feat(chat): show compaction summary on token hover

apps/desktop/src/components/ContextUsageInspector.tsx

@@ -354,7 +354,7 @@ export function ContextUsageInspector({
           <span>
             {t("chat.usageCompaction", { times: compaction.generation })}
           </span>
-          <strong>~{formatCompactTokenCount(compaction.summaryTokens)}</strong>
+          <strong title={compaction.summarized && !compaction.fallback && compaction.summary?.trim() ? compaction.summary : undefined}>~{formatCompactTokenCount(compaction.summaryTokens)}</strong>
         </div>
       ) : null}
     </div>

apps/desktop/src/features/chat/transcript/AssistantTurn.tsx

@@ -453,14 +453,14 @@ export const AssistantTurn = memo(function AssistantTurn({
  * turn item: a divider that says the earlier turns above it are now a summary.
  * It carries no actions — nothing about a persisted checkpoint is undoable.
  */
-export function CompactionRow({ mark }: { mark: ContextCompactionMark }) {
+export function CompactionRow({ mark }: { mark: ContextCompactionMark & { summary?: string } }) {
   const { t } = useTranslation();
   return (
     <div className="transcript-compaction-row" role="separator">
       <span className="transcript-compaction-label">
         {t("chat.compactionRow", { times: mark.generation })}
       </span>
-      <span className="transcript-compaction-detail">
+      <span className="transcript-compaction-detail" title={mark.summarized && !mark.fallback && mark.summary?.trim() ? mark.summary : undefined}>
         {mark.fallback
           ? t("chat.compactionRowSummaryFailed")
           : mark.summarized

apps/desktop/src/stores/app-state.ts

@@ -146,7 +146,7 @@ export type AppState = {
   /** Latest terminal outcome per session for compact sidebar feedback. */
   sessionOutcomes: Record<string, SidebarSessionOutcome>;
   /** Every checkpoint a session has installed, oldest first. */
-  sessionCompactions: Record<string, ContextCompactionMark[]>;
+  sessionCompactions: Record<string, (ContextCompactionMark & { summary?: string })[]>;
   providers: ProviderPublic[];
   /** Discovered model lists per provider id (composer model menu). */
   providerModels: Record<string, ModelInfo[]>;

apps/desktop/src/stores/app-store.ts

@@ -394,10 +394,12 @@ function persistCurrentSidebar(getState: () => AppState): void {
 
 /** Append a freshly installed checkpoint, or replace a retried one by id. */
 function withCompactionMark(
-  marks: ContextCompactionMark[] | undefined,
-  mark: ContextCompactionMark,
-): ContextCompactionMark[] {
-  return [...(marks ?? []).filter((existing) => existing.id !== mark.id), mark];
+  marks: AppState["sessionCompactions"][string] | undefined,
+  mark: AppState["sessionCompactions"][string][number],
+): AppState["sessionCompactions"][string] {
+  const existing = marks?.find((m) => m.id === mark.id);
+  const merged = { ...mark, summary: mark.summary ?? existing?.summary };
+  return [...(marks ?? []).filter((m) => m.id !== mark.id), merged];
 }
 
 let storeAccess: StoreAccess | null = null;

apps/desktop/src/stores/runtime/session-coordination.ts

@@ -154,7 +154,7 @@ export function createSessionCoordination({
     const records =
       session?.compactions ??
       (session?.compaction ? [session.compaction] : []);
-    const marks = records.map(contextCompactionMark);
+    const marks = records.map((record) => ({ ...contextCompactionMark(record), summary: record.summary }));
     set((state) => ({
       sessionCompactions:
         marks.length > 0

apps/desktop/test/context-compaction.test.mjs

@@ -158,7 +158,7 @@ test("a delegate gets the session's turn-boundary budget protection (ADR 0299)",
   // retention rule, and the degradation ladder of decision 4.
   assert.match(subagentContext, /prepareCompaction\(/);
   assert.match(subagentContext, /generateSummaryWithUsage\(/);
-  assert.match(subagentContext, /contextBudgetFor\(input\.model/);
+  assert.match(subagentContext, /contextBudgetFor\(model,/);
   assert.match(subagentContext, /delegateRetentionMode/);
   assert.match(subagentContext, /\? "active_turn"\s*: "completed_turn"/);
   assert.match(subagentContext, /degradedDelegateMessages/);
@@ -356,7 +356,7 @@ test("the transcript shows one row per compaction, the inspector the newest", ()
   assert.match(runtime, /checkpointDetailsWithGeneration/);
   assert.match(runtime, /mark: contextCompactionMark\(checkpoint\)/);
   // Both the durable records and the live event feed the same per-session list.
-  assert.match(store, /sessionCompactions: Record<string, ContextCompactionMark\[\]>/);
+  assert.match(store, /sessionCompactions: Record<string, \(ContextCompactionMark & \{ summary\?: string \}\)\[\]>/);
   assert.match(store, /rememberSessionCompactions\(id, detail\.session\)/);
   assert.match(store, /event\.type === "compaction_end" && event\.ok && event\.mark/);
   assert.match(store, /withCompactionMark\(/);