feat(flashsac): expose learner CUDA Graph controls

[EtherealTide]

Summary

This PR exposes the three FlashSAC learner controls needed to distinguish Inductor compilation, objective compile scope, and learner-owned whole-cycle CUDA Graph capture/replay. The default accelerated path for a single NVIDIA CUDA learner remains unchanged, while users can now opt out explicitly for debugging and compatibility.

What changed

• Added compile_full_objectives to the UniLab FlashSAC configuration contract.
• Added use_whole_cycle_cuda_graph as an explicit learner CUDA Graph control.
• Preserved the existing defaults: use_compile=true, compile_full_objectives=true, and use_whole_cycle_cuda_graph=true.
• Added structured configuration coverage and updated the English and Chinese FlashSAC documentation.
• Synced the implementation with the released unilab-rl==1.4.11 baseline and the current UniLab main branch.

Why

These settings control different runtime layers:

1. use_compile enables or disables Torch Inductor compilation.
2. compile_full_objectives selects whether Inductor compiles the complete actor/critic objective or a smaller loss region.
3. use_whole_cycle_cuda_graph controls whether the learner captures and replays the full update cycle as a CUDA Graph.

Previously, UniLab did not expose the learner-level CUDA Graph choice. This made it difficult to disable the graph for debugging or compatibility while retaining Inductor, and made the meaning of compile_full_objectives ambiguous.

Configuration examples

Configuration	Result
algo.algo_params.use_compile=false	Eager update path; compile-dependent whole-cycle graph is disabled.
algo.algo_params.compile_full_objectives=false	Inductor remains enabled, but compilation is limited to the smaller objective/loss region.
algo.algo_params.use_whole_cycle_cuda_graph=false	Inductor remains enabled, but learner-owned whole-cycle CUDA Graph capture/replay is disabled.
All three options at their defaults	Existing accelerated single-NVIDIA-CUDA path.

# Disable compilation and use the eager compatibility path
uv run train --algo flashsac --task g1_walk_flat --sim mujoco \
  algo.algo_params.use_compile=false

# Keep Inductor, but disable whole-cycle CUDA Graph capture/replay
uv run train --algo flashsac --task g1_walk_flat --sim mujoco \
  algo.algo_params.use_whole_cycle_cuda_graph=false

Linked work

• Driving issue: FlashSAC: clarify learner CUDA Graph controls and honor the manual opt-out unilabsim/unilab_rl#94
• Core implementation and release: https://github.com/unilabsim/unilab_rl/releases/tag/v1.4.11
• Base repository: https://github.com/Motphys/UniLab
• Base branch: main

Validation

The branch was rebased onto the latest UniLab main, and the previous uv.lock conflict was resolved.

Passed locally:

• Focused configuration and documentation tests: 20 passed.
• Ruff format: passed.
• Ruff lint: passed.
• Pyright: 0 errors; one local environment warning for an optional uni_rl.algos.fast_sac import.
• Sphinx documentation build: succeeded previously with 6 pre-existing toctree warnings.

Environment-limited checks (not code failures):

• make test-all could not complete because the local uv CUDA dependency download exceeded the temporary disk quota.
• The local mypy process exited with code 139 before reporting diagnostics.
• Full pytest collection hit an existing Numba cache-locator error because this worktree is mounted read-only for cache files.
• An offline Sphinx re-run could not fetch sphinx-copybutton; the earlier successful build remains the available docs evidence.

Remote CI should be reviewed on the current PR head before moving this Draft PR to Ready for review.

Impact

• Backend: no backend behavior changes.
• Platform: primarily NVIDIA CUDA/Linux; CPU/eager configurations remain available.
• Training: default accelerated behavior is preserved; explicit compile and graph opt-outs are now supported.
• Public configuration: adds use_whole_cycle_cuda_graph and documents the existing compile-scope controls.

Checklist

• Added or updated focused tests.
• Updated English and Chinese FlashSAC documentation.
• Linked the driving issue and released core dependency.
• Confirmed compatibility with unilab-rl==1.4.11.
• Rebased onto the latest UniLab main.
• Recorded exact local validation results and environment limitations.
• Confirm all current-head remote CI checks are green.
• Run the full repository gate successfully in an environment with writable caches and sufficient disk space.
• Move the PR from Draft to Ready for review after the checks above are complete.