fix: session handling and SDK async iteration

- Add sdk_conversation_id column to track SDK conversation separately from user session_id
- Queue processor looks up SDK conversation ID for resume instead of passing user session_id
- session_id "new" stores NULL initially, gets set from SDK on completion
- Custom session_ids are preserved (not overwritten by SDK)
- Worker catches SDK process exit error after messages are collected

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

worker/index.js

@@ -33,19 +33,26 @@ app.post("/process", async (req, res) => {
 
     const conv = query({ prompt, options });
     const messages = [];
-    for await (const msg of conv) {
-      messages.push(msg);
+    try {
+      for await (const msg of conv) {
+        messages.push(msg);
+      }
+    } catch (_) {
+      // SDK throws after process exits; messages already collected
     }
 
     const resultMsg = messages.find((m) => m.type === "result");
-    if (resultMsg && resultMsg.is_error) {
+    if (!resultMsg) {
+      return res.json({ success: false, error: "No result received from Claude" });
+    }
+    if (resultMsg.is_error) {
       return res.json({ success: false, error: resultMsg.result });
     }
 
     res.json({
       success: true,
-      result: resultMsg?.result || "",
-      session_id: resultMsg?.session_id || session_id,
+      result: resultMsg.result || "",
+      session_id: resultMsg.session_id || session_id,
     });
   } catch (error) {
     console.error("Process error:", error.message);
@@ -85,8 +92,12 @@ app.post("/summarize", async (req, res) => {
       },
     });
     const msgs = [];
-    for await (const msg of conv) {
-      msgs.push(msg);
+    try {
+      for await (const msg of conv) {
+        msgs.push(msg);
+      }
+    } catch (_) {
+      // SDK throws after process exits; messages already collected
     }
 
     const resultMsg = msgs.find((m) => m.type === "result");