fix(ui): remove duplicate reply range connectors

.changeset/quiet-reply-range-rails.md

@@ -0,0 +1,5 @@
+---
+"hunkdiff": patch
+---
+
+Stop drawing duplicate right-side range connectors on threaded reply cards.

packages/hunk/src/ui/diff/reviewRenderPlan.test.ts

@@ -164,6 +164,39 @@ describe("review render plan", () => {
     expect(inlineNotes.map((row) => row.rangeGuideConnection)).toEqual(["continue", "continue"]);
   });
 
+  test("connects only the root card of a reply thread to the external range rail", () => {
+    const theme = resolveTheme("github-dark-default", null);
+    const file = createDiffFile(
+      "thread",
+      "thread.ts",
+      "export const alpha = 1;\n",
+      "export const alpha = 2;\nexport const beta = 3;\n",
+    );
+    const rows = buildSplitRows(file, null, theme);
+    const notes = [
+      createVisibleAgentNote(file.metadata.hunks, {
+        id: "root",
+        annotation: { newRange: [2, 2], summary: "Root note" },
+        thread: { noteId: "root", depth: 0, hasNextSibling: false },
+      }),
+      createVisibleAgentNote(file.metadata.hunks, {
+        id: "child",
+        annotation: { newRange: [2, 2], summary: "Child reply" },
+        thread: { noteId: "child", parentId: "root", depth: 1, hasNextSibling: false },
+      }),
+    ];
+    const plannedRows = buildReviewRenderPlan({
+      fileId: file.id,
+      rows,
+      showHunkHeaders: true,
+      visibleAgentNotes: notes,
+    });
+    const inlineNotes = plannedRows.filter((row) => row.kind === "inline-note");
+
+    expect(inlineNotes).toHaveLength(2);
+    expect(inlineNotes.map((row) => row.rangeGuideConnection)).toEqual(["terminate", undefined]);
+  });
+
   test("connects a deletion-only anchor row directly into its inline note", () => {
     const theme = resolveTheme("github-dark-default", null);
     const file = createDiffFile(

packages/hunk/src/ui/diff/reviewRenderPlan.ts

@@ -493,7 +493,18 @@ export function buildReviewRenderPlan({
     );
 
     const anchoredNotes = placementsByAnchor.get(row.key) ?? [];
+    let remainingRootNotes = anchoredNotes.reduce(
+      (count, placement) => count + ((placement.note.thread?.depth ?? 0) === 0 ? 1 : 0),
+      0,
+    );
+
     anchoredNotes.forEach((placement) => {
+      const isThreadReply = (placement.note.thread?.depth ?? 0) > 0;
+      if (!isThreadReply) {
+        remainingRootNotes -= 1;
+      }
+      const hasLaterRootNote = remainingRootNotes > 0;
+
       plannedRows.push({
         kind: "inline-note",
         key: `inline-note:${placement.note.id}:${row.key}:${placement.noteIndex}`,
@@ -506,11 +517,14 @@ export function buildReviewRenderPlan({
         anchorSide: placement.anchorSide,
         noteCount: placement.noteCount,
         noteIndex: placement.noteIndex,
-        rangeGuideConnection: !noteGuideSideByRowKey.has(row.key)
-          ? undefined
-          : placement.noteIndex < placement.noteCount - 1 || rangeGuideContinuationRows.has(row.key)
-            ? "continue"
-            : "terminate",
+        // Replies already connect through the thread gutter on the left. Keep the
+        // external range rail on root cards so the thread has only one range connection.
+        rangeGuideConnection:
+          isThreadReply || !noteGuideSideByRowKey.has(row.key)
+            ? undefined
+            : hasLaterRootNote || rangeGuideContinuationRows.has(row.key)
+              ? "continue"
+              : "terminate",
       });
     });
   }