feat(cli): tht session list --json + session show --json (Task 7)

- Add _list_sessions(sessions_root) pure helper: scans sessions dir,
  returns list[dict] with id/status/question/summary/created_at/
  updated_at/author, sorted by created_at desc.
- Add `tht session list` command: --json emits pristine JSON array,
  human mode prints one line per session.
- Add --json flag to `tht session show`: emits manifest
  (model_dump by_alias) + phase (current_phase) + has_schema_linking.
- Tests: 8 tests in test_session_list_json.py (TDD red→green).
- Full suite: 230 passed (--ignore=tests/l2).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

harness/tests/test_session_list_json.py

@@ -0,0 +1,162 @@
+"""Tests for `tht session list --json` and `tht session show --json` (Task 7)."""
+import json
+
+import pytest
+from typer.testing import CliRunner
+
+from tht.cli.session_cmd import _list_sessions, session_app
+from tht.session.store import create_session
+
+
+def _make_db():
+    from tht.config import DatabaseConfig
+
+    return DatabaseConfig(
+        database="testdb",
+        user="testuser",
+        password="testpass",  # noqa: S106
+        **{"schema": "public"},
+    )
+
+
+# ---------------------------------------------------------------------------
+# Unit: _list_sessions helper
+# ---------------------------------------------------------------------------
+
+
+def test_list_sessions_returns_all_created(tmp_path):
+    db = _make_db()
+    m1 = create_session("prima domanda", db, tmp_path)
+    m2 = create_session("seconda domanda", db, tmp_path)
+    rows = _list_sessions(tmp_path)
+    ids = [r["id"] for r in rows]
+    assert m1.id in ids
+    assert m2.id in ids
+
+
+def test_list_sessions_required_keys(tmp_path):
+    db = _make_db()
+    create_session("qualsiasi domanda", db, tmp_path)
+    rows = _list_sessions(tmp_path)
+    assert len(rows) >= 1
+    required = {"id", "status", "question", "created_at"}
+    assert required.issubset(rows[0].keys())
+
+
+def test_list_sessions_sorted_desc(tmp_path):
+    db = _make_db()
+    create_session("prima", db, tmp_path)
+    create_session("seconda", db, tmp_path)
+    rows = _list_sessions(tmp_path)
+    dates = [r["created_at"] for r in rows]
+    assert dates == sorted(dates, reverse=True)
+
+
+def test_list_sessions_empty_dir(tmp_path):
+    rows = _list_sessions(tmp_path)
+    assert rows == []
+
+
+# ---------------------------------------------------------------------------
+# CLI: tht session list --json
+# ---------------------------------------------------------------------------
+
+
+def test_cli_list_json_valid(tmp_path, monkeypatch):
+    db = _make_db()
+    m = create_session("test question", db, tmp_path)
+
+    # Patch _load_config_or_exit so we don't need a real config file
+    from tht.cli import session_cmd
+
+    class FakePaths:
+        sessions = tmp_path
+
+    class FakeCfg:
+        paths = FakePaths()
+
+    monkeypatch.setattr(session_cmd, "_load_config_or_exit", lambda _: FakeCfg())
+
+    runner = CliRunner()
+    result = runner.invoke(session_app, ["list", "--json"])
+    assert result.exit_code == 0, result.output
+    rows = json.loads(result.output)
+    assert isinstance(rows, list)
+    ids = [r["id"] for r in rows]
+    assert m.id in ids
+
+
+def test_cli_list_human_no_json_noise(tmp_path, monkeypatch):
+    """Human mode must not emit JSON."""
+    db = _make_db()
+    create_session("human question", db, tmp_path)
+
+    from tht.cli import session_cmd
+
+    class FakePaths:
+        sessions = tmp_path
+
+    class FakeCfg:
+        paths = FakePaths()
+
+    monkeypatch.setattr(session_cmd, "_load_config_or_exit", lambda _: FakeCfg())
+
+    runner = CliRunner()
+    result = runner.invoke(session_app, ["list"])
+    assert result.exit_code == 0
+    # Must not be parseable as JSON array
+    with pytest.raises(json.JSONDecodeError):
+        json.loads(result.output)
+
+
+# ---------------------------------------------------------------------------
+# CLI: tht session show --json
+# ---------------------------------------------------------------------------
+
+
+def test_cli_show_json_valid(tmp_path, monkeypatch):
+    db = _make_db()
+    m = create_session("domanda show json", db, tmp_path)
+
+    from tht.cli import session_cmd
+
+    class FakePaths:
+        sessions = tmp_path
+
+    class FakeCfg:
+        paths = FakePaths()
+        database = db
+
+    monkeypatch.setattr(session_cmd, "_load_config_or_exit", lambda _: FakeCfg())
+
+    runner = CliRunner()
+    result = runner.invoke(session_app, ["show", m.id, "--json"])
+    assert result.exit_code == 0, result.output
+    data = json.loads(result.output)
+    assert data["id"] == m.id
+    assert "phase" in data
+    assert "has_schema_linking" in data
+
+
+def test_cli_show_json_stdout_pristine(tmp_path, monkeypatch):
+    """--json must produce only valid JSON on stdout (no ANSI color codes or extra lines)."""
+    db = _make_db()
+    m = create_session("pristine stdout test", db, tmp_path)
+
+    from tht.cli import session_cmd
+
+    class FakePaths:
+        sessions = tmp_path
+
+    class FakeCfg:
+        paths = FakePaths()
+        database = db
+
+    monkeypatch.setattr(session_cmd, "_load_config_or_exit", lambda _: FakeCfg())
+
+    runner = CliRunner()
+    result = runner.invoke(session_app, ["show", m.id, "--json"])
+    assert result.exit_code == 0, result.output
+    # stdout must parse cleanly as JSON
+    data = json.loads(result.output)
+    assert isinstance(data, dict)