feat(knowledge): nightly KnowledgeLintWorker — scheduled lint + orphan self-heal

[mkreyman]

What

Adds Loopctl.Workers.KnowledgeLintWorker — the scheduled "nightly refinement" loop for the knowledge wiki. The lint engine (Knowledge.lint/2) already existed but was only ever invoked on-demand via the API. This wires it onto a cron and takes a safe, automated repair action on the one finding that can be auto-fixed: orphans.

Both the Karpathy llm-wiki pattern (lint-and-act) and the Dan Martell second-brain workflow (nightly Claude refinement) independently converge on this loop. The platform had the engine; it lacked the orchestration.

Why now

The second-brain corpus is at ~77k articles. Lint runs clean except for ~1.9% orphan articles (zero inbound/outbound links). Nothing was scheduled to act on them, and entropy (orphans, drift) is invisible under brute-force search.

How it works

• :knowledge queue, max_attempts: 3, unique on {worker, args} within 60s.
• all_tenants fan-out mirroring ComputeSthWorker — lint is inherently per-tenant, so each active tenant lints in its own job (independent retries, no cross-tenant coupling). Suspended/inactive tenants are skipped.
• Per tenant: run Knowledge.lint/2, then re-enqueue the proven ArticleLinkingWorker for each orphan. Re-linking re-runs the pgvector similarity pass against the current corpus — so an article orphaned in January can find neighbors ingested months later. Deterministic, and makes no embedding-API calls (orphans missing an embedding simply no-op in the linking worker; backfilling those is a separate concern).
• Surfaces all findings via an immutable knowledge.lint_completed audit event carrying the full lint summary. Contradictions / coverage gaps / broken sources / stale counts need human judgment, so they are made observable in the change feed rather than auto-repaired.
• Scale-bounded: orphan re-link enqueues capped by :knowledge_lint_max_orphan_relink (default 500). When the true orphan count exceeds the cap, the gap is logged, never silently dropped — the remainder retries next run.
• Scheduled nightly at 04:00, after the 02:00–03:00 maintenance window.

Tests

test/loopctl/workers/knowledge_lint_worker_test.exs (async, 5 cases):

• per-tenant lint emits the knowledge.lint_completed audit event with the summary
• orphan re-linking outcome (two similar orphans → a relates_to link is created; orphans_relinked == 2)
• empty tenant (0 articles, 0 relinks)
• all_tenants fan-out lints both active tenants and skips a suspended one
• tenant isolation (lint summary counts only the caller tenant's articles)

Verification

Full pre-commit gate green locally: compile (--warnings-as-errors), mix format, credo --strict, dialyzer (0 errors), and the full suite (2977 tests, 0 failures).

Notes / follow-ups (not in this PR)

• Orphans that lack an embedding are not re-linkable here — an embedding-backfill pass is a separate, distinct gap.
• A genuine missing capability surfaced during review: ripple-on-ingest (updating neighbor article bodies when a new source extends/contradicts them) — ingest currently only creates ArticleLink edges. Tracked separately.