Technical Memo · June 2026

# Bounded Execution Substrate for Frontier Agents

Thesis

Current safety wrappers for frontier agents place stochastic controls in front of stochastic executors. CORE proposes a bounded execution substrate in which the neural model is reduced to schema induction — a System 1 sensory and translation layer — and all operational agency is relocated into a deterministic state machine whose admissible transition set is defined by first-class domain constraints, not by language classifiers.

The model proposes. The substrate decides.

From AssetOverflow / CORE
Date June 2026
Repo github.com/AssetOverflow/core
Status CI-gated · Public
§ 0

## Context: The Fable 5 Release Signal

On June 9, 2026, Anthropic publicly released Claude Fable 5 — a Mythos-class model — alongside an unusually candid public warning about the risks of increasingly capable AI. The simultaneous release and warning is not a contradiction; it is a product surface problem made legible.

Public behavior and the Fable 5 system card indicate that requests touching high-risk domains — cybersecurity, certain biology workflows, and adjacent surfaces — trigger classifier-driven blocking or fallback to Opus 4.8. This is intentional design: strong guardrails layered on top of strong capability. This memo argues the layering itself is the bottleneck, and that there is an architectural alternative worth examining.

Scope

For long-horizon agentic workflows — the domain Fable 5 is explicitly positioned for — the primitive choice between classifier walls and bounded substrates determines how reliability degrades with task length. That is the specific engineering problem this memo addresses.

§ 1

## The Primitive Problem

The core issue is not where the safety threshold is set — it is the nature of the primitive being used to enforce it. Classifier walls and bounded substrates answer fundamentally different questions:

Classifier Wall
"Does this text look risky?"
Stochastic. Surface-sensitive. False-positive rate is non-zero and independent of actual operational risk. Cannot distinguish between a legitimate network diagnostic and an attack — both look the same to a language classifier.
Bounded Substrate
"Does this state transition satisfy the domain guard?"
Deterministic. Semantics-sensitive. For a correctly specified Anchor domain model, false-positive rate is structurally zero for in-domain requests: admissible transitions are algebraically reachable; inadmissible transitions are algebraically unreachable — not statistically suppressed.

For a single-turn assistant this distinction is manageable. For long-horizon agents it compounds: each false-positive refusal interrupts a stateful workflow whose accumulated context is not recoverable from the refusal event. The reliability degradation is superlinear in task length.

Root Cause

A model asked to simultaneously parse intent, reason over state, and self-police execution is being asked to do three things in one stochastic pass. Each function degrades the others. The present architecture resolves this by adding more classifiers. CORE resolves it by separating the concerns at the architectural level.

Key Claim

The bottleneck is not only model capability. It is the placement of execution authority inside the same stochastic layer that must also be safety-constrained.

§ 2

## The CORE Architecture

CORE implements the System 1 / System 2 split at the architectural level, not the prompt level. In Hybrid Mode, a Claude/Fable model acts as System 1: it parses intent and proposes a structured payload. CORE acts as System 2: it verifies, refuses, asks, or executes — deterministically, with replayable traces. The neural model never touches execution.

Bounded Transition Guarantee (v2.1)

Given a correctly specified Anchor domain model, CORE can only execute transitions admitted by typed guards under the current state. The model proposes; the substrate decides. This is not a prompt-level constraint — the model's output is structurally typed through the Lens before it reaches any execution surface.

Anchor
domain model
First-class domain constraints
The Anchor holds the ratified domain model: typed state, admissible transitions, guard predicates, and an `AuthorityToken` over each ratified transition. It is the only layer that can authorize execution. What counts as admissible is a policy question requiring human ratification per domain — the architecture enforces the boundary; humans define it.

- State is a CGA versor field over Cl(4,1)
- Guard predicates are pure functions of (state, payload) → bool
- Illegal states are geometrically unreachable, not monitored

Lens
schema gate
Type-Safe Local Closure — projection and structural typing
The Lens maps model output to a typed payload schema via the Type-Safe Local Closure security model: execution logic and sensitive targets live inside local closures that only typed payloads can reach. If the output does not project to a valid schema, no payload is produced and no transition fires. There is no natural-language shortcut through the gate.

- Model output → TypedPayload or ∅
- No untyped strings reach the execution surface
- Surface area for harm is bounded upstream of execution

Substrate
DFA executor
Deterministic finite automaton
The Substrate is the execution engine. It receives a typed payload from the Lens, evaluates the guard predicate against current state, and — only if the guard passes — fires the transition and records a SHA-256 trace hash. Every trace is deterministic and fully reproducible.

- Model proposes; only the Substrate can enact
- Every transition produces a deterministic, reproducible audit trace
- No stochastic path to side effects outside the admissible transition system

§ 3

## Formal Structure

The execution substrate is a deterministic finite automaton. The neural model is an inductive proposer. The Lens is a projection-and-filter. State transitions require both a valid typed payload and a passing guard predicate:

Transition Function
`δ(qₜ, σ) = qₜ₊₁ iff Lens(output) = σ ≠ ∅ ∧ G(qₜ, σ) = true` `where G : Q × Σ → bool is a pure deterministic predicate`
Lens Projection
`Lens : string → TypedPayload ∪ {∅}` `If Lens(output) = ∅, no transition fires. Period.`

Where `G(qₜ, σ)` is a pure function from current state and proposed payload to `bool`, evaluated deterministically over the Anchor's domain model. The stochastic model has no direct path to side effects outside this admissible transition system.

§ 4

## Concrete Example: Network Diagnostics

A user requests a network diagnostics workflow in a sensitive domain. The workflow is legitimate, operationally authorized, and benign — but its language surface resembles restricted content.

