v10.17.0 zero-LLM daily consolidation cycle

The daily Nyx cycle now runs with zero LLM calls: cosine nominates (by
rank), NLI decides (admission gate + line-level dedup), a mechanical union
executes merges (selection, never generation). LLM-requiring work (weave,
synthesize, contradiction judging, cemelify) is the optional enrichment
tier. Evidence: benchmarks/weave-bench (NLI weave classification refuted
at 3% agreement; the phase-2 gate validated on production noise clusters)
and benchmarks/merge-bench (mechanical merge: 24/25 exact recovery on
ground truth, 100% line coverage and digit integrity by construction).

Added

• Mechanical merge engine (mnemos/consolidation/mechanical.py), the
  phase-2 default (MNEMOS_MERGE_ENGINE=mechanical|llm). Line union with
  bidirectional-entailment dedup at MNEMOS_MECH_MERGE_TAU (0.90; the one
  observed semantic false-duplicate scored 0.851, true duplicates ~1.0).
  Lines under MNEMOS_MECH_MERGE_MIN_LINE_CHARS (25) dedup by exact match
  only (short enumerated list lines are an NLI failure class). Newer
  phrasing wins; every output line is an input line verbatim, so fact
  preservation is provable rather than auditable.
• Phase-2 NLI admission gate (MNEMOS_CLUSTER_GATE=nli|off, tau
  MNEMOS_CLUSTER_GATE_TAU 0.70): cluster members must share at least one
  line-level bidirectional-entailment fact or they are ejected; clusters
  without shared facts dissolve unmerged. Replayed on the 2026-07-03
  production run: both cosine noise clusters dissolve entirely.
• Mutual top-k candidacy (MNEMOS_CANDIDACY=mutual-topk|threshold, k via
  MNEMOS_CANDIDACY_TOP_K): phase-2 pair candidacy from mutual
  nearest-neighbor rank instead of absolute cosine thresholds, which are
  noise in the compressed e5 space (measured: 45% of all active-pair
  similarities above 0.78).
• Phase-4 judge queue mode (MNEMOS_CONTRADICT_JUDGE=llm|queue|auto):
  keyless runs record NLI-flagged pairs as contradiction-candidate
  links; the next llm-judged run consumes the queue. auto resolves by
  key presence.
• Weave staleness guard: memories with outgoing superseded_by/evolves
  links are excluded as weave sources (stale state was being woven into
  fresh insights).
• Weave novelty gate (MNEMOS_WEAVE_NOVELTY_TAU, 0.85): a bridge insight
  entailed by either source alone is a restatement; the link is kept, the
  insight memory is not stored.
• Useful-loop: get() on a memory that retrieval logging recorded in the
  last 24h marks those retrieval_log rows useful=1. Zero-friction
  usefulness signal for measuring consolidation value.
• nli.line_max_duplicate and nli.p_entailment public scorers.

Changed

• Bridge insights are stored on the episodic layer: derivative content
  earns permanence through retrieval instead of squatting in the semantic
  tier.
• Phase 2B topic merge is retired under the mechanical engine
  (aggregating distinct same-topic facts is generative LLM-tier work);
  the legacy llm engine keeps both tiers.
• A missing LLM key no longer fails the cycle (replaces the v10.4.0
  loud-fail): LLM-tier phases are skipped with a grep-able WARNING and
  the zero-LLM phases run. MNEMOS_DISABLE_LLM=1 still opts into the
  same skip silently. Phase 0.5 cemelify additionally requires a key.

Fixed

• tests/test_v107_tier2.py fixture wrote to the developer's default DB
  whenever another test module imported mnemos first (DEFAULT_DB_PATH is
  frozen at import time); 419 fixture memories had accumulated and the
  tier-2 recall assert started flaking on KNN ties. The store is now
  constructed explicitly.