diff --git a/CHANGELOG.adoc b/CHANGELOG.adoc
index e77eeaf..5f1313a 100644
--- a/CHANGELOG.adoc
+++ b/CHANGELOG.adoc
@@ -13,6 +13,13 @@ https://semver.org/spec/v2.0.0.html[Semantic Versioning].
 
 ==== Changed
 
+* *Modality profiles distinguished from the fixed Octad schema* (vcl-ut#118):
+  adopted `modality profile` for versioned, implementation-specific modality
+  selections and `modality set` for membership alone. Clarified that VCL-UT's
+  `OctadSchema` and `VCLS` v1 remain fixed at eight modality slots; empty or
+  omitted schema fields do not signal profile membership or witness presence.
+  No type, JSON contract, or wire format changed. See
+  `docs/standards/MODALITY-PROFILES.adoc` and ADR-0007.
 * *Licensing and REUSE policy normalized*: software and package metadata use
   MPL-2.0; human-readable documentation uses CC-BY-SA-4.0. Removed the unused
   AGPL license text, corrected invalid PMPL SPDX declarations, and clarified
diff --git a/README.adoc b/README.adoc
index c172f5c..36a8f7e 100644
--- a/README.adoc
+++ b/README.adoc
@@ -132,6 +132,18 @@ it. Simple statements short-circuit at the early safety levels; proof-bearing
 statements and high-risk lifecycle transitions go through the deeper proof,
 effect, resource, and cross-cutting checks (L9-L10).
 
+[NOTE]
+====
+Keep a deployment's **modality profile** (which modalities it supports or
+enables) separate from the **Octad** and VCL-UT's `OctadSchema`. The Octad is
+the fixed eight-modality model; a subject may have data in only some of its
+slots. `OctadSchema` still has all eight schema slots, even when a slot has no
+field definitions. The current `VCLS` v1 wire format is fixed-arity and does
+not carry a modality profile. See
+link:docs/standards/MODALITY-PROFILES.adoc[the terminology and compatibility
+contract].
+====
+
 [source]
 ----
 User / system writes VCL
@@ -170,6 +182,8 @@ routine VCL safe.
 
 Prefer: consonance language, statement, transition, identity claim, consonance
 subject, modal witness, proof-bearing statement, verified transition, octad.
+When discussing implementation/deployment modality support, use *modality
+profile*; reserve `OctadSchema` for the fixed eight-slot schema.
 
 Avoid or qualify: query language, query, record, CRUD, delete, proof-carrying
 query, 6-modal engine, passive store. Use "query" only for a read-only syntactic
diff --git a/ROADMAP.adoc b/ROADMAP.adoc
index ae67c9d..6326dbd 100644
--- a/ROADMAP.adoc
+++ b/ROADMAP.adoc
@@ -74,9 +74,12 @@ These are ordered by value, not by version number.
 . *Discharge the two disclosed L10 residuals.* Transitive `ENTAILS`-cycle
   detection and proposition well-typedness, both recorded as owed in
   `verification/proofs/VERIFICATION-STANCE.adoc`.
-. *Retire the `HEXAD` keyword* once VeriSimDB's default modality context
-  carries all eight witnesses. The parser accepts both `OCTAD` and `HEXAD`
-  today for compatibility.
+. *Optional syntax cleanup: retire the legacy `HEXAD` spelling* when all
+  supported frontends can do so compatibly. The current Rust parser accepts
+  both `OCTAD` and `HEXAD` as the same `Source::Octad`; this is a source-name
+  alias, not a six-modality profile. Its deprecation is independent of which
+  modalities a deployment enables or which witnesses a subject populates.
+  See link:docs/standards/MODALITY-PROFILES.adoc[the profile/Octad contract].
 
 == Milestones
 
diff --git a/container/README.adoc b/container/README.adoc
index 5313b85..0f941fe 100644
--- a/container/README.adoc
+++ b/container/README.adoc
@@ -155,7 +155,7 @@ For k9-svc managed deployments:
 [source,bash]
 ----
 # Validate the deployment component
-nickel typecheck container/deploy.k9.ncl
+k9-svc validate container/deploy.k9.ncl
 
 # Deploy (requires Hunt-level authorisation)
 k9-svc deploy container/deploy.k9.ncl --env production
diff --git a/container/deploy.k9.ncl b/container/deploy.k9.ncl
index 06be343..382be69 100644
--- a/container/deploy.k9.ncl
+++ b/container/deploy.k9.ncl
@@ -1,3 +1,4 @@
+K9!
 # SPDX-License-Identifier: MPL-2.0
 # deploy.k9.ncl — VCL-total deployment component (Hunt level)
 #
@@ -8,65 +9,9 @@
 # It requires explicit authorisation via the Leash system.
 #
 # Usage:
-#   nickel typecheck container/deploy.k9.ncl
 #   k9-svc validate container/deploy.k9.ncl
 #   k9-svc deploy container/deploy.k9.ncl --env production
 
-# The component's pedigree (self-description across five layers)
-let component_pedigree = {
-  # ─────────────────────────────────────────────────────────────
-  # L1: The Snout — Identity
-  # ─────────────────────────────────────────────────────────────
-  metadata = {
-    name = "vcl-total-deploy",
-    version = "0.1.0",
-    breed = "application/vnd.k9+nickel",
-    magic_number = "K9!",
-    description = "VCL-total deployment component (Hunt level)",
-  },
-
-  # ─────────────────────────────────────────────────────────────
-  # L2: The Scent — Target Environment
-  # ─────────────────────────────────────────────────────────────
-  target = {
-    os = 'Linux,
-    is_edge = false,
-    requires_podman = true,
-    min_memory_mb = 256,
-  },
-
-  # ─────────────────────────────────────────────────────────────
-  # L3: The Leash — Security
-  # ─────────────────────────────────────────────────────────────
-  security = {
-    trust_level = 'Hunt,
-    allow_network = true,
-    allow_filesystem_write = true,
-    allow_subprocess = true,
-    # In production, replace with a real Ed25519 signature.
-    signature = "PLACEHOLDER-SIGNATURE-REQUIRED-FOR-HUNT",
-  },
-
-  # ─────────────────────────────────────────────────────────────
-  # L4: The Gut — Self-Validation
-  # ─────────────────────────────────────────────────────────────
-  validation = {
-    checksum = "sha256:placeholder",
-    pedigree_version = "1.0.0",
-    hunt_authorized = false,  # Must be set true after handshake
-  },
-
-  # ─────────────────────────────────────────────────────────────
-  # L5: The Muscle — Deployment Recipes
-  # ─────────────────────────────────────────────────────────────
-  recipes = {
-    install = "just container-build",
-    validate = "just container-verify",
-    deploy = "just container-up",
-    migrate = "just container-build && just container-up",
-  },
-} in
-
 # Deployment configuration
 let deployment = {
   # Target environments (dev / staging / production)
@@ -143,7 +88,61 @@ echo "K9: Rollback complete."
 
