fix(diagnostics): from_dict raises clear error on invalid status (Sentry HIGH)

- DiagnosticStatus(invalid_str) now caught and re-raised with valid
  options and from_legacy_dict pointer, instead of unhelpful enum error
- tests: add invalid status raises with guidance test

81 tests pass.

Author: rahuldass19

src/qwed_new/core/diagnostics.py

@@ -312,10 +312,20 @@ def from_dict(cls, data: Dict[str, Any]) -> "DiagnosticResult":
             ValueError: If agent_message is missing or empty — Layer 1
                         diagnostics are mandatory and cannot be defaulted
                         during deserialization.
+            ValueError: If status is a string not in DiagnosticStatus —
+                        use from_legacy_dict() for pre-#204 engine data.
         """
         status = data.get("status", "UNVERIFIABLE")
         if isinstance(status, str):
-            status = DiagnosticStatus(status)
+            try:
+                status = DiagnosticStatus(status)
+            except ValueError:
+                valid = ", ".join(s.value for s in DiagnosticStatus)
+                raise ValueError(
+                    f"from_dict: invalid status {status!r} — "
+                    f"must be one of: {valid}. "
+                    "Use from_legacy_dict() for pre-#204 engine data."
+                ) from None
 
         agent_message = data.get("agent_message")
         if not agent_message or not str(agent_message).strip():

tests/test_diagnostics.py

@@ -434,6 +434,14 @@ def test_from_dict_missing_agent_message_raises(self):
             DiagnosticResult.from_dict({"status": "UNVERIFIABLE"})
         self.assertIn("agent_message", str(ctx.exception))
 
+    def test_from_dict_invalid_status_raises_with_guidance(self):
+        """Invalid status string must raise with valid options + from_legacy_dict pointer."""
+        with self.assertRaises(ValueError) as ctx:
+            DiagnosticResult.from_dict({"status": "CORRECTION_NEEDED", "agent_message": "x"})
+        msg = str(ctx.exception)
+        self.assertIn("CORRECTION_NEEDED", msg)
+        self.assertIn("from_legacy_dict", msg)
+
     def test_from_dict_empty_agent_message_raises(self):
         with self.assertRaises(ValueError):
             DiagnosticResult.from_dict({"status": "UNVERIFIABLE", "agent_message": "  "})