feat(session): age-gated classification-aware auto-archive nightly job #1304

Acceptance Criteria

• With apply mode on, a junk-greeting/dead-cast/probe session older than the age gate is archived through the engine's archive primitive — and only time_archived changes.
• A session with pending todos is never archived regardless of bucket or age.
• A session updated within the age gate (default 48 h) is never archived.
• Dry-run (the default) reports what would archive — count + ids — and writes nothing.
• Each run appends one JSON receipt line (timestamp, mode, scanned, archived count, ids) to the shared receipts journal.
• An archived session is restorable via the existing unarchive path (round-trip verified in test).
• The job script runs green under --dry-run on a seeded temp DB fixture and exits nonzero on a hard failure (DB missing).

Testing Decisions

Extend the sessions-verb test file (it already covers archive/restore change-only-time_archived on seeded temp DBs) with classification-gated cases from the prior slice's classifier. The ops script gets a smoke path exercised in dry-run mode.

Key Decisions

• Archive threshold policy: archive ONLY on a deterministic junk bucket AND age ≥ 48 h — no LLM/model call anywhere in this path (the calibrated Jev middle layer is a deliberate future slice, see parent).
• Job lands as ops/<name>/run-<name>.sh + launchd plist + systemd unit pair, cadence nightly on the hub — the skill-freshness pattern, including the receipts journal and escalation convention.
• Config rides the session-retention preference file pattern (ops-dir JSON, fail-safe defaults, CLI-pref surfacing where it exists).

Constraints & Invariants

• Reversible only: archive, never delete; every bulk action logged with counts + ids.
• The engine owns archived-field mechanics — the job goes through the archive verb/primitive, never raw SQL writes to the live DB.
• Canonical DB is the only writer target; client DBs are read-only to this job.

Prior Art

• The sessions archive verb + retention module (CLI package) — the flow this gates.
• The skill-freshness ops job — the nightly-job pattern (receipts, dry-run, scheduler units).
• The engine session service's archive primitive — the mechanics, unchanged.

Source

Part of #1301 · Blocked by #1303 · spec of record: personal vault specs/spec-20260920-session-curation.md