feat(agents): RemoteAgent, thin proxy server for user-hosted remote agent services

responses_api_agents/remote_agent/README.md

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+# Remote Agent
+
+A thin agent server that brokers rollouts to an agent service you host yourself — in your own
+repo, on your own infrastructure. Your service implements one endpoint, `POST /v1/responses`:
+it receives the task's `responses_create_params`, runs its own agent loop (its own model and
+tools, however many turns it needs), and returns one finished Responses API trajectory.
+
+Gym keeps everything else on its side: this server seeds the session, holds the session
+cookies, verifies the trajectory on the resources server (`verifier_metadata` never leaves
+Gym), and reports the verify response — so your rollouts land in the standard artifacts and
+work with `gym eval profile`, aggregation, and (when your service routes its model calls
+through a Gym model server) token-id capture for training.
+
+## Contract for your service
+
+- `POST {agent_base_url}/v1/responses` with the row's `responses_create_params` as the JSON body.
+- Return a single finished Responses API object: the last output item is an assistant message,
+  no dangling tool calls, `usage` populated (`{input_tokens, output_tokens, total_tokens}`).
+- Failures on Gym's side never crash a collection run: they are recorded as reward-0 rows in
+  the failures sidecar and retried on resume.
+
+## Gym-hosted tools (optional)
+
+With `forward_session: true`, each request to your service carries two headers:
+`X-NeMo-Gym-Resources-Server-Url` and `X-NeMo-Gym-Session-Cookie`. Echo the cookie on every
+tool call you make against that URL and stateful environments work end to end. If your service
+runs on a different machine, set `advertised_resources_url` to an externally reachable URL —
+the default resolves to the resources server's bind address, which is typically a loopback
+address only valid on the Gym host. Without
+forwarding, tasks that declare tools are refused up front (instead of silently scoring 0)
+unless you set `assume_remote_tools: true` because your service implements the declared tools
+itself.
+
+## Run
+
+```bash
+gym env start --resources-server <your_env> # plus this agent's config
+gym eval run --no-serve +agent_name=remote_agent +input_jsonl_fpath=... +output_jsonl_fpath=...
+```

responses_api_agents/remote_agent/configs/remote_agent.yaml

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+remote_agent:
+  responses_api_agents:
+    remote_agent:
+      entrypoint: app.py
+      agent_base_url: ???
+      resources_server:
+        type: resources_servers
+        name: ???
+      concurrency: 32
+      remote_responses_timeout_secs: 1800.0
+      run_timeout_secs: 2100.0
+      forward_session: false
+      assume_remote_tools: false

responses_api_agents/remote_agent/requirements.txt

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+-e nemo-gym[dev] @ ../../