Say when a research run found no new sources

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/express/schedules.ts

@@ -365,6 +365,8 @@ export interface RunSummary {
   safe_error_code: string | null
   budget_spent: number | null
   has_readiness_issues: boolean
+  /** Research runs: what came of the sources found, e.g. no_new_sources when nothing was kept. */
+  source_outcome?: string | null
   created_at: string
   finished_at: string | null
 }