Subversion merge engine adapter

TortoiseGitMerge's DiffData.cpp uses Subversion's diff engine. Native three-pane conflict preparation now uses the pinned adapter for source alignment and result generation. Two-pane comparisons now request pinned Subversion ranges too. A short-lived Swift coordinate projection supports immediate native text/Undo updates while comparison is pending; transfers, difference navigation and inline highlighting wait for the authoritative result. Engine failures clear the comparison rather than publishing that projection as a completed diff. The Core API's legacy default Git path remains available for comparison tests; the native conflict window requests Subversion explicitly.

TurtleGitMergeDiff now adapts the actual pinned Subversion diff2/diff3 APIs into typed common/modified/latest/same/conflict ranges. It loads the private per-CPU libraries already packaged for GitSVN instead of adding a second copy of Subversion/APR. The adapter itself is universal, targets macOS 13 and links directly only to system libraries. Packaging includes its GPL source, license, reconstruction recipe, hashes and inherited sandbox signing configuration. The dynamic libraries retain the separate SVN source/license/audit record.

The Swift entry point keeps original Base/Mine/Theirs line arrays alongside engine ranges. Regex keys use the existing ECMAScript helper. Each source line is hex-framed as one engine token, so nine EOL styles, embedded NUL and regex replacements containing newlines cannot corrupt line counts. Original content is never overwritten by comparison keys. Helper output is checked for contiguous, bounded, complete mappings and valid segment kinds. Processes are cancellable and bounded; private input files are removed after completion.

Three-pane integration retains original numbered source rows, display-only removed Base rows, one-side gaps, identical changes and conflict colors. Common and identical changes prefer original Mine text, latest-only changes use Theirs, and conflicts retain the editor's marker-based representation. Regex selection is window-local and uses explicit dirty Save/discard/Cancel before regenerating from index stages. Cancel preserves the current result and Undo history. Successful reload resets history; Save-before-Reload retains unresolved stages until a separate Mark as resolved. Preparation, Close and Quit track owned cancellation.

Two-pane requests are debounced during typing and cancel superseded helpers. Original-text source selections and marked/edited annotations are remapped when Subversion publishes an alignment. Original source data and saved encoding/EOL choices remain independent of comparison keys.

Resolved children are now exported as validated metadata. Subversion repeats the parent Base range for each child while Mine/Theirs partition the parent sides. The renderer follows DiffData.cpp: the first child supplies removed-Base padding, and the parent remains unresolved. Shared child lines do not become automatically resolved result blocks.

Whitespace/case/EOL choices now use saved source defaults; see comparison options. Comment profiles now feed original-text comparison keys; see comment comparison. Remaining: profile overrides and complete source option/EOL acceptance, literal-marker handling, full libsvn segmentation equivalence, native layout, physical and signed App Store acceptance. Protocol 2 retains top-level conflict containers and their resolved children, validating containment, side partitions and repeated Base ranges. This is a backend foundation and native three-pane integration for the complete port, not certification of the full replacement editor.

Grouped integration evidence: 38 Core tests passed after a compile-time setter access repair. The focused native receiver then passed production preparation, regex rows, original Mine preference, Cancel/Undo, No Filter, discard and Save-before-Reload, explicit resolution, unchanged HEAD and Close cancellation. Its first Undo assertion was too early for AppKit's queued update; the repaired fixture waits for the actual editable view and Undo state. Offscreen content captures omitted SwiftUI toolbar text and were rejected. No new screenshots are published from that method. All owned windows/helpers exited. The receiver is included in the shared CI compilation; its new combined wrapper has not yet run remotely. See qa/three-pane-engine-integration-2026-10-12.json.

Two-pane integration: 52 grouped Core tests and the focused native receiver passed. Native checks cover Unicode typing/selection, Undo/Redo, marks, Include semantics, exact BOM/CRLF saves and cancellation of a started adapter. A real caret-handoff bug was repaired; the fixture's unmarked-save expectation was also corrected. Original UTF-16 Base bytes and executable permissions remained unchanged. See qa/two-pane-engine-integration-2026-10-12.json. Physical input, complete captures and signed acceptance remain open.

Subversion 1.14.5 has a repeated-line EOF edge case: a resolved child can extend one token beyond a parent side, followed by a -1 child length. Protocol 2 keeps those bounded raw starts/lengths for diagnostics. Its source-indexable ranges are nil for such children. Valid parent ranges remain authoritative for all result text and source reconstruction; padding uses only a valid first child. No negative length is converted into a Swift range or used to index a source.

Resolved-child validation: the initial grouped run passed the 21 existing conflict/source tests but found two engine/presentation failures. The EOF case above was repaired, and the old add/add fixture was updated for the source's new display-only padding row. All 16 engine/presentation cases then passed, including original-source reconstruction and intact parent block choices. The embedded protocol-2 adapter passed on arm64 and x86_64. See qa/resolved-children-2026-10-12.json; a clean rerun of the whole expanded group is not claimed. No frontend code changed in this batch.