feat(ui): add document revision diff viewer

Add a "View diff" option to the document three-dot menu (visible when
revision > 1) that opens a modal showing side-by-side changes between
revisions using react-diff-viewer-continued. Defaults to comparing the
current revision with its predecessor, with dropdowns to select any two
revisions.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

ui/package.json

@@ -30,7 +30,6 @@
     "@dnd-kit/sortable": "^10.0.0",
     "@dnd-kit/utilities": "^3.2.2",
     "@lexical/link": "0.35.0",
-    "lexical": "0.35.0",
     "@mdxeditor/editor": "^3.52.4",
     "@paperclipai/adapter-claude-local": "workspace:*",
     "@paperclipai/adapter-codex-local": "workspace:*",
@@ -41,17 +40,19 @@
     "@paperclipai/adapter-pi-local": "workspace:*",
     "@paperclipai/adapter-utils": "workspace:*",
     "@paperclipai/shared": "workspace:*",
-    "hermes-paperclip-adapter": "^0.2.0",
     "@radix-ui/react-slot": "^1.2.4",
     "@tailwindcss/typography": "^0.5.19",
     "@tanstack/react-query": "^5.90.21",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "cmdk": "^1.1.1",
+    "hermes-paperclip-adapter": "^0.2.0",
+    "lexical": "0.35.0",
     "lucide-react": "^0.574.0",
     "mermaid": "^11.12.0",
     "radix-ui": "^1.4.3",
     "react": "^19.0.0",
+    "react-diff-viewer-continued": "^4.2.0",
     "react-dom": "^19.0.0",
     "react-markdown": "^10.1.0",
     "react-router-dom": "^7.1.5",

ui/src/components/DocumentDiffModal.tsx

@@ -0,0 +1,169 @@
+import { useMemo, useState } from "react";
+import { useQuery } from "@tanstack/react-query";
+import type { DocumentRevision } from "@paperclipai/shared";
+import ReactDiffViewer, { DiffMethod } from "react-diff-viewer-continued";
+import { issuesApi } from "../api/issues";
+import { queryKeys } from "../lib/queryKeys";
+import { relativeTime } from "../lib/utils";
+import {
+  Dialog,
+  DialogContent,
+  DialogHeader,
+  DialogTitle,
+} from "@/components/ui/dialog";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/components/ui/select";
+
+function getRevisionLabel(revision: DocumentRevision) {
+  const actor = revision.createdByUserId
+    ? "board"
+    : revision.createdByAgentId
+      ? "agent"
+      : "system";
+  return `rev ${revision.revisionNumber} — ${relativeTime(revision.createdAt)} • ${actor}`;
+}
+
+export function DocumentDiffModal({
+  issueId,
+  documentKey,
+  latestRevisionNumber,
+  open,
+  onOpenChange,
+}: {
+  issueId: string;
+  documentKey: string;
+  latestRevisionNumber: number;
+  open: boolean;
+  onOpenChange: (open: boolean) => void;
+}) {
+  const { data: revisions } = useQuery({
+    queryKey: queryKeys.issues.documentRevisions(issueId, documentKey),
+    queryFn: () => issuesApi.listDocumentRevisions(issueId, documentKey),
+    enabled: open,
+  });
+
+  const sortedRevisions = useMemo(() => {
+    if (!revisions) return [];
+    return [...revisions].sort((a, b) => b.revisionNumber - a.revisionNumber);
+  }, [revisions]);
+
+  // Default: compare previous (latestRevisionNumber - 1) with current (latestRevisionNumber)
+  const [leftRevisionId, setLeftRevisionId] = useState<string | null>(null);
+  const [rightRevisionId, setRightRevisionId] = useState<string | null>(null);
+
+  const effectiveLeftId = leftRevisionId ?? sortedRevisions.find(
+    (r) => r.revisionNumber === latestRevisionNumber - 1,
+  )?.id ?? null;
+
+  const effectiveRightId = rightRevisionId ?? sortedRevisions.find(
+    (r) => r.revisionNumber === latestRevisionNumber,
+  )?.id ?? null;
+
+  const leftRevision = sortedRevisions.find((r) => r.id === effectiveLeftId) ?? null;
+  const rightRevision = sortedRevisions.find((r) => r.id === effectiveRightId) ?? null;
+
+  const leftBody = leftRevision?.body ?? "";
+  const rightBody = rightRevision?.body ?? "";
+
+  return (
+    <Dialog open={open} onOpenChange={onOpenChange}>
+      <DialogContent className="max-w-4xl max-h-[85vh] overflow-hidden flex flex-col">
+        <DialogHeader>
+          <DialogTitle>
+            Diff — <span className="font-mono text-sm">{documentKey}</span>
+          </DialogTitle>
+        </DialogHeader>
+
+        <div className="flex items-center gap-3 flex-wrap">
+          <div className="flex items-center gap-2 min-w-0">
+            <span className="text-xs text-muted-foreground shrink-0">Left:</span>
+            <Select
+              value={effectiveLeftId ?? ""}
+              onValueChange={(value) => setLeftRevisionId(value)}
+            >
+              <SelectTrigger className="h-8 w-56 text-xs">
+                <SelectValue placeholder="Select revision" />
+              </SelectTrigger>
+              <SelectContent>
+                {sortedRevisions.map((revision) => (
+                  <SelectItem key={revision.id} value={revision.id} className="text-xs">
+                    {getRevisionLabel(revision)}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+          <div className="flex items-center gap-2 min-w-0">
+            <span className="text-xs text-muted-foreground shrink-0">Right:</span>
+            <Select
+              value={effectiveRightId ?? ""}
+              onValueChange={(value) => setRightRevisionId(value)}
+            >
+              <SelectTrigger className="h-8 w-56 text-xs">
+                <SelectValue placeholder="Select revision" />
+              </SelectTrigger>
+              <SelectContent>
+                {sortedRevisions.map((revision) => (
+                  <SelectItem key={revision.id} value={revision.id} className="text-xs">
+                    {getRevisionLabel(revision)}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+        </div>
+
+        <div className="overflow-auto flex-1 rounded-md border border-border text-xs">
+          {!revisions ? (
+            <div className="p-6 text-center text-muted-foreground text-sm">Loading revisions...</div>
+          ) : !leftRevision || !rightRevision ? (
+            <div className="p-6 text-center text-muted-foreground text-sm">Select two revisions to compare.</div>
+          ) : leftRevision.id === rightRevision.id ? (
+            <div className="p-6 text-center text-muted-foreground text-sm">Both sides are the same revision.</div>
+          ) : (
+            <ReactDiffViewer
+              oldValue={leftBody}
+              newValue={rightBody}
+              splitView={false}
+              compareMethod={DiffMethod.WORDS}
+              useDarkTheme
+              leftTitle={`rev ${leftRevision.revisionNumber}`}
+              rightTitle={`rev ${rightRevision.revisionNumber}`}
+              styles={{
+                variables: {
+                  dark: {
+                    diffViewerBackground: "transparent",
+                    gutterBackground: "hsl(var(--muted) / 0.3)",
+                    addedBackground: "hsl(142 70% 25% / 0.3)",
+                    addedGutterBackground: "hsl(142 70% 25% / 0.4)",
+                    removedBackground: "hsl(0 70% 30% / 0.3)",
+                    removedGutterBackground: "hsl(0 70% 30% / 0.4)",
+                    wordAddedBackground: "hsl(142 70% 35% / 0.5)",
+                    wordRemovedBackground: "hsl(0 70% 40% / 0.5)",
+                    addedGutterColor: "hsl(var(--foreground))",
+                    removedGutterColor: "hsl(var(--foreground))",
+                    gutterColor: "hsl(var(--muted-foreground))",
+                    codeFoldGutterBackground: "hsl(var(--muted) / 0.2)",
+                    codeFoldBackground: "hsl(var(--muted) / 0.1)",
+                    emptyLineBackground: "transparent",
+                    codeFoldContentColor: "hsl(var(--muted-foreground))",
+                  },
+                },
+                contentText: {
+                  fontFamily: "inherit",
+                  fontSize: "13px",
+                  lineHeight: "1.6",
+                },
+              }}
+            />
+          )}
+        </div>
+      </DialogContent>
+    </Dialog>
+  );
+}

