Task 2.4.4 blocked: Prerequisites (bytecode infrastructure) not implemented

[Copilot]

Task 2.4.4 requires removing AST fields from IR instructions and replacing them with bytecode representations. Analysis shows this cannot proceed—the prerequisite bytecode infrastructure doesn't exist.

Current State

All IR instructions use AST fields exclusively:

// Current (Instructions.cs:377)
internal sealed record BranchInstruction(
    ExpressionNode Condition,
    int ConsequentIndex,
    int AlternateIndex
) : ExecutionInstruction(InstructionKind.Branch, -1);

// Expected after prerequisites (per issue)
internal sealed record BranchInstruction(
    int TrueTarget,
    int FalseTarget,
    ImmutableArray<ExpressionOp> ConditionOps  // doesn't exist yet
) : ExecutionInstruction;

Blocking Issues

• No bytecode types exist (ExpressionOp referenced in issue description is not defined)
• Handlers still evaluate AST: instruction.Condition.EvaluateExpression(environment, context)
• Emitters create instructions with AST fields only
• 15+ instructions affected (BranchInstruction, ThrowInstruction, ReturnInstruction, etc.)

Prerequisites Required

1. Task 2.4.1: Design expression bytecode format
2. Task 2.4.2: Update handlers to interpret bytecode instead of evaluating AST
3. Task 2.4.3: Update emitters to generate bytecode

Recommendation

Close this PR and create/prioritize issues for Tasks 2.4.1-2.4.3. This cleanup task is correctly scoped as "simple" but depends on substantial prerequisite work that represents the actual complexity.

Detailed analysis: /tmp/task-2.4.4-analysis.md

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Task 2.4.4: Remove AST fields from instructions</issue_title>
<issue_description>Parent: #414

Goal

Remove deprecated AST fields from IR instructions (cleanup).

Prerequisites

• All handlers updated (Task 2.4.2)
• All emitters updated (Task 2.4.3)
• Tests passing with bytecode-only

Approach

// Remove AST field
record BranchInstruction(
    int TrueTarget,
    int FalseTarget,
    ImmutableArray<ExpressionOp> ConditionOps  // now required, not optional
) : ExecutionInstruction;

Files

• src/Asynkron.JsEngine/Execution/Instructions/Instructions.cs

Complexity: Simple

• Remove nullable AST fields
• Make bytecode fields required
• Final cleanup step</issue_description>

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

• Fixes Task 2.4.4: Remove AST fields from instructions #524

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