feat: harden runtime readiness and session workflow

harness/tht/session/models.py

@@ -29,7 +29,7 @@ class _YamlModel(BaseModel):
 class SessionManifest(_YamlModel):
     id: str
     created_at: datetime
-    status: Literal["open", "closed", "finalized"] = "open"
+    status: Literal["open", "closed", "failed", "finalized"] = "open"
     question: str
     database: str
     db_schema: str = Field(alias="schema")

harness/tht/session/store.py

@@ -242,6 +242,25 @@ def close_session(session_id: str, sessions_root: Path) -> SessionManifest:
     return manifest
 
 
+def fail_session(session_id: str, sessions_root: Path) -> SessionManifest:
+    """Record a fatal managed-runtime failure without losing phase artifacts."""
+    manifest = load_session(session_id, sessions_root)
+    manifest.status = "failed"
+    manifest.updated_at = datetime.now(UTC)
+    manifest.updated_by = current_author()
+    manifest.to_yaml(sessions_root / session_id / MANIFEST)
+    return manifest
+
+def reopen_session(session_id: str, sessions_root: Path) -> SessionManifest:
+    """Mark a manually resumed session active again."""
+    manifest = load_session(session_id, sessions_root)
+    manifest.status = "open"
+    manifest.updated_at = datetime.now(UTC)
+    manifest.updated_by = current_author()
+    manifest.to_yaml(sessions_root / session_id / MANIFEST)
+    return manifest
+
+
 def _save_touched(manifest: SessionManifest, sessions_root: Path) -> SessionManifest:
     """Persist `manifest` updating updated_at/updated_by (single save path for mutations)."""
     manifest.updated_at = datetime.now(UTC)