Reset scroll on issue detail navigation

ui/src/lib/navigation-scroll.test.ts

@@ -39,6 +39,46 @@ describe("navigation-scroll", () => {
     ).toBe(false);
   });
 
+  it("resets scroll when navigating directly between issue detail routes", () => {
+    expect(
+      shouldResetScrollOnNavigation({
+        previousPathname: "/issues/PAP-1389",
+        pathname: "/issues/PAP-1346",
+        navigationType: "PUSH",
+        state: null,
+      }),
+    ).toBe(true);
+
+    expect(
+      shouldResetScrollOnNavigation({
+        previousPathname: "/PAP/issues/PAP-1389",
+        pathname: "/PAP/issues/PAP-1346",
+        navigationType: "REPLACE",
+        state: null,
+      }),
+    ).toBe(true);
+  });
+
+  it("does not treat non-detail issue routes as issue-to-issue navigation", () => {
+    expect(
+      shouldResetScrollOnNavigation({
+        previousPathname: "/projects/project-1/issues/all",
+        pathname: "/issues/PAP-1346",
+        navigationType: "PUSH",
+        state: null,
+      }),
+    ).toBe(false);
+
+    expect(
+      shouldResetScrollOnNavigation({
+        previousPathname: "/issues/PAP-1389",
+        pathname: "/projects/project-1/issues/all",
+        navigationType: "PUSH",
+        state: null,
+      }),
+    ).toBe(false);
+  });
+
   it("does not reset scroll on the initial render or when the pathname is unchanged", () => {
     expect(
       shouldResetScrollOnNavigation({

ui/src/lib/navigation-scroll.ts

@@ -14,6 +14,7 @@ export function shouldResetScrollOnNavigation(params: {
   if (previousPathname === null) return false;
   if (previousPathname === pathname) return false;
   if (navigationType === "POP") return false;
+  if (isIssueDetailPathChange(previousPathname, pathname)) return true;
   return hasSidebarScrollResetState(state);
 }
 
@@ -43,3 +44,20 @@ function hasSidebarScrollResetState(state: unknown): boolean {
   if (!state || typeof state !== "object") return false;
   return (state as Record<string, unknown>).paperclipSidebarScrollReset === true;
 }
+
+function isIssueDetailPathChange(previousPathname: string, pathname: string): boolean {
+  const previousIssueRef = readIssueDetailPathRef(previousPathname);
+  const nextIssueRef = readIssueDetailPathRef(pathname);
+  return previousIssueRef !== null && nextIssueRef !== null && previousIssueRef !== nextIssueRef;
+}
+
+function readIssueDetailPathRef(pathname: string): string | null {
+  const segments = pathname.split("/").filter(Boolean);
+  if (segments.length === 2 && segments[0] === "issues") {
+    return segments[1] ?? null;
+  }
+  if (segments.length === 3 && segments[1] === "issues") {
+    return segments[2] ?? null;
+  }
+  return null;
+}