feat(harness): persist CTE preview rows, add tht cte info, --doc for cte plan

WS1 of review-gates-v2: gives the JS gate (WS2) deterministic data to build the
cte_result v2 payload.

- CteTestRecord gains optional preview_rows (JSON-coerced, truncated cells);
  test_cmd populates it from the bounded result rows.
- New read-only `tht cte info <name> --session <id> [--json]`: plan
  index/total, persisted .sql, cte_plan_doc.json entry (if any), last
  CteTestRecord. Exits 1 with a clean stderr message on missing
  session/plan/name/sql.
- `tht cte plan --doc -` validates a chain-doc JSON (ctes[].name must match
  --name, same order) and writes it to cte_plan_doc.json; cte_plan.json stays
  a plain list[str] (load-bearing for tht.phase.next_cte). --doc is optional.

harness/tests/test_cte_info.py

@@ -0,0 +1,149 @@
+"""L1: `tht cte info <name>` — read-only CTE detail (plan position + sql + doc + last test).
+
+Feeds the JS gate (WS2) building the cte_result v2 payload: it needs index/total from
+cte_plan.json (same source as tht.phase.next_cte), the persisted .sql file, the optional
+cte_plan_doc.json entry, and the last CteTestRecord for the CTE. --json output must be
+pristine (only valid JSON on stdout).
+"""
+import json
+from datetime import datetime
+
+from typer.testing import CliRunner
+
+from tht.cli.cte_cmd import cte_app
+from tht.config import DatabaseConfig
+from tht.ctetest import CteTestRecord, append_cte_test
+from tht.decisions import append_decision
+from tht.session.store import create_session
+
+
+def _db():
+    return DatabaseConfig(database="testdb", user="u", password="p", **{"schema": "public"})  # noqa: S106
+
+
+def _patch_cfg(monkeypatch, tmp_path):
+    from tht.cli import cte_cmd
+
+    class FakePaths:
+        sessions = tmp_path
+
+    class FakeCfg:
+        paths = FakePaths()
+        database = _db()
+
+    monkeypatch.setattr(cte_cmd, "_load_config_or_exit", lambda _: FakeCfg())
+
+
+def _make_session(tmp_path, plan):
+    m = create_session("q", _db(), tmp_path)
+    sdir = tmp_path / m.id
+    (sdir / "cte_plan.json").write_text(json.dumps(plan))
+    (sdir / "ctes").mkdir(parents=True, exist_ok=True)
+    return m.id, sdir
+
+
+def test_info_happy_path_json(tmp_path, monkeypatch):
+    sid, sdir = _make_session(tmp_path, ["a", "b"])
+    (sdir / "ctes" / "b.sql").write_text("WITH b AS (SELECT 1)")
+    append_cte_test(sdir, CteTestRecord(
+        name="b", ts=datetime(2025, 1, 1, 12, 0), sql_hash="h1", status="ok",
+        columns=["x"], row_sample=1, execution_ms=5, preview_rows=[[1]],
+    ))
+    _patch_cfg(monkeypatch, tmp_path)
+
+    res = CliRunner().invoke(cte_app, ["info", "b", "--session", sid, "--json"])
+    assert res.exit_code == 0, res.output
+    data = json.loads(res.output)
+    assert data["name"] == "b"
+    assert data["index"] == 2
+    assert data["total"] == 2
+    assert data["plan"] == ["a", "b"]
+    assert data["sql"] == "WITH b AS (SELECT 1)"
+    assert data["approved"] is False
+    assert data["doc"] is None
+    assert data["last_test"]["sql_hash"] == "h1"
+    assert data["last_test"]["preview_rows"] == [[1]]
+
+
+def test_info_approved_true_when_decision_present(tmp_path, monkeypatch):
+    sid, sdir = _make_session(tmp_path, ["a"])
