Replace the single-side replace (and the short-lived accept-both button) with
additive accepts: each result conflict region starts EMPTY (thin marker bar), and
the gutter controls append a side in click order — > adds ours, < adds theirs
(first pick on top, next below), x clears. Controls stay visible after the first
pick so both sides can be stacked; empty/unresolved regions render a marker so they
stay visible. en/de keys updated; Ui 128 + Localization 16 green.
The between-pane gutter only offered single-side replace (accept ours / accept
theirs). Add an 'accept both' (⊕) control under the ours chevron that drops
ours-then-theirs into the result region, so a conflict can be combined in one
click instead of picking one side and hand-adding the other. en/de keys added.
Review follow-ups: coalesce gutter re-layout posts (avoid dispatcher flooding when
visual lines aren't ready), drop the zero-length deletable segment (undo hygiene),
and clear stale scroll-sync hooks on DataContext swap. Update Ui/CLAUDE.md to the
3-pane editor and log visual-verification items (incl. empty-side + alignment edges)
in docs/open.md.
Replace the Base|Ours|Theirs read-only columns + single-conflict result with a
whole-file 3-pane editor: Ours (read-only) | editable Result | Theirs (read-only),
reconstructed from the active file's segments so the panes line up on stable text.
- IBackgroundRenderer paints each conflict block (unresolved=blood, resolved=green)
across all three panes.
- Result document edits are gated by an IReadOnlySectionProvider (stable text is
read-only; only conflict regions, tracked via TextAnchors, are editable); edits
flow back to the owning block.
- Between-pane gutters host inline accept controls (>/< ) positioned per conflict;
click accepts ours/theirs into the result.
- Proportional synced vertical scroll across the panes; file switcher + change-nav
arrows (F8 / Shift+F8); active-file 'M conflicts - K resolved' readout.
- Merge block tints + AmberBrush tokens; en/de keys for the new labels.
Seam unchanged. App builds; Ui.Tests 128, Localization.Tests 16.
