fix: correct DSL mistakes from observed R1 failures

- ADX: clarify it is a FuncName inside {"kind":"func","name":"adx",...},
  not a Condition kind — with inline usage example (ADX > 25 filter)
- Expr "kind" field: add explicit note that every Expr object requires
  "kind"; {"field":"close"} without "kind" is rejected by the API
- MACD: add Example 4 showing full crossover strategy composed from
  bin_op(sub, ema12, ema26) and apply_func(ema,9) as signal line

All three mistakes were observed across consecutive R1-32B runs and
caused repeated API submission failures. Each prompt addition follows
the same pattern as the successful bollinger_upper fix.

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

src/prompts.rs

@@ -52,6 +52,10 @@ sma, ema, wma, rsi, std_dev, sum, highest, lowest, atr, supertrend, adx,
 bollinger_upper, bollinger_lower — applied to any candle field (open/high/low/close/volume)
 with configurable period and optional offset.
 
+These are FuncNames used INSIDE `{{"kind":"func","name":"...","period":N}}` expressions.
+`atr`, `adx`, and `supertrend` use OHLC internally and ignore the `field` parameter.
+To use ADX as a trend-strength filter: `{{"kind":"compare","left":{{"kind":"func","name":"adx","period":14}},"op":">","right":{{"kind":"literal","value":"25"}}}}`
+
 ### Composed indicators (apply_func)
 Apply rolling functions to arbitrary expressions: EMA of EMA, Hull MA (WMA of expression),
 VWAP (sum of close*volume / sum of volume), standard deviation of returns, etc.
@@ -146,6 +150,8 @@ Common mistakes to NEVER make:
 - `"kind": "bars_since_entry"` is a valid standalone Expr (no extra fields needed).
   Do NOT put `"bars_since_entry"` as a `"name"` inside `{{"kind":"func",...}}` — that is WRONG.
 - `"kind": "expr_field"` does NOT exist. Use `{{"kind":"field","field":"close"}}`.
+- Every Expr object MUST have a `"kind"` field. `{{"field":"close"}}` is WRONG — missing `"kind"`.
+  CORRECT: `{{"kind":"field","field":"close"}}`. The `"kind"` is never optional.
 - `rsi`, `adx`, `supertrend` are NOT valid inside `apply_func`. Use only `apply_func`
   with `ApplyFuncName` values: `highest`, `lowest`, `sma`, `ema`, `wma`, `std_dev`, `sum`,
   `bollinger_upper`, `bollinger_lower`.
@@ -154,6 +160,9 @@ Common mistakes to NEVER make:
 - `bollinger_upper` and `bollinger_lower` are FUNC NAMES, not Expr kinds. To compare close to the upper band:
   `{{"kind":"compare","left":{{"kind":"field","field":"close"}},"op":">","right":{{"kind":"func","name":"bollinger_upper","period":20}}}}`
   NEVER write `{{"kind":"bollinger_upper",...}}` — `bollinger_upper` is not an Expr kind.
+- `adx` is a FUNC NAME, not a Condition kind. To filter for strong trends (ADX > 25):
+  `{{"kind":"compare","left":{{"kind":"func","name":"adx","period":14}},"op":">","right":{{"kind":"literal","value":"25"}}}}`
+  NEVER write `{{"kind":"adx",...}}` — `adx` is not a Condition kind, it is a FuncName used inside `{{"kind":"func",...}}`.
 - `roc` (rate of change), `hma` (Hull MA), `vwap`, `macd`, `cci`, `stoch` are NOT supported.
   Use `sma`, `ema`, `wma`, `rsi`, `atr`, `adx`, `supertrend`, `std_dev`, `sum`, `highest`, `lowest`,
   `bollinger_upper`, `bollinger_lower` only.
@@ -324,6 +333,95 @@ Common mistakes to NEVER make:
 }}
 ```
 
+### Example 4 — MACD crossover (composed from primitives)
+
+MACD has no native support, but can be composed from `func` and `apply_func`.
+The MACD line is `EMA(12) - EMA(26)`; the signal line is `EMA(9)` of the MACD line.
+
+```json
+{{
+  "type": "rule_based",
+  "candle_interval": "4h",
+  "rules": [
+    {{
+      "comment": "Buy: MACD line crosses above signal line",
+      "when": {{
+        "kind": "all_of",
+        "conditions": [
+          {{"kind": "position", "state": "flat"}},
+          {{
+            "kind": "cross_over",
+            "left": {{
+              "kind": "bin_op", "op": "sub",
+              "left":  {{"kind": "func", "name": "ema", "period": 12}},
+              "right": {{"kind": "func", "name": "ema", "period": 26}}
+            }},
+            "right": {{
+              "kind": "apply_func", "name": "ema", "period": 9,
+              "expr": {{
+                "kind": "bin_op", "op": "sub",
+                "left":  {{"kind": "func", "name": "ema", "period": 12}},
+                "right": {{"kind": "func", "name": "ema", "period": 26}}
+              }}
+            }}
+          }}
+        ]
+      }},
+      "then": {{"side": "buy", "quantity": "0.001"}}
+    }},
+    {{
+      "comment": "Sell: MACD crosses below signal, OR 2% stop-loss, OR 72-bar time exit",
+      "when": {{
+        "kind": "all_of",
+        "conditions": [
+          {{"kind": "position", "state": "long"}},
+          {{
+            "kind": "any_of",
+            "conditions": [
+              {{
+                "kind": "cross_under",
+                "left": {{
+                  "kind": "bin_op", "op": "sub",
+                  "left":  {{"kind": "func", "name": "ema", "period": 12}},
+                  "right": {{"kind": "func", "name": "ema", "period": 26}}
+                }},
+                "right": {{
+                  "kind": "apply_func", "name": "ema", "period": 9,
+                  "expr": {{
+                    "kind": "bin_op", "op": "sub",
+                    "left":  {{"kind": "func", "name": "ema", "period": 12}},
+                    "right": {{"kind": "func", "name": "ema", "period": 26}}
+                  }}
+                }}
+              }},
+              {{
+                "kind": "compare",
+                "left": {{"kind": "field", "field": "close"}},
+                "op": "<",
+                "right": {{"kind": "bin_op", "op": "mul",
+                           "left": {{"kind": "entry_price"}},
+                           "right": {{"kind": "literal", "value": "0.98"}}}}
+              }},
+              {{
+                "kind": "compare",
+                "left": {{"kind": "bars_since_entry"}},
+                "op": ">=",
+                "right": {{"kind": "literal", "value": "72"}}
+              }}
+            ]
+          }}
+        ]
+      }},
+      "then": {{"side": "sell", "quantity": "0.001"}}
+    }}
+  ]
+}}
+```
+
+Key pattern: `apply_func` wraps any `Expr` tree, enabling EMA-of-expression (signal line),
+WMA-of-expression (Hull MA), or std_dev-of-returns. There is NO native `macd` func name —
+always compose it as `bin_op(sub, func(ema,12), func(ema,26))` as shown above.
+
 ## Anti-patterns to avoid
 
 - Don't use the same indicator for both entry and exit (circular logic)