Q15: show which messages each agent actually read

Runs record a context manifest once a model turn succeeds; the chat
marks each human message with the agents that read its current version.

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

src/main/services/task-prompts.ts

@@ -76,6 +76,7 @@ export interface ChatContextBlock {
   history: string;
   /** Messages after it: what this run answers. */
   fresh: string;
+  manifest: { history: Array<{ id: string; version: string }>; fresh: Array<{ id: string; version: string }>; omittedCount: number };
 }
 
 export interface AgentInstructionContext {