 # Export the component
 {
-  pedigree = component_pedigree,
+  # The component's pedigree (self-description across five layers)
+  pedigree = {
+    # ─────────────────────────────────────────────────────────────
+    # L1: The Snout — Identity
+    # ─────────────────────────────────────────────────────────────
+    metadata = {
+      name = "vcl-total-deploy",
+      version = "0.1.0",
+      breed = "application/vnd.k9+nickel",
+      magic_number = "K9!",
+      description = "VCL-total deployment component (Hunt level)",
+    },
+
+    # ─────────────────────────────────────────────────────────────
+    # L2: The Scent — Target Environment
+    # ─────────────────────────────────────────────────────────────
+    target = {
+      os = 'Linux,
+      is_edge = false,
+      requires_podman = true,
+      min_memory_mb = 256,
+    },
+
+    # ─────────────────────────────────────────────────────────────
+    # L3: The Leash — Security
+    # ─────────────────────────────────────────────────────────────
+    security = {
+      leash = 'Hunt,
+      trust_level = 'Hunt,
+      allow_network = true,
+      allow_filesystem_write = true,
+      allow_subprocess = true,
+      # In production, replace with a real Ed25519 signature.
+      signature = "PLACEHOLDER-SIGNATURE-REQUIRED-FOR-HUNT",
+    },
+
+    # ─────────────────────────────────────────────────────────────
+    # L4: The Gut — Self-Validation
+    # ─────────────────────────────────────────────────────────────
+    validation = {
+      checksum = "sha256:placeholder",
+      pedigree_version = "1.0.0",
+      hunt_authorized = false,  # Must be set true after handshake
+    },
+
+    # ─────────────────────────────────────────────────────────────
+    # L5: The Muscle — Deployment Recipes
+    # ─────────────────────────────────────────────────────────────
+    recipes = {
+      install = "just container-build",
+      validate = "just container-verify",
+      deploy = "just container-up",
+      migrate = "just container-build && just container-up",
+    },
+  },
   deployment = deployment,
   scripts = scripts,
 
diff --git a/docs/2026-07-21-workup-consonance-and-verisim.adoc b/docs/2026-07-21-workup-consonance-and-verisim.adoc
index db6abcf..bde657b 100644
--- a/docs/2026-07-21-workup-consonance-and-verisim.adoc
+++ b/docs/2026-07-21-workup-consonance-and-verisim.adoc
@@ -435,9 +435,15 @@ named `HexadType` throughout (`VCLTypes.res:50`, `:206`, `:270`,
 `VCLSubtyping.res:101`). The hexad-to-octad migration reached the variants and
 stopped before the defaults and the names.
 
-Note the same legacy is visible here: the parser still accepts `HEXAD`
-alongside `OCTAD`. That is deliberate compatibility, and it should be retired
-once VeriSimDB's default context carries all eight — not before.
+Terminology correction (2026-10-05): the six-entry `availableModalities`
+value is an implementation-specific modality set; if a versioned profile is
+introduced, it can describe that selection. It does not change the fixed
+eight-slot Octad model or VCL-UT's `OctadSchema`. In this repository's current
+Rust parser, `OCTAD` and `HEXAD` both map to the same `Source::Octad`, with
+`HEXAD` retained as a legacy source spelling. Alias removal is a separate
+cross-frontend compatibility decision; it is not gated on the default context
+listing all eight modalities. Other frontends must be checked independently.
+See link:standards/MODALITY-PROFILES.adoc[the profile/Octad contract].
 
 === The seam is unwired
 
@@ -480,8 +486,9 @@ Ordered by value delivered per unit of risk. Items 1-2 are in this repository;
 | 5
 | *Converge the checkers.* Once (4) is live, retire the ReScript checker's
   independent verdict in favour of the gate's, keeping the ReScript surface
-  parser and diagnostics. Then rename `HexadType` and retire the `HEXAD`
-  keyword together.
+  parser and diagnostics. Treat `HexadType` renaming and `HEXAD` alias removal
+  as separate compatibility cleanups; neither is implied by changing the
+  default modality set.
 | both
 
 | 6
diff --git a/docs/QUICKSTART.adoc b/docs/QUICKSTART.adoc
index 1d93e1f..4ec3131 100644
--- a/docs/QUICKSTART.adoc
+++ b/docs/QUICKSTART.adoc
@@ -120,7 +120,7 @@ Create a file called `my-query.vcltotal`:
 ----
 -- A query that exercises 6 of the 10 safety levels
 SELECT GRAPH, DOCUMENT
-FROM HEXAD 550e8400-e29b-41d4-a716-446655440000
+FROM OCTAD 550e8400-e29b-41d4-a716-446655440000
 WHERE FULLTEXT CONTAINS $searchTerm
 CONSUME AFTER 1 USE
 WITH SESSION ReadOnlyProtocol
@@ -260,7 +260,7 @@ Every function is total (`%default total`), every proof is real (zero
 
 Start with:
 
-- `Core.idr` — Foundation types (modalities, hexad references)
+- `Core.idr` — Foundation types (modalities, Octad source references)
 - `Linear.idr` — Simplest safety level (QTT linearity)
 - `Proofs.idr` — Cross-cutting invariants (see how levels compose)
 
diff --git a/docs/WHAT-IS-VERISIMDB.adoc b/docs/WHAT-IS-VERISIMDB.adoc
index 0c5d840..4d6b718 100644
--- a/docs/WHAT-IS-VERISIMDB.adoc
+++ b/docs/WHAT-IS-VERISIMDB.adoc
@@ -68,8 +68,12 @@ them in one system, with _automatic consistency guarantees_.
 
 === The Octad: One Entity, Eight Views
 
-Every piece of data in VeriSimDB is stored as an **octad** -- a single entity
-with up to eight simultaneous representations:
+VeriSimDB's **Octad** is a single-entity model with exactly eight named
+modality slots. A particular subject may have actual witness data in only a
+subset of those slots; “up to eight populated representations” describes
+runtime population, not a variable-length Octad schema. A deployment's
+modality profile, when defined by that implementation, is a separate statement
+about supported or enabled modalities:
 
 ----
 ┌─────────────────────────────────────────────────────────────┐
@@ -114,6 +118,15 @@ with up to eight simultaneous representations:
 | Geospatial coordinates and geometries -- where this entity is in the world
 |===
 
+These are the eight named Octad slots, not a promise that every subject has
+data in all eight. Keep four questions distinct: which modalities the model
+names, which a deployment supports (its *modality profile*), which fields the
+safety schema declares, and which witnesses are populated for a particular
+subject. VCL-UT's `OctadSchema` has a fixed slot for every modality; an empty
+slot in the schema input does not encode a deployment profile or runtime
+absence. See
+link:standards/MODALITY-PROFILES.adoc[the VCL-UT profile/Octad contract].
+
 === Why This Matters
 
 Suppose you have a customer record. In a traditional setup:
@@ -129,13 +142,15 @@ That is six copies of the same customer, in six different systems, with six
 different update mechanisms. When the customer changes their address, you have
 to update _all six_ -- and if any update fails or is delayed, your data drifts.
 
