fix(evidence): preserve legacy formula migration boundaries

harness/tht/evidence/session.py

@@ -64,11 +64,17 @@ def _formula_proposals(decisions: list["DecisionRecord"], linking: "SchemaLinkin
     A proposal remains in the persisted session artifact until a separate curator
     imports, reviews, and publishes it in the workspace repository.
     """
-    approved = {
-        decision.detail: decision.seq
+    retracted = {
+        decision.retracts
         for decision in decisions
-        if decision.type == "concept_formula_approved" and decision.detail
+        if decision.type == "decision_retracted" and decision.retracts is not None
     }
+    latest_f4_decision = {}
+    for decision in sorted(decisions, key=lambda item: item.seq):
+        if decision.seq in retracted or decision.subject != "phase:4" or not decision.detail:
+            continue
+        if decision.type in {"concept_formula_approved", "concept_formula_rejected"}:
+            latest_f4_decision[decision.detail] = decision
     proposals = []
     for formula in linking.concept_formulas:
         if not isinstance(formula, dict):
@@ -83,6 +89,9 @@ def _formula_proposals(decisions: list["DecisionRecord"], linking: "SchemaLinkin
         evidence_id = formula.get("evidence_id", formula.get("id", ""))
         if isinstance(evidence_id, str) and evidence_id.startswith("evidence:"):
             continue
+        decision = latest_f4_decision.get(concept)
+        if decision is None or decision.type != "concept_formula_approved":
+            continue
         proposals.append({
             "schema_version": 1,
             "kind": "formula_proposal",
@@ -91,7 +100,7 @@ def _formula_proposals(decisions: list["DecisionRecord"], linking: "SchemaLinkin
             "columns": columns,
             "sql": sql,
             "sources": formula.get("sources", []),
-            "decision_seq": approved.get(concept),
+            "decision_seq": decision.seq,
         })
     return proposals