Rebuild test_no_path_compression_find_stable on 4 nodes so the node it asks
about (3) sits two levels down under union-by-size; the old cell built
union(0,1);union(1,2) -> parent [0,0,0,0], so find(2) rewrote nothing and a
path-compressing find passed the cell that names the mechanism.
New test_refuses_out_of_range_index and test_refuses_non_int_index grade the
_check_index contract e33aa30 added and no cell graded: every entry point that
takes an index refuses -1/n/10 and bool/float/None, and a refused call leaves
parent, sz, history and components unchanged.
Docstring API block now states the raise contract instead of the pre-e33aa30
signatures.
Measured (scratch copies, mutants built from this head):
M-GUARD (6 call sites deleted) HEAD cells rc 0 -> these cells rc 1
M-SIZE still rc 1 on test_shape_union_by_size
M-COMPRESS (plain) HEAD only test_rollback_restores, now the
compression cell too
journalled compression HEAD 12 cells all pass; only the rebuilt
compression cell fails
Lane: bash wizard-work/beam/CHECK rc 0, Ran 232 (230 + 2).
ledger
beam