resumes
• Test "Intervene" → verify manual mode is enabled
• Test "Stop" → verify run ends cleanly

Terminal Fidelity

• Verify agent doesn't attempt ssh commands
• Check that forbidden commands trigger error messages
• Confirm ANSI codes are preserved in terminal output
• Test password validation: invalid password should trigger retry with error message
• Test password validation: valid password should advance to next level

Reasoning Visibility

• Start a run and observe chat panel
• Verify "THINKING" messages appear with blue styling
• Confirm full reasoning content is displayed (not just "Processing...")
• Test with different models to ensure consistent behavior

Error Recovery

• Simulate network issues (if possible) to test retry logic
• Verify agent recovers from temporary SSH connection failures
• Check that LLM API rate limits are handled gracefully

Cost Tracking

• Start a run and observe agent control panel
• Verify "TOKENS" and "COST" appear after first LLM call
• Confirm counts increment with each planning step
• Test with different models to see cost variations

Architecture Notes

Event Flow for Max-Retries

Agent (validateResult) 
  → Detects max retries 
  → Emits 'error' with "Max retries..." message
  → BanditAgentDO.updateStateFromEvent 
  → Checks error message for "Max retries"
  → Emits 'user_action_required' event
  → State set to 'paused' (not 'failed')
  → WebSocket → Frontend
  → useAgentWebSocket.onUserActionRequired callback
  → Terminal Interface shows AlertDialog
  → User clicks button
  → POST to /retry endpoint
  → BanditAgentDO.retryLevel resets count & resumes agent

Event Flow for Usage Tracking

Agent (planLevel) 
  → LLM invoke with retry logic
  → Extract token usage from response
  → Update state.totalTokens and state.totalCost
  → Emit 'usage_update' event
  → WebSocket → Frontend
  → useAgentWebSocket.onUsageUpdate callback
  → Terminal Interface updates agentState
  → AgentControlPanel renders updated metrics

Compatibility & Safety

• ✅ No changes to DO bindings or WS protocol
• ✅ All new features are additive (no breaking changes)
• ✅ Existing functionality preserved
• ✅ Fallback behavior for network errors (fail-open for password validation)
• ✅ Error messages are user-friendly and actionable
• ✅ Linter errors fixed, TypeScript types properly defined

Future Enhancements (Optional)

These were outlined in the plan but not implemented in this iteration:

Phase 2: PTY Streaming (Optional)

• Implement stream: true in /ssh/exec to send incremental PTY chunks
• Provides more 1:1 terminal experience with progressive rendering
• Feature-flagged for optional enablement

Phase 3: Persistent Interactive Shell (Optional)

• Implement /ssh/shell WebSocket endpoint for persistent PTY session
• Full TUI fidelity similar to opencode
• More complex implementation, requires careful state management

Deployment Notes

1. SSH Proxy: Redeploy to Fly.io with updated agent.ts

   cd ssh-proxy
   flyctl deploy
   

2. Cloudflare Worker: Deploy updated DO and routes

   cd bandit-runner-app
   pnpm run deploy
   

3. Environment Variables: No new variables required

4. Database/Storage: No schema changes

Summary

This implementation successfully addresses all three core issues while also adding error recovery and cost tracking. The agent is now:

• ✅ More robust (retry logic with exponential backoff)
• ✅ More transparent (reasoning visible, costs tracked)
• ✅ More reliable (command hygiene, password validation)
• ✅ More user-friendly (max-retries decision flow, clear error messages)
• ✅ Production-ready (proper error handling, type safety, no breaking changes)

The changes maintain backward compatibility and follow the plan's phased approach, delivering immediate improvements while leaving room for future enhancements.