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+from __future__ import annotations
+from dataclasses import dataclass, field
+from typing import List, Optional
+
+
+VALID_SELECTION_BASES = frozenset({
+    "score_rank",              # selected primarily by pipeline score rank
+    "safety_gate_passed",      # selected because it passed all safety screens
+    "novelty_evidence",        # selected due to novelty evidence (CFC/FNR)
+    "benchmark_performance",   # selected due to benchmark performance vs baselines
+    "expert_review",           # selected following expert human review
+    "calibration_signal",      # selected based on calibration-adjusted confidence
+    "diversity_criteria",      # selected to maximize batch diversity
+    "not_specified",           # selection basis not documented (should be avoided)
+})
+
+VALID_LEDGER_COMPLETENESS_GRADES = frozenset({
+    "complete",       # all expected artifact references are present
+    "partial",        # some expected artifacts are missing but core selection documented
+    "incomplete",     # major artifacts missing; selection not fully traceable
+    "not_assessed",   # completeness not checked
+})
+
+REQUIRED_SELECTION_ARTIFACT_TYPES = frozenset({
+    "BSP",   # batch selection proposal
+    "SEG",   # score vs enemy gap report
+    "SRG",   # scientific review readiness gate
+})
+
+VALID_SELECTION_OUTCOME_TYPES = frozenset({
+    "selected_for_pilot",
+    "selected_for_next_batch",
+    "selected_for_external_review",
+    "deselected_safety",
+    "deselected_low_score",
+    "deselected_insufficient_evidence",
+    "held_pending_review",
+})
+
+
+@dataclass
+class ArtifactReference:
+    artifact_type: str
+    artifact_id: str
+    influence_description: str
+
+
+@dataclass
+class SelectionTransparencyLedger:
+    stl_id: str
+    run_id: str
+    candidate_family_id: str
+    selection_basis: str
+    selection_outcome: str
+    completeness_grade: str
+    artifact_references: List[ArtifactReference]
+    n_artifacts_referenced: int
+    has_required_artifacts: bool
+    missing_required_artifact_types: List[str]
+    seg_id: Optional[str]
+    srg_id: Optional[str]
+    bsp_id: Optional[str]
+    dry_lab_only: bool
+    limitations: str
+    notes: str = ""
+
+
+@dataclass
+class STLValidationResult:
+    valid: bool
+    violations: List[str] = field(default_factory=list)
+
+
+def validate_selection_transparency_ledger(ledger: SelectionTransparencyLedger) -> STLValidationResult:
+    violations = []
+
+    if not ledger.stl_id.startswith("STL-"):
+        violations.append("stl_id must start with 'STL-'")
+
+    if not ledger.run_id:
+        violations.append("run_id is required")
+
+    if not ledger.candidate_family_id:
+        violations.append("candidate_family_id is required")
+
+    if ledger.candidate_family_id.startswith("TOY-"):
+        violations.append("TOY- candidate_family_id is not allowed in real STL- records")
+
+    if ledger.selection_basis not in VALID_SELECTION_BASES:
+        violations.append(
+            f"selection_basis '{ledger.selection_basis}' must be one of {sorted(VALID_SELECTION_BASES)}"
+        )
+
+    if ledger.selection_outcome not in VALID_SELECTION_OUTCOME_TYPES:
+        violations.append(
+            f"selection_outcome '{ledger.selection_outcome}' must be one of {sorted(VALID_SELECTION_OUTCOME_TYPES)}"
+        )
+
+    if ledger.completeness_grade not in VALID_LEDGER_COMPLETENESS_GRADES:
+        violations.append(
+            f"completeness_grade '{ledger.completeness_grade}' must be one of {sorted(VALID_LEDGER_COMPLETENESS_GRADES)}"
+        )
+
+    if ledger.n_artifacts_referenced != len(ledger.artifact_references):
+        violations.append(
+            f"n_artifacts_referenced ({ledger.n_artifacts_referenced}) must match len(artifact_references) ({len(ledger.artifact_references)})"
+        )
+
+    if ledger.n_artifacts_referenced < 1:
+        violations.append("at least one artifact_reference is required")
+
+    # Validate each artifact reference
+    for i, ref in enumerate(ledger.artifact_references):
+        if not ref.artifact_type:
+            violations.append(f"artifact_references[{i}].artifact_type is required")
+        if not ref.artifact_id:
+            violations.append(f"artifact_references[{i}].artifact_id is required")
+        if not ref.influence_description or len(ref.influence_description.strip()) < 5:
+            violations.append(f"artifact_references[{i}].influence_description must be at least 5 chars")
+
+    # Check presence of required artifacts
+    present_types = {ref.artifact_type for ref in ledger.artifact_references}
+    missing = sorted(REQUIRED_SELECTION_ARTIFACT_TYPES - present_types)
+    if sorted(ledger.missing_required_artifact_types) != missing:
+        violations.append(
+            f"missing_required_artifact_types {ledger.missing_required_artifact_types} does not match computed {missing}"