-In VeriSimDB, there is one octad for that customer. All eight views are
-maintained automatically. When the document modality updates, VeriSimDB detects
-that the vector embedding, graph relationships, and search index may have
-drifted, and triggers automatic re-normalisation.
+In VeriSimDB, that customer is modeled by one Octad with eight named slots.
+Which witnesses are supported by a deployment and which are populated for
+that subject are implementation/runtime matters; the fixed eight-slot model
+is independent of those choices. When document and vector witnesses are both
+present, for example, the engine can detect that the vector embedding may have
+drifted from the document and trigger re-normalisation.
 
-**You do not have to choose between MongoDB and Neo4j and Redis. You get all
-of them, and they stay in sync.**
+**The Octad supplies one identity model across modalities; it is not a promise
+that every deployment or subject has every witness populated.**
 
 === Drift Detection
 
@@ -150,7 +165,7 @@ When drift exceeds a configurable threshold, VeriSimDB:
 
 1. Identifies the most authoritative modality
 2. Regenerates the drifted modalities from it
-3. Validates consistency across all eight views
+3. Validates consistency across the applicable, populated witnesses (within the fixed Octad model)
 4. Updates everything atomically (all at once, or not at all)
 
 == The Three Query Paths
@@ -313,12 +328,13 @@ A proof technique discovered for VCL-total can be applied to PanLL, and vice ver
 | Concept | One-Sentence Summary
 
 | **VeriSimDB**
-| A database where every entity exists in 8 views simultaneously, with automatic
-  drift detection and repair.
+| A multi-modal engine whose Octad model has eight fixed modality slots; which
+  witnesses are supported or populated can vary by implementation and subject.
 
 | **Octad**
-| The 8 simultaneous representations of a single entity (graph, vector, tensor,
-  semantic, document, temporal, provenance, spatial).
+| The fixed eight-slot model for graph, vector, tensor, semantic, document,
+  temporal, provenance, and spatial witnesses; a subject need not populate all
+  eight slots.
 
 | **VCL**
 | The fast, unverified query language for VeriSimDB.
diff --git a/docs/WHY-TYPE-SAFETY-MATTERS.adoc b/docs/WHY-TYPE-SAFETY-MATTERS.adoc
index 5d342f0..019063d 100644
--- a/docs/WHY-TYPE-SAFETY-MATTERS.adoc
+++ b/docs/WHY-TYPE-SAFETY-MATTERS.adoc
@@ -168,10 +168,13 @@ FETCH orders.order_total WHERE orders.status = "completed"
 
 ==== Why It Matters for Databases
 
-In VeriSimDB, data exists across 8 modalities simultaneously (the octad). A
-typo in a modality reference could silently query the wrong view of your data.
-Schema binding ensures that every reference is checked against the live schema
-before the query runs.
+VeriSimDB's Octad names eight fixed modality slots, although a subject may
+have witness data in only a subset. A deployment's modality profile (which
+modalities it supports or enables) is a separate concept from both that fixed
+Octad and VCL-UT's `OctadSchema`. A typo in a modality reference could silently
+query the wrong view of your data; schema binding checks field references
+against the supplied schema. See
+link:standards/MODALITY-PROFILES.adoc[the profile/Octad contract].
 
 ---
 
@@ -436,10 +439,12 @@ FETCH OPTIONAL users WHERE users.email = ?email
 
 ==== Why It Matters for Databases
 
-In VeriSimDB, an entity's octad has exactly 8 modality slots but any subset
-might be populated. Cardinality safety ensures you know at compile time whether
-a modality query will return data or might be empty, eliminating an entire
-class of "expected data that was not there" bugs.
+In VeriSimDB, the Octad has exactly eight named modality slots, but any subset
+may have witness data for a particular entity. A modality profile can describe
+what an implementation supports; it does not prove that a subject has data in
+a supported modality. Cardinality safety concerns the possible result count,
+not the profile's modality count, and helps catch assumptions that a modality
+will necessarily return data when it might be empty.
 
 ---
 
diff --git a/docs/architecture/DECISIONS.adoc b/docs/architecture/DECISIONS.adoc
index b753f02..f0d3253 100644
--- a/docs/architecture/DECISIONS.adoc
+++ b/docs/architecture/DECISIONS.adoc
@@ -45,6 +45,11 @@ toc::[]
 |Epistemic types via S5 modal logic
 |Accepted
 |2026-04-10
+
+|ADR-0007
+|Separate modality profiles from the fixed Octad schema (see link:../decisions/0007-modality-profiles-vs-octad-schema.adoc[record])
+|Accepted
+|2026-10-05
 |===
 
