Per the decision: the contract is behavioral, and the two frontends
need not share a representation. manual_left_authority, its
initializer and its four writes are gone, and scroll_by_columns no
longer returns a bool nobody read. GPU authority is structural --- the
follow reaches the origin only through ensure_caret_painted, which
Q#F6's painted-before policy skips exactly when the user has scrolled
the caret off screen, and when the caret is on screen it is inside the
viewport where follow_left is a no-op. There is no follow to outrank.
L7b, GPU, found a live gap before it could witness anything. Q#R1's
keystroke case re-shapes only the affected line through
try_reshape_line and skips the full reshape --- and skipped clause 3's
clamp with it. A one-line delete that shortens the widest line could
therefore leave the viewport past the end of the text, with no later
event to repair it. The clamp now runs on that branch too, and the row
drives apply_loro_text_delta_batches and asserts the line count did not
change, so it cannot pass by taking the full-reshape branch instead.
The combined row is split four ways, each with its own mutation: L2
(height-only preserves --- the policy, not a latch), L7a (widening
clamps to the exact bound), L7b (content shrink through the incremental
path), L3 (a moved CursorByte pulls the viewport back). L3 exists
because removing the flag would otherwise leave the "until the cursor
changes" boundary unwitnessed --- the one thing the flag's name claimed
to govern. Its first version re-announced the caret's current byte,
which the arm treats as inert by design; it now moves it.
L2's mutation necessarily bites L7a --- an unconditional follow snaps
the origin to the caret before that row's widen --- and the doc names
that rather than leaving a predicted bite unexplained.
Gates: fmt; clippy --workspace --all-targets -D warnings; pmacs-gpu
317; --lib 2009; git diff --check.
Levi Neuwirth
269c52e5a7