[yunyv]

Reference issue

No matching issue or competing fix found for GridMap's per-axis index bounds. The open polygon comparison change in #1350 touches a different operation.

What does this implement/fix?

GridMap currently checks only the flattened storage index. This permits invalid x/y cell coordinates to alias a valid cell: for a 3-column, 2-row grid, writing to (3, 0) changes (0, 1), and reading (-1, 1) reads (2, 0). Neighbor updates in expand_grid can consequently mark cells across the opposite edge of the map.

Check each numeric cell index against its own axis bounds in the cell-value getter and setter, in addition to the existing flattened storage bounds. Out-of-bounds reads return the documented None, occupancy checks therefore treat them as occupied, and rejected writes return False without changing storage. Existing behavior for None inputs is unchanged.

• Preserve the existing flattened-index guard, value-type check, valid row-major indexing, and integer-valued float/NumPy integer inputs.
• Preserve the expansion neighbor stencil; only clip invalid neighbors at the grid edges.
• Add regressions for negative and upper-bound coordinates, coordinate pairs that cancel into valid flattened indices, valid cell storage, and expansion at opposite corners.
• Update the existing coverage-planner documentation's boundary explanation.

No parameter, dependency, animation, or CI configuration changes. Separate position-conversion and polygon issues are outside this fix.

Additional information

Linux / Python 3.14.8, with the repository-pinned runtime and development requirements and BLAS/OMP threads limited to one:

• Original source with the new regressions: 7 failed, 6 passed, 3 original tests deselected.
• Focused GridMap and sweep coverage-planner tests: 19 passed with warnings as errors.
• Scoped Ruff, Mapping mypy (25 source files), and git diff --check: passed.
• Final full bash runtests.sh: 169 passed in 158.40s, including changed-file Ruff, all configured mypy checks, and warnings as errors.
• Sphinx make html with -W -E -a (warnings as errors and full rebuild): passed. Generated boundary paragraph and parent navigation link verified. The pinned IPython emits its existing Python 3.14 SyntaxWarning during import.
• Browser visual inspection could not run: Chromium startup was blocked by the execution environment's Unix socket restriction. No screenshot, hardware, GPU, macOS, or Windows verification is claimed.

AI assistance was used for implementation and test preparation; no human review is claimed.

CheckList

• Did you add an unittest for your new example or defect fix?
• Did you add documents for your new example? (Updated the existing official page.)
• All CIs are green? (Hosted CI has not run for this draft.)