The previous commit CLAIMED the widest-line rule was shared. It was not.
The daemon called `src/display_width.rs`; the GPU folded through its own
private `advance_display_col`, a second copy of the same tab-stop and
Unicode-width arithmetic. The two agreed for ordinary input, so nothing
failed --- which is precisely why the claim was worth checking and why
asserting structural protection that does not exist is the defect, not
the duplication itself.
`pmacs_protocol::columns` now owns the rule, for the same reason
`scroll::follow_left` lives there: the protocol crate is the one place
both frontends already depend on. `advance_char`, `line_columns` and
`widest_line_columns` live there with their own rows; `display_width`
and the GPU both delegate.
The sharing is now demonstrated rather than described. Mutating the tab
stop inside `pmacs_protocol::columns` breaks the GPU's
`minimap_columns_match_code_tab_and_unicode_widths` --- a row that used
to run entirely through the private copy and could not have noticed.
Also restores `r4_p1_a_chrome_press_neither_arms_nor_moves_point`'s
opening line, "P1 --- a press on the band's MODE LINE begins nothing",
which my insertion had left attached to the B2 test. The attribute came
back last round; the first paragraph did not.
Levi Neuwirth
9e54cd2c5b