 ---
diff --git a/docs/architecture/TOPOLOGY.adoc b/docs/architecture/TOPOLOGY.adoc
index 883ac56..a998d13 100644
--- a/docs/architecture/TOPOLOGY.adoc
+++ b/docs/architecture/TOPOLOGY.adoc
@@ -64,7 +64,7 @@ query language.
                           │  │  Tensor, Semantic, Document,     │    │
                           │  │  Temporal, Provenance, Spatial)  │    │
                           │  │                                  │    │
-                          │  │  HEXAD addressing                │    │
+                          │  │  OCTAD source (HEXAD alias)      │    │
                           │  └──────────────────────────────────┘    │
                           └─────────────────────────────────────────┘
 ----
@@ -147,7 +147,7 @@ The dependency chain from theory to execution:
   ┌──────────────────────────────────────────────────────────────┐
   │                       VeriSimDB                               │
   │                                                               │
-  │  The database engine. 8 modalities, HEXAD addressing,         │
+  │  Fixed eight-slot Octad; OCTAD source, HEXAD legacy alias.    │
   │  Rust core, Elixir orchestration.                             │
   │                                                               │
   │  Receives: compiled query plans with proof certificates.      │
@@ -314,7 +314,7 @@ performance-critical type checking in the hot path.
   │  ┌──────────────────────────────────────────────────┐   │
   │  │ VeriSimDB Cluster                                │   │
   │  │   ↳ Rust core engine                             │   │
-  │  │   ↳ 8-modality HEXAD storage                     │   │
+  │  │   ↳ Fixed Octad slots; HEXAD is a source alias   │   │
   │  │   ↳ Receives compiled query plans + certificates  │   │
   │  └──────────────────────────────────────────────────┘   │
   └─────────────────────────────────────────────────────────┘
diff --git a/docs/decisions/0.2-AI-MANIFEST.a2ml b/docs/decisions/0.2-AI-MANIFEST.a2ml
index ac26298..25aeb80 100644
--- a/docs/decisions/0.2-AI-MANIFEST.a2ml
+++ b/docs/decisions/0.2-AI-MANIFEST.a2ml
@@ -9,3 +9,7 @@ parent: "../0.1-AI-MANIFEST.a2ml"
 ### [AI_MANIFEST]
 description: |
   Sub-unit of the docs pillar focusing on decisions.
+
+canonical_locations:
+  index: "README.adoc"
+  modality_profiles_octad: "0007-modality-profiles-vs-octad-schema.adoc"
diff --git a/docs/decisions/0007-modality-profiles-vs-octad-schema.adoc b/docs/decisions/0007-modality-profiles-vs-octad-schema.adoc
new file mode 100644
index 0000000..ef38b4f
--- /dev/null
+++ b/docs/decisions/0007-modality-profiles-vs-octad-schema.adoc
@@ -0,0 +1,64 @@
+= Architecture Decision Record: 0007 — Modality Profiles vs the Fixed Octad Schema
+// SPDX-License-Identifier: CC-BY-SA-4.0
+// Copyright (c) 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
+
+Date: 2026-10-05
+
+## Status
+
+Accepted. Normative terminology and compatibility detail:
+[`docs/standards/MODALITY-PROFILES.adoc`](../standards/MODALITY-PROFILES.adoc).
+Tracked by hyperpolymath/vcl-ut#118, aligned with
+hyperpolymath/verisimdb#299.
+
+## Context
+
+“Octad” names VeriSimDB's fixed eight-modality model and `OctadSchema` is a
+concrete eight-slot schema in the VCL-UT type checker and `VCLS` v1 wire
+codec. At the same time, implementations and deployments can support or enable
+different modality subsets. Calling both concepts “the schema” makes a
+capability/configuration choice look like a change to the fixed Octad record
+and risks implying that current VCL-UT transport accepts variable arity.
+
+Actual per-subject witness population is a third concern: an entity may have
+data in only some modalities even though the static schema has a slot for
+each. Empty schema fields do not encode whether a modality is supported or
+populated.
+
+## Decision
+
+- Use **modality profile** for a versioned, implementation-specific selection
+  of modalities supported or enabled at a declared scope.
+- Use **modality set** for membership alone, without implied policy or version.
+- Reserve **Octad** / **`OctadSchema`** for the current fixed eight-modality
+  model and its concrete eight-slot schema.
+- Treat profile membership, field declarations, and per-subject witness
+  population as separate facts.
+- Keep `OctadSchema`, the gate contract, and `VCLS` v1 unchanged. This decision
+  adds no profile type, negotiation, serialization, or variable-arity support.
+- Treat `HEXAD` as a legacy spelling of the Octad source in the current Rust
+  parser, not as a six-modality profile. Retiring that spelling is an
+  independent compatibility decision.
+
+## Consequences
+
+### Positive
+
+- Downstream discussions can describe non-Octad or implementation-specific
+  modality selections without renaming or weakening VCL-UT's fixed schema.
+- Schema, capability, and runtime-presence claims become auditable as separate
+  contracts.
+- Existing `OctadSchema` and `VCLS` v1 consumers retain their exact contract.
+
+### Negative
+
+- A profile cannot yet be passed to or validated by VCL-UT; integrations must
+  not mistake this vocabulary decision for implemented profile support.
+
+### Future work boundary
+
+If profile exchange becomes necessary, define a separate versioned type and
+transport that states scope, catalog, membership/cardinality, omission
+semantics, and the distinction between supported, enabled, and populated
+modalities. Do not encode a profile by omitting slots from `OctadSchema` or by
+reinterpreting the existing schema-version fields.
diff --git a/docs/decisions/README.adoc b/docs/decisions/README.adoc
index a70e749..c205d77 100644
--- a/docs/decisions/README.adoc
+++ b/docs/decisions/README.adoc
@@ -1,4 +1,27 @@
-// SPDX-FileCopyrightText: Copyright (c) 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
+// SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
 // SPDX-License-Identifier: CC-BY-SA-4.0
 