+    (sdir / "ctes" / "a.sql").write_text("WITH a AS (SELECT 1)")
+    append_decision(sdir, type="cte_approved", subject="a")
+    _patch_cfg(monkeypatch, tmp_path)
+
+    res = CliRunner().invoke(cte_app, ["info", "a", "--session", sid, "--json"])
+    assert res.exit_code == 0, res.output
+    data = json.loads(res.output)
+    assert data["approved"] is True
+
+
+def test_info_doc_present(tmp_path, monkeypatch):
+    sid, sdir = _make_session(tmp_path, ["a"])
+    (sdir / "ctes" / "a.sql").write_text("WITH a AS (SELECT 1)")
+    doc = {"ctes": [{"name": "a", "purpose": "p", "rationale": "r", "depends_on": []}]}
+    (sdir / "cte_plan_doc.json").write_text(json.dumps(doc, ensure_ascii=False))
+    _patch_cfg(monkeypatch, tmp_path)
+
+    res = CliRunner().invoke(cte_app, ["info", "a", "--session", sid, "--json"])
+    assert res.exit_code == 0, res.output
+    data = json.loads(res.output)
+    assert data["doc"] == {"purpose": "p", "rationale": "r", "depends_on": []}
+
+
+def test_info_last_test_none_when_no_records(tmp_path, monkeypatch):
+    sid, sdir = _make_session(tmp_path, ["a"])
+    (sdir / "ctes" / "a.sql").write_text("WITH a AS (SELECT 1)")
+    _patch_cfg(monkeypatch, tmp_path)
+
+    res = CliRunner().invoke(cte_app, ["info", "a", "--session", sid, "--json"])
+    assert res.exit_code == 0, res.output
+    data = json.loads(res.output)
+    assert data["last_test"] is None
+
+
+def test_info_last_test_is_most_recent_record(tmp_path, monkeypatch):
+    sid, sdir = _make_session(tmp_path, ["a"])
+    (sdir / "ctes" / "a.sql").write_text("WITH a AS (SELECT 1)")
+    append_cte_test(sdir, CteTestRecord(
+        name="a", ts=datetime(2025, 1, 1), sql_hash="old", status="ok",
+    ))
+    append_cte_test(sdir, CteTestRecord(
+        name="a", ts=datetime(2025, 1, 2), sql_hash="new", status="ok",
+    ))
+    _patch_cfg(monkeypatch, tmp_path)
+
+    res = CliRunner().invoke(cte_app, ["info", "a", "--session", sid, "--json"])
+    assert res.exit_code == 0, res.output
+    data = json.loads(res.output)
+    assert data["last_test"]["sql_hash"] == "new"
+
+
+def test_info_nonexistent_session_exit_1(tmp_path, monkeypatch):
+    _patch_cfg(monkeypatch, tmp_path)
+    res = CliRunner().invoke(cte_app, ["info", "a", "--session", "nope", "--json"])
+    assert res.exit_code == 1
+    assert res.stdout == ""  # stdout stays pristine JSON-or-nothing
+
+
+def test_info_missing_plan_exit_1(tmp_path, monkeypatch):
+    m = create_session("q", _db(), tmp_path)
+    _patch_cfg(monkeypatch, tmp_path)
+    res = CliRunner().invoke(cte_app, ["info", "a", "--session", m.id, "--json"])
+    assert res.exit_code == 1
+    assert res.stdout == ""
+
+
+def test_info_name_not_in_plan_exit_1(tmp_path, monkeypatch):
+    sid, sdir = _make_session(tmp_path, ["a"])
+    _patch_cfg(monkeypatch, tmp_path)
+    res = CliRunner().invoke(cte_app, ["info", "zzz", "--session", sid, "--json"])
+    assert res.exit_code == 1
+    assert res.stdout == ""
+
+
+def test_info_missing_sql_file_exit_1(tmp_path, monkeypatch):
+    sid, sdir = _make_session(tmp_path, ["a"])
+    _patch_cfg(monkeypatch, tmp_path)
+    res = CliRunner().invoke(cte_app, ["info", "a", "--session", sid, "--json"])
+    assert res.exit_code == 1
+    assert res.stdout == ""