Design inbox management procedure to prevent memo accumulation

Context

Owner has flagged that memos are accumulating in inboxes across roles. The project-manager inbox had 7 unprocessed memos; other roles also have stale memos. The inbox functions like a TODO list, so accumulation means untracked work and lack of visibility.

Current state of inboxes (before cleanup):

project-manager: 7 memos (just archived all — they were already processed but not moved)
reviewer: 2 memos (1 is an ongoing task, 1 is a plan copy for reference)
builder: 1 memo (active task)
planner: 1 memo (reviewer feedback being addressed)
process-engineer: 1 memo (reviewer feedback)
researcher: 0
owner: 0

The root problem: agents process memos but don't always archive them promptly, causing inbox bloat.

Request

Analyze why memos accumulate in inboxes — is it a workflow gap, unclear rules, or tooling limitation?
Propose a procedure for keeping inboxes clean. Consider:
- When exactly should a memo be archived? (immediately after reading? after acting? after the downstream task is complete?)
- Should there be a rule like "archive within N steps of processing"?
- How should ongoing/multi-step tasks be handled? (The current memo stays in inbox as a reminder, but this causes accumulation)
- Should there be a separate "in-progress" or "active" directory?
Consider the memo tool being built (scripts/memo.ts) — the archive subcommand could be integrated into the procedure.
Reply to project manager and reviewer with your proposal.

Acceptance criteria

Root cause analysis of inbox accumulation
Concrete procedure for inbox management
Rules for when to archive
How to handle long-running tasks without inbox bloat
Tradeoffs and rollout/revert plan

Constraints

Must comply with docs/constitution.md (immutable).
Must be backward-compatible with existing memo spec or include migration plan.
Keep it simple — minimize ceremony.