Dead fabrication stub: execute_function_step (engine.rs) is a pub fn with zero callers that zero-fills results — delete it

[avrabe]

Summary

StacklessEngine::execute_function_step (kiln-runtime/src/stackless/engine.rs:11524) is a dead pub fn with zero callers anywhere in the workspace (verified: grep execute_function_step outside its own definition matches nothing — not even tests). It is also a fabrication stub: it validates the function index, then returns zero-filled results without executing anything.

// Simulate step execution - in real implementation would execute instructions
// For now, return completed with default values
...
for result_type in &func_type.results {
    let default_value = match result_type {
        ValueType::I32 => Value::I32(0),
        ValueType::I64 => Value::I64(0),
        ...
        _ => Value::I32(0),
    };
    results.push(default_value)?;
}

This is the same fabrication family as SR-53 (#443, the arg-arity zero-fill, now fixed) and #412 — but for results, and unlike SR-53 it is currently not reachable (no live caller), so no user is receiving fake results from it today. That is the only reason this is low-severity rather than a correctness bug.

Why it should go

Two CLAUDE.md rules apply directly:

• NO DEAD CODE — "If code is unused and has no clear immediate purpose → DELETE IT." A pub fn with zero callers, no test, and a // For now placeholder body qualifies.
• Stub methods that return Ok(0)/Ok(()) without doing anything are BANNED — this returns zero-filled results as if it executed.

Leaving it is a latent trap: a future caller wiring up "step execution" would silently get fabricated results (✓ completed with all-zero outputs), exactly the class of bug SR-53/#412 were about — but with no arity signal to catch it.

Suggested fix

Delete execute_function_step (and any now-unused helpers it alone pulls in). If step-wise execution is genuinely planned, replace the body with Error::not_implemented_error(...) and add a tracking note — do not leave a stub that returns fabricated success.

Found by a fable subagent while fixing SR-53 (#443); reachability (zero callers) confirmed by grep on main (6e249068).