Add alpha-hardening ADRs and issue plan from pre-release audit.

Lock alpha scope, tracker auth, TOPLOC fraud verification, and deferred multi-tracker money-path work; supersede legacy fraud issues with ADR-0018.

Co-authored-by: Cursor <cursoragent@cursor.com>

.scratch/alpha-hardening/issues/21-honest-noise-calibration-corpus.md

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+Status: ready-for-human
+
+# 21 — Honest-noise TOPLOC calibration corpus
+
+## What to build
+
+Before enabling production TOPLOC audit thresholds, collect an **honest-noise baseline** across the heterogeneous volunteer fleet. Run identical inference jobs on every active node/GPU combo; measure the divergence envelope (TOPLOC exponent/mantissa deltas, logprob-rank spread) under real hardware variance.
+
+Per [ADR-0018 consequences](../../docs/adr/0018-fraud-detection-verification-and-reputation.md): threshold calibration requires an honest-noise corpus across the fleet before production thresholds.
+
+Research anchor: `.scratch/alpha-hardening/research-verifiable-inference.md` §8 layer 3 — "collect this first — run identical jobs across the current node fleet to measure the honest divergence envelope before setting thresholds."
+
+## Deliverables
+
+- [ ] Scripted benchmark job (fixed prompt, model preset, seed policy) runnable on all nodes
+- [ ] Aggregated corpus artifact (per node: GPU model, dtype, TOPLOC deltas vs reference)
+- [ ] Recommended tolerance thresholds documented (p99 honest envelope + safety margin)
+- [ ] Gate checklist: production audit enable blocked until corpus covers ≥N distinct hardware profiles (define N in runbook, suggest ≥3)
+
+## Acceptance criteria
+
+- [ ] Corpus collected from current fleet (or documented subset + extrapolation note)
+- [ ] Threshold constants in validator config derived from corpus, not guessed
+- [ ] False-positive rate estimate documented at chosen thresholds
+- [ ] README / runbook cross-link: **do not enable production audits** until this issue closes
+
+## ADR links
+
+- [ADR-0018](../../docs/adr/0018-fraud-detection-verification-and-reputation.md) — Consequences (honest-noise corpus)
+
+## Blocked by
+
+- `06-fraud-toploc-integration.md` (TOPLOC wired; calibration uses same primitive)
+
+## Blocks (prod gate)
+
+- Production enable of adaptive audit thresholds (issues 09–10 in prod)