fix(desktop): show unknown context usage after compaction

CHANGELOG.md

@@ -40,6 +40,15 @@
 
 ### Fixed
 
+- The composer's context gauge now falls back to its localized `Usage` label
+  instead of holding the pre-compaction figure after a compaction: no provider
+  has tokenized the replacement prompt yet, so the last real count is stale.
+  A `context_compaction_applied` boundary is persisted and forwarded over the
+  session subscription the moment a compaction lands, so a mid-turn fold
+  clears the figure while that turn is still running — the `context_compacted`
+  note stays the settlement-time display row — and only a measurement that
+  completed after the boundary restores it. A failed-open compaction is not a
+  boundary: that request went out with its full raw history.
 - Fixed a renderer crash dialog reporting React error #185 ("Maximum update depth
   exceeded") coming from the composer's prompt-history inline completion (#4117): the
   offer engine the 0.1.11 composer fed could flip-flop its announcement state on

apps/desktop/src/main/__tests__/conversation-owner.test.ts

@@ -27,6 +27,7 @@ import type { DesktopSessionSummary } from '../../shared/desktop-session-project
 import { createSessionCatalogController, SessionCatalogContext } from '../../renderer/application/contracts/session-catalog/session-catalog-state.js';
 import { ConversationProvider, ConversationServicesProvider, ConversationLifecycle, ConversationTranscriptRegion, ConversationComposerRegion, useAppShellSessionUiState, type ConversationObservationServices, type ConversationServices } from '../../renderer/features/conversation/index.js';
 import { renderConversationMarkdown, stubComposerGateInputs, stubConversationServices, useConversationOwner } from '../../renderer/features/conversation/testing.js';
+import type { LatestRequestUsage } from '../../renderer/application/contracts/session-inspector/latest-request-usage.js';
 import { cleanupFakeDom, installReactRenderer } from './fake-dom.js';
 import { withComposerSubmission } from './composer-submission-fixture.js';
 
@@ -97,7 +98,7 @@ function harness(options: {
   let setVisible!: (visible: boolean) => void;
   let setCovered!: (covered: boolean) => void;
   function Transcript(props: NonNullable<typeof transcript>) { transcript = props; transcriptRenders += 1; return null; }
-  function Composer(_props: { processing: boolean; pendingMessages?: readonly TransientUserMessageProjection[]; latestRequestUsageTokens?: number }) {
+  function Composer(_props: { processing: boolean; pendingMessages?: readonly TransientUserMessageProjection[]; latestRequestUsage?: LatestRequestUsage }) {
     composerRenders += 1;
     useEffect(() => { composerMounts += 1; return () => { composerUnmounts += 1; }; }, []);
     return null;