[jadenfix]

Description

MissionSpace.contains() can raise IndexError on a valid mission when placeholder words overlap. For example, a space with green, darkgreen and verydarkgreen raises on Get the verydarkgreen ball.. The overlap scan records some removal indices more than once, and deleting earlier entries shifts the remaining indices.

Remove each index once, working backwards. Added regressions for three nested words and for overlaps in two separate placeholder groups, with valid and invalid missions. Both crash cases fail before the fix. No new dependencies are required.

Validation: pytest (3,237 passed, 192 skipped), pytest --doctest-modules minigrid/ (15 passed), and pre-commit run --all-files all pass. The full Linux test matrix also passes on the exact PR commit: Python 3.10–3.14, plus Python 3.10 with Gymnasium 0.29.1 / NumPy 1.26.4 (3,237 passed, 192 skipped in each configuration). All latest-version doctests, pre-commit checks and package build pass.

Type of change

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

Checklist:

• I have run the pre-commit checks with pre-commit run --all-files
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective
• New and existing unit tests pass locally with my changes

No documentation update is needed for this internal fix.

Upstream pre-commit and the old-dependency / Python 3.10–3.13 test jobs pass. The Python 3.14 job was cancelled during tests; a maintainer rerun has been requested. The full fork matrix above passes against the exact PR commit.

Prepared with OpenAI Codex assistance.

[jadenfix]

@mwydmuch, could you approve the pending fork CI for this MissionSpace fix when convenient? It removes duplicate indices in reverse order so overlapping placeholders no longer raise IndexError. The full local suite and regression tests pass; validation is in the description. Thanks!

[jadenfix]

@mwydmuch, upstream pre-commit and the old-dependency / Python 3.10–3.13 test jobs now pass. Only the Python 3.14 job was cancelled during tests; could you rerun that job when convenient? The full matrix on my fork also passes against this PR's exact commit, linked in the description. Thanks!

[mwydmuch]

LGTM, thank @jadenfix fot the fix