feat: arXiv inbox tier for the Memory reading queue #57

Overview

The nightly strong-lensing digest ended in a Slack paste-block: the human copied
it into a Claude Code session, which appended the papers to reading-queue.md.
This replaces that hand-off with an inbox tier — the digest writes its
surviving papers straight into a new arxiv-inbox.md, the knowledge board
renders them with the one-tap actions the reading queue already has, and
un-acted lines lapse after seven days.

The ingest gate does not disappear, it moves: nothing reaches reading-queue.md
without a human tap. This is a deliberate reversal of the "the digest never
commits" constraint set by the paper-management pipeline (#35), and is recorded
as intentional rather than left to read as drift.

Shipped

Pushed straight to main on both repos at the author's direction — no PR on
either leg.

• arxiv-inbox.md — new root file, format documented in-file, allowlisted
  in validate_structure.py.
• scripts/inbox_actions.py — the single owner of the line format, the
  window and all four transitions (append / sweep / add / dismiss). Stdlib-only
  and idempotent. Neither board.py nor any workflow's shell re-expresses the
  format, and PyAutoMind's digest runs this script inside a checkout rather than
  writing the format itself.
• board.py — collects the inbox, renders it above the reading queue with a
  days-left column, and grows the ➕/✖️ tiers. Every action URL now emits
  file:, including the reading-queue ones, so the workflows never guess which
  file a tap refers to; the older scripts ignore the extra key.
• queue_actions.yml — one job, three labels. Whether to commit is decided
  by git status --porcelain rather than inferred from a status token, so a
  script that dies before printing cannot mis-close the issue.
• queue_filing.yml — an intake/cite tap on an inbox paper has no queue line
  to DONE-mark, so filing appends it to the queue already DONE-prefixed and
  clears the inbox line.
• arxiv_papers.yml — the survivors step runs after the Slack POST on
  purpose: the digest is the product, and a cross-repo failure must never cost
  the morning's post. Uses the existing PAT_PYAUTOLABS.

Decisions taken

• Lapse semantics: a lapsed line is deleted, not DONE-marked. The
  never-delete rule protects reading history; an un-acted suggestion is not
  history, and git holds it either way.
• Section routing: the digest is strong-lensing-only, so every paper routes
  to ## Strong Lensing. A multi-section inbox is deferred.

The label trap, hit again

A prefilled issues/new?…&labels=x URL silently drops x when the label does
not exist, and queue_actions.yml gates on the label — so a tapped button on a
missing label looks like it worked and does nothing. This is already recorded
from #42. Fixed structurally rather than by hand: the board now guarantees the
five labels its own buttons reference, on every render.

Worth knowing: knowledge_board.yml's on: push paths filter does not list the
workflow file itself, so the label step did not run on its own push and needed a
manual dispatch.

Validation

• 69 PyAutoMemory tests (35 new) + make validate green; 186 PyAutoMind tests green.
• spawn.py dry-run: PyAutoMemory-template unmatched: none, canary clean.
• Rehearsed end to end against a real clone with today's two survivors: append →
  board renders 7d-left rows → re-run adds nothing → sweep drops both on day eight.
• The knowledge_board.yml dispatch ran green and created queue-add / queue-dismiss.

Not yet proven live: the digest's own inbox step first runs on the
2026-08-25 02:00 UTC cron, and no button has been tapped yet.

Mind record: complete/2026/08/arxiv-inbox-tier.md.