vNext Phase 0–1: Articulation test net + lazy public-API facade (ADR-0017/0019)

[KraHsu]

Phases 0–1 of the vNext architecture refactor. Two concept-separated commits; full suite 488 passed, pyright 0 errors, lint-imports 6/6 kept.

test(entity) — Articulation state/binding test net (ADR-0019 PR-A)

Runtime-free coverage for Articulation via a stateful fake robot handle (no Genesis): bind/enumeration, joint-matching + the four actuator-coverage ValueError paths, joint/root write_*→refresh round-trips, reset, build_per_joint_tensor, implicit-PD write_joint_targets_partial, and empty-env_ids guards. This is the prerequisite regression net gating the Phase 5 decomposition (the graph previously showed only refresh/bind covered).

refactor(lab) — lazy public-API facade + clean-cut surface changes (ADR-0017)

• PR 1.1 — genelab.lab re-exports lazily: the 8-package import block moves under TYPE_CHECKING (type-only); runtime resolution is a module __getattr__ searching _SOURCE_MODULES (+ __dir__, from __future__ import annotations). import genelab.lab no longer eagerly drags in torch, and a new public symbol in a source package is reachable through lab without editing it. __all__ stays explicit and snapshot-guarded.
• PR 1.2 — remove GenesisBackendCfg (clean cut, no alias) from lab.py and the genelab.__init__ re-export plumbing.
• PR 1.3 — hard-rename the env protocol ManagerBasedEnv → ManagerBasedEnvProtocol across all three facades (lab, genelab, genelab.envs), resolving the long-standing collision with the concrete ManagerBasedRlEnv.
• Adds tests/test_public_api_snapshot.py: pins lab.__all__ (now 76) and extensions.__all__ (9) to inline frozenset baselines, guarding against accidental surface drift.

Reference audits (repo convention)

• GenesisBackendCfg removal — memory graph in_degree=0, out_degree=0; full-tree grep found only the definition + facade plumbing, no functional consumer (its "used by GeneLab runners" docstring was dead). Clean.
• ManagerBasedEnv rename — graph in_degree=1, out_degree=0 (re-export edge only); whole-word grep (isolating it from ManagerBasedEnvCfg / ManagerBasedRlEnv) confirmed no annotation/isinstance usage; examples + docs clean. Old name now absent tree-wide.

Verification

ruff clean · pyright 0 errors (full src/genelab) · lint-imports 6/6 kept · full suite 488 passed · public surface guarded at 76 names; GenesisBackendCfg/ManagerBasedEnv no longer resolvable on any facade.

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