guard non-function value bindings

bindValue invoked the bound property as a setter via an optional call,
which only guards null/undefined. A plain value (e.g. a number) threw
"is not a function" on input. Cache the binding and call it only when
it's a function, so plain values degrade to one-way (display + read).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: STRd6

source/index.civet

@@ -160,7 +160,9 @@ bindValue := (element: JadeletElement, value: JadeletAttribute, context: Context
   // inconsistencies.
   if value and typeof value is "object"
     element.oninput = element.onchange = ->
-      context[value.bind]? element.value
+      setter := context[value.bind]
+      if typeof setter is 'function'
+        setter.call context, element.value
       return
 
   bindObservable element, value, context, (newValue: string) ->

test/input.civet

@@ -30,3 +30,18 @@ describe "input", ->
 
     el := T()
     assert.equal el.value, "hello"
+
+  it "should accept a non-function (plain value) binding without throwing on input", ->
+    model :=
+      value: 5
+
+    input := template(model)
+
+    // initial value reflects the plain number
+    assert.equal input.value, "5"
+
+    // editing must not attempt to call the non-function binding
+    input.value = "7"
+    input.oninput()
+
+    assert.equal input.value, "7"