feat(harness): derive a 3-5 keyword session name (YAKE, no LLM)

New sessions get a concise Italian-keyword `name` instead of the truncated
question. `tht session new` (when no --name is given) derives it via a new
`_extract_name` helper using YAKE (pure-Python, unsupervised, Italian, no LLM),
dropping generic query verbs and keeping the top keywords in reading order;
falls back to `_summarize` if YAKE is unavailable. `create_session` core keeps
its `name=None` default — the policy lives at the CLI layer.

TDD: tests/test_session_name.py (unit + CliRunner integration). Full harness
suite 269 passed; ruff clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

harness/tests/test_session_name.py

@@ -0,0 +1,81 @@
+"""Tests for the keyword-based session name derivation (YAKE, no LLM).
+
+A new session's display `name` is a 3-5 word Italian-keyword summary of the question,
+derived at the CLI layer (`tht session new`) with no LLM. `create_session` core keeps its
+`name=None` default; the policy lives in `new_cmd`.
+"""
+import json
+
+from typer.testing import CliRunner
+
+from tht.config import DatabaseConfig
+from tht.cli.session_cmd import session_app
+from tht.session.store import _extract_name, _summarize, load_session
+
+
+def _db():
+    return DatabaseConfig(
+        database="testdb", user="u", password="p",  # noqa: S106
+        **{"schema": "public"},
+    )
+
+
+class _FakeCfg:
+    def __init__(self, sessions):
+        self.database = _db()
+        self.paths = type("P", (), {"sessions": sessions})()
+
+
+def test_extract_name_is_a_3_to_5_word_italian_summary():
+    q = "Elenca i pazienti anziani con esiti gravi nell'ultimo periodo."
+    name = _extract_name(q)
+    words = name.split()
+    assert 3 <= len(words) <= 5
+    # the generic query verb is dropped...
+    assert "elenca" not in [w.lower() for w in words]
+    # ...and the salient content survives
+    lower = name.lower()
+    assert "pazienti" in lower and "anziani" in lower
+    # deterministic
+    assert _extract_name(q) == name
+
+
+def test_extract_name_falls_back_to_summarize_on_failure(monkeypatch):
+    import tht.session.store as store
+
+    def boom(*a, **k):
+        raise RuntimeError("yake down")
+
+    monkeypatch.setattr(store.yake, "KeywordExtractor", boom)
+    q = "Elenca i pazienti anziani con esiti gravi."
+    assert _extract_name(q) == _summarize(q)
+
+
+def test_extract_name_empty_question_is_empty():
+    assert _extract_name("") == ""
+    assert _extract_name("   ") == ""
+
+
+def test_new_cmd_autonames_when_no_name(tmp_path, monkeypatch):
+    from tht.cli import session_cmd
+
+    monkeypatch.setattr(session_cmd, "_load_config_or_exit", lambda _: _FakeCfg(tmp_path))
+    q = "Mostra i pazienti con interventi recenti e complicazioni rilevanti."
+    res = CliRunner().invoke(session_app, ["new", q, "--json"])
+    assert res.exit_code == 0, res.output
+    sid = json.loads(res.output)["id"]
+    name = load_session(sid, tmp_path).name
+    assert name == _extract_name(q)
+    assert name and 3 <= len(name.split()) <= 5
+
+
+def test_new_cmd_explicit_name_wins(tmp_path, monkeypatch):
+    from tht.cli import session_cmd
+
+    monkeypatch.setattr(session_cmd, "_load_config_or_exit", lambda _: _FakeCfg(tmp_path))
+    res = CliRunner().invoke(
+        session_app, ["new", "Una domanda qualunque", "--name", "Mio nome", "--json"]
+    )
+    assert res.exit_code == 0, res.output
+    sid = json.loads(res.output)["id"]
+    assert load_session(sid, tmp_path).name == "Mio nome"