Fix: Create child environment for IR script execution

[Copilot]

Problem

IR script execution was overwriting GlobalEnvironment's slot 0 (Symbol.This → GlobalObject) with synthetic slots for loop iterators, causing global identifier resolution to fail with ReferenceError instead of the expected TypeError.

Solution

Create a child environment for IR synthetic slots when the parent environment already has slots:

public static JsValue RunScript(ExecutionPlan plan, JsEnvironment environment, EvaluationContext context)
{
    var irEnvironment = environment;
    if (plan.SlotCount > 0)
    {
        if (environment.HasSlots)
        {
            // Isolate IR slots from GlobalEnvironment
            irEnvironment = new JsEnvironment(environment, false, false, null, "ir-script-wrapper");
        }
        
        irEnvironment.InitializeSlots(plan.SlotCount, plan.RootScopeId);
        irEnvironment.PopulateSyntheticSlotNames(plan.SlotSymbols);
    }

    var runner = new ExecutionPlanRunner(plan, irEnvironment, context, 0);
    return runner.RunScriptInternal();
}

Benefits over offset-based approach:

• No runtime offset calculations
• Clean scope isolation matching JavaScript semantics
• Works with any pre-existing slots

Changes:

• Modified TypedAstEvaluator.ExecutionPlanRunner.Core.cs: Child environment creation logic
• Enabled 8 previously skipped tests in DebugScopeTests.cs

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Fix: Create child environment for IR script execution</issue_title>
<issue_description>Parent: #481

Goal

Implement Option C from the root cause analysis - create a child environment for IR slots.

Root Cause (from #481)

PopulateSyntheticSlotNames() overwrites slot 0 (Symbol.This → GlobalObject) with synthetic slots.

Solution

public static JsValue RunScript(ExecutionPlan plan, JsEnvironment environment, EvaluationContext context)
{
    var irEnvironment = environment;
    if (plan.SlotCount > 0 && environment.HasSlots)
    {
        // Create child environment for IR slots to avoid clobbering GlobalEnvironment
        irEnvironment = new JsEnvironment(environment, false, false, null, "ir-script-wrapper");
        irEnvironment.InitializeSlots(plan.SlotCount, plan.RootScopeId);
        irEnvironment.PopulateSyntheticSlotNames(plan.SlotSymbols);
    }
    else if (plan.SlotCount > 0)
    {
        irEnvironment.InitializeSlots(plan.SlotCount, plan.RootScopeId);
        irEnvironment.PopulateSyntheticSlotNames(plan.SlotSymbols);
    }

    var runner = new ExecutionPlanRunner(plan, irEnvironment, context, 0);
    return runner.RunScriptInternal();
}

Files

• src/Asynkron.JsEngine/Ast/TypedAstEvaluator.ExecutionPlanRunner.Core.cs

Complexity: Simple

• Clear fix path from analysis
• Localized change</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Fix: Create child environment for IR script execution #548

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