Add timing-indifference contract and fix form input components

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

docs/skills/form-input/SKILL.md

@@ -9,6 +9,21 @@ description: Creating custom form input components that extend Form_Input_Abstra
 
 Form input components extend `Form_Input_Abstract` which implements a template method pattern. The base class handles value buffering, events, and the val() interface. Concrete classes only implement how to get and set values.
 
+## Core Contract: Timing Indifference
+
+**Callers must never care about component lifecycle timing.**
+
+`.val(value)` must produce identical results whether called:
+- Before the component initializes (buffered, applied at `_mark_ready()`)
+- After the component initializes (applied immediately via `_set_value()`)
+- At any point during the component's lifecycle
+
+This is non-negotiable. If a caller needs to use `await component.ready()` or timing tricks to make `val()` work, **the component is broken**.
+
+**Implementation requirement**: Your `_set_value()` must work identically whether called during initial value application (via `_mark_ready()`) or later (via direct `val()` calls). If your implementation relies on initialization state or timing, you've violated this contract.
+
+---
+
 ## Template Method Pattern
 
 **Base class handles:**
@@ -76,6 +91,18 @@ _set_value(value) {
 }
 ```
 
+### String/Number Value Coercion
+
+Input components must accept both string and numeric values. A select with options `"3"`, `"5"`, `"9"` must work with `.val(3)` or `.val("3")`.
+
+```javascript
+_set_value(value) {
+    // Convert to string for comparison with option values
+    const str_value = value == null ? '' : str(value);
+    this.tom_select.setValue(str_value, true);
+}
+```
+
 ### _mark_ready()
 
 Call in `on_ready()` to apply buffered values and mark component ready: