diff --git a/src/ITensors.jl b/src/ITensors.jl
index 408da78..e25b668 100644
--- a/src/ITensors.jl
+++ b/src/ITensors.jl
@@ -14,9 +14,9 @@ module ITensors
 # re-exports `NDTensors`, so `using ITensorsITensorBaseCompat.ITensors: scalartype` must
 # also work — and bring in the ones this submodule's own methods build on
 # (`scalartype` / `datatype`).
+import ..NDTensors: map_diag, map_diag!
 import Base: truncate
-using ..NDTensors: @Algorithm_str, Algorithm, data, datatype, dense, denseblocks, map_diag,
-    map_diag!, scalartype
+using ..NDTensors: @Algorithm_str, Algorithm, data, datatype, dense, denseblocks, scalartype
 
 include("itensor.jl")
 
@@ -38,6 +38,8 @@ export
     qr, svd, eigen, factorize, factorize_svd,
     # Diagonal manipulation
     map_diag, map_diag!,
+    # Operator exponential
+    exp,
     # Storage / element-type accessors
     scalartype, datatype, array, data,
     # Dense / quantum-number no-ops
diff --git a/src/NDTensors.jl b/src/NDTensors.jl
index 3b32b2b..1e468c1 100644
--- a/src/NDTensors.jl
+++ b/src/NDTensors.jl
@@ -5,7 +5,7 @@
 module NDTensors
 
 using BackendSelection: @Algorithm_str, Algorithm
-using ITensorBase: ITensorBase, AbstractITensor, inds, unnamed
+using ITensorBase: ITensorBase, AbstractITensor, unnamed
 
 #
 # Storage / element type accessors. `scalartype` is the scalar (element) type;
@@ -21,35 +21,12 @@ denseblocks(T::AbstractITensor) = T
 dense(T::AbstractITensor) = T
 
 #
-# Diagonal manipulation. Legacy `map_diag(f, T)` applies `f` to the diagonal of a
-# (diagonal-like) tensor; used on factorization spectra (singular values /
-# eigenvalues). Reproduced via the same diagonal machinery as `delta`.
-_diagcartesian(arr, k) = CartesianIndex(ntuple(Returns(k), ndims(arr)))
-function map_diag(f, T::AbstractITensor)
-    arr = copy(unnamed(T))
-    for k in 1:minimum(size(arr))
-        idx = _diagcartesian(arr, k)
-        arr[idx] = f(arr[idx])
-    end
-    return arr[inds(T)...]
-end
-function map_diag!(f, T::AbstractITensor)
-    arr = unnamed(T)
-    for k in 1:minimum(size(arr))
-        idx = _diagcartesian(arr, k)
-        arr[idx] = f(arr[idx])
-    end
-    return T
-end
-# Out-of-place-into-`dest` form `map_diag!(f, dest, src)`: write `f` of `src`'s diagonal
-# onto `dest`'s diagonal (TNQS calls it with `dest === src` for an in-place diagonal map).
-function map_diag!(f, dest::AbstractITensor, src::AbstractITensor)
-    d, s = unnamed(dest), unnamed(src)
-    for k in 1:minimum(size(s))
-        d[_diagcartesian(d, k)] = f(s[_diagcartesian(s, k)])
-    end
-    return dest
-end
+# Diagonal manipulation. Legacy `map_diag(f, T)` / `map_diag!` apply `f` to a tensor's
+# diagonal (used on factorization spectra). These names belong to `NDTensors` in the real
+# ecosystem, so the generic functions live here; the `AbstractITensor` methods are defined
+# in the sibling `ITensors` submodule, the layer that owns the tensor type.
+function map_diag end
+function map_diag! end
 
 # The algorithm dispatch tag (legacy `Algorithm` / `@Algorithm_str`) comes from
 # BackendSelection.jl, which NDTensors re-exports in the real ecosystem; imported above
diff --git a/src/SiteTypes.jl b/src/SiteTypes.jl
index 0de9aec..be4ef25 100644
--- a/src/SiteTypes.jl
+++ b/src/SiteTypes.jl
@@ -14,7 +14,6 @@
 # (`src/lib/SiteTypes/`), re-exported by `ITensors`; reproduced as a submodule here.
 module SiteTypes
 
-using ..ITensors: combinedind, combiner, dag, inds
 using ITensorBase: ITensorBase, AbstractITensor, Index
 using LinearAlgebra: LinearAlgebra
 
