Feature Request: Expose sessions_spawn via Tool API (for Lobster / external orchestration)

Summary

Expose sessions_spawn (subagent spawning) as an available tool through the OpenClaw Tool API endpoint (/api/tools/call), so that external orchestrators like Lobster can spawn isolated agent sessions as pipeline steps.

Use Case

We're building a multi-agent AI organization where specialized agents (PM, Builder, Designer, Tester, Auditor) execute sequentially in a development pipeline. Each agent has its own system prompt (agents/*.md) and follows pod-specific rules (pods/*.md).

Current Problem

When Felix (the orchestrator agent) chains subagent spawns via sessions_spawn, each completion notification accumulates in Felix's context window:

subagent1 完了通知 (数千トークン) → Felix context に蓄積
subagent2 完了通知 (数千トークン) → Felix context に蓄積
× 6-8 steps → context 肥大 → timeout

Attempted Solution

We installed Lobster and created a .lobster workflow file to orchestrate the pipeline:

steps:
  - id: pm
    # spawn PM agent
  - id: builder  
    # spawn Builder agent
  - id: tester
    # spawn Tester agent
  - id: review
    # spawn Auditor agent
  - id: approval
    approval: "Approve delivery?"
  - id: deploy
    # spawn Operator agent

Lobster's approval gates, sequential execution, and context isolation work perfectly. However, sessions_spawn is not available via the Tool API:

lobster 'openclaw.invoke --tool sessions_spawn --action run --args-json "{...}"'
# → 404: Tool not available: sessions_spawn

This means we cannot spawn OpenClaw subagents from Lobster pipelines, forcing us to either:

1. Fall back to Felix-mediated chaining (context bloat problem remains)
2. Use raw CLI calls (loses OpenClaw agent management, tools, memory)

Proposed Solution

Expose sessions_spawn (and optionally sessions_send, sessions_yield) through the Tool API so that openclaw.invoke can call them from Lobster pipelines.

This would enable:

• Durable multi-agent pipelines via Lobster with full OpenClaw subagent capabilities
• Context isolation (each agent runs in its own session, no context bloat)
• Built-in approval gates (Lobster's approval: steps)
• Resume tokens (pipeline can pause and resume across gateway restarts)

Environment

• OpenClaw: 2026.4.2
• Lobster: 2026.1.21-1
• OS: macOS (Apple Silicon)

Related

• Lobster docs: https://docs.openclaw.ai/tools/lobster
• Task Flow docs: https://docs.openclaw.ai/automation/taskflow