fix: replace negligible 0.001 quantity with meaningful sizing guidance

The previous example quantity "0.001" represented <1% of the $10k
initial balance for BTC and near-zero exposure for ETH/SOL, making
P&L and Sharpe results statistically meaningless.

- Update Quantity section with instrument-appropriate reference values
  (BTC: 0.01 ≈ $800, ETH: 3.0 ≈ $600, SOL: 50.0 ≈ $700)
- Replace "0.001" with "0.01" in all four working examples
- Explain that 5–10% of $10k initial balance is the sizing target
- Explicitly warn against "0.001" as it produces negligible exposure

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/prompts.rs

@@ -74,14 +74,22 @@ bars_since_entry — complete bars elapsed since position was opened
 balance — free balance of a named asset (e.g. "usdt", "usdc")
 
 ### Quantity
-Action quantity MUST be a fixed decimal string that parses as a floating-point number,
-e.g. `"quantity": "0.001"`.
+Action quantity MUST be a fixed decimal string that parses as a floating-point number.
 NEVER use an expression object for quantity — only plain decimal strings are accepted.
 NEVER use placeholder strings like `"ATR_SIZED"`, `"FULL_BALANCE"`, `"percent_of_balance"`,
 `"dynamic"`, `"all"`, or any non-numeric string — these will be rejected immediately.
 To exit a position, use the SAME decimal string as the entry rule — the backtester matches
 open quantity automatically. There is no "close all" concept; just repeat the entry quantity.
 
+Size your quantity to represent roughly 5–10% of the initial $10,000 USDC balance at
+approximate current prices. Reference values (adjust if market prices differ significantly):
+- BTC: `"0.01"` ≈ $800 (8% of $10k)
+- ETH: `"3.0"` ≈ $600 (6% of $10k)
+- SOL: `"50.0"` ≈ $700 (7% of $10k)
+Since strategies run across all instruments with the same quantity string, choose a value
+appropriate for the primary instrument you are designing for. Avoid `"0.001"` — it produces
+negligible exposure and makes results statistically meaningless.
+
 ### Multi-timeframe
 Any expression can reference a different timeframe via "timeframe" field.
 Use higher timeframes as trend filters, lower timeframes for entry precision.
@@ -194,7 +202,7 @@ Common mistakes to NEVER make:
           {{"kind": "ema_trend", "period": 50, "direction": "above"}}
         ]
       }},
-      "then": {{"side": "buy", "quantity": "0.001"}}
+      "then": {{"side": "buy", "quantity": "0.01"}}
     }},
     {{
       "comment": "Sell: EMA9 crosses below EMA21, OR 2% stop-loss, OR 72-bar time exit",
@@ -222,7 +230,7 @@ Common mistakes to NEVER make:
           }}
         ]
       }},
-      "then": {{"side": "sell", "quantity": "0.001"}}
+      "then": {{"side": "sell", "quantity": "0.01"}}
     }}
   ]
 }}
@@ -245,7 +253,7 @@ Common mistakes to NEVER make:
           {{"kind": "bollinger", "period": 20, "band": "below_lower"}}
         ]
       }},
-      "then": {{"side": "buy", "quantity": "0.001"}}
+      "then": {{"side": "buy", "quantity": "0.01"}}
     }},
     {{
       "comment": "Sell: RSI recovers above 55, OR 3% stop-loss, OR 48-bar time exit",
@@ -273,7 +281,7 @@ Common mistakes to NEVER make:
           }}
         ]
       }},
-      "then": {{"side": "sell", "quantity": "0.001"}}
+      "then": {{"side": "sell", "quantity": "0.01"}}
     }}
   ]
 }}
@@ -300,7 +308,7 @@ Common mistakes to NEVER make:
           }}
         ]
       }},
-      "then": {{"side": "buy", "quantity": "0.001"}}
+      "then": {{"side": "buy", "quantity": "0.01"}}
     }},
     {{
       "comment": "Sell: 2-ATR stop-loss below entry price, OR 48-bar time exit",
@@ -335,7 +343,7 @@ Common mistakes to NEVER make:
           }}
         ]
       }},
-      "then": {{"side": "sell", "quantity": "0.001"}}
+      "then": {{"side": "sell", "quantity": "0.01"}}
     }}
   ]
 }}
@@ -375,7 +383,7 @@ The MACD line is `EMA(12) - EMA(26)`; the signal line is `EMA(9)` of the MACD li
           }}
         ]
       }},
-      "then": {{"side": "buy", "quantity": "0.001"}}
+      "then": {{"side": "buy", "quantity": "0.01"}}
     }},
     {{
       "comment": "Sell: MACD crosses below signal, OR 2% stop-loss, OR 72-bar time exit",
@@ -420,7 +428,7 @@ The MACD line is `EMA(12) - EMA(26)`; the signal line is `EMA(9)` of the MACD li
           }}
         ]
       }},
-      "then": {{"side": "sell", "quantity": "0.001"}}
+      "then": {{"side": "sell", "quantity": "0.01"}}
     }}
   ]
 }}
@@ -440,8 +448,8 @@ always compose it as `bin_op(sub, func(ema,12), func(ema,26))` as shown above.
 - Don't ignore fees — a strategy needs to overcome 0.1% per round trip
 - Always gate buy rules with position state "flat" and sell rules with "long"
 - Never add a short-entry (sell when flat) rule — spot markets are long-only
-- Never use an expression object for `quantity` — it must always be a plain decimal string like `"0.001"`
-- Never use a placeholder string for `quantity` — `"ATR_SIZED"`, `"FULL_BALANCE"`, `"dynamic"`, etc. are all invalid and will be rejected. Use `"0.001"` or similar.
+- Never use an expression object for `quantity` — it must always be a plain decimal string like `"0.01"`
+- Never use a placeholder string for `quantity` — `"ATR_SIZED"`, `"FULL_BALANCE"`, `"dynamic"`, etc. are all invalid and will be rejected. Use `"0.01"` or similar.
 "##
     )
 }