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app.py

@@ -206,24 +206,36 @@ def _format_chat(system_prompt: str, user_prompt: str) -> str:
     return _tokenizer.apply_chat_template(messages, tokenize=False, add_generation_prompt=True)
 
 def llm_explain(structured_message: str) -> str:
-    # Graceful fallback
+    # Deterministic, number-rich fallback
     if (not _USE_LLM) or (_tokenizer is None) or (_pipe is None):
         try:
             d = json.loads(structured_message)
-            so = d["verdicts"]["strength_ok"]
-            sv = d["verdicts"]["service_ok"]
-            s_msg = "OK" if so else "NOT OK"
-            v_msg = "OK" if sv else "NOT OK"
-            return f"Like a sturdy spatula holding a pancake: strength is {s_msg} and deflection (L/180) is {v_msg}."
+            r = d["results"]
+            v = d["verdicts"]
+            inp = d["inputs_SI"]
+            L = float(inp["L_m"])
+            Sy = float(inp["Sy_MPa"])
+            sigma = float(r["sigma_max_MPa"])
+            delta = float(r["delta_mm"])
+            delta_allow = L/180.0*1e3  # mm
+
+            s_msg = "OK" if v["strength_ok"] else "NOT OK"
+            d_msg = "OK" if v["service_ok"] else "NOT OK"
+            return (
+                f"Strength {s_msg} (σ_max={sigma:.2f} MPa vs Sy={Sy:.0f} MPa); "
+                f"deflection {d_msg} (δ={delta:.2f} mm vs L/180={delta_allow:.2f} mm)."
+            )
         except Exception:
             return "Quick take: strength and deflection (L/180) checks computed; see the table and math."
+
+    # LLM path (only if model actually loads)
     system_prompt = (
         "You explain engineering to a smart 5-year-old using a quick food analogy. "
         "You ALWAYS respond in exactly ONE friendly sentence."
     )
     user_prompt = (
         "Here are the inputs, formulas, and results for a cantilever beam calculation.\n"
-        "Summarize whether the beam is OK in strength and deflection.\n\n"
+        "Summarize whether the beam is OK in strength and deflection, with one short food analogy.\n\n"
         + structured_message
     )
     formatted = _format_chat(system_prompt, user_prompt)