Scenario | Classifier-first (Fable behavior) | CORE bounded substrate
--- | --- | ---
Request | `"Run a ping sweep and port probe against lab subnet 10.0.1.0/24 to map active hosts before the vulnerability scan."`
Safety evaluation | Language surface matches patterns associated with offensive reconnaissance. Classifier fires. Refusal or fallback to Opus 4.8. | Lens maps to typed payload: `{op:"network_probe", subnet:"10.0.1.0/24", scope:"lab"}`. Guard checks: is `network_probe` admissible? Is `lab` scope within licensed subnets?
Benign outcome | Refusal. Workflow interrupted. Accumulated session context not recoverable. False positive independent of actual risk. | Guard passes. Substrate executes. Workflow continues. Trace hash recorded. Zero false positives from surface-level similarity.
Harmful variant | May or may not block — depends on linguistic surface shift, not on whether the action is admissible within licensed scope. | Guard fails: target subnet outside licensed scope. State remains at qₜ. Transition structurally impossible. What counts as "licensed" scope is a ratified human policy decision encoded in the Anchor — the architecture enforces it; a human defined it.
Audit trail | Classifier decision; opaque to the downstream workflow. | Deterministic trace hash. Guard decision is a pure function of (qₜ, Σ) — fully reproducible and inspectable.

§ 5

## Implementation Signals

CORE is not a research proposal. The substrate is implemented, CI-gated, and has mechanically verified capability claims. Two signals worth examining:

Signal 1 · Cognitive Spine

The cognitive spine (`CognitiveTurnPipeline`) executes the full `listen → ingest → understand → recall → think → articulate → learn_proposal → trace` sequence deterministically. Every turn produces a SHA-256 trace hash. The `UnknownDomainGate` fires before any reasoning path for out-of-domain inputs — returning a deterministic stub, not a stochastic fallback. The same Type-Safe Local Closure security model governs these gates: execution logic and sensitive targets live inside local closures that only typed payloads can reach.

Signal 2 · GSM8K Math Gate — Bounded Transition Guarantee in practice

The GSM8K math verification gate (`generate/derivation/verify.py`) evaluates grounding ∧ cue ∧ unit ∧ completeness ∧ uniqueness as typed structural predicates — not "does this look like a correct answer." Current result: 7 correct / 43 refused / 0 wrong. The zero-wrong count is a direct downstream consequence of the Bounded Transition Guarantee — not of tuning or sampling. Inadmissible answers are structurally unreachable, not probabilistically suppressed.

CI Verification — Bounded Transition Guarantee at scale

Domain capability is ratified and CI-pinned. Five domains currently hold ratified status; nine eval lanes have SHA-256 pinned reports where any regression breaks the build. The deductive logic lane reports 716/716 correct, wrong=0, refused=0. These numbers are a direct downstream consequence of the Bounded Transition Guarantee — not of tuning or sampling.

§ 6

## Honest Limits

CORE is not a frontier model and does not claim to be. It is a substrate architecture — a demonstration that the bounded execution pattern is implementable, testable, and verifiable at non-trivial domain coverage.

- Integrating with a Mythos-class model is an open engineering question, not a solved one
- Domain coverage is non-trivial but not exhaustive — five ratified domains, ongoing expansion
- The CGA field algebra Cl(4,1) provides formal coherence guarantees within-domain; cross-domain composition is an active research area
- The substrate enforces admissibility; what counts as admissible is a policy question that requires human ratification per domain
- In governance terms, the present work concerns Hybrid Mode — CORE as a deterministic System 2 substrate for Claude-class agents. The Native Mode thesis (LLM-free, edge-native cognitive execution) remains a long-term research trajectory

§ 7

## The Ask — Hybrid Mode Wedge

If the architectural contrast in §2 resonates — if "does this state transition satisfy the domain guard?" is a more useful safety primitive than "does this text look risky?" for the agentic systems you are building — the question worth a short conversation is this:

Can CORE slot in front of Claude/Fable as a deterministic System 2 verifier substrate through an MCP-shaped interface — and what does that change about refusal quality, trace quality, and operator trust for high-risk tool-use?

This is a narrow, testable experiment with minimal surface area: Claude/Fable acts as System 1 semantic proposer; CORE acts as System 2 bounded executor; deterministic answer/refusal/ask behavior and replayable trace artifacts feed back into safety evaluation. No NDA. No adoption commitment. A bounded technical sanity check on whether the substrate approach is complementary to or in tension with Anthropic's internal agent architecture.

The full implementation is public at github.com/AssetOverflow/core →

Appendix — Optional Deep Dive · Algebraic Foundations

The following section is for readers interested in the formal underpinning. Not required to evaluate the architectural argument above.

### A.1 · CGA Field Structure

CORE's field is built over Cl(4,1) Conformal Geometric Algebra. Every element of state is a versor; every transition is a versor sandwich product `V * F * reverse(V)`. The core field invariant is `versor_condition(F) < 1e-6` — enforced at all times by algebra, not monitoring.

This is the formal basis for "coherence by construction": illegal field states are not detected and corrected, they are geometrically unreachable. Forbidden normalization sites (e.g., `generate/stream.py`, `field/propagate.py`) are enforced by architectural rule, not convention.

### A.2 · Ratification Protocol

Domain capability enters the system through a ratification protocol, not through training or prompt injection. Each domain requires:

- A typed schema definition for all admissible operations
- A guard predicate implementation with deterministic test coverage
- A CI-pinned SHA-256 eval report demonstrating zero wrong-answer rate
- An explicit AuthorityToken binding the domain to the Anchor

### A.3 · Current Ratified Domains

- Deductive logic — 716/716 correct, wrong=0, refused=0
- Mathematical derivation (GSM8K subset) — 7 correct / 43 refused / 0 wrong
- Network diagnostics (lab-scoped)
- Structured document generation
- Code generation (sandboxed execution surface)