Handle single-world coupled MPM resets

[maxkra15]

Description

Handle the single-world coupled implicit-MPM reset case extracted from #6875.

Isaac Lab represents “reset the only local world” with the canonical mask [True, False], where the final entry selects global entities. Newton MPM cannot apply that masked reset to a one-world grid whose partition has no environment offsets, even though selecting the only local world is equivalent to resetting the full local grid.

For a one-world coupler containing MPM, this change promotes that local selection to an unmasked full-grid reset through the root coupled solver. Newton already synchronizes the coupled entry states through Newton #3649, so Isaac Lab resets only its current parent state and adds no MPM-manager API.

Non-MPM coupled solvers retain the existing device-mask path. Multi-world MPM masks are not promoted because a full reset would incorrectly clear every environment; partial reset of a shared multi-world grid still requires isolated grids or a Newton-side solution.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Validation

• uv run --frozen isaaclab -f
• uv run --frozen --extra test python -m pytest source/isaaclab_contrib/test/coupling/test_coupler.py -q — 53 passed
• Confirmed the regression test fails without the override and passes with it.
• Reproduced the real Newton failure for masked one-world MPM reset, then verified that one full root-solver reset succeeds and overwrites a deliberately stale parent output state.

Checklist

• I have read and understood the contribution guidelines
• I have run the pre-commit checks
• My changes generate no new warnings
• I have added tests that prove the fix is effective
• I have added a changelog fragment for the touched package
• My name already exists in CONTRIBUTORS.md
• Documentation changes are not required for this internal reset-lifecycle fix

[greptile-apps]

Greptile Summary

The PR fixes single-world coupled MPM resets by converting the canonical local-only mask into a full-grid reset through the root coupled solver.

• Adds a narrowly guarded MPM reset override for one-world coupled configurations.
• Preserves device-mask behavior for non-MPM and multi-world coupled solvers.
• Adds regression coverage for promoted, empty, non-MPM, and multi-world reset masks.
• Documents the fix in the contrib changelog.

Confidence Score: 5/5

The PR appears safe to merge, with the new behavior constrained to the documented single-world coupled MPM reset case.

The override matches the established reset lifecycle and canonical mask shape, while its guards and tests preserve existing non-MPM, empty-mask, and multi-world behavior.

Important Files Changed

Filename	Overview
source/isaaclab_contrib/isaaclab_contrib/coupling/coupler.py	Adds a guarded reset override that promotes only the canonical selected single-world MPM mask to the root solver’s full-reset path.
source/isaaclab_contrib/test/coupling/test_coupler.py	Covers successful promotion, empty-mask no-op behavior, preservation of non-MPM device masks, and multi-world fallthrough.
source/isaaclab_contrib/changelog.d/maxkra15-coupled-mpm-reset.rst	Accurately records the single-world coupled MPM reset fix.

_{Reviews (1): Last reviewed commit: "Simplify coupled MPM reset handling" | Re-trigger Greptile}

[isaaclab-review-bot]

Isaac Lab Review Bot

Reviewed the narrowly gated reset override that promotes the canonical single-local-world MPM mask to an unmasked root coupled-solver reset. The changed path is covered for selected and empty masks, non-MPM solvers, and multi-world MPM configurations; no candidate findings were supplied or supported.

• Design and architecture: The override is confined to one-world coupled solvers containing an MPM entry and delegates all other cases to the existing reset path. Its correctness depends on the documented canonical mask layout and Newton’s coupled-state synchronization; the host mask read and unmasked reset are limited to that exceptional configuration.
• API: No public symbols, configuration fields, exports, or defaults change. The private classmethod preserves the inherited reset signature, and the isaaclab_contrib changelog fragment is present under a correctly formatted Fixed section.
• Implementation: The promoted branch resets the root solver’s current parent state with world_mask=None and flags=0. Tests exercise promotion of [True, False], the empty-mask no-op, preservation of the device-mask path for non-MPM solvers, and non-promotion for multi-world MPM solvers. The all-false MPM case intentionally returns without forwarding the mask, a small behavioral distinction consistent with an empty reset.

No blocking issues. No inline issue met the actionable-evidence threshold; the assessment above records the review feedback.

Automated review; human maintainers own approval decisions.