Fix silent API error handling in chat

Frontend now properly detects HTTP errors and displays meaningful
error messages instead of showing a stuck typing indicator. Backend
logs API key presence and request details for easier debugging.

https://claude.ai/code/session_015z3yZxNNfXF63JuQDuPbEG

app/main.py

@@ -80,7 +80,18 @@ def _detect_phase(reply: str, current_phase: int) -> int:
 
 @app.post("/api/chat", response_model=ChatResponse)
 async def api_chat(req: ChatRequest):
+    import os
+    api_key = os.environ.get("OPENROUTER_API_KEY", "")
+    base_url = os.environ.get("LLM_BASE_URL", "")
+    model = os.environ.get("LLM_MODEL", "")
+    if not api_key:
+        logger.error("OPENROUTER_API_KEY is not set!")
+        return JSONResponse(status_code=500, content={"error": "Cle API non configuree (OPENROUTER_API_KEY manquant)"})
+    if not base_url:
+        logger.warning("LLM_BASE_URL is not set, will use OpenAI default")
+
     try:
+        logger.info(f"Chat request: mode={req.mode}, topic={req.topic[:50]}, phase={req.phase}, model={model}")
         rag_chunks = retrieve(req.message)
         system_prompt = build_system_prompt(req.mode, req.topic, req.phase, rag_chunks)
 
@@ -88,6 +99,7 @@ async def api_chat(req: ChatRequest):
         messages.append({"role": "user", "content": req.message})
 
         reply = await chat(system_prompt, messages)
+        logger.info(f"LLM reply received ({len(reply)} chars)")
         detected_phase = _detect_phase(reply, req.phase)
 
         return ChatResponse(reply=reply, phase=detected_phase)

static/app.js

@@ -255,9 +255,21 @@
                 history: state.history.slice(0, -1) // send history before this message
             })
         })
-        .then(function (res) { return res.json(); })
+        .then(function (res) {
+            if (!res.ok) {
+                return res.json().then(function (err) {
+                    throw new Error(err.error || "Erreur serveur " + res.status);
+                });
+            }
+            return res.json();
+        })
         .then(function (data) {
             setTyping(false);
+            if (!data.reply) {
+                addMessage("assistant", "Reponse vide du serveur. Verifiez la configuration API.");
+                btnSend.disabled = false;
+                return;
+            }
             state.phase = data.phase;
             state.history.push({ role: "assistant", content: data.reply });
             state.timestamps.push(Date.now());
@@ -268,7 +280,8 @@
         })
         .catch(function (err) {
             setTyping(false);
-            addMessage("assistant", "Erreur de connexion. Veuillez reessayer.");
+            console.error("sendMessage error:", err);
+            addMessage("assistant", "Erreur: " + (err.message || "Connexion impossible. Veuillez reessayer."));
             btnSend.disabled = false;
         });
     }
@@ -458,9 +471,21 @@
                 history: []
             })
         })
-        .then(function (res) { return res.json(); })
+        .then(function (res) {
+            if (!res.ok) {
+                return res.json().then(function (err) {
+                    throw new Error(err.error || "Erreur serveur " + res.status);
+                });
+            }
+            return res.json();
+        })
         .then(function (data) {
             setTyping(false);
+            if (!data.reply) {
+                addMessage("assistant", "Reponse vide du serveur. Verifiez la configuration API.");
+                btnSend.disabled = false;
+                return;
+            }
             state.phase = data.phase;
             state.history.push({ role: "assistant", content: data.reply });
             state.timestamps.push(Date.now());
@@ -469,9 +494,10 @@
             btnSend.disabled = false;
             chatInput.focus();
         })
-        .catch(function () {
+        .catch(function (err) {
             setTyping(false);
-            addMessage("assistant", "Erreur de connexion. Veuillez reessayer.");
+            console.error("startSession error:", err);
+            addMessage("assistant", "Erreur: " + (err.message || "Connexion impossible. Veuillez reessayer."));
             btnSend.disabled = false;
         });
     }