[PerchAnton]

EditState::update_layer_properties indexes layers[layer] after checks that allow a missing index through. A stale index, usize::MAX, or an empty buffer therefore panics instead of returning an error. This affects both locked and unlocked property requests.

Check that the target exists before starting an undo group or building an undo operation. Add tests for invalid indices, an empty buffer, preserving the existing redo branch, and valid lock changes remaining undoable. No dependency or UI behavior change is included.

Validation on Windows / Rust 1.96: before the fix, two regression tests panic at layer_operations.rs:843 and the valid-operation control passes. After the fix, all three new tests and all 43 existing layer-operation tests pass. The existing test file was run unchanged through an isolated Cargo harness against the local patched crates with default features disabled; the full workspace suite has not been run locally. rustfmt and git diff --check pass. Upstream CI remains to be checked.

AI-assisted investigation and implementation with Codex.

[PerchAnton]

Thanks for reviewing and merging the fix. I appreciate your time and help!