fix(mail): BigInt-Serialisierung blockierte Phase-2-Persistierung

imapflow.status() liefert uidValidity als BigInt. Der Code reichte den BigInt in
JSON.stringify (patchFolderScanState) → 'TypeError: Do not know how to serialize
a BigInt' → vom stummen connection-level catch verschluckt → weder
patchFolderScanState noch markFullSweepDone liefen je → folder_scan_state blieb
{} + last_full_sweep_at NULL → inkrementeller Scan aktivierte nie (immer Full-Sweep).

Fix:
- serverUidValidity: Number((status).uidValidity ?? 0) — BigInt → number vor JSON.
- Stumme catches (auth/lock/conn) loggen jetzt; Persist-Calls (patchFolderScanState
  x2, markFullSweepDone) in eigene try/catch mit console.error — Diagnostik bleibt
  drin für Post-Deploy-Verify.

Lokal verifiziert: Build EXIT 0, imapflow extern.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/server/api/mail/scan-internal.post.ts

@@ -78,7 +78,8 @@ export default defineEventHandler(async (event) => {
     let imapAuth: { user: string; accessToken: string } | { user: string; pass: string };
     try {
       imapAuth = await resolveImapAuth(connection, oauthClientIds);
-    } catch {
+    } catch (authErr) {
+      console.error(`[scan-internal] resolveImapAuth failed for ${connection.email}:`, authErr);
       continue;
     }
 
@@ -136,7 +137,8 @@ export default defineEventHandler(async (event) => {
         let lock: any;
         try {
           lock = await imap.getMailboxLock(mb.path);
-        } catch {
+        } catch (lockErr) {
+          console.warn(`[scan-internal] ${connection.email} | ${mb.path} | getMailboxLock failed, skipping folder:`, lockErr);
           continue;
         }
         try {
@@ -149,16 +151,25 @@ export default defineEventHandler(async (event) => {
             uidValidity: true,
           });
           const msgCount = (status as any).messages ?? 0;
-          const serverUidValidity: number = (status as any).uidValidity ?? 0;
+          // imapflow liefert uidValidity als BigInt (IMAP-Spec: 32-bit unsigned).
+          // Number() konvertiert BigInt sicher — UIDVALIDITY ist max 2^32-1, weit unter
+          // Number.MAX_SAFE_INTEGER (2^53-1), kein Präzisionsverlust möglich.
+          // Ohne Number() würde JSON.stringify({uidvalidity: BigInt(x)}) werfen und
+          // patchFolderScanState still crashen (verschluckt vom äußeren catch {}).
+          const serverUidValidity: number = Number((status as any).uidValidity ?? 0);
 
           if (msgCount === 0) {
             // Ordner leer — trotzdem Zustand für diesen Ordner persistieren
             // (verhindert endloses Re-Fetching auf leere Ordner).
             if (serverUidValidity > 0) {
-              await patchFolderScanState(connection.id, mb.path, {
+              try {
-                lastUid: 0,
+                await patchFolderScanState(connection.id, mb.path, {
-                uidvalidity: serverUidValidity,
+                  lastUid: 0,
-              });
+                  uidvalidity: serverUidValidity,
+                });
+              } catch (e) {
+                console.error(`[scan-internal] persist failed — patchFolderScanState(${mb.path}, empty folder):`, e);
+              }
             }
             continue;
           }
@@ -353,10 +364,14 @@ export default defineEventHandler(async (event) => {
           }, 0);
 
           if (maxUid > 0 && serverUidValidity > 0) {
-            await patchFolderScanState(connection.id, mb.path, {
+            try {
-              lastUid: maxUid,
+              await patchFolderScanState(connection.id, mb.path, {
-              uidvalidity: serverUidValidity,
+                lastUid: maxUid,
-            });
+                uidvalidity: serverUidValidity,
+              });
+            } catch (e) {
+              console.error(`[scan-internal] persist failed — patchFolderScanState(${mb.path}, maxUid=${maxUid}, uidvalidity=${serverUidValidity}):`, e);
+            }
           }
         } finally {
           lock.release();
@@ -365,12 +380,17 @@ export default defineEventHandler(async (event) => {
 
       // ─── Full-Sweep abschließen ─────────────────────────────────────────────
       if (needsFullSweep) {
-        await markFullSweepDone(connection.id);
+        try {
-        console.log(`[scan-internal] ${connection.email} | full-sweep complete, lastFullSweepAt updated`);
+          await markFullSweepDone(connection.id);
+          console.log(`[scan-internal] ${connection.email} | full-sweep complete, lastFullSweepAt updated`);
+        } catch (e) {
+          console.error(`[scan-internal] persist failed — markFullSweepDone(${connection.id}):`, e);
+        }
       }
 
       await imap.logout();
-    } catch {
+    } catch (connErr) {
+      console.error(`[scan-internal] connection-level error for ${connection.email}:`, connErr);
       try {
         await imap.logout();
       } catch {}