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/tht/cli/session_cmd.py

@@ -1,3 +1,4 @@
+import json
 from pathlib import Path
 
 import typer
@@ -22,6 +23,47 @@ def load_session_or_exit(cfg, session_id: str):
         raise typer.Exit(code=1)
 
 
+def _list_sessions(sessions_root: Path) -> list[dict]:
+    """Return session summary dicts sorted by created_at desc (pure helper, no I/O side-effects)."""
+    from tht.session.models import SessionManifest
+
+    MANIFEST_NAME = "session_manifest.yaml"
+    out = []
+    if not sessions_root.exists():
+        return out
+    for d in sessions_root.iterdir():
+        manifest_path = d / MANIFEST_NAME
+        if not manifest_path.exists():
+            continue
+        m = SessionManifest.from_yaml(manifest_path)
+        out.append({
+            "id": m.id,
+            "status": m.status,
+            "question": m.question,
+            "summary": m.summary,
+            "created_at": m.created_at.isoformat(),
+            "updated_at": m.updated_at.isoformat() if m.updated_at else None,
+            "author": m.author,
+        })
+    out.sort(key=lambda r: r["created_at"], reverse=True)
+    return out
+
+
+@session_app.command("list")
+def list_cmd(
+    json_out: bool = typer.Option(False, "--json", help="Emetti JSON su stdout (pristine)."),
+    config: Path = CONFIG_OPT,
+) -> None:
+    """Elenca le sessioni esistenti."""
+    cfg = _load_config_or_exit(config)
+    rows = _list_sessions(cfg.paths.sessions)
+    if json_out:
+        typer.echo(json.dumps(rows, ensure_ascii=False, indent=2))
+        return
+    for r in rows:
+        typer.echo(f"{r['id']}  [{r['status']}]  {r['summary'] or r['question'][:60]}")
+
+
 @session_app.command("new")
 def new_cmd(
     question: str = typer.Argument(..., help="La domanda in linguaggio naturale."),
@@ -56,13 +98,29 @@ def set_question_cmd(
 
 
 @session_app.command("show")
-def show_cmd(session_id: str = typer.Argument(...), config: Path = CONFIG_OPT) -> None:
+def show_cmd(
+    session_id: str = typer.Argument(...),
+    json_out: bool = typer.Option(False, "--json", help="Emetti JSON su stdout (pristine)."),
+    config: Path = CONFIG_OPT,
+) -> None:
     """Stato della sessione: manifest + decisioni registrate (per la ripresa)."""
     from tht.decisions import list_decisions
+    from tht.phase import current_phase
 
     cfg = _load_config_or_exit(config)
     manifest = load_session_or_exit(cfg, session_id)
-    decisions = list_decisions(session_dir(cfg, session_id))
+    sdir = session_dir(cfg, session_id)
+
+    if json_out:
+        has_schema_linking = (sdir / "schema_linking.json").exists()
+        phase = current_phase(sdir)
+        data = manifest.model_dump(mode="json", by_alias=True)
+        data["phase"] = phase
+        data["has_schema_linking"] = has_schema_linking
+        typer.echo(json.dumps(data, ensure_ascii=False, indent=2))
+        return
+
+    decisions = list_decisions(sdir)
     typer.echo(f"id       : {manifest.id}")
     typer.echo(f"stato    : {manifest.status}")
     typer.echo(f"domanda  : {manifest.question}")
@@ -70,7 +128,7 @@ def show_cmd(session_id: str = typer.Argument(...), config: Path = CONFIG_OPT) -
     typer.echo(f"decisioni: {len(decisions)}")
     for d in decisions[-10:]:
         typer.echo(f"  [{d.seq}] {d.type}: {d.subject}" + (f" — {d.detail}" if d.detail else ""))
-    linking = session_dir(cfg, session_id) / "schema_linking.json"
+    linking = sdir / "schema_linking.json"
     typer.echo(f"schema_linking.json: {'presente' if linking.exists() else 'assente'}")