Fix custom_script execution + add templates for expression/function kinds

- custom_script now uses exec-style (assign to `result`) matching the
  built-in templates — previously auto-wrapped in def compute() which
  had no return statement, causing state and channel vars to silently fail
- function kind unchanged: auto-wraps body as def compute(x,t); use return
- Add SCRIPT_TEMPLATES for expression, function, custom_script kinds;
  shown automatically when user switches to a script kind (replacing stale
  code from previous kind)
- New channels default to template when no saved code exists

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

1 files changed, 22 insertions, 5 deletions

diff --git a/core/signal_processor.py b/core/signal_processor.py
index 8ac4d8c..e2752cd 100644
--- a/core/signal_processor.py
+++ b/core/signal_processor.py
@@ -286,7 +286,8 @@ class DerivedChannel:
 
                 self._fn = _expr_fn
 
-            elif self.kind in ("function", "custom_script"):
+            elif self.kind == "function":
+                # Auto-wrap body as def compute(x, t): ... return <value>
                 src = self.script
                 if not src.strip().startswith("def compute"):
                     src = "def compute(x, t):\n" + "\n".join(
@@ -297,9 +298,8 @@ class DerivedChannel:
                 _fn_ref = _exec_ns["compute"]
                 _state  = self._exec_state
 
-                def _script_fn(inputs, t, sv,
-                               _f=_fn_ref, _ns=_exec_ns, _st=_state, _names=src_names):
-                    # refresh mutable globals before each call so scripts see live values
+                def _fn_fn(inputs, t, sv,
+                           _f=_fn_ref, _ns=_exec_ns, _st=_state, _names=src_names):
                     _ns["vars"]  = sv
                     _ns["state"] = _st
                     for i, name in enumerate(_names):
@@ -307,7 +307,24 @@ class DerivedChannel:
                             _ns[name] = inputs[i]
                     return float(_f(inputs, t))
 
-                self._fn = _script_fn
+                self._fn = _fn_fn
+
+            elif self.kind == "custom_script":
+                # Exec-style: script assigns to `result`
+                code = compile(self.script, "<custom_script>", "exec")
+                _state = self._exec_state
+
+                def _cs_fn(inputs, t, sv, _code=code, _names=src_names, _st=_state):
+                    ns = {"x": inputs, "t": t, "math": math, "vars": sv, "state": _st}
+                    for i, name in enumerate(_names):
+                        if i < len(inputs):
+                            ns[name] = inputs[i]
+                    exec(_code, ns)
+                    if "result" not in ns:
+                        raise NameError("custom_script must assign to 'result'")
+                    return float(ns["result"])
+
+                self._fn = _cs_fn
 
             else:
                 # Built-in kinds handled in SignalProcessor._compute_derived