Q3: record a structured handoff on every delegated task

create_task now pins upstream files by content hash and carries the
source task, source thread, verified facts, open questions and
acceptance criteria into the assignee's prompt.

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

tests/unit/org-structure.test.ts

@@ -31,7 +31,7 @@ describe("org structure", () => {
       orgId,
       agent: { id: agentId, modelProviderId: providerId, modelId: "gpt-5.4" },
       taskProjectId: null,
-      taskGoalId: null,
+      taskGoalId: null, taskId: null, sourceThreadId: null,
       workspace: null,
     });