refactor: remove dead getCancelledCompactionKey storage helper

The getCancelledCompactionKey function and its entry in the
EPHEMERAL_WORKSPACE_KEY_FUNCTIONS array became dead code when
useResumeManager.ts (its only consumer) was deleted. Remove both
the function definition and the ephemeral-keys array reference.

Author: mux-bot[bot]

src/common/constants/storage.ts

@@ -248,14 +248,6 @@ export function getAutoRetryKey(workspaceId: string): string {
   return `${workspaceId}-autoRetry`;
 }
 
-/**
- * Get storage key for cancelled compaction tracking.
- * Stores compaction-request user message ID to verify freshness across reloads.
- */
-export function getCancelledCompactionKey(workspaceId: string): string {
-  return `workspace:${workspaceId}:cancelled-compaction`;
-}
-
 /**
  * Get the localStorage key for the selected agent definition id for a scope.
  * Format: "agentId:{scopeId}"
@@ -673,7 +665,6 @@ export function getPostCompactionStateKey(workspaceId: string): string {
  * Additional ephemeral keys to delete on workspace removal (not copied on fork)
  */
 const EPHEMERAL_WORKSPACE_KEY_FUNCTIONS: Array<(workspaceId: string) => string> = [
-  getCancelledCompactionKey,
   getPendingWorkspaceSendErrorKey,
   getPlanContentKey, // Cache only, no need to preserve on fork
   getPostCompactionStateKey, // Cache only, no need to preserve on fork