[Workflow] Default core tasks to RSL-RL

[StafaH]

Splits the default RL-library change from #6980.\n\n- Resolves default_agent from task registration when --rl_library is omitted.\n- Registers RSL-RL as the default for core tasks, including a Pendulum RSL-RL config.\n- Adds dispatch coverage and a breaking-change fragment.\n\nValidation: uv run python -m pytest source/isaaclab_rl/test/test_entrypoints.py -q (11 passed, 2 skipped).\n\nSupersedes the RSL-RL portion of #6980.

[greptile-apps]

Greptile Summary

Adds task-driven RL backend selection so unified training and playback commands use each task's registered default when --rl_library is omitted.

• Registers RSL-RL as the default backend for core tasks.
• Adds an RSL-RL PPO configuration for the Pendulum task.
• Adds dispatch tests and documents the CLI behavior change.

Confidence Score: 5/5

The PR appears safe to merge with no concrete blocking or non-blocking defects identified.

Default resolution follows the repository's established task-name normalization and registry contracts, while the new Pendulum configuration matches the environment conversion and RSL-RL observation-group conventions.

Important Files Changed

Filename	Overview
source/isaaclab_rl/isaaclab_rl/entrypoints/dispatch.py	Resolves a supported default backend from task registration while preserving explicit selection and existing error handling.
source/isaaclab_rl/test/test_entrypoints.py	Adds focused coverage for dispatch through a task-registered default backend.
source/isaaclab_tasks/isaaclab_tasks/core/pendulum/agents/rsl_rl_ppo_cfg.py	Adds a structurally valid PPO runner configuration matching the Pendulum task's converted single-agent observation group.
source/isaaclab_tasks/isaaclab_tasks/core/pendulum/init.py	Registers the new Pendulum RSL-RL configuration and selects it as the task default.
source/isaaclab_tasks/isaaclab_tasks/core/cartpole/init.py	Marks RSL-RL as the default for each registered core Cartpole variant.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    CLI["train/play CLI"] --> Explicit{"--rl_library supplied?"}
    Explicit -- Yes --> Backend["Dispatch selected backend"]
    Explicit -- No --> Task["Read --task"]
    Task --> Registry["Import task registrations and query Gym spec"]
    Registry --> Default{"Supported default_agent?"}
    Default -- Yes --> Backend
    Default -- No --> Help["Show backend selector error/help"]

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_{Reviews (1): Last reviewed commit: "Default core tasks to RSL-RL" | Re-trigger Greptile}

[isaaclab-review-bot]

Isaac Lab Review Bot

The task-registry-driven RSL-RL default is coherent with existing registration metadata, but default resolution introduces an unguarded runtime dependency on isaaclab_tasks before backend launch.

• Design and architecture: Keeping the default backend in task registration is data-driven, but _resolve_default_library now crosses from isaaclab_rl into isaaclab_tasks during CLI parsing. The import should be guarded so unavailable or pre-launch task registration cannot replace the established selector fallback with an exception.
• API: Explicit --rl_library selection remains unchanged. When it is omitted, however, an unavailable or failing isaaclab_tasks import can now raise instead of returning the existing missing-selection help and exit code 2.
• Implementation: The dispatch and argument-forwarding paths are otherwise consistent, and the Pendulum configuration follows sibling RSL-RL configs. The new dispatch test replaces isaaclab_tasks with a stub, so it does not cover the real import path responsible for the compatibility concern.

Minor fixes needed. Posted 1 actionable finding inline.

Automated review; human maintainers own approval decisions.

[isaaclab-review-bot]

🟡 Warning · Design Architecture — Unguarded task-registry import during CLI parsing

_resolve_default_library runs inside run_cli, before _run_backend starts the backend that constructs AppLauncher, and imports isaaclab_tasks unguarded. This module otherwise defers even isaaclab.app to stay lightweight, and task packages pull in Kit-dependent isaaclab.envs modules. An install without isaaclab_tasks (or a pre-launch import failure) now raises instead of returning the previous exit-2 message. Guard the import and fall back to None.

[AntoineRichard]

One concern on pendulum, otherwise LGTM

[AntoineRichard]

Pendulum is MARL only, will that work with RSL_RL?

[AntoineRichard]

Not sure if we should use RSL_RL