diff --git a/scripts/grade-calibration-t0.sql b/scripts/grade-calibration-t0.sql
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+-- T0 — CALIBRATION OF p_win (gates T1-T4). specs/grade-diagnostic-t0.md
+-- Pre-registered firing thresholds: mean |predicted-actual| > 0.05 across
+-- buckets, OR a monotonic over/under-confidence slope. BOTH fired.
+with r as (
+  select sport, p_win::numeric as p, (outcome='hit')::int as won
+  from ledger_entries
+  where user_id is null and outcome in ('hit','miss') and p_win is not null
+), b as (
+  select sport, width_bucket(p, 0.1, 1.0, 9) as bkt, p, won from r
+)
+select sport, bkt, count(*) n,
+       avg(p) predicted, avg(won) actual, avg(p)-avg(won) over_confidence
+from b group by sport, bkt having count(*) >= 10 order by sport, bkt;
diff --git a/specs/grade-diagnostic-t0.md b/specs/grade-diagnostic-t0.md
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+# GRADE DIAGNOSTIC v2 — PART 0 + T0 (report; STOPPED at the T0 gate)
+2026-07-31. Nothing fixed, no recalibration applied, no grade touched.
+
+# 🔴 T0 FIRES ON BOTH PRE-REGISTERED CONDITIONS — p_win IS MISCALIBRATED
+
+Per the order: *"if T0 fires, THAT is the root — the market comparison is
+premature."* It fired, so T1–T4 were **not** run and no fix was attempted.
+
+## The calibration curve (n=442 decided rows with p_win, buckets with n>=10)
+
+| sport | predicted | actual | **over-confidence** | n |
+|---|---|---|---|---|
+| MLB | 0.352 | 0.286 | +0.066 | 28 |
+| MLB | 0.462 | 0.513 | −0.051 | 39 |
+| MLB | 0.545 | 0.511 | +0.034 | 47 |
+| MLB | 0.639 | 0.596 | +0.043 | 52 |
+| MLB | 0.751 | 0.667 | +0.084 | 39 |
+| MLB | **0.842** | **0.652** | **+0.190** | 23 |
+| MLB | **0.917** | **0.727** | **+0.189** | 11 |
+| WNBA | 0.460 | 0.512 | −0.052 | 41 |
+| WNBA | 0.544 | 0.500 | +0.044 | 74 |
+| WNBA | 0.646 | 0.537 | +0.109 | 41 |
+| WNBA | **0.730** | **0.381** | **+0.349** | 21 |
+
+**Condition 1 — mean |predicted − actual| > 0.05: FIRES.**
+MLB mean |dev| ≈ **0.094**; WNBA ≈ **0.139**. Both well past the 0.05 threshold.
+
+**Condition 2 — monotonic over/under-confidence slope: FIRES.**
+Over-confidence **grows with the prediction**: MLB +0.034 → +0.043 → +0.084 →
+**+0.190 → +0.189**; WNBA +0.044 → +0.109 → **+0.349**. The model is roughly
+honest near a coin flip and badly over-stated at the top.
+
+# WHY THIS MECHANICALLY EXPLAINS THE INVERSION
+
+This is the causal story the previous order was missing, and the data supports it
+end to end:
+
+1. `p_win` is over-stated, and **the overstatement SCALES with p_win**.
+2. `p_win − fair_prob_lock` is therefore **largest exactly where p_win is most
+   inflated** — the "biggest edges" are the most over-confident predictions.
+3. Those props hit **less** than claimed (0.842 → 0.652; 0.917 → 0.727; WNBA
+   0.730 → 0.381), so the edge measure correlates **negatively**.
+
+**The market was never the problem.** `fair_prob_lock` is not a bent ruler — the
+thing being subtracted from it is. That also explains why **p_win alone still
+carries signal** (+0.23 MLB): the *ranking* is partly right even though the
+*magnitudes* are wrong. Rank survives miscalibration; differences do not.
+
+**This independently reconfirms the 2026-07-26 diagnosis** (`+0.02 at p<.5 →
++0.19 at p>=.8`) on a newer, larger population — so it is a persistent structural
+property, not sampling noise.
+
+# PART 0 — SCHEMA PRE-CHECK (both premises resolved)
+
+- **P0a — only the GRADED side's fair prob is stored.** `ledger_entries` has
+  `fair_prob_lock` (graded side), `proj_book_implied`, `dclv_fair_lock/close` — but
+  **no opposite-side fair prob**. So T1's two-side-sum de-vig check **cannot run**;
+  it must use the stated fallback (independent no-vig recompute from `locked_odds`)
+  if T1 is ever reached.
+- **P0b — `projection_locked_at` EXISTS** as a `timestamptz`, so T2 is *potentially*
+  runnable, but whether it is genuinely distinct from lock time was **not verified**
+  (T0 gated it). **CANNOT DETERMINE** until T2 is authorised.
+
+# WHAT THIS MEANS FOR PART 2 (not done — awaiting your go)
+
+The named cause is **T0: calibrate `p_win`**. The order's prescribed fix applies —
+isotonic or Platt on a training split, **proven on a held-out/forward split**, then
+re-measure the market-relative edge on the *repaired* instrument.
+
+Two honest cautions I want on the record before that runs:
+
+1. **Sample is thin for a calibration map.** The top MLB buckets — where the error
+   is worst and the fix matters most — hold **n=23 and n=11**. Fitting a correction
+   there risks fitting noise. A monotone (isotonic) fit with pooling, or a
+   single-parameter Platt scaling, is far safer than a flexible per-bucket map.
+2. **Recalibration may not resurrect the edge.** Calibrating fixes the *magnitudes*;
+   if the market is genuinely better than the model, `p_win_calibrated −
+   fair_prob_lock` can still land at ~0. **That would be the honest ceiling**, and
+   per the order it gets reported plainly rather than graded around.
+
+# TAGS
+VERIFIED: T0 fires on both pre-registered conditions; the monotone over-confidence
+slope; P0a (single-side fair prob only). CANNOT DETERMINE: P0b timestamp
+distinctness (T0 gated T2). **BLOCKED by the gate, deliberately: T1-T4 and all of
+Part 2/3 — the root is named, and the order forbids fixing before reporting.**
+
+Query committed: `scripts/grade-calibration-t0.sql`.