ui/src/components/IssueDocumentsSection.tsx

@@ -29,7 +29,8 @@ import {
   DropdownMenuSeparator,
   DropdownMenuTrigger,
 } from "@/components/ui/dropdown-menu";
-import { Check, ChevronDown, ChevronRight, Copy, Download, FilePenLine, FileText, MoreHorizontal, Plus, Trash2, X } from "lucide-react";
+import { Check, ChevronDown, ChevronRight, Copy, Diff, Download, FilePenLine, FileText, MoreHorizontal, Plus, Trash2, X } from "lucide-react";
+import { DocumentDiffModal } from "./DocumentDiffModal";
 
 type DraftState = {
   key: string;
@@ -162,6 +163,7 @@ export function IssueDocumentsSection({
   const [highlightDocumentKey, setHighlightDocumentKey] = useState<string | null>(null);
   const [revisionMenuOpenKey, setRevisionMenuOpenKey] = useState<string | null>(null);
   const [selectedRevisionIds, setSelectedRevisionIds] = useState<Record<string, string | null>>({});
+  const [diffViewKey, setDiffViewKey] = useState<string | null>(null);
   const autosaveDebounceRef = useRef<ReturnType<typeof setTimeout> | null>(null);
   const copiedDocumentTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null);
   const hasScrolledToHashRef = useRef(false);
@@ -929,6 +931,12 @@ export function IssueDocumentsSection({
                         <Download className="h-3.5 w-3.5" />
                         Download document
                       </DropdownMenuItem>
+                      {doc.latestRevisionNumber > 1 ? (
+                        <DropdownMenuItem onClick={() => setDiffViewKey(doc.key)}>
+                          <Diff className="h-3.5 w-3.5" />
+                          View diff
+                        </DropdownMenuItem>
+                      ) : null}
                       {canDeleteDocuments ? <DropdownMenuSeparator /> : null}
                       {canDeleteDocuments ? (
                         <DropdownMenuItem
@@ -1174,6 +1182,20 @@ export function IssueDocumentsSection({
           );
         })}
       </div>
+
+      {diffViewKey && (() => {
+        const diffDoc = sortedDocuments.find((d) => d.key === diffViewKey);
+        if (!diffDoc) return null;
+        return (
+          <DocumentDiffModal
+            issueId={issue.id}
+            documentKey={diffDoc.key}
+            latestRevisionNumber={diffDoc.latestRevisionNumber}
+            open
+            onOpenChange={(open) => { if (!open) setDiffViewKey(null); }}
+          />
+        );
+      })()}
     </div>
   );
 }