Add full shell, replaceable Omics adapter and bilingual interaction

Implement approved specification #32 and tickets #33-#37. Keep host authentication server-verified and pin session interaction language. Compile scoped base selectors for browser compatibility and retain full gutters during CSS pruning.

harness/tht/session/store.py

@@ -135,7 +135,7 @@ def create_session(
 
 def new_session_manifest(
     question: str, db: DatabaseConfig, *, provider=None, model=None, thinking=None,
-    workspace_id=None, workspace_revision=None, name=None,
+    workspace_id=None, workspace_revision=None, name=None, interaction_language=None,
 ) -> SessionManifest:
     """Create an unsaved UUIDv4 manifest for a repository-owned session."""
     now = datetime.now(UTC)
@@ -145,9 +145,24 @@ def new_session_manifest(
         summary=_summarize(question), updated_at=now, updated_by=current_author(),
         provider=provider, model=model, thinking=thinking, workspace_id=workspace_id,
         workspace_revision=workspace_revision, name=name,
+        interaction_language=interaction_language,
     )
 
 
+def pin_interaction_language(manifest: SessionManifest, workspace_language: str) -> bool:
+    """Apply legacy compatibility once, while the repository holds its writer lock."""
+    from tht.session.language import validate_language_tag
+
+    if manifest.interaction_language is not None:
+        return False
+    if manifest.status == "finalized" or manifest.archived:
+        raise SessionError("Session is read-only (finalized or archived)")
+    manifest.interaction_language = validate_language_tag(workspace_language)
+    manifest.updated_at = datetime.now(UTC)
+    manifest.updated_by = current_author()
+    return True
+
+
 _ASSUMPTIONS_HEADING = re.compile(
     r"^#{1,6}\s+(?:assunzioni|assumptions)\s*$", re.IGNORECASE | re.MULTILINE
 )