fix(clustering): raise coverage floor 0.5 -> 0.6 to gate degenerate stablecoin fits

[elluff]

Why

Follow-up to #75 / #76. Those shipped the clusterability machinery (fit_coverage, the scheduler gate, anti-flap, the unclusterable_fit marker) with MIN_CLUSTER_COVERAGE = 0.5, calibrated on synthetic fits. Mainnet data (2026-07-23) shows the real degenerate stablecoin-validator fits land just above that floor, so the gate never engaged for them.

Data

Contract	window (N)	clusters	coverage
Strike Finance	2000	5	0.52 (drift pinned ~1.0)
Djed v2	2000	4	0.58 (drift climbing)
Djed v2 (healthy)	~1100	2	0.97

Both degenerate fits reproduce the same majority-DBSCAN-noise model on every re-fit, so re-clustering is structurally futile: at 0.5 they still nagged "re-analyze", still burned one re-fit per anti-flap interval, and their contract_anomaly rows were never marked unclusterable_fit.

Change

MIN_CLUSTER_COVERAGE default 0.5 -> 0.6. 0.6 sits in the wide empty gap between the degenerate regime (0.52–0.58) and a healthy fit (0.97), so it gates the former and leaves the latter clusterable.

Recall safety

model_unclusterable only affects the scheduler re-fit decision, the UI nag, and the evidence-only unclusterable_fit marker. classify + IsolationForest/LOF novelty scoring run every tick regardless; no verdict, publish, or band logic changes. Raising the floor only reduces futile re-fits and adds honest UI/marking. It silences no detection.

Tests

• test_default_floor_gates_degenerate_fits_but_not_healthy_ones: pins the observed coverages (0.52, 0.58 gate; 0.97 does not).
• test_default_floor_stops_strike_style_tight_loop: end-to-end at Strike's numbers (drift 1.0, cov 0.522, recent fit) → classify, not the re-fit loop.
• Existing threshold-relative scheduler/API tests unchanged and green. Full sidecar suite: 495 passed.

Mainnet

Already applied live as MIN_CLUSTER_COVERAGE=0.6 in /opt/tms/.env (sidecar recreated, verified: Strike/Djed-2000 → unclusterable=True, recluster_recommended=False). The env override becomes redundant once the app/clustering images are rebuilt on this default.

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