Introduction

The pluggable architecture of DeepSeek Harness (DSH) provides a foundation for workflow extension. In real development, agents often need to share context or collaborate: one Session may be holding an in-progress implementation, while another Session needs that context to review it or continue the work. Directly copying history loses contextual details, and creating a second independent Harness instance increases system overhead and complexity.

dsh-cross-session aims to solve communication between different Sessions within the same DSH process. It does not require an extra daemon or network port; instead, it runs as a standard plugin inside the existing DSH runtime, allowing Sessions to discover each other, send instructions, and observe execution results.

Plugin Positioning

This is an independent project maintained by community developer Wha1eChai (not an official DeepSeek AI product), licensed under MIT. It provides cross-Session discovery and communication within the same runtime for DSH, and belongs to the “workflow” plugin category.

Core Features

The plugin provides six core tools for controlling the behavior of a target Session:

  1. Discovery (fleet_list): Lists all live root Sessions currently online in the DSH process.
  2. Inspection (fleet_inspect): Reads a bounded summary of the target Session to confirm the target identity.
  3. Send (fleet_send): Appends follow-up work to the target’s next turn queue.
  4. Steer (fleet_steer): Changes the target’s behavioral direction at the boundary of its turn.
  5. Wait (fleet_wait): Observes a completed turn of the target Session containing a specific message.
  6. Cancel (fleet_cancel): Explicitly stops the root task work of the target Session.

Note: fleet_send is used to wait until the target has finished processing the current turn before executing follow-up work; fleet_steer is used to change direction at the boundary of the current turn. If the target is idle, the steering operation wakes it up and starts processing the input.

Installation and Activation

Installing this plugin requires specifying a version number (currently 0.1.0-rc.1).

  1. Run the installation command:
    dsh plugin --profile web add @wha1echai/dsh-cross-session@0.1.0-rc.1
  1. Edit the DSH configuration file to enable message sending and steering. By default, the plugin only provides read-only discovery. Add the following configuration to cordis.patch.yml:
    - id: dsh-cross-session-tools
      name: '@wha1echai/dsh-cross-session/tool'
      config:
        controlMode: message
  1. Restart the DSH process.

Usage Flow

fleet_send and fleet_steer require a confirmation flow for safety. Model tools do not write arbitrary Session IDs directly.

  1. Discover the target: Call fleet_list to list current sessions.
  2. Confirm identity: Call fleet_inspect to check the target state and confirm the specific Session ID.
  3. Perform the operation: Based on the confirmed choice, call fleet_send, fleet_steer, or fleet_cancel.
  4. Observe the result: If needed, call fleet_wait to observe a completed turn of the target.

Example Scenarios:
* Target session:
> “When contacted through Fleet, summarize the request, complete it normally, and reply with a short result.”
* Calling session:
> “Find another live root Session, inspect it, and send it a small task. If fleet_wait is available, wait for the turn that receives the message.”

Security and Limitations

  • Runtime environment: The plugin runs entirely inside the existing DSH process. It does not start a new daemon or listen on additional network ports.
  • Resource consumption: fleet_send and fleet_steer trigger model requests and tool calls, so they consume model and tool resources.
  • Cancellation limitation: fleet_cancel can only interrupt ongoing work; it cannot roll back work already accepted by a model or tool.
  • Cross-process limitation: Communication across processes, devices, or multiple Runtimes is not currently supported.
  • Configuration mode: controlMode only controls model-visible tools. It does not replace DSH’s approval mechanism, tools/pre-execute, or ctx.tools.guard() policies.

Summary

dsh-cross-session provides a toolset for managing inter-Session collaboration within the same DSH process. For developers who need parallel task management, context reuse, or pipeline collaboration within one Harness, it is a practical tool. Before use, review the source code and license, and enable write permissions only in appropriate agent combinations.