Replace the static-threshold admissibility gate with a ranked-with-
margin check that is scale-invariant under blade-norm variation.
Phase 4 characterization established no single global threshold
separates the v2 mechanism-isolation cases (blade norms vary ~10x);
margins between top and second-ranked candidates do, because they
scale with the blade norm and carry the relative ordering the
geometry actually delivers.
New primitives in generate/admissibility.py:
RankedCandidate — (index, word, score)
MarginVerdict — admit/reject + top + margin + full ranking
rank_candidates_by_blade — sort admissible set by cga_inner desc,
strict > tie-break by ascending vocab index
check_margin — admit top iff score>0 AND margin>=delta
Selection semantics in margin mode are blade-rank-driven: the top-
ranked admissible candidate IS the admitted destination. Differs
from threshold mode (field-driven _nearest_next then per-candidate
gate). Both modes coexist; threshold is the default and ADR-0024
acceptance evidence is preserved byte-for-byte.
Wired through:
core/config.py admissibility_mode="threshold" (default)
admissibility_margin=0.4
chat/runtime.py forwards both fields
generate/stream.py margin_mode_active branch — ranks the
candidate set once per step, admits or
raises InnerLoopExhaustion with the full
ranking in rejected_attempts
Default delta = 0.4 chosen from the v2 case margins:
V2-001: 0.596 V2-002: 0.456 V2-003: 13.27
V2-004: 3.37 V2-005: 12.74
min = 0.456 → 0.4 admits all 5 with headroom; 0.5 would refuse
V2-002. The default is falsifiable: Phase 5 may surface a case
below 0.4, which should be reported as an architectural finding
rather than patched per-case.
Acceptance evidence (tests/test_margin_admissibility.py, 13 passing):
5/5 v2 cases pass in margin mode; forbidden_token in every
case's rejected_attempts ranking
Refusal-on-insufficient-margin: delta=0.9 on V2-001 (margin
0.597) raises InnerLoopExhaustion with full ranking; no silent
boundary fallback
Threshold mode byte-identical with or without margin plumbing
5 reruns produce identical canonical trace steps
Strict > tie-break: equal scores resolve to lower-index winner
deterministically
Invariants preserved:
versor_condition < 1e-6 — rotor V is constructed only for the
admitted candidate; margin mode adds no normalization/repair site
Deterministic replay — strict > tie-break now load-bearing in
rank_candidates_by_blade alongside vocab.nearest
No approximate recall, no cosine similarity, no HNSW/ANN; pure
rank-and-difference on exact cga_inner scores
No new code in field/propagate.py, algebra/versor.py,
vault/store.py, or chat/runtime.respond()
Suite results:
full: 1037 passed, 2 skipped (+13 new margin tests)
core eval cognition: 13/13, 100% intent_accuracy,
100% versor_closure_rate
ADR-0026 documents the contract, the single-delta rationale, the
falsifiability story, and the residual risks. Margin mode is
flag-gated default-off; a future ADR may promote it to default
after Phase 5's diversified families confirm the single delta
holds (or surface the architectural finding if it doesn't).
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