T81 Foundation

Determinism Surface Registry

1. Purpose

Define what is and is not guaranteed to be deterministic in the T81 system.

Clarify that determinism guarantees apply only to explicitly verified surfaces.

Threat modeling for these surfaces is documented in DETERMINISM_THREAT_MODEL.md.

Reference:

• spec/supplemental/deterministic-core-profile-v1.md (Core Definitions)
• docs/governance/FREEZE_ENFORCEMENT.md (Break Protocols)
• docs/governance/SPEC_AUTHORITY_MODEL.md (Hierarchy)
• docs/status/VERIFIED_SURFACE_AUDIT.md (Traceability Audit)
• docs/guides/jit-equivalence-plan.md (Future Roadmap)

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2. Definition of a Determinism Surface

A determinism surface is:

A subsystem boundary for which identical input and configuration must produce bit-identical output across supported architectures. “Supported architectures” are defined by the platforms listed in the root README under Compatibility for the current major version.

Clarify:

• Surfaces must have explicit verification.
• Surfaces without verification are not guaranteed.

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3. Verified Determinism Surfaces

Surface	Scope	Guarantee	Verification Mechanism	CI Enforced	Status
TISC Opcode Semantics	Instruction Behavior	Bit-Exact	tests/cpp/vm_determinism_property_test.cpp tests/cpp/test_tritwise_backend_equivalence.cpp	Yes (ci.yml)	Verified
VM Interpreter Execution	Dispatch Loop	Bit-Exact	tests/cpp/vm_trace_test.cpp tests/cpp/vm_determinism_property_test.cpp	Yes (ci.yml)	Verified
Data Type Canonical Encoding	Binary Format (Trit/Tryte)	Bit-Exact	tests/cpp/v1_canonical_numeric_contract_test.cpp tests/cpp/tisc_binary_io_determinism_test.cpp	Yes (ci.yml)	Verified
Soft-Float Deterministic Math	T81Float Operations	Strict Rounding	tests/cpp/test_T81Float_arithmetic.cpp tests/cpp/test_T81Float_rounding.cpp	Yes (ci.yml)	Verified
Compiler Bytecode Emission	T81Lang to TISC	Bit-Exact (Fixtures)	scripts/ci/t81lang_repro_gate.py	Yes (repro-ledger.yml)	Partial
T3K Quantization	GGUF Encoding	Bit-Exact	scripts/ci/t3k_repro_gate.py	Yes (repro-ledger.yml)	Verified

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4. Non-Deterministic or Undefined Surfaces

Explicitly list areas that are:

• Experimental
• Not yet verified
• Outside determinism scope

Excluded / Out of Scope:

• Real-time Scheduling: Execution timing is platform-dependent.
• Network IO: Network latency and packet ordering are not deterministic.
• Hardware FPU: Native hardware floating-point behavior (outside of T81Float soft-float wrappers) is not guaranteed.
• Performance Determinism: Runtime latency is not guaranteed to be constant.

Experimental / Planned:

• Distributed Cognitive Tiers (experimental/tiers/, experimental/distributed/): Consensus determinism is planned but not verified.
• JIT Optimizations: Trace-JIT equivalence is planned but currently stubbed.
• External Hardware Accelerators: Behavior on non-CPU devices is currently undefined.

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5. Verification Map

Surface	Test Path	CI Job	Repro Script
TISC Execution	tests/cpp/vm_determinism_property_test.cpp	ci.yml	N/A
Tritwise Ops	tests/cpp/test_tritwise_backend_equivalence.cpp	ci.yml	N/A
Compiler Repro	tests/fixtures/t81lang_determinism/*.t81	repro-ledger.yml	scripts/ci/t81lang_repro_gate.py
Quantization	N/A	repro-ledger.yml	scripts/ci/t3k_repro_gate.py

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6. Breach Handling Reference

Reference:

• docs/governance/FREEZE_ENFORCEMENT.md

State:

A regression on a verified surface is classified as a critical defect and must not be merged unresolved.

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7. Scope Boundaries

Clarify:

Determinism does NOT mean:

• Real-time scheduling guarantees
• Network determinism
• Performance determinism
• Hardware FPU determinism (outside soft-float)

This prevents overclaim drift.

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