-= decisions Unit
+= Architecture Decisions
+:toc: preamble
+
+Accepted and superseded architecture decisions for VCL-UT. The historical
+architecture ADR index is at
+link:../architecture/DECISIONS.adoc[docs/architecture/DECISIONS.adoc]; ADR-0007
+is cross-indexed there and its full record is stored here.
+
+[cols="1,3,1"]
+|===
+|ADR |Decision |Status
+
+|link:0001-adopt-rsr-standard.adoc[0001]
+|Adopt the Rhodium Standard Repository template
+|Accepted
+
+|link:0002-ffi-attestation-trust-boundary.adoc[0002]
+|Use recomputation-PCC over wasm32 with C-ABI attestation as fallback
+|Accepted
+
+|link:0007-modality-profiles-vs-octad-schema.adoc[0007]
+|Distinguish implementation-specific modality profiles from the fixed Octad schema
+|Accepted
+|===
diff --git a/docs/standards/0.2-AI-MANIFEST.a2ml b/docs/standards/0.2-AI-MANIFEST.a2ml
index c147c6f..d96db7e 100644
--- a/docs/standards/0.2-AI-MANIFEST.a2ml
+++ b/docs/standards/0.2-AI-MANIFEST.a2ml
@@ -8,4 +8,7 @@ parent: "../0.1-AI-MANIFEST.a2ml"
 ---
 ### [AI_MANIFEST]
 description: |
-  Standards unit for high-rigor verification.
+  Standards unit for high-rigor verification and cross-layer contracts.
+
+canonical_locations:
+  modality_profiles: "MODALITY-PROFILES.adoc"
diff --git a/docs/standards/MODALITY-PROFILES.adoc b/docs/standards/MODALITY-PROFILES.adoc
new file mode 100644
index 0000000..0a8d424
--- /dev/null
+++ b/docs/standards/MODALITY-PROFILES.adoc
@@ -0,0 +1,190 @@
+// SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
+// SPDX-License-Identifier: CC-BY-SA-4.0
+
+= Modality Profiles and the Fixed Octad Contract
+Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+:revdate: 2026-10-05
+:toc: preamble
+:icons: font
+
+[.lead]
+This specification separates implementation-specific *modality profiles* from
+VCL-UT's fixed, eight-slot `OctadSchema`. It defines vocabulary and records the
+current contract; it does not add a profile API or change any wire format.
+
+== Status and Scope
+
+This is the accepted terminology clarification for
+https://github.com/hyperpolymath/vcl-ut/issues/118[vcl-ut#118], aligned with
+the related https://github.com/hyperpolymath/verisimdb/issues/299[VeriSimDB
+proposal]. It describes the VCL-UT contract present on 2026-10-05. The
+`OctadSchema` type, gate JSON contract, `VCLS` v1 codec, and accepted statement
+syntax are unchanged.
+
+This document does *not* claim that VCL-UT or VeriSimDB currently negotiates,
+serializes, or validates a modality profile. The profile terms below are
+available for architecture and documentation; a runtime profile contract
+would need its own implementation and versioned interface.
+
+== Terms
+
+Modality::
+A named kind of modal witness. VCL-UT's current Octad catalog is exactly
+Graph, Vector, Tensor, Semantic, Document, Temporal, Provenance, and Spatial.
+
+Modality set::
+A collection whose meaning is only membership: which modality names are in
+that set. The generic term does not impose a fixed cardinality, version, or
+policy. A modality set is not, by itself, a schema or a capability contract.
+
+Modality profile::
+A versioned, implementation-specific selection of modalities that are
+supported or enabled at an explicitly stated scope (for example, an
+implementation, deployment, tenant, or subject). The profile's own contract
+must define its scope, versioning, cardinality/membership representation, and
+the meaning of omitted members (including any required/optional/unsupported
+semantics). The word *profile* alone defines none of those wire-level details.
+
+Octad::
+VCL-UT's specific fixed model with eight named modality slots. An individual
+subject may have witness data in only some of those slots; sparse runtime
+population does not make the Octad structure variable-arity.
+
+`OctadSchema`::
+VCL-UT's static schema value: eight named slot members (graph, vector,
+tensor, semantic, document, temporal, provenance, and spatial), each carrying
+a `ModalitySchema`. It describes declared fields and their types/nullability;
+it is not a modality profile, a per-subject population bitmap, or a record of
+which modalities a deployment supports.
+
+Populated/present modality::
+A statement about whether a subject has actual witness data in a modality at a
+particular point in time. This runtime fact is distinct from profile support,
+from a schema's field declarations, and from the fixed arity of `OctadSchema`.
+
+== Keep Four Questions Separate
+
+[cols="1,2,3"]
+|===
+|Question |Term |What it says
+
+|Which modality names exist in this language's model?
+|Modality catalog
+|VCL-UT's current catalog contains the eight named Octad modalities.
+
+|Which modalities can or will an implementation use?
+|Modality profile / modality set
+|An implementation-specific capability or configuration choice. VCL-UT has
+  no profile object or profile transport today.
+
+|Which fields and field types can the checker resolve?
+|`OctadSchema`
+|The static schema passed to the checker, with a fixed slot for each Octad
+  modality. An empty field list declares no fields for that slot; it does not
+  declare the modality unsupported or physically absent.
+
+|Which witnesses have data for this subject now?
+|Population / presence
+|Runtime state. It is not represented by `OctadSchema` or inferred from an
+  empty field list.
+|===
+
+In particular, *supported*, *enabled*, *schema-described*, and *populated* are
+not synonyms. If an implementation wants to make those states interchangeable,
+its own profile/runtime contract must state and validate that rule.
+
+== VCL-UT Contract Today
+
+=== The schema is exactly eight slots
+
+`src/core/Schema.idr` defines `OctadSchema` as eight named fields, in this
+order: Graph, Vector, Tensor, Semantic, Document, Temporal, Provenance, and
+Spatial. The Rust mirror is `src/interface/parse/src/schema.rs`. There is no
+variable-length modality collection and no profile field in either type.
+
+The binary `VCLS` v1 schema stream carries exactly eight `ModalitySchema`
+payloads in canonical record order, with no modality-count prefix. Its v1
+codec version is not a modality-profile version; it is not a variable-arity
+profile transport. The decoder reads those eight payloads and rejects trailing
+bytes. See
+link:../../src/interface/parse/WIRE-FORMAT.adoc[the wire-format contract].
+
+=== JSON omission does not change the arity
+
+The `vclt-gate` request may omit the top-level `schema`; that path constructs
+an empty `OctadSchema` containing all eight slots. In the JSON `schema` object,
+a modality key may also be omitted; the current parser fills that fixed slot
+with an empty field list. The resulting value is still an eight-slot
+`OctadSchema`.
+
+An omitted key or an empty `fields` array therefore means only that no field
+definitions were supplied for that slot to this checker input. It does *not*
+mean “this deployment does not support the modality,” “this subject has no
+witness here,” or “the profile has fewer modalities.” The gate request's
+`schema_version: 1` versions the gate request contract; it does not identify a
+modality profile. See
+link:../vclt-gate-contract.adoc[the gate contract].
+
+=== `OCTAD` and `HEXAD` are source spellings, not profiles
+
+The current Rust parser accepts `OCTAD` and `HEXAD` in a direct `FROM` source
+and maps both to the same `Source::Octad` value. `HEXAD` is the legacy spelling
+in that parser; it does not mean “select six modalities.” This terminology
+decision does not remove either spelling or define alias support in other
+frontends. Any eventual syntax cleanup is independent of a deployment's
+modality profile and requires its own compatibility decision.
+
+=== Wildcard projection is not a profile
+
+The EBNF describes `SELECT *` as selecting all modalities exposed in the target
+context. That is a statement-projection rule whose available set must be
+defined by the execution context; it does not encode a profile in the
+statement, add/remove `OctadSchema` slots, or change `VCLS` arity.
+
+== Examples
+
+[cols="1,3"]
+|===
+|Situation |Correct reading
+
+|A subject currently has Graph and Document witnesses.
+|Those are two populated modalities in a fixed eight-slot Octad. The statement
+  says nothing by itself about the deployment's profile or the schema arity.
+
+|A deployment-specific profile lists Graph, Vector, and Document.
+|That is a three-member modality set *if and when* a separately specified
+  profile contract defines it. VCL-UT does not currently encode this object in
+  `OctadSchema` or `VCLS` v1.
+
+|The gate input supplies `"graph": {"fields": [...]}` and omits `"spatial"`.
+|The JSON parser materializes both fixed slots; the Spatial slot has an empty
+  field list. This is not a claim that Spatial is unsupported or unpopulated.
+
+|A statement uses `FROM HEXAD id`.
+|In the current Rust parser this is a legacy spelling for the same Octad source
+  as `FROM OCTAD id`; it is not a request for a six-modality profile.
+|===
+
+== Compatibility and Future Profile Work
+
+Keep `OctadSchema` and `VCLS` v1 fixed-arity and unchanged. Do not overload the
+current schema type, gate `schema_version`, or `VCLS` version with profile
+selection or profile versioning.
+
+If a future integration needs profiles on the wire, define a separate,
+explicitly versioned profile type and transport. At minimum, that contract must
+name its scope, identify its supported modality catalog, state membership and
+cardinality unambiguously, define what omission means, and distinguish
+capability from per-subject witness presence. It must not imply that an
+`OctadSchema` decoder accepts arbitrary modality counts. Keep such API/schema
+work separate from this terminology decision and version it according to the
+consumer contract.
+
+== References
+
+* `src/core/Schema.idr` — the dependent `OctadSchema` definition.
+* `src/interface/parse/src/schema.rs` — the Rust mirror.
+* `src/interface/parse/WIRE-FORMAT.adoc` — the exact `VCLS` v1 codec.
+* `docs/vclt-gate-contract.adoc` — the JSON gate input contract.
+* `docs/decisions/0007-modality-profiles-vs-octad-schema.adoc` — the
+  architecture decision that adopts this distinction.
diff --git a/docs/standards/README.adoc b/docs/standards/README.adoc
index 9402c0b..ebe2b04 100644
--- a/docs/standards/README.adoc
+++ b/docs/standards/README.adoc
@@ -2,3 +2,17 @@
 // SPDX-License-Identifier: CC-BY-SA-4.0
 
