Fix new-question landing and question-language HITL

Reset the activity panel when starting a new question so the landing navigation is restored. Detect and persist the original question language, pass it through runtime and widget descriptors, and scope HITL controls to that language.

Validated with gate, session, backend and frontend tests, TypeScript checks, Ruff and strict docs build. Rebuilt and restarted local core/frontend; both healthy and serving HTTP successfully.

harness/tht/cli/session_cmd.py

@@ -178,7 +178,8 @@ def list_cmd(
 def new_cmd(
     question: str = typer.Argument(..., help="La domanda in linguaggio naturale."),
     interaction_language: str = typer.Option(
-        None, "--interaction-language", help="BCP-47 interaction language; defaults to workspace language."
+        None, "--interaction-language",
+        help="BCP-47 fallback for ambiguous questions; otherwise use the question's language.",
     ),
     provider: str = typer.Option(None, "--provider", help="Provider LLM (es. zai, anthropic)."),
     model: str = typer.Option(None, "--model", help="Modello LLM (es. glm-5.2)."),
@@ -193,10 +194,11 @@ def new_cmd(
     from tht.session.store import _extract_name, new_session_manifest, render_question_md
 
     cfg = _load_config_or_exit(config)
-    from tht.session.language import validate_language_tag
+    from tht.session.language import question_interaction_language
 
     try:
-        language = validate_language_tag(
+        language = question_interaction_language(
+            question,
             interaction_language if interaction_language is not None else getattr(cfg, "language", "en")
         )
     except ValueError as exc:
@@ -209,7 +211,7 @@ def new_cmd(
     repository.create(manifest)
     repository.write_artifact(manifest.id, "question", render_question_md(question))
     if json_out:
-        typer.echo(json.dumps({"id": manifest.id}, ensure_ascii=False))
+        typer.echo(json.dumps({"id": manifest.id, "interaction_language": language}, ensure_ascii=False))
         return
     typer.secho(f"OK: sessione creata ({manifest.id})", fg=typer.colors.GREEN)
     typer.echo(manifest.id)
@@ -384,7 +386,7 @@ def ensure_interaction_language_cmd(
     json_out: bool = typer.Option(False, "--json", help="Emit pristine JSON."),
     config: Path = CONFIG_OPT,
 ) -> None:
-    """Pin a missing legacy language from the workspace; never override a saved value."""
+    """Pin a missing language from the question; never override a saved value."""
     cfg = _load_config_or_exit(config)
     manifest = ensure_session_language_or_exit(cfg, session_id)
     if json_out:

harness/tht/session/language.py

@@ -1,5 +1,9 @@
 """Session language policy, independent of workspace document content."""
 import re
+from functools import lru_cache
+
+from langdetect import DetectorFactory, LangDetectException
+from langdetect.detector_factory import PROFILES_DIRECTORY
 
 _LANGUAGE_TAG = re.compile(
     r"(?P<language>[A-Za-z]{2,8})(?:-(?P<script>[A-Za-z]{4}))?"
@@ -21,3 +25,36 @@ def validate_language_tag(value: str) -> str:
     if match["region"]:
         parts.append(match["region"].upper())
     return "-".join(parts) + match["rest"].lower()
+
+
+@lru_cache(maxsize=1)
+def _question_detector_factory() -> DetectorFactory:
+    factory = DetectorFactory()
+    factory.seed = 0
+    factory.load_profile(PROFILES_DIRECTORY)
+    return factory
+
+
+def question_interaction_language(question: str, fallback: str) -> str:
+    """Pin confidently detected prose language; short/ambiguous/code input uses the hint."""
+    fallback = validate_language_tag(fallback)
+    prose = re.sub(r"```[\s\S]*?```|`[^`]*`|\b\w*_\w*\b", " ", question)
+    if re.match(
+        r"\s*(?:SELECT\s+.+\s+FROM\b|WITH\s+\w+\s+AS\s*\(|INSERT\s+INTO\b|"
+        r"UPDATE\s+\w+\s+SET\b|DELETE\s+FROM\b|CREATE\s+TABLE\b)",
+        prose, re.IGNORECASE | re.DOTALL,
+    ):
+        return fallback
+    if sum(character.isalpha() for character in prose) < 12:
+        return fallback
+    detector = _question_detector_factory().create()
+    detector.append(prose)
+    try:
+        candidates = detector.get_probabilities()
+    except LangDetectException:
+        return fallback
+    if not candidates or candidates[0].prob < 0.90:
+        return fallback
+    detected = validate_language_tag(candidates[0].lang)
+    # Preserve a regional preference when it agrees with the detected language.
+    return fallback if detected.split("-")[0] == fallback.split("-")[0] else detected

harness/tht/session/store.py

@@ -151,13 +151,13 @@ def new_session_manifest(
 
 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
+    from tht.session.language import question_interaction_language
 
     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.interaction_language = question_interaction_language(manifest.question, workspace_language)
     manifest.updated_at = datetime.now(UTC)
     manifest.updated_by = current_author()
     return True