@@ -140,27 +139,6 @@ function op(::OpName"CPHASE", ::SiteType"S=1/2"; ϕ)
     return ComplexF64[1 0 0 0; 0 1 0 0; 0 0 1 0; 0 0 0 cis(ϕ)]
 end
 
-# TYPE PIRACY (temporary): extends `Base.exp` for an operator `ITensor` (matricize over the
-# index/prime pairs, exponentiate, rebuild). Legacy ITensors provided `exp(::ITensor)`; gates
-# defined as `exp` of a Hamiltonian operator rely on it (e.g. a user
-# `op(::OpName"MyZRot", ...) = exp(-im θ/2 * op("Z", s))`). To de-pirate: make this compat-owned
-# (an `exp` in this module, not a `Base.exp` method), inferring the prime-pair codomain/domain and
-# forwarding to ITensorBase's matricization `exp(a, dimnames_codomain, dimnames_domain)` — which
-# already exists and is graded-capable, so this dense combiner-based version goes away. Not an
-# upstream candidate (the upstream matricization `exp` is the target, not a `Base.exp(::ITensor)`).
-function Base.exp(t::AbstractITensor)
-    p0 = filter(i -> ITensorBase.plev(i) == 0, collect(inds(t)))
-    isempty(p0) && error("exp(::ITensor) expects indices paired as (i, prime(i))")
-    p1 = map(ITensorBase.prime, p0)
-    cr, cc = combiner(Tuple(p1)), combiner(Tuple(p0))
-    tc = (t * cr) * cc
-    rci, cci = combinedind(cr), combinedind(cc)
-    d = length(rci)
-    M = ComplexF64[tc[rci => a, cci => b] for a in 1:d, b in 1:d]
-    E = exp(M)[rci, cci]
-    return (E * dag(cr)) * dag(cc)
-end
-
 export @OpName_str, @SiteType_str, OpName, SiteType, op, state
 
 end
diff --git a/src/itensor.jl b/src/itensor.jl
index c022f09..7885adc 100644
--- a/src/itensor.jl
+++ b/src/itensor.jl
@@ -3,9 +3,9 @@
 #
 # Strategy (see ITensorDevelopmentPlans api_migration_map.md):
 #   - Names below are thin wrappers over ITensorBase / TensorAlgebra / MatrixAlgebraKit.
-#   - `combiner`, the factorization return shapes, `map_diag`, the operator/SiteType
-#     system, and the boundary-MPS (ITensorMPS) paths are NOT wrapped here; they need
-#     callsite translation or upstream stack work and are tracked separately.
+#   - The factorization return shapes, the operator/SiteType system, and the boundary-MPS
+#     (ITensorMPS) paths are NOT wrapped here; they need callsite translation or upstream
+#     stack work and are tracked separately.
 #
 # ITensorBase keeps most of this API internal (unexported), so we reach for the
 # qualified names and re-publish the legacy spellings into this namespace.
@@ -162,13 +162,6 @@ end
 itensor(array, is) = array[is...]
 itensor(array, is...) = array[is...]
 
-# TYPE PIRACY (temporary, compat-owned — NOT an upstream candidate): adds a rank-0
-# `ITensor(x::Number)` constructor, which ITensorBase deliberately omits and does not plan to
-# support. Legacy ITensors uses it as a multiplicative identity to seed a product accumulator
-# (`out = ITensor(1); out *= t; ...`). Kept here for now; the accumulator call sites get rewritten
-# to a different pattern later, retiring this method rather than upstreaming it.
-ITensorBase.ITensor(x::Number) = nameddims(fill(x), ())
-
 # Random ITensor over the given indices (legacy `random_itensor`).
 random_itensor(eltype::Type, is::Index...) = randn(eltype, is...)
 random_itensor(eltype::Type, is::Union{Tuple, AbstractVector}) = randn(eltype, is...)
@@ -487,21 +480,6 @@ end
 # the `NDTensors` submodule and are imported into this one.)
 array(T::AbstractITensor) = unnamed(T)
 
