diff --git a/src/interface/abi/Iseriser/ABI/Capstone.idr b/src/interface/abi/Iseriser/ABI/Capstone.idr
new file mode 100644
index 0000000..f27dfa7
--- /dev/null
+++ b/src/interface/abi/Iseriser/ABI/Capstone.idr
@@ -0,0 +1,70 @@
+-- SPDX-License-Identifier: MPL-2.0
+-- Copyright (c) 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
+--
+||| Layer-5 CAPSTONE: the end-to-end ABI SOUNDNESS CERTIFICATE for iseriser.
+|||
+||| This module proves NO new domain theorem. Its sole job is to ASSEMBLE the
+||| already-discharged proof layers into ONE inhabited value, so that the full
+||| ABI contract is shown to hold *together*. The certificate ties the chain:
+|||
+|||   manifest/doctrine model  (Types: Component, Scaffold, Result)
+|||     -> Layer-2 flagship     (Semantics.completeIsConformant — the canonical
+|||                              positive control: the complete five-component
+|||                              scaffold IS Conformant)
+|||     -> Layer-3 invariant    (Invariants.extendedGeneratedConformant — the
+|||                              upward-closure / monotonicity witness: a
+|||                              generated-then-extended scaffold stays Conformant)
+|||     -> Layer-4 FFI seam     (FfiSeam.resultToIntInjective — distinct ABI
+|||                              outcomes never collide on the C wire)
+|||
+||| into a single end-to-end soundness statement. `abiContractDischarged` is the
+||| capstone value: it is constructed ENTIRELY from the existing exported
+||| witnesses/theorems of the prior layers. If ANY prior layer were unsound,
+||| this value would not typecheck. There is no fresh proof obligation here —
+||| only genuine composition.
+
+module Iseriser.ABI.Capstone
+
+import Iseriser.ABI.Types
+import Iseriser.ABI.Semantics
+import Iseriser.ABI.Invariants
+import Iseriser.ABI.FfiSeam
+
+%default total
+
+--------------------------------------------------------------------------------
+-- The capstone certificate
+--------------------------------------------------------------------------------
+
+||| `ABISound` bundles the KEY proven facts of the iseriser ABI into one record.
+||| Each field is the TYPE of an already-proven theorem from a prior layer; the
+||| only way to inhabit the record is to supply those real witnesses.
+|||
+|||   * `flagship`  : the Layer-2 flagship property holds on the canonical
+|||                   positive-control instance (`Semantics.completeScaffold` is
+|||                   `Conformant`).
+|||   * `invariant` : the Layer-3 deeper invariant holds — conformance is
+|||                   upward-closed under extension, witnessed on the generated
+|||                   scaffold extended by one component.
+|||   * `ffiInjective` : the Layer-4 FFI-seam guarantee — `resultToInt` is
+|||                   injective, so distinct ABI outcomes never collide on the
+|||                   wire. Stored as the full injectivity statement.
+public export
+record ABISound where
+  constructor MkABISound
+  flagship     : Conformant Semantics.completeScaffold
+  invariant    : Conformant (extend [Manifest] Invariants.generatedScaffold)
+  ffiInjective : (a, b : Result) -> resultToInt a = resultToInt b -> a = b
+
+||| THE CAPSTONE. A single inhabited value assembled purely from the existing
+||| exported witnesses of Layers 2-4. Its mere existence certifies that the
+||| flagship property, the deeper invariant, and the FFI-seam injectivity are
+||| ALL simultaneously discharged for this ABI — manifest model -> ABI proofs
+||| -> FFI seam, sealed end to end.
+public export
+abiContractDischarged : ABISound
+abiContractDischarged =
+  MkABISound
+    completeIsConformant            -- Layer-2 flagship positive control
+    extendedGeneratedConformant     -- Layer-3 upward-closure invariant witness
+    resultToIntInjective            -- Layer-4 FFI-seam injectivity
diff --git a/src/interface/abi/iseriser-abi.ipkg b/src/interface/abi/iseriser-abi.ipkg
index 1dc8105..d905fe3 100644
--- a/src/interface/abi/iseriser-abi.ipkg
+++ b/src/interface/abi/iseriser-abi.ipkg
@@ -12,3 +12,4 @@ modules = Iseriser.ABI.Types
         , Iseriser.ABI.Semantics
         , Iseriser.ABI.Invariants
         , Iseriser.ABI.FfiSeam
+        , Iseriser.ABI.Capstone