 = Standards Unit
+:toc: preamble
+
+This unit contains the repository's normative technical and terminology
+contracts.
+
+[cols="2,4"]
+|===
+|Document |Contract
+
+|link:MODALITY-PROFILES.adoc[Modality profiles and the fixed Octad contract]
+|Defines the distinction between implementation-specific modality profiles,
+  runtime witness population, and VCL-UT's fixed eight-slot `OctadSchema` and
+  `VCLS` v1 wire contract.
+|===
diff --git a/docs/vcl-total-grammar.ebnf b/docs/vcl-total-grammar.ebnf
index db43817..8dff96a 100644
--- a/docs/vcl-total-grammar.ebnf
+++ b/docs/vcl-total-grammar.ebnf
@@ -85,7 +85,7 @@ modality_spec = 'GRAPH', [graph_projection]
               | 'TEMPORAL', [temporal_projection]
               | 'PROVENANCE', [provenance_projection]
               | 'SPATIAL', [spatial_projection]
-              | '*' ;  (* All available modalities *)
+              | '*' ;  (* All modalities exposed in the target context; OctadSchema stays 8-slot *)
 
 modality_name = 'GRAPH' | 'VECTOR' | 'TENSOR' | 'SEMANTIC'
               | 'DOCUMENT' | 'TEMPORAL' | 'PROVENANCE' | 'SPATIAL' ;
@@ -105,10 +105,13 @@ spatial_projection   = '(', spatial_fields, ')' ;
    ============================================================================ *)
 from_clause = 'FROM', source_spec ;
 
-source_spec = hexad_source | federation_source | store_source ;
+source_spec = octad_source | federation_source | store_source ;
 
-(* Direct hexad reference *)
-hexad_source = 'HEXAD', uuid ;
+(* Direct reference to one Octad identity; this does not select a modality profile. *)
+octad_source = octad_keyword, (uuid | identifier | string_literal) ;
+
+(* OCTAD is preferred. HEXAD is a legacy alias for the same fixed Octad source. *)
+octad_keyword = 'OCTAD' | 'HEXAD' ;
 
 (* Federation pattern (multiple nodes) *)
 federation_source = 'FEDERATION', node_pattern, [drift_policy] ;
@@ -284,7 +287,7 @@ proof_spec_list = proof_spec, { 'AND', proof_spec } ;
 
 proof_spec = proof_type, '(', contract_name, ')', [proof_params] ;
 
-proof_type = 'EXISTENCE'       (* Hexad exists and is accessible *)
+proof_type = 'EXISTENCE'       (* Octad subject exists and is accessible *)
            | 'CITATION'        (* Citation chain is valid *)
            | 'ACCESS'          (* User has access rights *)
            | 'INTEGRITY'       (* Data has not been tampered with *)
@@ -533,7 +536,7 @@ comment = '--', { ? any character except newline ? }, '\n'  (* Line comment *)
 keywords = 'SELECT' | 'FROM' | 'WHERE' | 'PROOF' | 'LIMIT' | 'OFFSET'
          | 'GRAPH' | 'VECTOR' | 'TENSOR' | 'SEMANTIC' | 'DOCUMENT'
          | 'TEMPORAL' | 'PROVENANCE' | 'SPATIAL'
-         | 'HEXAD' | 'FEDERATION' | 'STORE'
+         | 'OCTAD' | 'HEXAD' | 'FEDERATION' | 'STORE'
          | 'WITH' | 'DRIFT' | 'STRICT' | 'REPAIR' | 'TOLERATE' | 'LATEST'
          | 'AND' | 'OR' | 'NOT'
          | 'SIMILAR' | 'TO' | 'WITHIN' | 'NEAREST' | 'USING'
diff --git a/docs/vclt-gate-contract.adoc b/docs/vclt-gate-contract.adoc
index beca016..c162bc1 100644
--- a/docs/vclt-gate-contract.adoc
+++ b/docs/vclt-gate-contract.adoc
@@ -83,7 +83,7 @@ The gate explicitly does **NOT**:
 ----
 {
   "schema_version": 1,
-  "statement": "ASSERT GRAPH.knows FROM HEXAD 'e-1' WHERE depth < 3 LIMIT 10",
+  "statement": "ASSERT GRAPH.knows FROM OCTAD 'e-1' WHERE depth < 3 LIMIT 10",
   "schema": { "...": "OctadSchema JSON, optional — see §Schema payload" }
 }
 ----
@@ -191,7 +191,20 @@ corpus soundness proof carries through to the gate.
 
 The optional `schema` object mirrors `src/interface/parse/src/schema.rs`
 `OctadSchema` (itself a 1:1 mirror of `src/core/Schema.idr`): the eight
-modality schemas in record order, each a list of field definitions.
+modality schemas in record order, each a list of field definitions. This is a
+fixed eight-slot schema payload, not a modality profile or a variable-length
+selection of modalities.
+
+In this JSON form, individual modality keys are optional. A missing key is
+normalized by the current gate parser to that modality's fixed slot with an
+empty `fields` list. Omitting the entire top-level `schema` constructs an
+empty schema with all eight slots. Empty fields mean “no field declarations
+were supplied here”; they do not mean unsupported, disabled, or unpopulated.
+The request's `schema_version` versions this gate JSON contract, not a
+modality profile. For the fixed `VCLS` v1 binary contract and the profile
+terminology, see
+link:../src/interface/parse/WIRE-FORMAT.adoc[WIRE-FORMAT.adoc] and
+link:standards/MODALITY-PROFILES.adoc[MODALITY-PROFILES.adoc].
 
