docs(feasibility): standing feasibility assessment + seam-class/evidence-tier regularity matrix

[arena-ai-coding-agent]

What

A recon-level feasibility assessment of the -iser family, written as a standing policy document rather than a one-off review:

• docs/FEASIBILITY.adoc — the assessment itself: what the project is trying to achieve (product / thesis / estate, assessed separately), the overall verdict, the seam classification, evidence tiers, the language bar, per-language verdicts, and the recommended shape.
• docs/feasibility-matrix.toml — machine-readable form: all 29 -isers classified by seam class (6 injector / 14 service / 9 scaffolder), evidence tier (T0–T3), and language level (L0–L3, estate languages), each with a grounded note.
• README.adoc / docs/ATLAS.adoc — pointers to the assessment, and a re-scoped statement of the family promise.

Why

The headline promise ("superpowers … without you ever learning those languages", a "formally verified" ABI for 28 runtimes, aspects that "compose … without knowing about each other") is infeasible as stated for structural reasons — semantic guarantees do not cross C ABIs, manifests conserve rather than abolish the learning curve, runtimes each assume they own the process, and a 28-language proof programme is CompCert-scale per language.

The re-scoped programme — verified binding generators + foreign-runtime services + pattern scaffolders, each claiming only what crosses its seam — is feasible, has deep prior art, and is already partly demonstrated in-estate: chapeliser's Provable lane is green on main (Idris2 proofs check, Zig FFI tests, golden codegen, generated Chapel compiled and run by chpl in CI), and abi-emit-manifest/abi-verify is a genuinely reusable drift gate.

The regularity introduced (the point of the PR)

• Seam classification — injector / service / scaffolder; an -iser may claim only what its seam carries. Class is a property of the semantics, not of ambition.
• Evidence tiers T0–T3 — claims may not outrun what CI machine-checks; chapeliser's Provable lane is the family template.
• Language bar L0–L3 — an -iser over an estate language below L2 (ABI-stable) is labelled experimental; the -iser's spec-forcing role is named, not hidden.
• Claim hygiene — precise wording rules for "formally verified", "without learning", "provably safe ethical constraints", etc.
• One-flagship concentration — chapeliser + futharkiser + one estate-language flagship to Tier 3; the rest to maintenance.

Notable per-language verdicts (focused set)

-iser	Verdict	One-line core issue
a2mliser	feasible, HIGH	canonicalisation of TOML/YAML is the hard core; key distribution is the product problem
k9iser	feasible, HIGH	needs a real grammar (build on Nickel?); mined contracts must be schemas/ranges, not frozen literals
eclexiaiser	feasible, MEDIUM	typed units cross the seam; runtime budgets can only guard/report, never prove
chapeliser	feasible, HIGH	flagship; green end-to-end Provable lane; ≥2-node multilocale is the frontier
futharkiser	feasible, HIGH	easiest true T2→T3 win; needs a CI lane that installs the futhark compiler
Idris2-as-ABI	feasible if right-scoped	invest in seam-contract authority + drift gate; cross-runtime marshalling proofs are infeasible

Notes for reviewers

• No code changes; docs + one TOML matrix only.
• The matrix is deliberately opinionated — it is meant to be argued with, then maintained as the standing record.
• Evidence used: iseriser HEAD 6397682, both satellites, sibling -iser repos (sizes/CI/stars), chapeliser's green Provable lane, and the language repos (eclexia, a2ml, phronesis, …).

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