TAS-154: Minimal universal substrate acceptance gate

[AtlantisPleb]

Summary

Public Tassadar needs minimal universal substrate acceptance gate so the executor lane can widen honestly without collapsing profile boundaries, portability, or refusal posture.

Roadmap position

• Tranche: Tranche M | Universal-computation closeout
• Strategic phase: Phase 11 terminal closeout
• Tranche goal: Make Turing-complete support a benchmarked, challengeable terminal contract.
• Why this tranche exists: This is the theorem-to-product bridge that turns the universality path into an explicit end-state contract.
• Dependency context: Sequences after TAS-153 inside Tranche M and still depends on the landed baseline through TAS-102.

Problem

There is still no single gate that says the system now has the ingredients required for universal computation.

Hypothesis

A gate over conditional control, mutable memory, spill/tape extension, persistent continuation, machine-step replay, witness workloads, portability, and refusal truth will make Turing-complete support auditable.

Public source anchors

• docs/TASSADAR_WASM_RUNBOOK.md
• docs/ROADMAP_TASSADAR.md
• docs/ARCHITECTURE.md

Target surfaces

• psionic-eval
• psionic-provider
• psionic-runtime
• scripts/

Claim class

• promotion discipline / execution truth

Initial scope

• implement the smallest honest subsystem changes across psionic-eval, psionic-provider, psionic-runtime, scripts/ that close the named gap
• add deterministic fixtures, receipts, reports, or capability rows that make the new posture machine-legible
• update public docs and capability language only where the new bounded surface is actually supported
• keep unsupported shapes on explicit typed refusal paths rather than widening implicitly
• make the terminal claim refer to one declared substrate and explicit witnesses, not to broad or rhetorical universality language

Validation and benchmark expectations

• gate checker
• missing-prerequisite negative tests
• and green publication only when every universality witness and substrate requirement passes
• add negative coverage for unsupported or out-of-profile behavior
• update any machine-readable receipt, report, capability row, or acceptance artifact touched by this lane

Claim-discipline requirements

• keep the capability bounded to named profiles or declared semantic windows
• do not let this issue imply arbitrary Wasm, broad internal compute, or broader served posture unless an explicit promotion gate is part of the task
• preserve explicit refusal reasons for unsupported module shapes, effects, portability envelopes, or semantic families
• keep theory-green, operator-green, and served-green verdicts separate; no terminal claim should silently widen public posture

Done when

• the named surfaces land with deterministic tests, fixtures, or reports that exercise the new bounded capability
• public docs reflect the new capability, limit, or refusal posture in bounded language
• the claim remains benchmarked or promoted only at the level explicitly supported by the landed evidence
• the corresponding acceptance, publication, or verdict gate is green on positives and suppresses unsupported cases on negatives

Status

• seeded