 [source,json]
 ----
@@ -307,7 +320,7 @@ Request:
 [source,json]
 ----
 { "schema_version": 1,
-  "statement": "INSPECT GRAPH.knows FROM HEXAD 'e-1' WHERE depth < 3 LIMIT 10",
+  "statement": "INSPECT GRAPH.knows FROM OCTAD 'e-1' WHERE depth < 3 LIMIT 10",
   "schema": { "graph": { "fields": [ { "name": "depth", "ty": "TInt", "nullable": false, "indexed": true } ] },
               "vector": {"fields":[]}, "tensor": {"fields":[]}, "semantic": {"fields":[]},
               "document": {"fields":[]}, "temporal": {"fields":[]}, "provenance": {"fields":[]}, "spatial": {"fields":[]} } }
diff --git a/docs/wikis/GLOSSARY.adoc b/docs/wikis/GLOSSARY.adoc
index d7cbece..c61b144 100644
--- a/docs/wikis/GLOSSARY.adoc
+++ b/docs/wikis/GLOSSARY.adoc
@@ -106,9 +106,22 @@ transaction handles.
 == M
 
 Modality (VeriSimDB)::
-One of the 8 views of an entity in VeriSimDB's octad: graph, vector, tensor,
-semantic, document, temporal, provenance, spatial. Each modality stores a
-different representation of the same data.
+A named kind of modal witness. VCL-UT's current Octad catalog has exactly
+eight: graph, vector, tensor, semantic, document, temporal, provenance, and
+spatial. A catalog entry does not by itself say whether a deployment supports
+it or a subject currently has data in it.
+
+Modality profile::
+A versioned, implementation-specific selection of supported or enabled
+modalities at a declared scope. Its own contract must define versioning,
+membership/cardinality, and what omission means. VCL-UT currently has no
+runtime profile type or profile wire format; this term is distinct from
+`OctadSchema`.
+
+Modality set::
+A collection that states modality membership only. The term carries no fixed
+cardinality, version, or capability policy; use *modality profile* when those
+implementation-specific semantics are intended.
 
 Modal type::
 A type that carries information about its context -- for example, whether data
@@ -125,9 +138,15 @@ to prevent silent failures.
 == O
 
 Octad::
-The core data structure in VeriSimDB: a single entity with up to 8 simultaneous
-representations (the 8 modalities). Every entity exists across all populated
-modalities, and VeriSimDB keeps them in sync.
+VeriSimDB's specific fixed model of eight named modality slots. A subject may
+have witness data in only a subset of the slots; sparse runtime population
+does not make the Octad structure variable-arity.
+
+`OctadSchema`::
+VCL-UT's fixed-arity schema value with one `ModalitySchema` for each of the
+eight Octad modalities. It declares fields and their types; it does not encode
+a deployment's modality profile or per-subject witness presence. An empty
+field list is not an unsupported/absent-modality marker.
 
 == P
 
@@ -210,9 +229,10 @@ VCL with all 10 levels of type safety. The subject of this project. If
 successful, it replaces VCL-DT as THE type-safe query path for VeriSimDB.
 
 VeriSimDB::
-A multi-modal database engine where every entity exists across up to 8
-simultaneous representations (the octad), with automatic drift detection and
-self-normalisation.
+A multi-modal database engine whose Octad model names eight modality slots.
+Which slots are supported/enabled and which have witness data for a particular
+subject are distinct implementation and runtime questions; neither changes
+the fixed arity of VCL-UT's `OctadSchema`.
 
 == Z
 
diff --git a/examples/inspect.vcl b/examples/inspect.vcl
index 6185d07..c50f77f 100644
--- a/examples/inspect.vcl
+++ b/examples/inspect.vcl
@@ -5,17 +5,19 @@
 -- VCL statements are propositions and epistemic requests to a consonance
 -- engine, not queries against a passive store (see README.adoc). The
 -- read-style `SELECT ... FROM ...` surface below is the epistemic-inspection
--- convenience; `HEXAD <uuid>` is the legacy keyword naming the octad source
--- (the eight modal witnesses). VCL-total decides admissibility of any
+-- convenience; `OCTAD <uuid>` is the preferred spelling and `HEXAD <uuid>` is
+-- a legacy alias for the same fixed eight-slot Octad source. Neither spelling
+-- selects a modality profile. VCL-total decides admissibility of any
 -- proof-bearing statement before it affects live consonance state.
 
 -- Epistemic inspection: read consonance state across modal witnesses.
-SELECT GRAPH.*, DOCUMENT.*, VECTOR.* FROM HEXAD 'entity-001'
+SELECT GRAPH.*, DOCUMENT.*, VECTOR.* FROM OCTAD 'entity-001'
 
 -- Inspect cross-modal drift between two witnesses.
-SELECT * FROM HEXAD 'entity-001'
+SELECT * FROM OCTAD 'entity-001'
   WHERE DRIFT(VECTOR, DOCUMENT) > 0.3
 
+-- The legacy spelling remains accepted by the current Rust parser.
 -- Proof-bearing statement: VCL-total must discharge the attached obligation
 -- (existence + provenance) before the result is admissible.
 SELECT GRAPH.* FROM HEXAD 'entity-001'
diff --git a/src/core/Grammar.idr b/src/core/Grammar.idr
index 089c9a5..688a5ff 100644
--- a/src/core/Grammar.idr
+++ b/src/core/Grammar.idr
@@ -222,7 +222,7 @@ mutual
   ||| FROM clause source.
   public export
   data Source
-    = SrcOctad String             -- HEXAD <uuid>
+    = SrcOctad String             -- OCTAD <uuid>; HEXAD is a legacy spelling
     | SrcFederation String        -- FEDERATION <pattern>
     | SrcStore String             -- STORE <id>
 
diff --git a/src/core/Schema.idr b/src/core/Schema.idr
index e000c0f..8d31c5d 100644
--- a/src/core/Schema.idr
+++ b/src/core/Schema.idr
@@ -8,6 +8,10 @@
 ||| their types, and nullability — enabling Level 1 (schema binding) and
 ||| Level 3 (null safety) checking at compile time.
 |||
+||| `OctadSchema` is the fixed eight-slot schema, not a modality profile.
+||| Empty fields in a slot do not encode deployment support or per-subject
+||| witness presence. See `docs/standards/MODALITY-PROFILES.adoc`.
+|||
 ||| Key properties proved:
 |||   - Field lookup is total (every reference resolves or fails explicitly)
 |||   - Type assignment is unique (no field has two types)
diff --git a/src/interface/parse/WIRE-FORMAT.adoc b/src/interface/parse/WIRE-FORMAT.adoc
index 3cd6f44..7df8e0f 100644
--- a/src/interface/parse/WIRE-FORMAT.adoc
+++ b/src/interface/parse/WIRE-FORMAT.adoc
@@ -123,7 +123,7 @@ mis-parse:
 
 Header: `56 43 4C 53` ("VCLS") then `u16` version (`01 00` for v1).
 