+        )
+
+    expected_has_required = len(missing) == 0
+    if ledger.has_required_artifacts != expected_has_required:
+        violations.append(
+            f"has_required_artifacts ({ledger.has_required_artifacts}) inconsistent with missing types ({missing})"
+        )
+
+    # complete grade requires has_required_artifacts
+    if ledger.completeness_grade == "complete" and not ledger.has_required_artifacts:
+        violations.append(
+            "completeness_grade='complete' requires has_required_artifacts=True"
+        )
+
+    # incomplete grade must not have all required artifacts
+    if ledger.completeness_grade == "incomplete" and ledger.has_required_artifacts and not missing:
+        violations.append(
+            "completeness_grade='incomplete' should not have all required artifacts present"
+        )
+
+    # not_specified selection_basis is a weak signal
+    if ledger.selection_basis == "not_specified":
+        violations.append(
+            "selection_basis='not_specified' is not allowed; document the actual selection basis"
+        )
+
+    # ID field prefix checks
+    if ledger.seg_id is not None and not ledger.seg_id.startswith("SEG-"):
+        violations.append("seg_id must start with 'SEG-' when provided")
+
+    if ledger.srg_id is not None and not ledger.srg_id.startswith("SRG-"):
+        violations.append("srg_id must start with 'SRG-' when provided")
+
+    if ledger.bsp_id is not None and not ledger.bsp_id.startswith("BSP-"):
+        violations.append("bsp_id must start with 'BSP-' when provided")
+
+    if not ledger.dry_lab_only:
+        violations.append("dry_lab_only must be True for STL- records")
+
+    if not ledger.limitations or len(ledger.limitations.strip()) < 10:
+        violations.append("limitations must be a non-empty string (at least 10 characters)")
+
+    return STLValidationResult(valid=len(violations) == 0, violations=violations)
+
+
+def build_selection_transparency_ledger(
+    stl_id: str,
+    run_id: str,
+    candidate_family_id: str,
+    selection_basis: str,
+    selection_outcome: str,
+    artifact_references: List[ArtifactReference],
+    limitations: str,
+    notes: str = "",
+    seg_id: Optional[str] = None,
+    srg_id: Optional[str] = None,
+    bsp_id: Optional[str] = None,
+) -> SelectionTransparencyLedger:
+    present_types = {ref.artifact_type for ref in artifact_references}
+    missing = sorted(REQUIRED_SELECTION_ARTIFACT_TYPES - present_types)
+    has_required = len(missing) == 0
+
+    if has_required and len(artifact_references) >= len(REQUIRED_SELECTION_ARTIFACT_TYPES):
+        completeness_grade = "complete"
+    elif missing and len(missing) < len(REQUIRED_SELECTION_ARTIFACT_TYPES):
+        completeness_grade = "partial"
+    elif not artifact_references:
+        completeness_grade = "incomplete"
+    else:
+        completeness_grade = "partial"
+
+    ledger = SelectionTransparencyLedger(
+        stl_id=stl_id,
+        run_id=run_id,
+        candidate_family_id=candidate_family_id,
+        selection_basis=selection_basis,
+        selection_outcome=selection_outcome,
+        completeness_grade=completeness_grade,
+        artifact_references=artifact_references,
+        n_artifacts_referenced=len(artifact_references),
+        has_required_artifacts=has_required,
+        missing_required_artifact_types=missing,
+        seg_id=seg_id,
+        srg_id=srg_id,
+        bsp_id=bsp_id,
+        dry_lab_only=True,
+        limitations=limitations,
+        notes=notes,
+    )
+    result = validate_selection_transparency_ledger(ledger)
+    if not result.valid:
+        raise ValueError(f"Invalid STL: {result.violations}")
+    return ledger
+
+
+def format_selection_transparency_ledger(ledger: SelectionTransparencyLedger) -> str:
+    lines = [
+        f"Selection Transparency Ledger — {ledger.stl_id}",
+        f"Run: {ledger.run_id}  |  Family: {ledger.candidate_family_id}",
+        f"Selection Basis: {ledger.selection_basis}",
+        f"Outcome: {ledger.selection_outcome}",
+        f"Completeness Grade: {ledger.completeness_grade}",
+        f"Artifacts Referenced: {ledger.n_artifacts_referenced}",
+        f"Required Artifacts Present: {ledger.has_required_artifacts}",
+    ]
+    if ledger.missing_required_artifact_types:
+        lines.append(f"Missing Required: {', '.join(ledger.missing_required_artifact_types)}")
+    for ref in ledger.artifact_references:
+        lines.append(f"  [{ref.artifact_type}] {ref.artifact_id}: {ref.influence_description}")
+    if ledger.seg_id:
+        lines.append(f"SEG Link: {ledger.seg_id}")
+    if ledger.srg_id:
+        lines.append(f"SRG Link: {ledger.srg_id}")
+    if ledger.bsp_id:
+        lines.append(f"BSP Link: {ledger.bsp_id}")
+    lines.append(f"Limitations: {ledger.limitations}")
+    if ledger.notes:
+        lines.append(f"Notes: {ledger.notes}")
+    lines.append("dry_lab_only: True")
+    return "\n".join(lines)