fix(ui): support unified diff patch format in session changes viewer

Session diffs now use a compact patch field instead of storing full
before/after content. Added parsePatchToBeforeAfter utility to extract
before/after from unified diff format, and updated MonacoDiffViewer to
accept patch prop as alternative to before/after strings.

packages/ui/src/components/file-viewer/monaco-diff-viewer.tsx

@@ -1,15 +1,17 @@
-import { createEffect, createSignal, onCleanup, onMount } from "solid-js"
+import { createEffect, createMemo, createSignal, onCleanup, onMount } from "solid-js"
 import { loadMonaco } from "../../lib/monaco/setup"
 import { getOrCreateTextModel } from "../../lib/monaco/model-cache"
 import { inferMonacoLanguageId } from "../../lib/monaco/language"
 import { ensureMonacoLanguageLoaded } from "../../lib/monaco/setup"
 import { useTheme } from "../../lib/theme"
+import { parsePatchToBeforeAfter } from "../../lib/diff-utils"
 
 interface MonacoDiffViewerProps {
   scopeKey: string
   path: string
-  before: string
-  after: string
+  patch?: string
+  before?: string
+  after?: string
   viewMode?: "split" | "unified"
   contextMode?: "expanded" | "collapsed"
   wordWrap?: "on" | "off"
@@ -23,6 +25,16 @@ export function MonacoDiffViewer(props: MonacoDiffViewerProps) {
   let monaco: any = null
   const [ready, setReady] = createSignal(false)
 
+  const resolvedContent = createMemo(() => {
+    if (props.patch !== undefined && props.patch !== null) {
+      return parsePatchToBeforeAfter(props.patch)
+    }
+    return {
+      before: props.before ?? "",
+      after: props.after ?? "",
+    }
+  })
+
   const disposeEditor = () => {
     try {
       diffEditor?.setModel(null as any)
@@ -115,11 +127,12 @@ export function MonacoDiffViewer(props: MonacoDiffViewerProps) {
   createEffect(() => {
     if (!ready() || !monaco || !diffEditor) return
     const languageId = inferMonacoLanguageId(monaco, props.path)
+    const { before, after } = resolvedContent()
     const beforeKey = `${props.scopeKey}:diff:${props.path}:before`
     const afterKey = `${props.scopeKey}:diff:${props.path}:after`
 
-    const original = getOrCreateTextModel({ monaco, cacheKey: beforeKey, value: props.before, languageId })
-    const modified = getOrCreateTextModel({ monaco, cacheKey: afterKey, value: props.after, languageId })
+    const original = getOrCreateTextModel({ monaco, cacheKey: beforeKey, value: before, languageId })
+    const modified = getOrCreateTextModel({ monaco, cacheKey: afterKey, value: after, languageId })
     diffEditor.setModel({ original, modified })
 
     void ensureMonacoLanguageLoaded(languageId).then(() => {

packages/ui/src/components/instance/shell/right-panel/tabs/ChangesTab.tsx

@@ -115,23 +115,22 @@ const ChangesTab: Component<ChangesTabProps> = (props) => {
             }
           >
             {(file) => (
-              <Suspense
-                fallback={
-                  <div class="file-viewer-empty">
-                    <span class="file-viewer-empty-text">{props.t("instanceInfo.loading")}</span>
-                  </div>
-                }
-              >
-                <LazyMonacoDiffViewer
-                  scopeKey={scopeKey()}
-                  path={String(file().file || "")}
-                  before={String((file() as any).before || "")}
-                  after={String((file() as any).after || "")}
-                  viewMode={props.diffViewMode()}
-                  contextMode={props.diffContextMode()}
-                  wordWrap={props.diffWordWrapMode()}
-                />
-              </Suspense>
+<Suspense
+                  fallback={
+                    <div class="file-viewer-empty">
+                      <span class="file-viewer-empty-text">{props.t("instanceInfo.loading")}</span>
+                    </div>
+                  }
+                >
+                  <LazyMonacoDiffViewer
+                    scopeKey={scopeKey()}
+                    path={String(file().file || "")}
+                    patch={String((file() as any).patch || "")}
+                    viewMode={props.diffViewMode()}
+                    contextMode={props.diffContextMode()}
+                    wordWrap={props.diffWordWrapMode()}
+                  />
+                </Suspense>
             )}
           </Show>
         </div>