Merge whitespace display

Baseline: 7338078f8ddd924b8cddee35f512f2286072136d, BaseView.cpp::DrawLineEnding and its space/tab drawing, MainFrm.cpp::OnViewWhitespaces.

Both native comparison windows now expose View → Show Whitespaces and Line-ending icons. Merge Editor Settings has the same saved options through its existing Apply/Cancel transaction. Source defaults are retained: whitespace visible and IconLFs off. Unlike Windows registry editing, macOS exposes IconLFs as a native control. View choices apply to every text pane in that window; Settings Apply refreshes open windows through their existing preferences notification.

The native overlay draws the source's two-point space rectangle, tab arrow and ending paths. CRLF bends from the top before returning left; CR returns left; LFCR returns left then down; LF points diagonally down-left. VT/FF/NEL/LS/PS add the source separator rule and ending arrow. Unended lines have no ending symbol. Tabs follow native glyph geometry and the current tab stops rather than replacing the buffer with expanded spaces.

Icon mode reuses the original unmodified LineEndingCR.ico, LineEndingLF.ico and LineEndingCRLF.ico, with pinned blob and SHA-256 provenance. As upstream, icon mode draws only these three styles. When both compared rows have different real endings, the icon background uses the original inline added/removed palette; the two-pane Inline diff switch gates that background.

Markers use UTF-16 display coordinates. Aligned panes use captured original ending metadata, never the synthetic LF used to display a gap or an unended final line. Removed Base rows retain their original endings. Merged/Base raw text uses the shared nine-ending parser. Only ASCII spaces and tabs are marked; Unicode nonbreaking spaces are retained without being mislabeled. Marker plans are cached between draws, and visible-glyph bounds limit painting. Appearance changes use native dynamic marker colors and original image alpha. Dark-mode icons tint the original silhouette using an opaque resolved native foreground; the bundled ICO bytes remain unchanged.

Rendering changes no text-storage characters, source numbers, selection offsets, copy/export data, draft bytes, Undo history or comparison keys. Toggling it does not spawn an engine helper or mark the document dirty. Busy/Quit/retired models refuse stale View dispatch. This adds display controls; the existing whitespace conversion commands remain separate editing operations.

Evidence and remaining work

Thirty-four grouped Core tests passed, including all nine endings, UTF-16 emoji/ NFD offsets, real versus synthetic endings, gap rows, comparison ending changes, source defaults/persistence and the existing ending/whitespace/source/presentation and original icon tests. The unsigned Debug build passed with existing diagnostic noise. See the batch record.

Two combined native receiver runs passed the production owners, including three-pane visibility updates and two-pane source markers, persistence, stale busy refusal and unchanged selection/history/text/files. Visual review exposed insufficient dark-icon contrast. After an AppKit import-name repair, the icon callback was changed to capture a color resolved under the view's actual appearance. A focused whitespace-only receiver and final build passed; the inspected final captures show readable arrows on dark backgrounds. The Core suite was not repeated for these rendering changes. Actual app/Finder resource auditing also passed, including all 294 bundled original icon resources.

The website includes four native component captures (shapes/icons, light/dark). They are source text-view captures, not full-window or physical menu acceptance. All owned windows/helpers closed. No installed application was launched.

Remaining acceptance: full physical menu/Settings Apply/Cancel, native CR/LF and rare-ending glyph geometry, long-line/high-contrast/resize behavior, three-pane inline-diff controls and full character-difference equivalence, wrapping/folding integration, minimum-OS and signed sandbox acceptance. This does not certify complete TortoiseGitMerge or application parity.