fix(render): map author spans to landedText coords (INV-49/50 coloring alignment) (#64)

renderReview diffs against landedText (current minus pending proposals), so block
offsets are landedText-relative while authorSpans arrive in currentText coords. A
colored block after a length-changing pending proposal was mis-colored. Map the
spans through toLanded so authorship coloring stays aligned.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/trackChangesModel.test.ts

@@ -392,6 +392,26 @@ describe("renderReview", () => {
     // the applied paragraph is NOT also emitted as a word-merged changed block
     expect(html).not.toContain("<del>brown</del>"); // no double-render of the change as a baseline diff
   });
+
+  test("renderReview keeps author coloring aligned on a block AFTER a length-changing pending proposal (INV-49/50)", () => {
+    // block 1 has a pending proposal whose applied text is MUCH LONGER than its
+    // original; block 2 carries a Claude authorship span (in currentText coords).
+    const baseline = "one short.\n\ntwo stable here.\n";
+    const current = "one MUCH LONGER REPLACED TEXT.\n\ntwo stable here.\n";
+    const proposals: ProposalView[] = [{
+      id: "pr_1",
+      anchorStart: current.indexOf("one MUCH LONGER REPLACED TEXT."),
+      anchorEnd: current.indexOf("one MUCH LONGER REPLACED TEXT.") + "one MUCH LONGER REPLACED TEXT.".length,
+      replaced: "one short.",
+      replacement: "one MUCH LONGER REPLACED TEXT.",
+      original: "one short.",
+    }];
+    const sStart = current.indexOf("stable");
+    const authorSpans = [{ start: sStart, end: sStart + "stable".length, author: "claude" as const }];
+    const html = renderReview(baseline, current, authorSpans, proposals);
+    // the Claude coloring wraps "stable" exactly — not shifted by the proposal's length delta.
+    expect(html).toMatch(/<span class="cw-by-claude">stable<\/span>/);
+  });
 });
 
 import { renderTrackChanges as rtc2 } from "../src/trackChangesModel";