feat(app): better diff/code comments (#14621)

Co-authored-by: adamelmore <2363879+adamdottv@users.noreply.github.com>
Co-authored-by: David Hill <iamdavidhill@gmail.com>

packages/app/src/context/comments.test.ts

@@ -150,4 +150,37 @@ describe("comments session indexing", () => {
       dispose()
     })
   })
+
+  test("update changes only the targeted comment body", () => {
+    createRoot((dispose) => {
+      const comments = createCommentSessionForTest({
+        "a.ts": [line("a.ts", "a1", 10), line("a.ts", "a2", 20)],
+      })
+
+      comments.update("a.ts", "a2", "edited")
+
+      expect(comments.list("a.ts").map((item) => item.comment)).toEqual(["a1", "edited"])
+
+      dispose()
+    })
+  })
+
+  test("replace swaps comment state and clears focus state", () => {
+    createRoot((dispose) => {
+      const comments = createCommentSessionForTest({
+        "a.ts": [line("a.ts", "a1", 10)],
+      })
+
+      comments.setFocus({ file: "a.ts", id: "a1" })
+      comments.setActive({ file: "a.ts", id: "a1" })
+      comments.replace([line("b.ts", "b1", 30)])
+
+      expect(comments.list("a.ts")).toEqual([])
+      expect(comments.list("b.ts").map((item) => item.id)).toEqual(["b1"])
+      expect(comments.focus()).toBeNull()
+      expect(comments.active()).toBeNull()
+
+      dispose()
+    })
+  })
 })