-# TYPE PIRACY (temporary, compat-owned — NOT an upstream candidate): extends
-# `Adapt.adapt_structure` for `AbstractITensor` with an eltype target. Using
-# `Adapt.adapt_structure` for eltype *conversion* is an abuse of Adapt.jl (Adapt is for
-# storage/device adaptation, not changing the scalar type), so this does not belong upstream.
-# Kept here for now; the eltype-conversion call sites get rewritten with a different pattern
-# later, retiring this shim rather than upstreaming it.
-#
-# Legacy `adapt(eltype)(t)` converts an ITensor's scalar (element) type. ITensorBase's
-# Adapt integration adapts the storage array/device type but leaves the element type
-# alone, so reproduce the eltype conversion for a `Number` target (used by
-# `adapt(eltype)(state(...))` to build typed product states).
-function Adapt.adapt_structure(::Type{elt}, T::AbstractITensor) where {elt <: Number}
-    return nameddims(convert(AbstractArray{elt}, unnamed(T)), ITensorBase.dimnames(T))
-end
-
 # `swapind`: swap two indices (legacy convenience over `replaceinds`).
 swapind(T::AbstractITensor, i::Index, j::Index) = replaceinds(T, i => j, j => i)
 
@@ -568,29 +546,57 @@ function settags(i::Index, d::AbstractDict)
     end
     return i
 end
-# TYPE PIRACY (temporary, compat-owned — NOT an upstream candidate): the two methods below add
-# `ITensorBase.Index` constructors taking a tag string / tag dict, a legacy positional-tag form
-# ITensorBase does not plan to support (the next-gen spelling passes tags via the `tags` keyword
-# argument). Kept here for now; the call sites get modernized to the `tags` kwarg later, retiring
-# these methods rather than upstreaming them.
-#
-# Legacy positional tagged-index constructor `Index(dim, "tag")`.
-ITensorBase.Index(dim::Integer, tagstr::AbstractString) = settags(Index(dim), tagstr)
-# Build a fresh index carrying a tag dictionary (legacy `Index(dim, tags(i))`, where
-# the next-gen `tags` returns a `Dict{String, String}`).
-function ITensorBase.Index(dim::Integer, tags::AbstractDict)
-    i = Index(dim)
-    for (k, v) in tags
-        i = ITensorBase.settag(i, k, v)
-    end
-    return i
-end
 function hastags(i::Index, tagstr::AbstractString)
     return all(
         haskey(tags(i), String(strip(t))) for t in split(tagstr, ",") if !isempty(strip(t))
     )
 end
 
+#
+# Diagonal manipulation. The `map_diag` / `map_diag!` generics belong to `NDTensors`
+# (imported into this module); their `AbstractITensor` methods live here at the ITensor
+# layer.
+_diagcartesian(arr, k) = CartesianIndex(ntuple(Returns(k), ndims(arr)))
+function map_diag(f, T::AbstractITensor)
+    arr = copy(unnamed(T))
+    for k in 1:minimum(size(arr))
+        idx = _diagcartesian(arr, k)
+        arr[idx] = f(arr[idx])
+    end
+    return arr[inds(T)...]
+end
+function map_diag!(f, T::AbstractITensor)
+    arr = unnamed(T)
+    for k in 1:minimum(size(arr))
+        idx = _diagcartesian(arr, k)
+        arr[idx] = f(arr[idx])
+    end
+    return T
+end
+# Out-of-place-into-`dest` form `map_diag!(f, dest, src)`: write `f` of `src`'s diagonal
+# onto `dest`'s diagonal (TNQS calls it with `dest === src` for an in-place diagonal map).
+function map_diag!(f, dest::AbstractITensor, src::AbstractITensor)
+    d, s = unnamed(dest), unnamed(src)
+    for k in 1:minimum(size(s))
+        d[_diagcartesian(d, k)] = f(s[_diagcartesian(s, k)])
+    end
+    return dest
+end
+
+#
+# Owned `exp` (avoids type piracy: `AbstractITensor` is not ours, so we do not add a
+# `Base.exp` method for it). Legacy `ITensors.exp(::ITensor)` exponentiates an operator
+# ITensor over its `(i, prime(i))` index pairs by forwarding to ITensorBase's
+# graded-capable matricization `Base.exp(a, codomain, domain)`. Other arguments forward
+# to `Base.exp`.
+exp(x) = Base.exp(x)
+function exp(t::AbstractITensor)
+    p0 = filter(i -> ITensorBase.plev(i) == 0, collect(inds(t)))
+    isempty(p0) && error("exp(::ITensor) expects indices paired as (i, prime(i))")
+    p1 = map(ITensorBase.prime, p0)
+    return Base.exp(t, Tuple(p1), Tuple(p0))
+end
+
 # TODO (small inline residue — can't be a drop-in shim):
 #   - `contract` / `inner` / `truncate`: consumers *extend* these (method definitions),
 #     so the call sites drop the `ITensors.` qualifier to extend the generics this