A2 of the refined sequencing. Proves (deterministically, not by assertion) what a
long-running CORE life costs to persist per turn on a constrained offline device.
Measures the Shape B+ checkpoint BYTES per turn (session_state.json) over the real
turn loop — bytes, not wall-clock latency (machine-dependent → flaky). Reuses the L10
continuity corpus.
Measured cliff: save_session_state re-serializes the FULL snapshot every turn, so
per-turn bytes are O(n) in the accumulated life — 3,811 → 88,189 bytes (23x) over 24
turns, ~1.3KB/vault-entry re-written every turn. That blocks continuous-life at the edge.
The gate encodes the edge REQUIREMENT (≤16 KiB/turn regardless of session length) as
xfail(strict): it fails today (documenting the cliff), runs green in CI, and flips to
a hard failure the moment incremental/append-only persistence (O(Δ)/turn) lands —
forcing us to retire it. Plus a regression ceiling (passes today) and a determinism
check (the byte metric is reproducible → a valid gate).
The fix is algorithmic (incremental persistence, Python/Ring-2), NOT a language
rewrite. Tagged core/array_codec.py as the locked reference contract for a future
gated Ring-1 Zig byte-exact codec (ADR-0196 G0-G8) — step 3, only after the O(Δ) fix
and only if this gate proves the codec is still the bottleneck. See contract.md.
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