-Body — `OctadSchema` is the 8 modality schemas in `Grammar.idr`/
+Body — `OctadSchema` is exactly the 8 modality schemas in `Grammar.idr`/
 `Schema.idr` record order (fixed arity, no count):
 
 `ModalitySchema` (graph), `ModalitySchema` (vector),
@@ -136,6 +136,16 @@ otherwise). Same totality contract as the `Statement` decoder;
 `VqlType`'s recursion is fuel-bounded identically (every node ≥ 1
 discriminant byte).
 
+[IMPORTANT]
+====
+This fixed-arity `OctadSchema` stream does not encode a modality profile,
+profile version, selected-subset count, or per-subject witness-presence bit.
+Empty fields inside a slot remain an empty schema for that slot, not a signal
+to omit it. A variable-cardinality modality profile requires a distinct,
+versioned contract; it is not a `VCLS` v1 encoding. See
+link:../../../docs/standards/MODALITY-PROFILES.adoc[the profile/Octad contract].
+====
+
 == Totality contract
 
 The decoder is *total*: bounds-checked, no panics, every malformed
diff --git a/src/interface/parse/src/parser.rs b/src/interface/parse/src/parser.rs
index 0bd1826..38277ce 100644
--- a/src/interface/parse/src/parser.rs
+++ b/src/interface/parse/src/parser.rs
@@ -453,10 +453,13 @@ fn parse_select_item(p: &mut P) -> Result<SelectItem, ParseError> {
     p.err("expected a SELECT item (`*`, MODALITY[.field], or AGG(expr))")
 }
 
+/// Parses a FROM source: `OCTAD <id>`, `HEXAD <id>`,
+/// `FEDERATION <pattern>`, or `STORE <id>`.
+///
+/// `OCTAD` (preferred) and `HEXAD` (legacy alias) name the same
+/// `Source::Octad`; neither spelling selects a modality profile.
+/// Returns a parse error for an unknown source kind or missing identifier.
 fn parse_source(p: &mut P) -> Result<Source, ParseError> {
-    // `OCTAD`/`HEXAD <id>`, `FEDERATION <pattern>`, `STORE <id>`.
-    // OCTAD/HEXAD both accepted (grammar comment vs constructor name
-    // disagree); reconciled with the ReScript bridge in a later slice.
     if p.is_kw("OCTAD") || p.is_kw("HEXAD") {
         p.bump();
         return Ok(Source::Octad(parse_source_arg(p)?));
diff --git a/src/interface/parse/src/schema.rs b/src/interface/parse/src/schema.rs
index 1515967..1969453 100644
--- a/src/interface/parse/src/schema.rs
+++ b/src/interface/parse/src/schema.rs
@@ -56,7 +56,10 @@ pub struct ModalitySchema {
 }
 
 /// `Schema.idr`: `record OctadSchema` — the 8 modality schemas, in
-/// record order (fixed arity; no length prefix on the wire).
+/// record order (fixed arity; no length prefix on the wire). This is a static
+/// schema, not a deployment's modality profile or a per-subject presence map;
+/// an empty field list does not mean that the modality is unsupported or
+/// unpopulated. See `docs/standards/MODALITY-PROFILES.adoc`.
 #[derive(Debug, Clone, PartialEq)]
 pub struct OctadSchema {
     pub graph: ModalitySchema,
diff --git a/src/interface/parse/tests/parse.rs b/src/interface/parse/tests/parse.rs
index abed127..b55a8c0 100644
--- a/src/interface/parse/tests/parse.rs
+++ b/src/interface/parse/tests/parse.rs
@@ -9,7 +9,7 @@
 #![allow(clippy::unwrap_used, clippy::expect_used, clippy::panic)]
 
 use proptest::prelude::*;
-use vcltotal_parse::{parse, parse_op};
+use vcltotal_parse::{ast::Source, parse, parse_op};
 
 proptest! {
     #![proptest_config(ProptestConfig::with_cases(4096))]
@@ -62,6 +62,16 @@ fn known_good_queries_parse() {
     }
 }
 
+/// Verifies that legacy `HEXAD` and preferred `OCTAD` produce the same source.
+#[test]
+fn legacy_hexad_spelling_is_the_same_octad_source() {
+    let preferred = parse("SELECT * FROM OCTAD 'subject-1'").expect("OCTAD source parses");
+    let legacy = parse("SELECT * FROM HEXAD 'subject-1'").expect("legacy HEXAD parses");
+
+    assert_eq!(preferred.source, Source::Octad("subject-1".to_string()));
+    assert_eq!(legacy.source, preferred.source);
+}
+
 // ── Deep nesting must fail-closed (typed error), NOT overflow the stack ──
 // Regression for the adversarial-review finding: the recursive-descent
 // expression grammar (parens, NOT chains, sub-queries) is depth-guarded so
diff --git a/verification/proofs/corpus/VclTotal/Core/Grammar.idr b/verification/proofs/corpus/VclTotal/Core/Grammar.idr
index 089c9a5..688a5ff 100644
--- a/verification/proofs/corpus/VclTotal/Core/Grammar.idr
+++ b/verification/proofs/corpus/VclTotal/Core/Grammar.idr
@@ -222,7 +222,7 @@ mutual
   ||| FROM clause source.
   public export
   data Source
-    = SrcOctad String             -- HEXAD <uuid>
+    = SrcOctad String             -- OCTAD <uuid>; HEXAD is a legacy spelling
     | SrcFederation String        -- FEDERATION <pattern>
     | SrcStore String             -- STORE <id>
 
diff --git a/verification/proofs/corpus/VclTotal/Core/Schema.idr b/verification/proofs/corpus/VclTotal/Core/Schema.idr
index e000c0f..8d31c5d 100644
--- a/verification/proofs/corpus/VclTotal/Core/Schema.idr
+++ b/verification/proofs/corpus/VclTotal/Core/Schema.idr
@@ -8,6 +8,10 @@
 ||| their types, and nullability — enabling Level 1 (schema binding) and
 ||| Level 3 (null safety) checking at compile time.
 |||
+||| `OctadSchema` is the fixed eight-slot schema, not a modality profile.
+||| Empty fields in a slot do not encode deployment support or per-subject
+||| witness presence. See `docs/standards/MODALITY-PROFILES.adoc`.
+|||
 ||| Key properties proved:
 |||   - Field lookup is total (every reference resolves or fails explicitly)
 |||   - Type assignment is unique (no field has two types)