feat: implement e2e HITL messaging with dapr and message gateway

[bsalsingh]

PR: End-to-End HITL Messaging + Dapr Integration + Spec & Gateway Foundation

Description

This PR introduces a complete foundation for an agentic messaging system with Human-in-the-Loop (HITL) support, along with Dapr-based communication and formalized specifications.

Key Highlights

• Message Gateway Module

  • Introduced a dedicated message gateway to handle routing and orchestration of messages across the system.

• Dapr Integration

  • Added specs defining Dapr-based architecture.
  • Implemented pub/sub messaging using Dapr for decoupled communication.

• End-to-End Messaging Flows

  • Implemented basic non-HITL flow for automated message processing.
  • Added full HITL-enabled messaging flow, enabling human intervention in the loop.
  • Fixed issues related to threaded replies to ensure correct message chaining.

• Specification & Documentation

  • Created initial spec draft and iterated with review summaries.
  • Updated constitution and related specs for consistency.
  • Added plan.md to outline system direction.
  • Updated C1, C2, C3 chart documentation.

Motivation

This PR lays the groundwork for a scalable, event-driven agentic system by:

• Enabling modular communication via Dapr
• Supporting human-in-the-loop workflows
• Establishing clear architectural specifications
• Introducing a gateway abstraction for future extensibility

Dependencies

• Dapr runtime (pub/sub component configured)
• Redis (or configured pub/sub backend)
• Node.js environment for gateway and agents

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Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

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How Has This Been Tested?

Test Coverage

• End-to-end non-HITL messaging flow
• End-to-end HITL-enabled messaging flow
• Dapr pub/sub message propagation
• Thread reply handling validation

Test Instructions

1. Start Dapr with pub/sub component configured
2. Run message gateway service
3. Trigger:
   • Non-HITL flow → verify automatic processing
   • HITL flow → verify pause, human input, and resume
4. Validate message routing and thread continuity

Test Configuration:

• SDK: Node.js
• Toolchain: Dapr 1.17.x
• OS / Environment: Local development (Docker/Kubernetes optional)

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Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have added comments, especially in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix or feature works (integration-level tested)
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules