feat(detection-core): anti-shortcut probes and fitted-component admission gate

src/openultrasast/core/__init__.py

@@ -4,31 +4,55 @@ Owns contracts only -- no analysis logic. Arms implement the trace contract;
 runners and consumers adopt coverage, budget, provenance, and admission contracts.
 """
 
+from openultrasast.core.admission import (
+    REPORT_SCHEMA_KEYS,
+    AdmissionManifest,
+    AdmissionManifestError,
+    validate_admission_manifest,
+)
 from openultrasast.core.budget import Budget, BudgetGateFailure, Complexity, check_budget, derive_budget
 from openultrasast.core.coverage import Coverage, InstrumentFailure, ResolutionOutcome, check_reads
+from openultrasast.core.probes import (
+    FittedComponentBlocked,
+    ProbeResult,
+    ShortcutDetected,
+    assert_no_shortcut,
+    require_admission_evidence,
+    reversed_pair_probe,
+)
 from openultrasast.core.provenance import ProvenanceMismatch, stamp, verify_stamp
 from openultrasast.core.trace import Guard, Hop, TraceRecord, Witness
 from openultrasast.core.verdict import BoundedSilence, Judgment, ProvenClaim, as_clean
 
 __all__ = [
+    "REPORT_SCHEMA_KEYS",
+    "AdmissionManifest",
+    "AdmissionManifestError",
     "BoundedSilence",
     "Budget",
     "BudgetGateFailure",
     "Complexity",
     "Coverage",
+    "FittedComponentBlocked",
     "Guard",
     "Hop",
     "InstrumentFailure",
     "Judgment",
+    "ProbeResult",
     "ProvenClaim",
     "ProvenanceMismatch",
     "ResolutionOutcome",
+    "ShortcutDetected",
     "TraceRecord",
     "Witness",
     "as_clean",
+    "assert_no_shortcut",
     "check_budget",
     "check_reads",
     "derive_budget",
+    "require_admission_evidence",
+    "reversed_pair_probe",
     "stamp",
+    "validate_admission_manifest",
     "verify_stamp",
 ]

src/openultrasast/core/probes.py

@@ -0,0 +1,67 @@
+"""Anti-shortcut probes for fitted components (Req 8, 9).
+
+A fitted prompt, threshold, or model must not separate a fix from its reversed fix
+using shape features (diff size, deletion count, line counts): that is pool-specific
+shortcut learning, the 2026-10-14 deletion-count 0.90 finding. A component making any
+detection claim must also carry per-repository holdout evidence and a GO admission on
+an untouched population.
+"""
+
+from __future__ import annotations
+
+from collections.abc import Callable, Mapping
+from dataclasses import dataclass
+from typing import Any
+
+
+class ShortcutDetected(ValueError):
+    """A component separates a fix from its reversed fix by its decision features."""
+
+
+class FittedComponentBlocked(ValueError):
+    """A fitted component claims detection without holdout + admission evidence."""
+
+
+@dataclass(frozen=True)
+class ProbeResult:
+    """Outcome of one reversed-pair probe."""
+
+    separated: bool
+    fix_score: float
+    reversed_score: float
+
+
+def reversed_pair_probe(
+    score_fn: Callable[[Mapping[str, Any]], float], fix_change: Mapping[str, Any], reversed_change: Mapping[str, Any]
+) -> ProbeResult:
+    """Score a fix and its reversed fix; separated=True means the features shortcut."""
+    fix_score = float(score_fn(fix_change))
+    reversed_score = float(score_fn(reversed_change))
+    return ProbeResult(separated=fix_score != reversed_score, fix_score=fix_score, reversed_score=reversed_score)
+
+
+def assert_no_shortcut(
+    score_fn: Callable[[Mapping[str, Any]], float], fix_change: Mapping[str, Any], reversed_change: Mapping[str, Any]
+) -> None:
+    """Raise ShortcutDetected when the component separates fix from reversed fix."""
+    result = reversed_pair_probe(score_fn, fix_change, reversed_change)
+    if result.separated:
+        raise ShortcutDetected(f"shape shortcut: fix={result.fix_score} vs reversed={result.reversed_score}")
+
+
+def require_admission_evidence(*, holdout_passed: bool, admission_decision: str) -> None:
+    """Block any fitted-component claim without holdout and an admission GO (Req 8.2)."""
+    if not holdout_passed:
+        raise FittedComponentBlocked("fitted component lacks per-repository holdout evidence")
+    if admission_decision != "GO":
+        raise FittedComponentBlocked(f"fitted component admission decision is {admission_decision!r}, not GO")
+
+
+__all__ = [
+    "FittedComponentBlocked",
+    "ProbeResult",
+    "ShortcutDetected",
+    "assert_no_shortcut",
+    "require_admission_evidence",
+    "reversed_pair_probe",
+]