feat: Fleet client

[dzorlu]

PR: Fleet environments (OpenEnv)

This PR documents and refines the Fleet runtime integration for OpenEnv.

What this enables

• Run OpenEnv environments on Fleet (remote) with no local Docker.
• Keep a strict split between:
  • Orchestration (HTTP): reset / step / state
  • Agent actions (MCP): tools/list + tools/call

What this is not

• This is not the local “Dockerized env server + env container” setup.
• There is no container/provider abstraction here; Fleet hosts the runtime remotely (HTTP env server + MCP service). The client only connects.

Main abstractions

• FleetEnvClient (HTTP): orchestrator handle for reset/step/state.
• FleetMCPTools (MCP): agent handle for listing/calling tools.
  • Unions tools across Fleet’s MCP endpoints (today often api/v1/mcp and mcp)
  • Returns tools in OpenAI “tools” dict format (via convert_tool_format)
  • Routes tool calls to the owning endpoint (cached after discovery)

Quickstart

• Install: pip install "openenv-core[fleet]"
• Set: export FLEET_API_KEY="..."
• Run: python examples/fleet_env_example.py <env_key>

Plea see the README for a deeper discussion and TODOs.