Stage 4 of the QoL arc, framing revision 4 (approved). Under
`truncate`, text past the right edge was UNREACHABLE; moving the cursor
now brings it into view. Automatic only — no commands, no bindings, no
new interaction island (Q#HS2).
THE CONTRACT. `view_left` is an unsnapped per-window display column
(Q#HS7(a)), and each line derives its own effective edge during the
walk it already performs from column 0. Starting at 0 is not laziness:
tab expansion depends on the absolute column from the line start, so a
walk beginning at the edge would put tab stops in the wrong place. The
walk stays line-absolute and only the emit translates.
Where the edge bisects a wide glyph on a given line (Q#HS7(c′)), its
trailing cell paints a styled BLANK rather than a `Continuation` — that
glyph means "the cell before me is a wide glyph's head", and here that
cell is off-screen, so emitting it would name a cell nobody painted.
The mapping designates that cell to the glyph's START byte, which keeps
`byte_at_place` total over visible cells and makes the character the
user scrolled toward clickable. Tabs keep FORWARD rounding (Q#HS7(c″))
— preserved, not chosen.
DECORATIONS TRAVEL WITH THE TEXT. The first version of this commit
translated the base glyph walk and nothing else, which split the frame
in half: at `view_left = 10` a glyph from source column 10 painted at
screen column 0 while its syntax style, diagnostic underline, search
wash and `BufferStyleOverlay` span painted at screen column 10 — or
vanished. Decorations drifting off the characters they describe,
silently, and only once a window had been scrolled.
Every such site carried the same two lines (`start_col.min(max_cols)`,
`end_col.min(max_cols)`), correct only while the left edge was pinned
at zero. `Viewport::visible_cols` is now the one rule all FIVE adopters
share — syntax/LSP styling, diagnostic underlines, search washes,
`BufferStyleOverlay`, and the selection painter — so a future decorator
inherits the translation instead of re-deriving it. It also subsumes
the old `end_col <= start_col` guard rather than sitting beside it.
`StyleSpanOverlay` and `VirtualCellOverlay` are deliberately untouched:
they are documented as viewport-relative, so translating them would be
the mirror defect.
The selection painter was nearly a sixth site with its own copy of the
rule, which I justified by a width it supposedly needed and the
viewport lacked. That was FALSE — the render viewport's
`cell_size.cols` is already `rect.size.cols - gutter_w` and its origin
already sits past the gutter. It now takes that same viewport and drops
its `rect`/`gutter_w` parameters entirely. A canonical rule with one
honest exception is not canonical.
The selection painter had the same defect with a worse failure mode: it
asked `pos_to_display` through the LIVE context, which returns `None`
for a position left of the edge, so a selection beginning off-screen
and reaching into view took `continue` and painted NOTHING. That is the
common shape, not an edge case — select rightward from column 0 past
the window width and the view scrolls with the cursor.
TWO THINGS THE TESTS FOUND, both in `pos_to_display`. My framing note
said a caret sits between characters so never lands inside a glyph;
true for the caret, false for the DESIGNATION direction — the glyph's
start byte must map to its visible trailing cell, so `screen_col` needs
the straddle rule and not a bare subtraction. And the `take == 0` early
return short-circuited the translation entirely, so byte 0 looked
visible at every offset.
`view_left` is inert under `wrap` BY CONSTRUCTION —
`LayoutCtx::effective_left` and `Viewport::left_edge` return 0 while
wrapping — rather than by every caller remembering.
Persisted per leaf at DESKTOP_VERSION 1 (Q#HS5) with both approval
conditions: `#[serde(default)]` and a literal v1 JSON fixture omitting
the field, hand-written because a generated one would gain the field
and prove nothing.
Also: `view_left: window.view_left` in the render viewport, not a
literal 0. My mechanical fill put 0 there and it is EXACTLY the
`aa3cd4d` defect — coordinates and the indicator following the scroll
while the painter stays pinned at column 0.
BITE, per clause. Forcing `bisected = false` fails the multi-line
straddle witness; dropping the backward designation fails the
round-trip witness; removing `#[serde(default)]` fails the v1 fixture;
pinning `visible_cols` to an absolute clamp fails all three decorator
witnesses; restoring the selection painter's live-context lookup fails
the off-screen-start selection witness. Each alone. And with selection
now reading the shared helper, pinning `visible_cols` to an absolute
clamp fails the selection witnesses TOO — which is the check that the
duplication is really gone rather than merely reworded.
One unrelated red, logged as R7 in ci-red-signatures.md — the first
this session with a COMPLETE signature, so a matchable row rather than
a U note. `pmacs-gpu`'s managed-retry attach hit a BrokenPipe once
under full-sweep load and did not reproduce (6 isolated runs plus a
clean 113-target sweep). Per the rerun rule that is intermittence only,
and the row explicitly does not claim harmlessness. Not attributed to
this lane: Stage 4 touches no `pmacs-gpu` file and adds no wire
surface.
Gates: fmt; clippy --workspace --all-targets -D warnings, both
configurations; `cargo test --workspace --no-fail-fast -- --skip
basedpyright` 113 targets exit 0, and the same with --features crdt,
113 targets exit 0; git diff --check. No protocol change, so no version
bump and no protocol-bump matrix.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016bqGA6s9tTUFzYpbeW3tai
Levi Neuwirth
bec8fc9aae