Zooming a terminal with Ctrl +/- left the TUI showing the previous
frame through the new one. Q#FG1 = A, as approved.
THE RULE WAS ALREADY WRITTEN DOWN, ON A PRIVATE FIELD.
src/instance_render.rs:36 says remote frontends "must blank their local
buffer before applying the deltas" — the binding contract, in the one
place a consumer author will never look. The protocol type said only
that full_grid marks "the initial sync ... versus an incremental
frame": a label, from which no obligation follows. So FG-INV now lives
on InstanceMessage::CellDelta, where whoever writes the next frontend
reads it. A resync is a picture of the screen's INK, not of the screen.
The producer diffs against a blank grid, so a cell that should be blank
produces no span. src/frontend.rs then took `CellDelta { spans, .. }`
and discarded the flag. That was correct for exactly one frame — the
fresh-attach frame, which follows Frontend::new's Clear — and wrong for
every resize after, which follows nothing. A font-size change is the
worst case because the terminal reflows in place rather than dropping
content, so the maximum number of stale glyphs survive.
emit_cell_delta joins emit_span and emit_status_overlay as a pure
helper over a writer; apply_message routes through it. No struct
change, no generic parameter, no new pattern.
WHY SEVEN TESTS MISSED IT. Every one asserts the producer SETS the
flag; none asserted a consumer ACTS on it, and no runtime reader
existed workspace-wide. "Add a test for the flag" had already been
done and did not help. Handoff §5's enforcement-vs-documentation drift,
in a second register.
Three unit witnesses, each bitten independently. The empty-spans case
earns its own test rather than folding into the others: under the
plausible `spans.is_empty()` early return the ordering test still
PASSES and only that one fails — and an empty resync is exactly the
frame whose entire content is the blanking.
The PTY acceptance drives a real SIGWINCH, and its mark is anchored to
CONTENT rather than time. A time-based settle was written first and is
unusable: a settled pmacs screen emits per-frame bytes forever, so
"output stopped growing" never becomes true. Anchoring just past the
first painted byte excludes both startup clears by construction —
Frontend::new clears before any frame exists, and the first frame is
itself a resync whose clear precedes its own spans. Bitten against the
original defect: 34,831 bytes after the first painted frame, no CSI 2 J
anywhere in them.
What it does not prove, stated here rather than found in review: the
suites assert on raw bytes, with no screen model and no vt100/termwiz/
vte dependency. This shows pmacs emitted a blank at the right moment,
not that the screen ended correct.
Verified: fmt, clippy, diff-check, --lib 1900/0, crdt 2085/0, m4 150/0,
gpu 221/0, and the grid-driving suites — full_grid_resync 1/1, vterm
1/2/3 9+9+5, m5_5 15, m5_8 5, bottom_panel_stage1 47.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Levi Neuwirth
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