fix: Red-team schema should document snapshot-isolation methodology for lm_eth fields (#1083)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

evidence/README.md

@@ -265,6 +265,38 @@ Records one adversarial red-team run against a candidate optimizer.
 | `attacks[].delta_bps` | integer | LM ETH change in basis points |
 | `attacks[].insight` | string | Key finding from this strategy |
 
+### Snapshot-Isolation Methodology
+
+All red-team runs use **snapshot isolation** as the standard methodology. This
+ensures that each attack is evaluated independently against the same initial
+state, rather than against a cumulative balance modified by prior attacks.
+
+**How it works:**
+
+1. Before the first attack, the test runner records the initial `lm_eth_before`
+   value and takes an Anvil snapshot via `vm.snapshot()`.
+2. Each attack executes against this snapshot: run the attack, measure
+   `lm_eth_after`, compute `delta_bps`, then revert to the snapshot via
+   `vm.revertTo()`.
+3. The next attack begins from the exact same chain state as the previous one.
+
+**Field semantics under snapshot isolation:**
+
+| Field | Semantics |
+|-------|-----------|
+| `lm_eth_before` | LM total ETH at the shared initial snapshot — identical for every attack in the run |
+| `lm_eth_after` | LM total ETH measured after this specific attack, before reverting |
+| `attacks[].delta_bps` | Change relative to the shared `lm_eth_before`, not relative to any prior attack |
+
+**Key implications:**
+
+- `lm_eth_before` and `lm_eth_after` reflect **per-attack state**, not
+  cumulative historical balance. Each attack sees the same starting ETH.
+- Attack results are independent and order-insensitive — reordering attacks does
+  not change any individual `delta_bps` value.
+- The top-level `lm_eth_after` and `eth_extracted` fields reflect the
+  worst-case single attack, not a sum of all attacks.
+
 ---
 
 ## Schema: `holdout/YYYY-MM-DD-prNNN.json`