feat(harness): add local session repository

harness/tht/session/store.py

@@ -1,6 +1,7 @@
 import json
 import os
 import shutil
+import uuid
 from datetime import UTC, datetime
 from pathlib import Path
 
@@ -8,7 +9,6 @@ import yake
 
 from tht.config import DatabaseConfig
 from tht.session.models import SessionManifest
-from tht.textutil import slugify
 
 MANIFEST = "session_manifest.yaml"
 MAX_SLUG_CHARS = 40
@@ -88,12 +88,13 @@ def render_question_md(question: str, assumptions: list[str] | None = None) -> s
 
 
 def _new_id(question: str, sessions_root: Path, stamp: str) -> str:
-    base = f"{stamp}-{slugify(question)[:MAX_SLUG_CHARS].rstrip('-')}"
-    candidate, n = base, 1
-    while (sessions_root / candidate).exists():
-        n += 1
-        candidate = f"{base}-{n}"
-    return candidate
+    """Create an opaque UUIDv4 session identifier.
+
+    ``question``, ``sessions_root`` and ``stamp`` remain accepted temporarily so
+    existing workflow callers do not need to change as the repository boundary
+    is introduced.
+    """
+    return str(uuid.uuid4())
 
 
 def create_session(