feat(harness): decisions.py ported + decision_retracted for step rollback (D15)

- ported from ChironeWp3 (22 DecisionType, append-only jsonl, monotonic seq)
- added decision_retracted type + retracts field for step-level rollback (D15):
  the retracted decision stays in the audit log, effective_decisions() (Task A5)
  will exclude it from the active view
- 5 tests: retract marker + monotonic seq + retracts default + empty session +
  literal includes retracted. All 13 harness tests pass.

harness/nsp/decisions.py

@@ -0,0 +1,85 @@
+from datetime import UTC, datetime
+from pathlib import Path
+from typing import Literal
+
+from pydantic import BaseModel
+
+DECISIONS_FILE = "review_decisions.jsonl"
+
+# 22 tipi di ChironeWp3 (verified leggendo session/decisions.py) + 1 nuovo (D15):
+# `decision_retracted` per il rollback a granularità step (ritira una decisione
+# senza cancellarne la riga dal log di audit; effective_decisions la onora).
+DecisionType = Literal[
+    "concept_clarified",
+    "question_rewritten",
+    "table_promoted",
+    "table_excluded",
+    "column_corrected",
+    "join_modified",
+    "evidence_accepted",
+    "evidence_rejected",
+    "ambiguity_open",
+    "memory_rejected",
+    "cte_approved",
+    "cte_corrected",
+    "cte_rejected",
+    "sql_revised",
+    "sql_approved",
+    "sql_rejected",
+    "phase_approved",
+    "phase_auto_approved",
+    "phase_reopened",
+    "phase_skipped",
+    "datamart_requested",
+    "datamart_declined",
+    # D15: marker di ritrazione. subject = "phase:N", retracts = decision_seq ritirata.
+    # Resta nel log di audit (append-only); effective_decisions() la esclude dalla vista.
+    "decision_retracted",
+]
+
+
+class DecisionRecord(BaseModel):
+    seq: int
+    ts: datetime
+    type: DecisionType
+    subject: str
+    detail: str = ""
+    rationale: str = ""
+    # D15: se type == "decision_retracted", indica quale seq viene ritirata.
+    retracts: int | None = None
+
+
+def list_decisions(session_dir: Path) -> list[DecisionRecord]:
+    path = session_dir / DECISIONS_FILE
+    if not path.exists():
+        return []
+    return [
+        DecisionRecord.model_validate_json(line)
+        for line in path.read_text().splitlines()
+        if line.strip()
+    ]
+
+
+def append_decision(
+    session_dir: Path,
+    *,
+    type: str,
+    subject: str,
+    detail: str = "",
+    rationale: str = "",
+    retracts: int | None = None,
+) -> DecisionRecord:
+    record = DecisionRecord(
+        seq=len(list_decisions(session_dir)) + 1,
+        ts=datetime.now(UTC),
+        type=type,
+        subject=subject,
+        detail=detail,
+        rationale=rationale,
+        retracts=retracts,
+    )
+    path = session_dir / DECISIONS_FILE
+    path.parent.mkdir(parents=True, exist_ok=True)
+    with path.open("a") as f:
+        f.write(record.model_dump_json() + "\n")
+    return record

harness/tests/test_decisions_retract.py

@@ -0,0 +1,66 @@
+from nsp.decisions import append_decision, list_decisions
+
+
+def test_decision_retracted_in_audit_but_marked(tmp_path):
+    """Una decisione ritirata resta nel log di audit (append-only) ma porta il marker."""
+    session = tmp_path / "s1"
+    session.mkdir()
+    d1 = append_decision(
+        session, type="table_promoted", subject="phase:4", detail="t1", rationale="r"
+    )
+    d2 = append_decision(
+        session,
+        type="decision_retracted",
+        subject="phase:4",
+        detail="wrong answer, retry",
+        rationale="user picked back",
+        retracts=d1.seq,
+    )
+    all_decisions = list_decisions(session)
+    assert len(all_decisions) == 2  # entrambe nel log di audit
+    assert all_decisions[0].seq == 1
+    assert all_decisions[0].type == "table_promoted"
+    assert all_decisions[1].seq == 2
+    assert all_decisions[1].type == "decision_retracted"
+    assert all_decisions[1].retracts == 1  # marker verso la decisione ritirata
+
+
+def test_append_decision_assigns_monotonic_seq(tmp_path):
+    session = tmp_path / "s2"
+    session.mkdir()
+    d1 = append_decision(session, type="phase_approved", subject="phase:1")
+    d2 = append_decision(session, type="phase_approved", subject="phase:2")
+    d3 = append_decision(session, type="question_rewritten", subject="phase:3", detail="new q")
+    assert (d1.seq, d2.seq, d3.seq) == (1, 2, 3)
+    assert d3.detail == "new q"
+    # re-read from disk: seq preserved
+    loaded = list_decisions(session)
+    assert [d.seq for d in loaded] == [1, 2, 3]
+
+
+def test_retracts_defaults_none(tmp_path):
+    """Le decisioni normali hanno retracts=None (non serializzato come null rumoroso)."""
+    session = tmp_path / "s3"
+    session.mkdir()
+    d = append_decision(session, type="concept_clarified", subject="phase:1", detail="x")
+    assert d.retracts is None
+    # round-trip via JSON
+    loaded = list_decisions(session)
+    assert loaded[0].retracts is None
+
+
+def test_empty_session_returns_empty_list(tmp_path):
+    session = tmp_path / "empty"
+    session.mkdir()
+    assert list_decisions(session) == []
+
+
+def test_decision_type_literal_includes_retracted():
+    """decision_retracted e' un tipo valido (pydantic lo accetta)."""
+    from nsp.decisions import DecisionRecord
+    from datetime import datetime, UTC
+    d = DecisionRecord(
+        seq=1, ts=datetime.now(UTC), type="decision_retracted",
+        subject="phase:4", retracts=1,
+    )
+    assert d.type == "decision_retracted"