Function ingress_expr

crates/kernel/src/ingress.rs:597–1374

(
  root_expr: &Arc<IxonExpr>,
  root_arena: u64,
  ctx: &Ctx<'_, M>,
  intern: &mut InternTable<M>,
  ixon_env: &IxonEnv,
  cache: &mut ExprCache<M>,
  univ_cache: &mut UnivCache<M>,
  stats: &mut Co

  };
  let changed = univ_idxs
    .iter()
    .zip(ingressed.iter())
    .any(|(&idx, k)| !ixon_matches_kuniv(stored_at(idx), k));
  if !changed {
    return None;
  }
  let spellings: Box<[Arc<IxonUniv>]> =
    univ_idxs.iter().map(|&idx| stored_at(idx).clone()).collect();
  Some(UnivDecor::Const(spellings))
}

/// Stage-2 decoration source for a `Const`-shaped occurrence
/// (canonicity §10.6): a `univ_patches` entry keyed by the occurrence's
/// (post-mdata) arena index carries the FULL original spelling list in
/// the virtual index space — decorate from it. Without a patch, fall
/// back to the stage-1 mk*-rebuild test against the stored primary
/// entries; on canonical tables the fallback never fires (P3), but it
/// keeps hand-built raw-table fixtures exercised. Meta mode only — call
/// inside `M::meta_field_try`.
fn univ_args_decor_at<M: KernelMode>(
  arena_idx: u64,
  univ_idxs: &[u64],
  ctx: &Ctx<'_, M>,
  ingressed: &[KUniv<M>],
) -> Result<Option<UnivDecor>, String> {
  let Some(patch_idxs) = ctx.univ_patch(arena_idx) else {
    return Ok(univ_args_decor(univ_idxs, ctx, ingressed));
  };
  if patch_idxs.len() != ingressed.len() {
    return Err(format!(
      "univ patch at arena index {arena_idx} has {} entries but the \
       occurrence has {} level args",
      patch_idxs.len(),
      ingressed.len()
    ));
  }
  let mut spellings = Vec::with_capacity(patch_idxs.len());
  for &vidx in patch_idxs {
    spellings.push(ctx.univ_at_virtual(vidx)?.clone());
  }
  let changed = spellings
    .iter()
    .zip(ingressed.iter())
    .any(|(s, k)| !ixon_matches_kuniv(s, k));
  Ok(if changed {
    Some(UnivDecor::Const(spellings.into_boxed_slice()))
  } else {
    None
  })
}

// ============================================================================
// Expression ingress (iterative)
// ============================================================================

enum ExprFrame<M: KernelMode> {
  Process {
    expr: Arc<IxonExpr>,