@@ -0,0 +1,162 @@
+from __future__ import annotations
+from dataclasses import dataclass, field
+
+
+VALID_DECISIONS = frozenset({"selected", "rejected", "deferred"})
+
+VALID_STAGES = frozenset({"nomination", "screening", "ranking", "shortlisting"})
+
+
+@dataclass
+class DecisionEntry:
+    candidate_family_id: str
+    decision: str
+    decision_stage: str
+    rationale: str
+    evidence_artifact_ids: list[str]
+    decided_at: str
+
+
+@dataclass
+class SelectionAuditTrail:
+    sat_id: str
+    batch_id: str
+    pipeline_version: str
+    n_entries: int
+    entries: list[DecisionEntry]
+    n_selected: int
+    n_rejected: int
+    n_deferred: int
+    final_shortlist_ids: list[str]
+    dry_lab_only: bool
+    limitations: list[str]
+    created_at: str
+
+
+@dataclass
+class SATValidationResult:
+    valid: bool
+    violations: list[str] = field(default_factory=list)
+
+
+def validate_selection_audit_trail(trail: SelectionAuditTrail) -> SATValidationResult:
+    violations = []
+
+    if not trail.sat_id.startswith("SAT-"):
+        violations.append("sat_id must start with 'SAT-'")
+
+    if not trail.dry_lab_only:
+        violations.append("dry_lab_only must be True")
+
+    if trail.n_entries != len(trail.entries):
+        violations.append(
+            f"n_entries ({trail.n_entries}) must equal len(entries) ({len(trail.entries)})"
+        )
+
+    expected_selected = sum(1 for e in trail.entries if e.decision == "selected")
+    if trail.n_selected != expected_selected:
+        violations.append(
+            f"n_selected ({trail.n_selected}) must equal count of selected entries ({expected_selected})"
+        )
+
+    expected_rejected = sum(1 for e in trail.entries if e.decision == "rejected")
+    if trail.n_rejected != expected_rejected:
+        violations.append(
+            f"n_rejected ({trail.n_rejected}) must equal count of rejected entries ({expected_rejected})"
+        )
+
+    expected_deferred = sum(1 for e in trail.entries if e.decision == "deferred")
+    if trail.n_deferred != expected_deferred:
+        violations.append(
+            f"n_deferred ({trail.n_deferred}) must equal count of deferred entries ({expected_deferred})"
+        )
+
+    expected_shortlist = sorted({e.candidate_family_id for e in trail.entries if e.decision == "selected"})
+    if trail.final_shortlist_ids != expected_shortlist:
+        violations.append(
+            f"final_shortlist_ids {trail.final_shortlist_ids} must equal sorted selected family IDs {expected_shortlist}"
+        )
+
+    for entry in trail.entries:
+        if entry.candidate_family_id.startswith("TOY-"):
+            violations.append(f"TOY- candidate_family_id ('{entry.candidate_family_id}') is not allowed")
+
+        if entry.decision not in VALID_DECISIONS:
+            violations.append(
+                f"decision '{entry.decision}' must be one of {sorted(VALID_DECISIONS)} for {entry.candidate_family_id}"
+            )
+
+        if entry.decision_stage not in VALID_STAGES:
+            violations.append(
+                f"decision_stage '{entry.decision_stage}' must be one of {sorted(VALID_STAGES)} for {entry.candidate_family_id}"
+            )
+
+        if not entry.rationale:
+            violations.append(f"rationale must be non-empty for {entry.candidate_family_id}")
+
+        if entry.evidence_artifact_ids != sorted(entry.evidence_artifact_ids):
+            violations.append(
+                f"evidence_artifact_ids must be sorted for {entry.candidate_family_id}"
+            )
+
+    if not trail.limitations:
+        violations.append("limitations must be non-empty")
+
+    return SATValidationResult(valid=len(violations) == 0, violations=violations)
+
+
+def build_selection_audit_trail(
+    sat_id: str,
+    batch_id: str,
+    pipeline_version: str,
+    decision_dicts: list[dict],
+    limitations: list[str],
+    created_at: str,
+) -> SelectionAuditTrail:
+    entries: list[DecisionEntry] = []
+    for d in decision_dicts:
+        entries.append(
+            DecisionEntry(
+                candidate_family_id=d["candidate_family_id"],
+                decision=d["decision"],
+                decision_stage=d["decision_stage"],
+                rationale=d["rationale"],
+                evidence_artifact_ids=sorted(d.get("evidence_artifact_ids", [])),
+                decided_at=d.get("decided_at", ""),
+            )
+        )
+
+    n_entries = len(entries)
+    n_selected = sum(1 for e in entries if e.decision == "selected")
+    n_rejected = sum(1 for e in entries if e.decision == "rejected")
+    n_deferred = sum(1 for e in entries if e.decision == "deferred")
+    final_shortlist_ids = sorted({e.candidate_family_id for e in entries if e.decision == "selected"})
+
+    return SelectionAuditTrail(
+        sat_id=sat_id,
+        batch_id=batch_id,
+        pipeline_version=pipeline_version,
+        n_entries=n_entries,
+        entries=entries,
+        n_selected=n_selected,
+        n_rejected=n_rejected,
+        n_deferred=n_deferred,
+        final_shortlist_ids=final_shortlist_ids,
+        dry_lab_only=True,
+        limitations=limitations,
+        created_at=created_at,
+    )
+
+
+def format_selection_audit_trail(trail: SelectionAuditTrail) -> str:
+    lines = [
+        f"Selection Audit Trail — {trail.sat_id}",
+        f"Batch: {trail.batch_id}  |  Pipeline: {trail.pipeline_version}",
+        f"Entries: {trail.n_entries}  |  Selected: {trail.n_selected}  |  "
+        f"Rejected: {trail.n_rejected}  |  Deferred: {trail.n_deferred}",
+        f"Final Shortlist ({len(trail.final_shortlist_ids)}): {', '.join(trail.final_shortlist_ids) or '(none)'}",
+        f"Created: {trail.created_at}",
+        f"Limitations: {'; '.join(trail.limitations)}",
+        f"dry_lab_only: {trail.dry_lab_only}",
+    ]
+    return "\n".join(lines)